Bloom syndrome (BSyn) is characterized by severe pre- and postnatal growth deficiency, immune abnormalities, sensitivity to sunlight, insulin resistance, and a high risk for many cancers that occur at an early age. Despite their very small head circumference, most affected individuals have normal intellectual ability. Women may be fertile but often have early menopause, and men tend to be infertile, with only one confirmed case of paternity. Serious medical complications that are more common than in the general population and that also appear at unusually early ages include chronic obstructive pulmonary disease, diabetes mellitus as a result of insulin resistance, and cancer of a wide variety of types and anatomic sites.

Menkes disease (MNK) is an X-linked recessive disorder characterized by generalized copper deficiency. The clinical features result from the dysfunction of several copper-dependent enzymes.

Prader-Willi syndrome (PWS) is characterized by severe hypotonia and feeding difficulties in early infancy, followed in later infancy or early childhood by excessive eating and gradual development of morbid obesity (unless eating is externally controlled). Motor milestones and language development are delayed. All individuals have some degree of cognitive impairment. A distinctive behavioral phenotype (with temper tantrums, stubbornness, manipulative behavior, and obsessive-compulsive characteristics) is common. Hypogonadism is present in both males and females and manifests as genital hypoplasia, incomplete pubertal development, and, in most, infertility. Short stature is common (if not treated with growth hormone); characteristic facial features, strabismus, and scoliosis are often present.

Dubowitz syndrome (DS) is a rare multiple congenital syndrome characterized primarly by growth retardation, microcephaly, distinctive facial dysmorphism, cutaneous eczema, a mild to severe intellectual deficit and genital abnormalities.

Johanson-Blizzard syndrome is an autosomal recessive disorder characterized by poor growth, mental retardation, and variable dysmorphic features, including aplasia or hypoplasia of the nasal alae, abnormal hair patterns or scalp defects, and oligodontia. Other features include hypothyroidism, sensorineural hearing loss, imperforate anus, and pancreatic exocrine insufficiency (summary by Al-Dosari et al., 2008).

Smith-Lemli-Opitz syndrome (SLOS) is a congenital multiple-anomaly / cognitive impairment syndrome caused by an abnormality in cholesterol metabolism resulting from deficiency of the enzyme 7-dehydrocholesterol (7-DHC) reductase. It is characterized by prenatal and postnatal growth restriction, microcephaly, moderate-to-severe intellectual disability, and multiple major and minor malformations. The malformations include distinctive facial features, cleft palate, cardiac defects, underdeveloped external genitalia in males, postaxial polydactyly, and 2-3 syndactyly of the toes. The clinical spectrum is wide; individuals with normal development and only minor malformations have been described.

Williams syndrome (WS) is characterized by cardiovascular disease (elastin arteriopathy, peripheral pulmonary stenosis, supravalvar aortic stenosis, hypertension), distinctive facies, connective tissue abnormalities, intellectual disability (usually mild), a specific cognitive profile, unique personality characteristics, growth abnormalities, and endocrine abnormalities (hypercalcemia, hypercalciuria, hypothyroidism, and early puberty). Feeding difficulties often lead to poor weight gain in infancy. Hypotonia and hyperextensible joints can result in delayed attainment of motor milestones.

The FLNB disorders include a spectrum of phenotypes ranging from mild to severe. At the mild end are spondylocarpotarsal synostosis (SCT) syndrome and Larsen syndrome; at the severe end are the phenotypic continuum of atelosteogenesis types I (AOI) and III (AOIII) and Piepkorn osteochondrodysplasia (POCD). SCT syndrome is characterized by postnatal disproportionate short stature, scoliosis and lordosis, clubfeet, hearing loss, dental enamel hypoplasia, carpal and tarsal synostosis, and vertebral fusions. Larsen syndrome is characterized by congenital dislocations of the hip, knee, and elbow; clubfeet (equinovarus or equinovalgus foot deformities); scoliosis and cervical kyphosis, which can be associated with a cervical myelopathy; short, broad, spatulate distal phalanges; distinctive craniofacies (prominent forehead, depressed nasal bridge, malar flattening, and widely spaced eyes); vertebral anomalies; and supernumerary carpal and tarsal bone ossification centers. Individuals with SCT syndrome and Larsen syndrome can have midline cleft palate and hearing loss. AOI and AOIII are characterized by severe short-limbed dwarfism; dislocated hips, knees, and elbows; and clubfeet. AOI is lethal in the perinatal period. In individuals with AOIII, survival beyond the neonatal period is possible with intensive and invasive respiratory support. Piepkorn osteochondrodysplasia (POCD) is a perinatal-lethal micromelic dwarfism characterized by flipper-like limbs (polysyndactyly with complete syndactyly of all fingers and toes, hypoplastic or absent first digits, and duplicated intermediate and distal phalanges), macrobrachycephaly, prominant forehead, hypertelorism, and exophthalmos. Occasional features include cleft palate, omphalocele, and cardiac and genitourinary anomalies. The radiographic features at mid-gestation are characteristic.

PAFAH1B1-related lissencephaly/subcortical band heterotopia (SBH) comprises a spectrum of severity. Affected newborns typically have mild-to-moderate hypotonia, feeding difficulties, and poor head control. During the first years, neurologic examination typically demonstrates poor visual tracking and response to sounds, axial hypotonia, and mild distal spasticity that can transition over time to more severe spasticity. Seizures occur in more than 90% of individuals with lissencephaly and often include infantile spasms. Seizures are often drug resistant, but even with good seizure control, the best developmental level achieved (excluding the few individuals with partial lissencephaly) is the equivalent of about age three to five months. In individuals with PAFAH1B1-related lissencephaly/SBH, developmental delay ranges from mild to severe. Other findings in PAFAH1B1-related lissencephaly/SBH include feeding issues and aspiration (which may result in need for gastrostomy tube placement), progressive microcephaly, and occasional developmental regression.

GLI3-related Pallister-Hall syndrome (GLI3-PHS) is characterized by a spectrum of anomalies ranging from polydactyly, asymptomatic bifid epiglottis, and hypothalamic hamartoma at the mild end to laryngotracheal cleft with neonatal lethality at the severe end. Individuals with mild GLI3-PHS may be incorrectly diagnosed as having isolated postaxial polydactyly type A. Individuals with GLI3-PHS can have pituitary insufficiency and may die as neonates from undiagnosed and untreated adrenal insufficiency.

INSR-related severe syndromic insulin resistance comprises a phenotypic spectrum that is a continuum from the severe phenotype Donohue syndrome (DS) (also known as leprechaunism) to the milder phenotype Rabson-Mendenhall syndrome (RMS). DS at the severe end of the spectrum is characterized by severe insulin resistance (hyperinsulinemia with associated fasting hypoglycemia and postprandial hyperglycemia), severe prenatal growth restriction and postnatal growth failure, hypotonia and developmental delay, characteristic facies, and organomegaly involving heart, kidneys, liver, spleen, and ovaries. Death usually occurs before age one year. RMS at the milder end of the spectrum is characterized by severe insulin resistance that, although not as severe as that of DS, is nonetheless accompanied by fluctuations in blood glucose levels, diabetic ketoacidosis, and – in the second decade – microvascular complications. Findings can range from severe growth delay and intellectual disability to normal growth and development. Facial features can be milder than those of DS. Complications of longstanding hyperglycemia are the most common cause of death. While death usually occurs in the second decade, some affected individuals live longer.

Neonatal hemochromatosis (NH) is characterized by hepatic failure in the newborn period and heavy iron staining in the liver. In addition, there is marked siderosis of extrahepatic tissues, including the heart and pancreas (Driscoll et al., 1988). Whitington (2007) postulated that some cases of neonatal hemochromatosis result from maternal alloimmunity directed at the fetal liver, and therefore do not represent an inherited mendelian disorder. Other causes may result from metabolic disease or perinatal infection. In particular, he commented that the disorder is not related to the family of inherited liver diseases that fall under the classification of hereditary hemochromatosis (see, e.g., 235200). Whitington (2007) proposed the term 'congenital alloimmune hepatitis.' In the past, the disorder has loosely been labeled 'neonatal hepatitis' and 'giant cell hepatitis,' which are pathologic findings in the liver representing a common response to a variety of insults, including cholestatic disorders and infection, among others (Fawaz et al., 1975; Knisely et al., 1987; Kelly et al., 2001).

GLB1-related disorders comprise two phenotypically distinct lysosomal storage disorders: GM1 gangliosidosis and mucopolysaccharidosis type IVB (MPS IVB). The phenotype of GM1 gangliosidosis constitutes a spectrum ranging from severe (infantile) to intermediate (late-infantile and juvenile) to mild (chronic/adult). Type I (infantile) GM1 gangliosidosis begins before age 12 months. Prenatal manifestations may include nonimmune hydrops fetalis, intrauterine growth restriction, and placental vacuolization; congenital dermal melanocytosis (Mongolian spots) may be observed. Macular cherry-red spot is detected on eye exam. Progressive central nervous system dysfunction leads to spasticity and rapid regression; blindness, deafness, decerebrate rigidity, seizures, feeding difficulties, and oral secretions are observed. Life expectancy is two to three years. Type II can be subdivided into the late-infantile (onset age 1-3 years) and juvenile (onset age 3-10 years) phenotypes. Central nervous system dysfunction manifests as progressive cognitive, motor, and speech decline as measured by psychometric testing. There may be mild corneal clouding, hepatosplenomegaly, and/or cardiomyopathy; the typical course is characterized by progressive neurologic decline, progressive skeletal disease in some individuals (including kyphosis and avascular necrosis of the femoral heads), and progressive feeding difficulties leading to aspiration risk. Type III begins in late childhood to the third decade with generalized dystonia leading to unsteady gait and speech disturbance followed by extrapyramidal signs including akinetic-rigid parkinsonism. Cardiomyopathy develops in some and skeletal involvement occurs in most. Intellectual impairment is common late in the disease with prognosis directly related to the degree of neurologic impairment. MPS IVB is characterized by skeletal dysplasia with specific findings of axial and appendicular dysostosis multiplex, short stature (below 15th centile in adults), kyphoscoliosis, coxa/genu valga, joint laxity, platyspondyly, and odontoid hypoplasia. First signs and symptoms may be apparent at birth. Bony involvement is progressive, with more than 84% of adults requiring ambulation aids; life span does not appear to be limited. Corneal clouding is detected in some individuals and cardiac valvular disease may develop.

ATP6V0A2-related cutis laxa is characterized by generalized cutis laxa, findings associated with generalized connective tissue disorder, developmental delays, and a variety of neurologic findings including abnormality on brain MRI. At birth, hypotonia, overfolded skin, and distinctive facial features are present and enlarged fontanelles are often observed. During childhood, the characteristic facial features and thick or coarse hair may become quite pronounced. The skin findings decrease with age, although easy bruising and Ehlers-Danlos-like scars have been described in some. In most (not all) affected individuals, cortical and cerebellar malformations are observed on brain MRI. Nearly all affected individuals have developmental delays, seizures, and neurologic regression.

Red cell pyruvate kinase deficiency is the most common cause of hereditary nonspherocytic hemolytic anemia. PK deficiency is also the most frequent enzyme abnormality of the glycolytic pathway (Zanella et al., 2005).

The branchiooculofacial syndrome (BOFS) is characterized by: branchial (cervical or infra- or supra-auricular) skin defects that range from barely perceptible thin skin or hair patch to erythematous "hemangiomatous" lesions to large weeping erosions; ocular anomalies that can include microphthalmia, anophthalmia, coloboma, and nasolacrimal duct stenosis/atresia; and facial anomalies that can include ocular hypertelorism or telecanthus, broad nasal tip, upslanted palpebral fissures, cleft lip or prominent philtral pillars that give the appearance of a repaired cleft lip (formerly called "pseudocleft lip") with or without cleft palate, upper lip pits, and lower facial weakness (asymmetric crying face or partial 7th cranial nerve weakness). Malformed and prominent pinnae and hearing loss from inner ear and/or petrous bone anomalies are common. Intellect is usually normal.

Nijmegen breakage syndrome (NBS) is characterized by progressive microcephaly, early growth deficiency that improves with age, recurrent respiratory infections, an increased risk for malignancy (primarily lymphoma), and premature ovarian failure in females. Developmental milestones are attained at the usual time during the first year; however, borderline delays in development and hyperactivity may be observed in early childhood. Intellectual abilities tend to decline over time. Recurrent pneumonia and bronchitis may result in respiratory failure and early death. Other reported malignancies include solid tumors (e.g., medulloblastoma, glioma, rhabdomyosarcoma).

Wiedemann-Rautenstrauch syndrome (WDRTS) is a rare autosomal recessive neonatal progeroid disorder characterized by intrauterine growth retardation, failure to thrive, short stature, a progeroid appearance, hypotonia, and variable mental impairment (summary by Toriello, 1990). Average survival in WDRTS is 7 months, although survival into the third decade of life has been reported (Akawi et al., 2013).

ATP6V0A2-related cutis laxa is characterized by generalized cutis laxa, findings associated with generalized connective tissue disorder, developmental delays, and a variety of neurologic findings including abnormality on brain MRI. At birth, hypotonia, overfolded skin, and distinctive facial features are present and enlarged fontanelles are often observed. During childhood, the characteristic facial features and thick or coarse hair may become quite pronounced. The skin findings decrease with age, although easy bruising and Ehlers-Danlos-like scars have been described in some. In most (not all) affected individuals, cortical and cerebellar malformations are observed on brain MRI. Nearly all affected individuals have developmental delays, seizures, and neurologic regression.

Any centronuclear myopathy in which the cause of the disease is a mutation in the BIN1 gene.

Short-rib thoracic dysplasia (SRTD) with or without polydactyly refers to a group of autosomal recessive skeletal ciliopathies that are characterized by a constricted thoracic cage, short ribs, shortened tubular bones, and a 'trident' appearance of the acetabular roof. SRTD encompasses Ellis-van Creveld syndrome (EVC) and the disorders previously designated as Jeune syndrome or asphyxiating thoracic dystrophy (ATD), short rib-polydactyly syndrome (SRPS), and Mainzer-Saldino syndrome (MZSDS). Polydactyly is variably present, and there is phenotypic overlap in the various forms of SRTDs, which differ by visceral malformation and metaphyseal appearance. Nonskeletal involvement can include cleft lip/palate as well as anomalies of major organs such as the brain, eye, heart, kidneys, liver, pancreas, intestines, and genitalia. Some forms of SRTD are lethal in the neonatal period due to respiratory insufficiency secondary to a severely restricted thoracic cage, whereas others are compatible with life (summary by Huber and Cormier-Daire, 2012 and Schmidts et al., 2013). There is phenotypic overlap with the cranioectodermal dysplasias (Sensenbrenner syndrome; see CED1, 218330). Patients with a clinical diagnosis of Beemer-Langer syndrome have been found to carry mutations in the IFT80 gene (611177); see SRTD2, 611263. For a discussion of genetic heterogeneity of short-rib thoracic dysplasia, see SRTD1 (208500).

Microcephalic osteodysplastic primordial dwarfism type II (MOPDII), the most common form of microcephalic primordial dwarfism, is characterized by extreme short stature and microcephaly along with distinctive facial features. Associated features that differentiate it from other forms of primordial dwarfism and that may necessitate treatment include: abnormal dentition, a slender bone skeletal dysplasia with hip deformity and/or scoliosis, insulin resistance / diabetes mellitus, chronic kidney disease, cardiac malformations, and global vascular disease. The latter includes neurovascular disease such as moyamoya vasculopathy and intracranial aneurysms (which can lead to strokes), coronary artery disease (which can lead to premature myocardial infarctions), and renal vascular disease. Hypertension, which is also common, can have multiple underlying causes given the complex comorbidities.

Lenz-Majewski hyperostotic dwarfism is a rare condition characterized by intellectual disability, sclerosing bone dysplasia, distinct craniofacial and dental anomalies, loose skin, and distal limb anomalies, particularly brachydactyly and symphalangism. Patients have multiple radiographic abnormalities due to progressive generalized hyperostosis that affects the cranium, vertebrae, and diaphyses of tubular bones, leading to severe growth retardation (summary by Sousa et al., 2014).

Monosomy 18q is a partial deletion of the long arm of chromosome 18 characterized by highly variable phenotype, most commonly including hypotonia, developmental delay, short stature, growth hormone deficiency, hearing loss and external ear anomalies, intellectual disability, palatal defects, dysmorphic facial features, skeletal anomalies (foot deformities, tapering fingers, scoliosis) and mood disorders.

Mulibrey nanism (MUL) is a rare autosomal recessive growth disorder with prenatal onset, including occasional progressive cardiomyopathy, characteristic facial features, failure of sexual maturation, insulin resistance with type 2 diabetes, and an increased risk for Wilms tumor (summary by Hamalainen et al., 2006).

Cockayne syndrome (referred to as CS in this GeneReview) spans a continuous phenotypic spectrum that includes: CS type I, the "classic" or "moderate" form; CS type II, a more severe form with symptoms present at birth; this form overlaps with cerebrooculofacioskeletal (COFS) syndrome; CS type III, a milder and later-onset form; COFS syndrome, a fetal form of CS. CS type I is characterized by normal prenatal growth with the onset of growth and developmental abnormalities in the first two years. By the time the disease has become fully manifest, height, weight, and head circumference are far below the fifth percentile. Progressive impairment of vision, hearing, and central and peripheral nervous system function leads to severe disability; death typically occurs in the first or second decade. CS type II is characterized by growth failure at birth, with little or no postnatal neurologic development. Congenital cataracts or other structural anomalies of the eye may be present. Affected children have early postnatal contractures of the spine (kyphosis, scoliosis) and joints. Death usually occurs by age five years. CS type III is a phenotype in which major clinical features associated with CS only become apparent after age two years; growth and/or cognition exceeds the expectations for CS type I. COFS syndrome is characterized by very severe prenatal developmental anomalies (arthrogryposis and microphthalmia).

Cockayne syndrome (referred to as CS in this GeneReview) spans a continuous phenotypic spectrum that includes: CS type I, the "classic" or "moderate" form; CS type II, a more severe form with symptoms present at birth; this form overlaps with cerebrooculofacioskeletal (COFS) syndrome; CS type III, a milder and later-onset form; COFS syndrome, a fetal form of CS. CS type I is characterized by normal prenatal growth with the onset of growth and developmental abnormalities in the first two years. By the time the disease has become fully manifest, height, weight, and head circumference are far below the fifth percentile. Progressive impairment of vision, hearing, and central and peripheral nervous system function leads to severe disability; death typically occurs in the first or second decade. CS type II is characterized by growth failure at birth, with little or no postnatal neurologic development. Congenital cataracts or other structural anomalies of the eye may be present. Affected children have early postnatal contractures of the spine (kyphosis, scoliosis) and joints. Death usually occurs by age five years. CS type III is a phenotype in which major clinical features associated with CS only become apparent after age two years; growth and/or cognition exceeds the expectations for CS type I. COFS syndrome is characterized by very severe prenatal developmental anomalies (arthrogryposis and microphthalmia).

Intellectual developmental disorder-109 (MRX109) is characterized by mildly to moderately impaired intellectual development associated with learning difficulties, communication deficits, attention problems, hyperactivity, and autistic behavior (summary by Bensaid et al., 2009). The disorder, which is associated with a fragile site on chromosome Xq28 (FRAXE), can be caused either by silencing of the FMR2 gene as a consequence of a CCG expansion located upstream of this gene or by deletion within the gene (Stettner et al., 2011).

Jacobsen syndrome (JBS) is a contiguous gene deletion syndrome with major clinical features of growth retardation, psychomotor retardation, trigonocephaly, divergent intermittent strabismus, epicanthus, telecanthus, broad nasal bridge, short nose with anteverted nostrils, carp-shaped upper lip, retrognathia, low-set dysmorphic ears, bilateral camptodactyly, hammertoes, and isoimmune thrombocytopenia (Fryns et al., 1986, Epstein, 1986).

The pseudoaminopterin syndrome (aminopterin syndrome sine aminopterin; ASSA) is a multiple congenital anomaly disorder characterized by ossification defects of the skull, dysmorphic facial features, delayed development, and variable limb defects. The clinical features resemble the embryopathy caused by maternal treatment with the folic acid antagonist aminopterin, which has been recognized since 1952 (Thiersch, 1952) when aminopterin was used as an abortifacient. The characteristic phenotype of the children who survived infancy after having been exposed to aminopterin or its methyl derivative, methotrexate, in early pregnancy included a very unusual facies, skull anomalies, and skeletal defects (summary by Fraser et al., 1987).

Filippi syndrome is characterized by short stature, microcephaly, syndactyly, intellectual disability, and facial dysmorphism consisting of bulging forehead, broad and prominent nasal bridge, and diminished alar flare. Common features include cryptorchidism, speech impairment, and clinodactyly of the fifth finger, Some patients exhibit visual disturbances, polydactyly, seizures, and/or ectodermal abnormalities, such as nail hypoplasia, long eyelashes, hirsutism, and microdontia (summary by Hussain et al., 2014).

An extremely rare syndrome with characteristics of facial dysmorphism, severe intellectual deficiency, cardiac and intestinal anomalies, and growth retardation. Only four cases have been reported in the literature, in three unrelated families. Dysmorphic features include bilateral cleft lip and palate, bulbous nasal tip and eye anomalies. The condition seems to be inherited as an autosomal recessive trait.

Peters plus syndrome is characterized by anterior chamber eye anomalies, short limbs with broad distal extremities, characteristic facial features, cleft lip/palate, and variable developmental delay / intellectual disability. The most common anterior chamber defect is Peters' anomaly, consisting of central corneal clouding, thinning of the posterior cornea, and iridocorneal adhesions. Cataracts and glaucoma are common. Developmental delay is observed in about 80% of children; intellectual disability can range from mild to severe.

A very rare syndrome with characteristics of microcephaly, craniosynostosis, glaucoma, growth failure and visceral malformations. Only three cases have been reported in the literature in three unrelated families. Dysmorphic features include trigonocephaly, exotropia, cleft palate, beaked nose and low-set ears. All the affected patients have associated congenital visceral malformations including congenital heart defects, diaphragmatic hernia, genital or cerebral abnormalities. The demonstration of congenital glaucoma, hallmark of the syndrome, in the father of an affected patient, supports autosomal dominant inheritance. Prognosis is poor.

Lowry-Wood syndrome (LWS) is characterized by multiple epiphyseal dysplasia and microcephaly. Patients exhibit intrauterine growth retardation and short stature, as well as developmental delay and intellectual disability. Retinal degeneration has been reported in some patients (Farach et al., 2018; Shelihan et al., 2018). Microcephalic osteodysplastic primordial dwarfism type I (MOPD1; 210710) and Roifman syndrome (RFMN; 616651), the features of which overlap with those of Lowry-Wood syndrome, are also caused by biallelic mutation in the RNU4ATAC gene.

A very rare syndrome described in two siblings with manifestation of prenatal onset of growth deficiency, microcephaly, hypoplastic genitalia, and birth onset of convulsions.

Marden-Walker syndrome (MWKS) is characterized by psychomotor retardation, a mask-like face with blepharophimosis, micrognathia and a high-arched or cleft palate, low-set ears, kyphoscoliosis, and joint contractures. Other features may include Dandy-Walker malformation with hydrocephalus and vertebral abnormalities (summary by Schrander-Stumpel et al., 1993). There are 2 distal arthrogryposis syndromes with features overlapping those of Marden-Walker syndrome that are also caused by heterozygous mutation in PIEZO2: distal arthrogryposis type 3 (DA3, or Gordon syndrome; 114300) and distal arthrogryposis type 5 (DA5; 108145), which are distinguished by the presence of cleft palate and ocular abnormalities, respectively. McMillin et al. (2014) suggested that the 3 disorders may represent variable expressivity of the same condition.

Myhre syndrome is a connective tissue disorder with multisystem involvement, progressive and proliferative fibrosis that may occur spontaneously or following trauma or surgery, mild-to-moderate intellectual disability, and in some instances, autistic-like behaviors. Organ systems primarily involved include: cardiovascular (congenital heart defects, long- and short-segment stenosis of the aorta and peripheral arteries, pericardial effusion, constrictive pericarditis, restrictive cardiomyopathy, and hypertension); respiratory (choanal stenosis, laryngotracheal narrowing, obstructive airway disease, or restrictive pulmonary disease), gastrointestinal (pyloric stenosis, duodenal strictures, severe constipation); and skin (thickened particularly on the hands and extensor surfaces). Additional findings include distinctive craniofacial features and skeletal involvement (intrauterine growth restriction, short stature, limited joint range of motion). To date, 55 individuals with molecularly confirmed Myhre syndrome have been reported.

Bohring-Opitz syndrome (BOS) is characterized by distinctive facial features and posture, growth failure, variable but usually severe intellectual disability, and variable anomalies. The facial features may include microcephaly or trigonocephaly / prominent (but not fused) metopic ridge, hypotonic facies with full cheeks, synophrys, glabellar and eyelid nevus flammeus (simplex), prominent globes, widely set eyes, palate anomalies, and micrognathia. The BOS posture, which is most striking in early childhood and often becomes less apparent with age, is characterized by flexion at the elbows with ulnar deviation and flexion of the wrists and metacarpophalangeal joints. Feeding difficulties in early childhood, including cyclic vomiting, have a significant impact on overall health; feeding tends to improve with age. Seizures are common and typically responsive to standard epileptic medications. Minor cardiac anomalies and transient bradycardia and apnea may be present. Affected individuals may experience recurrent infections, which also tend to improve with age. Isolated case reports suggest that individuals with BOS are at greater risk for Wilms tumor than the general population, but large-scale epidemiologic studies have not been conducted.

Schimke immunoosseous dysplasia (SIOD) is characterized by spondyloepiphyseal dysplasia (SED) resulting in short stature, nephropathy, and T-cell deficiency. Radiographic manifestations of SED include ovoid and mildly flattened vertebral bodies, small ilia with shallow dysplastic acetabular fossae, and small deformed capital femoral epiphyses. Nearly all affected individuals have progressive steroid-resistant nephropathy, usually developing within five years of the diagnosis of growth failure and terminating with end-stage renal disease. The majority of tested individuals have T-cell deficiency and an associated risk for opportunistic infection, a common cause of death. SIOD involves a spectrum that ranges from an infantile or severe early-onset form with a greater risk of death during childhood to a juvenile or milder later-onset form with likely survival into adulthood if renal disease is appropriately treated.

SHORT syndrome is a mnemonic for short stature, hyperextensibility, ocular depression (deeply set eyes), Rieger anomaly, and teething delay. It is now recognized that the features most consistently observed in SHORT syndrome are mild intrauterine growth restriction (IUGR); mild to moderate short stature; partial lipodystrophy (evident in the face, and later in the chest and upper extremities, often sparing the buttocks and legs); and a characteristic facial gestalt. Insulin resistance may be evident in mid-childhood or adolescence, although diabetes mellitus typically does not develop until early adulthood. Other frequent features include Axenfeld-Rieger anomaly or related ocular anterior chamber dysgenesis, delayed dentition and other dental issues, and sensorineural hearing loss.

Dyskeratosis congenita and related telomere biology disorders (DC/TBD) are caused by impaired telomere maintenance resulting in short or very short telomeres. The phenotypic spectrum of telomere biology disorders is broad and includes individuals with classic dyskeratosis congenita (DC) as well as those with very short telomeres and an isolated physical finding. Classic DC is characterized by a triad of dysplastic nails, lacy reticular pigmentation of the upper chest and/or neck, and oral leukoplakia, although this may not be present in all individuals. People with DC/TBD are at increased risk for progressive bone marrow failure (BMF), myelodysplastic syndrome or acute myelogenous leukemia, solid tumors (usually squamous cell carcinoma of the head/neck or anogenital cancer), and pulmonary fibrosis. Other findings can include eye abnormalities (epiphora, blepharitis, sparse eyelashes, ectropion, entropion, trichiasis), taurodontism, liver disease, gastrointestinal telangiectasias, and avascular necrosis of the hips or shoulders. Although most persons with DC/TBD have normal psychomotor development and normal neurologic function, significant developmental delay is present in both forms; additional findings include cerebellar hypoplasia (Hoyeraal Hreidarsson syndrome) and bilateral exudative retinopathy and intracranial calcifications (Revesz syndrome and Coats plus syndrome). Onset and progression of manifestations of DC/TBD vary: at the mild end of the spectrum are those who have only minimal physical findings with normal bone marrow function, and at the severe end are those who have the diagnostic triad and early-onset BMF.

Decreased fetal activity associated with multiple joint contractures, facial anomalies and pulmonary hypoplasia. Ultrasound examination may reveal polyhydramnios, ankylosis, scalp edema, and decreased chest movements (reflecting pulmonary hypoplasia).

Transaldolase deficiency (TALDOD) is a rare inborn error of pentose metabolism. Typical features include intrauterine growth restriction, triangular face, loose wrinkly skin at birth, and development of progressive liver failure (summary by Lee-Barber et al., 2019).

3-Phosphoserine phosphatase deficiency is an extremely rare form of serine deficiency syndrome (see this term) characterized clinically by congenital microcephaly and severe psychomotor retardation in the single reported case to date, which was associated with Williams syndrome (see this term).

Saul-Wilson syndrome (SWS) is a skeletal dysplasia characterized by profound short stature, distinctive craniofacial features, short distal phalanges of fingers and toes, and often clubfoot. Early development (primarily speech and motor) is delayed; cognition is normal. Other findings can include hearing loss (conductive, sensorineural, and mixed), lamellar cataracts, and/or rod-cone retinal dystrophy. To date, 16 affected individuals have been reported.

Nicolaides-Baraitser syndrome (NCBRS) is characterized by sparse scalp hair, prominence of the inter-phalangeal joints and distal phalanges due to decreased subcutaneous fat, characteristic coarse facial features, microcephaly, seizures, and developmental delay / intellectual disability. Seizures are of various types and can be difficult to manage. Developmental delay / intellectual disability (ID) is severe in nearly a half, moderate in a third, and mild in the remainder. Nearly a third never develop speech or language skills.

Dyskeratosis congenita and related telomere biology disorders (DC/TBD) are caused by impaired telomere maintenance resulting in short or very short telomeres. The phenotypic spectrum of telomere biology disorders is broad and includes individuals with classic dyskeratosis congenita (DC) as well as those with very short telomeres and an isolated physical finding. Classic DC is characterized by a triad of dysplastic nails, lacy reticular pigmentation of the upper chest and/or neck, and oral leukoplakia, although this may not be present in all individuals. People with DC/TBD are at increased risk for progressive bone marrow failure (BMF), myelodysplastic syndrome or acute myelogenous leukemia, solid tumors (usually squamous cell carcinoma of the head/neck or anogenital cancer), and pulmonary fibrosis. Other findings can include eye abnormalities (epiphora, blepharitis, sparse eyelashes, ectropion, entropion, trichiasis), taurodontism, liver disease, gastrointestinal telangiectasias, and avascular necrosis of the hips or shoulders. Although most persons with DC/TBD have normal psychomotor development and normal neurologic function, significant developmental delay is present in both forms; additional findings include cerebellar hypoplasia (Hoyeraal Hreidarsson syndrome) and bilateral exudative retinopathy and intracranial calcifications (Revesz syndrome and Coats plus syndrome). Onset and progression of manifestations of DC/TBD vary: at the mild end of the spectrum are those who have only minimal physical findings with normal bone marrow function, and at the severe end are those who have the diagnostic triad and early-onset BMF.

Cornelia de Lange syndrome (CdLS) encompasses a spectrum of findings from mild to severe. Severe (classic) CdLS is characterized by distinctive facial features, growth restriction (prenatal onset; <5th centile throughout life), hypertrichosis, and upper-limb reduction defects that range from subtle phalangeal abnormalities to oligodactyly (missing digits). Craniofacial features include synophrys, highly arched and/or thick eyebrows, long eyelashes, short nasal bridge with anteverted nares, small widely spaced teeth, and microcephaly. Individuals with a milder phenotype have less severe growth, cognitive, and limb involvement, but often have facial features consistent with CdLS. Across the CdLS spectrum IQ ranges from below 30 to 102 (mean: 53). Many individuals demonstrate autistic and self-destructive tendencies. Other frequent findings include cardiac septal defects, gastrointestinal dysfunction, hearing loss, myopia, and cryptorchidism or hypoplastic genitalia.

6q24-related transient neonatal diabetes mellitus (6q24-TNDM) is defined as transient neonatal diabetes mellitus caused by genetic aberrations of the imprinted locus at 6q24. The cardinal features are: severe intrauterine growth retardation, hyperglycemia that begins in the neonatal period in a term infant and resolves by age 18 months, dehydration, and absence of ketoacidosis. Macroglossia and umbilical hernia may be present. 6q24-TNDM associated with a multilocus imprinting disturbance (MLID) can be associated with marked hypotonia, congenital heart disease, deafness, neurologic features including epilepsy, and renal malformations. Diabetes mellitus usually starts within the first week of life and lasts on average three months but can last longer than a year. Although insulin is usually required initially, the need for insulin gradually declines over time. Intermittent episodes of hyperglycemia may occur in childhood, particularly during intercurrent illnesses. Diabetes mellitus may recur in adolescence or later in adulthood. Women who have had 6q24-TNDM are at risk for relapse during pregnancy.

The Martinez-Frias syndrome is characterized by pancreatic hypoplasia, intestinal atresia, and gallbladder aplasia or hypoplasia, with or without tracheoesophageal fistula. There is considerable phenotypic overlap between Martinez-Frias syndrome and Mitchell-Riley syndrome (MTCHRS; 615710), the latter being characterized by neonatal diabetes in addition to the features of the Martinez-Frias syndrome, but without tracheoesophageal fistula (Smith et al., 2010).

Syndromic microphthalmia-9 (MCOPS9), also referred to as pulmonary hypoplasia-diaphragmatic hernia-anophthalmia-cardiac defect, is characterized by bilateral clinical anophthalmia, pulmonary hypoplasia/aplasia, cardiac malformations, and diaphragmatic defects. The phenotype is variable, ranging from isolated clinical anophthalmia or microphthalmia to complex presentations involving the cardiac, pulmonary, diaphragmatic, and renal systems. At its most severe, infants are born without pulmonary structures and die soon after birth (Marcadier et al., 2015).

Most characteristically, Aicardi-Goutières syndrome (AGS) manifests as an early-onset encephalopathy that usually, but not always, results in severe intellectual and physical disability. A subgroup of infants with AGS present at birth with abnormal neurologic findings, hepatosplenomegaly, elevated liver enzymes, and thrombocytopenia, a picture highly suggestive of congenital infection. Otherwise, most affected infants present at variable times after the first few weeks of life, frequently after a period of apparently normal development. Typically, they demonstrate the subacute onset of a severe encephalopathy characterized by extreme irritability, intermittent sterile pyrexias, loss of skills, and slowing of head growth. Over time, as many as 40% develop chilblain skin lesions on the fingers, toes, and ears. It is becoming apparent that atypical, sometimes milder, cases of AGS exist, and thus the true extent of the phenotype associated with pathogenic variants in the AGS-related genes is not yet known.

Combined oxidative phosphorylation deficiency is an autosomal recessive multisystem disorder with variable manifestations resulting from a defect in the mitochondrial oxidative phosphorylation (OXPHOS) system. Onset occurs at or soon after birth, and features can include growth retardation, microcephaly, hypertonicity, axial hypotonia, encephalopathy, cardiomyopathy, and liver dysfunction. Death usually occurs in the first weeks or years of life (summary by Smits et al., 2011). Genetic Heterogeneity of Combined Oxidative Phosphorylation Deficiency See also COXPD2 (610498), caused by mutation in the MRPS16 gene (609204) on 10q22; COXPD3 (610505), caused by mutation in the TSFM gene (604723) on 12q14; COXPD4 (610678), caused by mutation in the TUFM gene (602389) on 16p11; COXPD5 (611719), caused by mutation in the MRPS22 gene (605810) on 3q23; COXPD6 (300816), caused by mutation in the AIFM1 gene (300169) on Xq26; COXPD7 (613559), caused by mutation in the MTRFR gene (613541) on 12q24; COXPD8 (614096), caused by mutation in the AARS2 gene (612035) on 6p21; COXPD9 (614582), caused by mutation in the MRPL3 gene (607118) on 3q22; COXPD10 (614702), caused by mutation in the MTO1 gene (614667) on 6q13; COXPD11 (614922), caused by mutation in the RMND1 gene (614917) on 6q25; COXPD12 (614924), caused by mutation in the EARS2 gene (612799) on 16p13; COXPD13 (614932), caused by mutation in the PNPT1 gene (610316) on 2p16; COXPD14 (614946), caused by mutation in the FARS2 gene (611592) on 6p25; COXPD15 (614947), caused by mutation in the MTFMT gene (611766) on 15q; COXPD16 (615395), caused by mutation in the MRPL44 gene (611849) on 2q36; COXPD17 (615440), caused by mutation in the ELAC2 gene (605367) on 17p11; COXPD18 (615578), caused by mutation in the SFXN4 gene (615564) on 10q26; COXPD19 (615595), caused by mutation in the LYRM4 gene (613311) on 6p25; COXPD20 (615917), caused by mutation in the VARS2 gene (612802) on 6p21; COXPD21 (615918), caused by mutation in the TARS2 gene (612805) on 1q21; COXPD22 (616045), caused by mutation in the ATP5A1 gene (164360) on 18q12; COXPD23 (616198), caused by mutation in the GTPBP3 (608536) gene on 19p13; COXPD24 (616239), caused by mutation in the NARS2 gene (612803) on 11q14; COXPD25 (616430), caused by mutation in the MARS2 gene (609728) on 2q33; COXPD26 (616539), caused by mutation in the TRMT5 gene (611023) on 14q23; COXPD27 (616672), caused by mutation in the CARS2 gene (612800) on 13q34; COXPD28 (616794), caused by mutation in the SLC25A26 gene (611037) on 3p14; COXPD29 (616811), caused by mutation in the TXN2 gene (609063) on 22q12; COXPD30 (616974), caused by mutation in the TRMT10C gene (615423) on 3q12; and COXPD31 (617228), caused by mutation in the MIPEP gene (602241) on 13q12; COXPD32 (617664), caused by mutation in the MRPS34 gene (611994) on 16q13; COXPD33 (617713), caused by mutation in the C1QBP gene (601269) on 17p13; and COXPD34 (617872), caused by mutation in the MRPS7 gene (611974) on 17q25; COXPD35 (617873), caused by mutation in the TRIT1 gene (617840) on 1p34; COXPD36 (617950), caused by mutation in the MRPS2 gene (611971) on 9q34; COXPD37 (618329), caused by mutation in the MICOS13 gene (616658) on 19p13; COXPD38 (618378), caused by mutation in the MRPS14 gene (611978) on 1q23; COXPD39 (618397), caused by mutation in the GFM2 gene (606544) on 5q13; COXPD40 (618835), caused by mutation in the QRSL1 gene (617209) on 6q21; COXPD41 (618838), caused by mutation in the GATB gene (603645) on 4q31; COXPD42 (618839), caused by mutation in the GATC gene (617210) on 12q24; COXPD43 (618851), caused by mutation in the TIMM22 gene (607251) on 17p13; COXPD44 (618855), caused by mutation in the FASTKD2 gene (612322) on 2q33; COXPD45 (618951), caused by mutation in the MRPL12 gene (602375) on 17q25; COXPD46 (618952), caused by mutation in the MRPS23 gene (611985) on 17q22; COXPD47 (618958), caused by mutation in the MRPS28 gene (611990) on 8q21; COXPD48 (619012), caused by mutation in the NSUN3 gene (617491) on 3q11; COXPD49 (619024), caused by mutation in the MIEF2 gene (615498) on 17p11; COXPD50 (619025), caused by mutation in the MRPS25 gene (611987) on 3p25; COXPD51 (619057), caused by mutation in the PTCD3 gene (614918) on 2p11; COXPD52 (619386), caused by mutation in the NFS1 gene (603485) on 20q11; COXPD53 (619423), caused by mutation in the C2ORF69 gene (619219) on 2q33; and COXPD54 (619737), caused by mutation in the PRORP gene (609947) on 14q13.; COXPD55 (619743), caused by mutation in the POLRMT gene (601778) on 19p13; COXPD56 (620139), caused by mutation in the TAMM41 gene (614948) on 3p25; COXPD57 (620167), caused by mutation in the CRLS1 gene (608188) on 20p12; COXPD58 (620451), caused by mutation in the TEFM gene (616422) on 17q11; and COXPD59 (620646), caused by mutation in the MRPL39 gene (611845) on 21q21.

Fanconi anemia (FA) is characterized by physical abnormalities, bone marrow failure, and increased risk for malignancy. Physical abnormalities, present in approximately 75% of affected individuals, include one or more of the following: short stature, abnormal skin pigmentation, skeletal malformations of the upper and/or lower limbs, microcephaly, and ophthalmic and genitourinary tract anomalies. Progressive bone marrow failure with pancytopenia typically presents in the first decade, often initially with thrombocytopenia or leukopenia. The incidence of acute myeloid leukemia is 13% by age 50 years. Solid tumors – particularly of the head and neck, skin, and genitourinary tract – are more common in individuals with FA.

Fanconi anemia (FA) is characterized by physical abnormalities, bone marrow failure, and increased risk for malignancy. Physical abnormalities, present in approximately 75% of affected individuals, include one or more of the following: short stature, abnormal skin pigmentation, skeletal malformations of the upper and/or lower limbs, microcephaly, and ophthalmic and genitourinary tract anomalies. Progressive bone marrow failure with pancytopenia typically presents in the first decade, often initially with thrombocytopenia or leukopenia. The incidence of acute myeloid leukemia is 13% by age 50 years. Solid tumors – particularly of the head and neck, skin, and genitourinary tract – are more common in individuals with FA.

Emanuel syndrome is characterized by pre- and postnatal growth deficiency, microcephaly, hypotonia, severe developmental delays, ear anomalies, preauricular tags or pits, cleft or high-arched palate, congenital heart defects, kidney abnormalities, and genital abnormalities in males.

Insulin-like growth factor I deficiency (IGF1D) is characterized by severe pre- and postnatal growth failure, sensorineural deafness, and impaired motor and intellectual development (summary by Bonapace et al., 2003).

Intellectual disability-brachydactyly-Pierre Robin syndrome is a rare developmental defect during embryogenesis syndrome characterized by mild to moderate intellectual disability and phsychomotor delay, Robin sequence (incl. severe micrognathia and soft palate cleft) and distinct dysmorphic facial features (e.g. synophris, short palpebral fissures, hypertelorism, small, low-set, and posteriorly angulated ears, bulbous nose, long/flat philtrum, and bow-shaped upper lip). Skeletal anomalies, such as brachydactyly, clinodactyly, small hands and feet, and oral manifestations (e.g. bifid, short tongue, oligodontia) are also associated. Additional features reported include microcephaly, capillary hemangiomas on face and scalp, ventricular septal defect, corneal clouding, nystagmus and profound sensorineural deafness.

Fanconi anemia (FA) is characterized by physical abnormalities, bone marrow failure, and increased risk for malignancy. Physical abnormalities, present in approximately 75% of affected individuals, include one or more of the following: short stature, abnormal skin pigmentation, skeletal malformations of the upper and/or lower limbs, microcephaly, and ophthalmic and genitourinary tract anomalies. Progressive bone marrow failure with pancytopenia typically presents in the first decade, often initially with thrombocytopenia or leukopenia. The incidence of acute myeloid leukemia is 13% by age 50 years. Solid tumors – particularly of the head and neck, skin, and genitourinary tract – are more common in individuals with FA.

X-linked lethal multiple pterygium syndrome is a rare, genetic, developmental defect during embryogenesis characterized by the typical lethal multiple pterygium syndrome presentation (comprising of multiple pterygia, severe arthrogryposis, cleft palate, cystic hygromata and/or fetal hydrops, skeletal abnormalities and fetal death in the 2nd or 3rd trimester) with an X-linked pattern of inheritance.

The classic features of TARP syndrome are talipes equinovarus, atrial septal defect, Robin sequence (micrognathia, cleft palate, and glossoptosis), and persistent left superior vena cava. Not all patients have all classic features. Some patients have the additional features of central nervous system dysfunction, renal abnormalities, variable cardiac anomalies including hypertrophic obstructive cardiomyopathy, and variable distal limb defects including syndactyly. Most patients die in late prenatal or early postnatal stages (summary by Kaeppler et al., 2018).

Lipodystrophy-intellectual disability-deafness syndrome is an extremely rare form of genetic lipodystrophy (see this term), reported in 3 patients from one family to date, characterized by generalized congenital lipodystrophy, low birth weight, progressive sensorineural deafness occurring in childhood, intellectual deficit, progressive osteopenia, delayed skeletal maturation, skeletal abnormalities described as slender, undermineralized tubular bones, and dense metaphyseal striations in the distal femur, ulna and radius of older patients. Autosomal recessive inheritance has been suggested.

Diaphanospondylodysostosis is a rare, recessively inherited, perinatal lethal skeletal disorder. The primary skeletal characteristics include small chest, abnormal vertebral segmentation, and posterior rib gaps containing incompletely differentiated mesenchymal tissue. Consistent craniofacial features include ocular hypertelorism, epicanthal folds, depressed nasal bridge with short nose, and low-set ears. The most commonly described extraskeletal finding is nephroblastomatosis with cystic kidneys, but other visceral findings have been described in some cases (summary by Funari et al., 2010).

Gaucher disease (GD) encompasses a continuum of clinical findings from a perinatal lethal disorder to an asymptomatic type. The identification of three major clinical types (1, 2, and 3) and two other subtypes (perinatal-lethal and cardiovascular) is useful in determining prognosis and management. GD type 1 is characterized by the presence of clinical or radiographic evidence of bone disease (osteopenia, focal lytic or sclerotic lesions, and osteonecrosis), hepatosplenomegaly, anemia and thrombocytopenia, lung disease, and the absence of primary central nervous system disease. GD types 2 and 3 are characterized by the presence of primary neurologic disease; in the past, they were distinguished by age of onset and rate of disease progression, but these distinctions are not absolute. Disease with onset before age two years, limited psychomotor development, and a rapidly progressive course with death by age two to four years is classified as GD type 2. Individuals with GD type 3 may have onset before age two years, but often have a more slowly progressive course, with survival into the third or fourth decade. The perinatal-lethal form is associated with ichthyosiform or collodion skin abnormalities or with nonimmune hydrops fetalis. The cardiovascular form is characterized by calcification of the aortic and mitral valves, mild splenomegaly, corneal opacities, and supranuclear ophthalmoplegia. Cardiopulmonary complications have been described with all the clinical subtypes, although varying in frequency and severity.

X-linked microhydranencephaly is a male-lethal disorder characterized by intrauterine growth retardation, extreme microcephaly, and lack of fetal movement on prenatal ultrasound, with death in utero or stillbirth. Autopsy shows limb contractures with talipes equinovarus and hypoplastic lungs and kidneys. Brain findings are consistent with severe holoprosencephaly or near-anencephaly. Obligate carrier females may show a milder phenotype of short stature and microcephaly (Hockey et al., 1988; Carroll et al., 2017). An autosomal recessive form of microhydranencephaly (MHAC; 605013) is caused by mutation in the NDE1 gene (609449).

Catel-Manzke syndrome is characterized by the Pierre Robin anomaly, which comprises cleft palate, glossoptosis, and micrognathia, and a unique form of bilateral hyperphalangy in which there is an accessory bone inserted between the second metacarpal and its corresponding proximal phalanx, resulting in radial deviation of the index finger (summary by Manzke et al., 2008).

Fanconi anemia (FA) is characterized by physical abnormalities, bone marrow failure, and increased risk for malignancy. Physical abnormalities, present in approximately 75% of affected individuals, include one or more of the following: short stature, abnormal skin pigmentation, skeletal malformations of the upper and/or lower limbs, microcephaly, and ophthalmic and genitourinary tract anomalies. Progressive bone marrow failure with pancytopenia typically presents in the first decade, often initially with thrombocytopenia or leukopenia. The incidence of acute myeloid leukemia is 13% by age 50 years. Solid tumors – particularly of the head and neck, skin, and genitourinary tract – are more common in individuals with FA.

IMAGe syndrome is an acronym for the major findings of intrauterine growth restriction (IUGR), metaphyseal dysplasia, adrenal hypoplasia congenita, and genitourinary abnormalities (in males). Findings reported in individuals with a clinical and/or molecular diagnosis include: IUGR; Some type of skeletal abnormality (most commonly delayed bone age and short stature, and occasionally, metaphyseal and epiphyseal dysplasia of varying severity); Adrenal insufficiency often presenting in the first month of life as an adrenal crisis or (rarely) later in childhood with failure to thrive and recurrent vomiting; Genital abnormalities in males (cryptorchidism, micropenis, and hypospadias) but not in females. Hypotonia and developmental delay are reported in some individuals; cognitive outcome appears to be normal in the majority of individuals.

Roifman syndrome is a multisystem disorder characterized by growth retardation, spondyloepiphyseal dysplasia, retinal dystrophy, distinctive facial dysmorphism, and immunodeficiency (summary by de Vries et al., 2006).

The AMME complex is an X-linked contiguous gene deletion syndrome with features of Alport syndrome, mental retardation, midface hypoplasia, and elliptocytosis in affected males (summary by Meloni et al., 2002).

This syndrome has characteristics of intrauterine growth retardation, renal dysgenesis and a unilobed or absent thymus. It has been described in three girls born to a nonconsanguineous couple.

Patients with mutations in the receptor for insulin-like growth factor I show intrauterine growth retardation and postnatal growth failure, resulting in short stature and microcephaly. Other features may include delayed bone age, developmental delay, and dysmorphic features.

Bartsocas-Papas syndrome-1 (BPS1) is an autosomal recessive disorder characterized by multiple popliteal pterygia, ankyloblepharon, filiform bands between the jaws, cleft lip and palate, and syndactyly. Early lethality is common, although survival into childhood and beyond has been reported (summary by Mitchell et al., 2012). Genetic Heterogeneity of Bartsocas-Papas Syndrome Bartsocas-Papas syndrome-2 (BPS2) is caused by mutation in the CHUK gene (600664). A less severe form of popliteal pterygium syndrome (PPS; 119500) is caused by mutation in the IRF6 gene (607199).

Mosaic variegated aneuploidy (MVA) syndrome is a rare disorder in which some cells in the body have an abnormal number of chromosomes instead of the usual 46 chromosomes, a situation known as aneuploidy. Most commonly, cells have an extra chromosome, which is called trisomy, or are missing a chromosome, which is known as monosomy. In MVA syndrome, some cells are aneuploid and others have the normal number of chromosomes, which is a phenomenon known as mosaicism. Typically, at least one-quarter of cells in affected individuals have an abnormal number of chromosomes. Because the additional or missing chromosomes vary among the abnormal cells, the aneuploidy is described as variegated.\n\nThere are at least three types of MVA syndrome, each with a different genetic cause. Type 1 is the most common and displays the classic signs and symptoms described above. Type 2 appears to have slightly different signs and symptoms than type 1, although the small number of affected individuals makes it difficult to define its characteristic features. Individuals with MVA syndrome type 2 grow slowly before and after birth; however, their head size is typically normal. Some people with MVA syndrome type 2 have unusually short arms. Individuals with MVA syndrome type 2 do not seem to have an increased risk of cancer. Another form of MVA syndrome is characterized by a high risk of developing Wilms tumor. Individuals with this form may also have other signs and symptoms typical of MVA syndrome type 1.\n\nIn MVA syndrome, growth before birth is slow (intrauterine growth restriction). After birth, affected individuals continue to grow at a slow rate and are shorter than average. In addition, they typically have an unusually small head size (microcephaly). Another common feature of MVA syndrome is an increased risk of developing cancer in childhood. Cancers that occur most frequently in affected individuals include a cancer of muscle tissue called rhabdomyosarcoma, a form of kidney cancer known as Wilms tumor, and a cancer of the blood-forming tissue known as leukemia.\n\nLess commonly, people with MVA syndrome have eye abnormalities or distinctive facial features, such as a broad nasal bridge and low-set ears. Some affected individuals have brain abnormalities, the most common of which is called Dandy-Walker malformation. Intellectual disability, seizures, and other health problems can also occur in people with MVA syndrome.

A rare disorder characterized by intrauterine growth retardation and intermittent locking of the finger joints. It has been described in two individuals: a mother and her daughter. The mode of transmission is autosomal dominant.

Cerebrooculofacioskeletal syndrome is a severe, progressive neurologic disorder characterized by prenatal onset of arthrogryposis, microcephaly, and growth failure. Postnatal features include severe developmental delay, congenital cataracts (in some), and marked UV sensitivity of the skin. Survival beyond 6 years of age is rare. COFS represents the severe end of the spectrum of disorders caused by mutations in nucleotide excision repair (NER) genes, with Cockayne syndrome and xeroderma pigmentosum being milder NER-related phenotypes (summary by Drury et al., 2014). For a phenotypic description and a discussion of genetic heterogeneity of cerebrooculofacioskeletal syndrome, see COFS1 (214150).

Cerebrooculofacioskeletal syndrome-4 (COFS4) is a severe autosomal recessive disorder characterized by growth retardation, dysmorphic facial features, arthrogryposis, and neurologic abnormalities. Cellular studies show a defect in both transcription-coupled and global genome nucleotide excision repair (TC-NER and GG-NER) (summary by Jaspers et al., 2007 and Kashiyama et al., 2013). For a discussion of genetic heterogeneity of cerebrooculofacioskeletal syndrome, see 214150.

Any COFS syndrome in which the cause of the disease is a mutation in the ERCC2 gene.

Wiedemann-Steiner syndrome (WSS) is characterized by developmental delay, intellectual disability, and characteristic facial features, with or without additional congenital anomalies. The facial features include thick eyebrows with lateral flare, vertically narrow and downslanted palpebral fissures, widely spaced eyes, long eyelashes, wide nasal bridge, broad nasal tip, thin vermilion of the upper lip, and thick scalp hair. About 60% of affected individuals have hypertrichosis cubiti ("hairy elbows"), which was once thought to be pathognomic for the syndrome, with a majority having hypertrichosis of other body parts. Other clinical features include feeding difficulties, prenatal and postnatal growth restriction, epilepsy, ophthalmologic anomalies, congenital heart defects, hand anomalies (such as brachydactyly and clinodactyly), hypotonia, vertebral anomalies (especially fusion anomalies of the cervical spine), renal and uterine anomalies, immune dysfunction, brain malformations, and dental anomalies.

In people with multiple pterygium syndrome, Escobar type, the webbing typically affects the skin of the neck, fingers, forearms, inner thighs, and backs of the knee. People with this type may also have arthrogryposis. A side-to-side curvature of the spine (scoliosis) is sometimes seen. Affected individuals may also have respiratory distress at birth due to underdeveloped lungs (lung hypoplasia). People with multiple pterygium syndrome, Escobar type usually have distinctive facial features including droopy eyelids (ptosis), outside corners of the eyes that point downward (downslanting palpebral fissures), skin folds covering the inner corner of the eyes (epicanthal folds), a small jaw, and low-set ears. Males with this condition can have undescended testes (cryptorchidism). This condition does not worsen after birth, and affected individuals typically do not have muscle weakness later in life.\n\nThe two forms of multiple pterygium syndrome are differentiated by the severity of their symptoms. Multiple pterygium syndrome, Escobar type (sometimes referred to as Escobar syndrome) is the milder of the two types. Lethal multiple pterygium syndrome is fatal before birth or very soon after birth.\n\nLethal multiple pterygium syndrome has many of the same signs and symptoms as the Escobar type. In addition, affected fetuses may develop a buildup of excess fluid in the body (hydrops fetalis) or a fluid-filled sac typically found on the back of the neck (cystic hygroma). Individuals with this type have severe arthrogryposis. Lethal multiple pterygium syndrome is associated with abnormalities such as underdevelopment (hypoplasia) of the heart, lung, or brain; twisting of the intestines (intestinal malrotation); kidney abnormalities; an opening in the roof of the mouth (a cleft palate); and an unusually small head size (microcephaly). Affected individuals may also develop a hole in the muscle that separates the abdomen from the chest cavity (the diaphragm), a condition called a congenital diaphragmatic hernia. Lethal multiple pterygium syndrome is typically fatal in the second or third trimester of pregnancy.\n\nMultiple pterygium syndrome is a condition that is evident before birth with webbing of the skin (pterygium) at the joints and a lack of muscle movement (akinesia) before birth. Akinesia frequently results in muscle weakness and joint deformities called contractures that restrict the movement of joints (arthrogryposis). As a result, multiple pterygium syndrome can lead to further problems with movement such as arms and legs that cannot fully extend.

Microcephaly-micromelia syndrome (MIMIS) is a severe autosomal recessive disorder that usually results in death in utero or in the perinatal period. Affected individuals have severe growth retardation with microcephaly and variable malformations of the limbs, particularly the upper limbs. Defects include radial ray anomalies, malformed digits, and clubfeet (summary by Evrony et al., 2017).

A rare, primary bone dysplasia characterized by prenatal and postnatal growth retardation, short stature, cortical thickening and medullary stenosis of the long bones, absent diploic space in the skull bones, hypocalcemia due to the hypoparathyroidism, small hands and feet, delayed mental and motor development, intellectual disability, dental anomalies, and dysmorphic features, including prominent forehead, small deep-set eyes, beaked nose, and micrognathia.

Hydrolethalus-1 (HLS1) is an autosomal recessive lethal malformation syndrome characterized by hydrocephaly with absent upper midline structures of the brain, micrognathia, and polydactyly. Various other features such as cleft lip or palate, club feet, anomalies of the ears, eyes, and nose, keyhole-shaped defect in the occipital bone, abnormal genitalia, and congenital heart and respiratory organ defects have also been observed in affected individuals. Affected individuals are stillborn or die shortly after birth (summary by Mee et al., 2005). Genetic Heterogeneity of Hydrolethalus Syndrome See also HLS2 (614120), caused by mutation in the KIF7 gene (611254) on chromosome 15q26.

Hall-Riggs syndrome is a very rare syndrome consisting of microcephaly with facial dysmorphism, spondylometaepiphyseal dysplasia and severe intellectual deficit.

The proliferative vasculopathy and hydranencephaly-hydrocephaly syndrome is a rare, autosomal recessive, usually prenatally lethal disorder characterized by hydranencephaly, a distinctive glomerular vasculopathy in the central nervous system and retina, and diffuse ischemic lesions of the brain stem, basal ganglia, and spinal cord with calcifications. It is usually diagnosed by ultrasound between 26 and 33 weeks' gestation (summary by Meyer et al., 2010). Rarely, affected individuals may survive, but are severely impaired with almost no neurologic development (Kvarnung et al., 2016).

2,4-Dienoyl-CoA reductase deficiency (DECRD) is a rare autosomal recessive inborn error of metabolism resulting in mitochondrial dysfunction due to impaired production of NADPH, which is an essential cofactor for several mitochondrial enzymes. Affected individuals have a variable phenotype: some may have severe neurologic symptoms and metabolic dysfunction beginning in early infancy, whereas others may present with more subtle features, such as childhood-onset optic atrophy or intermittent muscle weakness. The variable severity is putatively dependent on the effect of the mutation on the NADK2 enzyme. Biochemical analysis typically shows hyperlysinemia, due to defective activity of the mitochondrial NADP(H)-dependent enzyme AASS (605113), which is usually a benign finding. More severe cases have increased C10:2-carnitine levels, due to defective activity of the enzyme DECR (DECR1; 222745) (summary by Houten et al., 2014 and Pomerantz et al., 2018).

Yunis-Varon syndrome (YVS) is a severe autosomal recessive disorder characterized by skeletal defects, including cleidocranial dysplasia and digital anomalies, and severe neurologic involvement with neuronal loss. Enlarged cytoplasmic vacuoles are found in neurons, muscle, and cartilage. The disorder is usually lethal in infancy (summary by Campeau et al., 2013).

A rare mitochondrial disorder due to a defect in mitochondrial protein synthesis with characteristics of neonatal onset of severe metabolic acidosis and respiratory distress, persistent lactic acidosis with episodes of metabolic crises, developmental regression, microcephaly, abnormal gaze fixation and pursuit, axial hypotonia with limb spasticity and reduced spontaneous movements. Neuroimaging studies reveal polymicrogyria, white matter abnormalities and multiple cystic brain lesions, including basal ganglia, and cerebral atrophy. Decreased activity of complex I and IV have been determined in muscle biopsy.

Neonatal diabetes mellitus with congenital hypothyroidism (NDH) syndrome is characterized by intrauterine growth retardation and onset of nonimmune diabetes mellitus within the first few weeks of life. Other features include renal parenchymal disease, primarily renal cystic dysplasia, and hepatic disease, with hepatitis in some patients and hepatic fibrosis and cirrhosis in others. Facial dysmorphism, when present, consistently involves low-set ears, epicanthal folds, flat nasal bridge, long philtrum, and thin upper lip. Most patients exhibit developmental delay (Dimitri et al., 2015).

3-Methylglutaconic aciduria type V (MGCA5) is an autosomal recessive disorder characterized by the onset of dilated or noncompaction cardiomyopathy in infancy or early childhood. Many patients die of cardiac failure. Other features include microcytic anemia, growth retardation, mild ataxia, mild muscle weakness, genital anomalies in males, and increased urinary excretion of 3-methylglutaconic acid. Some patients may have optic atrophy or delayed psychomotor development (summary by Davey et al., 2006 and Ojala et al., 2012). For a discussion of genetic heterogeneity of 3-methylglutaconic aciduria, see MGCA type I (250950).

Autosomal recessive distal hereditary motor neuronopathy-1 (HMNR1) is characterized by distal and proximal muscle weakness and diaphragmatic palsy that leads to respiratory distress. Without intervention, most infants with the severe form of the disease die before 2 years of age. Affected individuals present in infancy with inspiratory stridor, weak cry, recurrent bronchopneumonia, and swallowing difficulties. The disorder is caused by distal and progressive motor neuronopathy resulting in muscle weakness (summary by Perego et al., 2020). Genetic Heterogeneity of Autosomal Recessive Distal Hereditary Motor Neuronopathy See also HMNR2 (605726), caused by mutation in the SIGMAR1 gene (601978); HMNR3 (607088) (encompassing Harding HMN types III and IV), which maps to chromosome 11q13; HMNR4 (611067), caused by mutation in the PLEKHG5 gene (611101); HMNR5 (614881), caused by mutation in the DNAJB2 gene (604139); HMNR6 (620011), caused by mutation in the REEP1 gene (609139); HMNR7 (619216), caused by mutation in the VWA1 gene (611901); HMNR8 (618912), caused by mutation in the SORD gene (182500); HMNR9 (620402), caused by mutation in the COQ7 gene (601683); and HMRN10 (620542), caused by mutation in the VRK1 gene (602168).

Microcephalic osteodysplastic primordial dwarfism type I is a severe autosomal recessive skeletal dysplasia characterized by dwarfism, microcephaly, and neurologic abnormalities, including mental retardation, brain malformations, and ocular/auditory sensory deficits. Patients often die in early childhood (summary by Pierce and Morse, 2012).

A very rare multiple congenital anomalies syndrome with characteristics of limb deficiencies and renal anomalies that include split hand-split foot malformation, renal agenesis, polycystic kidneys, uterine anomalies and severe mandibular hypoplasia.

GRACILE syndrome is an autosomal recessive lethal disorder characterized by fetal growth retardation, lactic acidosis, aminoaciduria, cholestasis, and abnormalities in iron metabolism. Patients develop fulminant lactic acidosis during the first day of life. Despite intensive care, about half of affected infants die during the first days of life, and the remainder within 4 months of life. Finnish and British patients have been reported, with slightly different phenotypes; the British patients have additional features of complex III deficiency and neurologic symptoms (Visapaa et al., 2002).

Meckel syndrome is a rare autosomal recessive lethal condition characterized by an occipital meningoencephalocele, enlarged kidneys with multicystic dysplasia and fibrotic changes in the portal area of the liver and with ductal proliferation, and postaxial polydactyly. For a more complete phenotypic description and information on genetic heterogeneity, see MKS1 (249000).

Combined oxidative phosphorylation deficiency type 3 is an extremely rare clinically heterogenous disorder described in about 5 patients to date. Clinical signs included hypotonia, lactic acidosis, and hepatic insufficiency, with progressive encephalomyopathy or hypertrophic cardiomyopathy.

Koolen-de Vries syndrome (KdVS) is characterized by developmental delay / intellectual disability, neonatal/childhood hypotonia, dysmorphisms, congenital malformations, and behavioral features. Psychomotor developmental delay is noted in all individuals from an early age. The majority of individuals with KdVS function in the mild-to-moderate range of intellectual disability. Other findings include speech and language delay (100%), epilepsy (~33%), congenital heart defects (25%-50%), renal and urologic anomalies (25%-50%), and cryptorchidism (71% of males). Behavior in most is described as friendly, amiable, and cooperative.

Immunodeficiency-54 is an autosomal recessive primary immunodeficiency characterized by severe intra- and extrauterine growth retardation, microcephaly, decreased numbers of natural killer (NK) cells, and recurrent viral infections, most often affecting the respiratory tract and leading to respiratory failure. Affected individuals also have adrenal insufficiency requiring corticosteroid replacement therapy and may have an increased susceptibility to cancer. Laboratory studies of patient cells showed a DNA repair defect (summary by Gineau et al., 2012).

Wolf-Hirschhorn syndrome is a congenital malformation syndrome characterized by pre- and postnatal growth deficiency, developmental disability of variable degree, characteristic craniofacial features ('Greek warrior helmet' appearance of the nose, high forehead, prominent glabella, hypertelorism, high-arched eyebrows, protruding eyes, epicanthal folds, short philtrum, distinct mouth with downturned corners, and micrognathia), and a seizure disorder (Battaglia et al., 2008).

Meckel syndrome is an autosomal recessive pre- or perinatal lethal disorder characterized by a combination of renal cysts and variably associated features including developmental anomalies of the central nervous system (typically occipital encephalocele), hepatic ductal dysplasia and cysts, and postaxial polydactyly (summary by Baala et al., 2007). For a more complete phenotypic description and information on genetic heterogeneity of Meckel syndrome, see MKS1 (249000).

Distal monosomy 15q is a rare chromosomal anomaly syndrome characterized by pre- and postnatal growth restriction, developmental delay, variable degrees of intellectual disability, hand and foot anomalies (e.g. brachy-/clinodactyly, talipes equinovarus, nail hypoplasia, proximally placed digits) and mild craniofacial dysmorphism (incl. microcephaly, triangular face, broad nasal bridge, micrognathia). Neonatal lymphedema, heart malformations, aplasia cutis congenita, aortic root dilatation, and autistic spectrum disorder have also been reported.

Diamond-Blackfan anemia (DBA) is characterized by a profound normochromic and usually macrocytic anemia with normal leukocytes and platelets, congenital malformations in up to 50%, and growth deficiency in 30% of affected individuals. The hematologic complications occur in 90% of affected individuals during the first year of life. The phenotypic spectrum ranges from a mild form (e.g., mild anemia or no anemia with only subtle erythroid abnormalities, physical malformations without anemia) to a severe form of fetal anemia resulting in nonimmune hydrops fetalis. DBA is associated with an increased risk for acute myelogenous leukemia (AML), myelodysplastic syndrome (MDS), and solid tumors including osteogenic sarcoma.

Chromosome 2p16.1-p15 deletion syndrome is a neurodevelopmental disorder characterized by delayed psychomotor development, intellectual disability, and variable but distinctive dysmorphic features, including microcephaly, bitemporal narrowing, smooth and long philtrum, hypertelorism, downslanting palpebral fissures, broad nasal root, thin upper lip, and high palate. Many patients have behavioral disorders, including autistic features, as well as structural brain abnormalities, such as pachygyria or hypoplastic corpus callosum. Those with deletions including the BCL11A gene (606557) also have persistence of fetal hemoglobin (HbF), which is asymptomatic and does not affected hematologic parameters or susceptibility to infection (summary by Funnell et al., 2015). Point mutation in the BCL11A gene causes intellectual developmental disorder with persistence of fetal hemoglobin (617101), which shows overlapping features. See also fetal hemoglobin quantitative trait locus-5 (HBFQTL5; 142335).

Diamond-Blackfan anemia (DBA) is characterized by a profound normochromic and usually macrocytic anemia with normal leukocytes and platelets, congenital malformations in up to 50%, and growth deficiency in 30% of affected individuals. The hematologic complications occur in 90% of affected individuals during the first year of life. The phenotypic spectrum ranges from a mild form (e.g., mild anemia or no anemia with only subtle erythroid abnormalities, physical malformations without anemia) to a severe form of fetal anemia resulting in nonimmune hydrops fetalis. DBA is associated with an increased risk for acute myelogenous leukemia (AML), myelodysplastic syndrome (MDS), and solid tumors including osteogenic sarcoma.

Connective tissue disorder due to lysyl hydroxylase-3 deficiency is a rare, genetic disease, caused by lack of lysyl hydrohylase 3 (LH3) activity, characterized by multiple tissue and organ involvement, including skeletal abnormalities (club foot, progressive scoliosis, osteopenia, pathologic fractures), ocular involvement (flat retinae, myopia, cataracts) and hair, nail and skin anomalies (coarse, abnormally distributed hair, skin blistering, reduced palmar creases, hypoplastic nails). Patients also present intrauterine growth retardation, facial dysmorphism (flat facial profile, low-set ears, shallow orbits, short and upturned nose, downturned corners of mouth) and joint flexion contractures. Growth and developmental delay, bilateral sensorineural deafness, friable diaphragm and later-onset spontaneous vascular ruptures are additional reported features.

SLC25A24 Fontaine progeroid syndrome is a multisystem connective tissue disorder characterized by poor growth, abnormal skeletal features, and distinctive craniofacial features with sagging, thin skin, and decreased subcutaneous fat suggesting an aged appearance that is most pronounced in infancy and improves with time. Characteristic radiographic features include turribrachycephaly with widely open anterior fontanelle, craniosynostosis, and anomalies of the terminal phalanges. Cardiovascular, genitourinary, ocular, and gastrointestinal abnormalities may also occur. To date, 13 individuals with a molecularly confirmed diagnosis of SLC25A24 Fontaine progeroid syndrome have been described.

X-linked intellectual disability-craniofacioskeletal syndrome is a rare, hereditary, syndromic intellectual disability characterized by craniofacial and skeletal abnormalities in association with mild intellectual disability in females and early postnatal lethality in males. In addition to mild cognitive impairment, females present with microcephaly, short stature, skeletal features and extra temporal lobe gyrus. In males, intrauterine growth impairment, cardiac and urogenital anomalies have been reported.

Syndrome with the association of toe syndactyly, facial dysmorphism including telecanthus and a broad nasal tip, urogenital malformations and anal atresia. Around ten cases have been reported so far. The syndrome is caused by mutations in the FAM58A gene (located on the X chromosome) encoding a protein of unknown function.

Three M syndrome is characterized by severe pre- and postnatal growth deficiency (final height 5-6 SD below the mean; i.e., 120-130 cm), characteristic facies, and normal intelligence. Additional features of three M syndrome include short broad neck, prominent trapezii, deformed sternum, short thorax, square shoulders, winged scapulae, hyperlordosis, short fifth fingers, prominent heels, and loose joints. Males with three M syndrome have hypogonadism and occasionally hypospadias.

A rare chromosomal anomaly syndrome, resulting from the partial deletion of the long arm of chromosome 22, outside the DiGeorge critical region. The phenotype is characterized by prematurity, pre- and post-natal growth retardation, developmental delay (particularly speech), mild intellectual disability, variable cardiac defects, and minor skeletal anomalies (such as clinodactyly). Dysmorphic features present in half of the individuals include microcephaly, arched eyebrows, deep set eyes, narrow upslanting palpebral fissures, ear abnormalities (low-set ears, tags and pits), hypoplastic alae nasi, smooth philtrum, down-turned mouth, thin upper lip, retro/micrognatia and pointed chin. For certain very distal deletions including the <i>SMARCB1</i> gene, there is a risk of developing malignant rhabdoid tumours. Most deletions are <i>de novo </i>.

Syndrome that has characteristics of female to male sex reversal and developmental anomalies of the kidneys, adrenal glands and lungs. The syndrome is lethal and has been described in three fetuses. It is caused by homozygous missense mutations in the WNT4 gene. It is transmitted as an autosomal recessive trait.

Mitchell-Riley syndrome is characterized by neonatal diabetes, pancreatic hypoplasia, intestinal atresia, and gallbladder aplasia or hypoplasia. There is considerable phenotypic overlap between Mitchell-Riley syndrome and Martinez-Frias syndrome (601346), the latter being characterized by the features of the Mitchell-Riley syndrome except for neonatal diabetes, and including tracheoesophageal fistula in some patients (Smith et al., 2010).

The phenotype of autosomal recessive cutis laxa type II (ARCL2) includes cutis laxa of variable severity, abnormal growth, developmental delay, and associated skeletal abnormalities (summary by Morava et al., 2009). No specific clinical features distinguish ARCL2A (219200), which includes a glycosylation defect, and ARCL2B, in which abnormal glycosylation has not been reported (Morava et al., 2009; Guernsey et al., 2009). For a phenotypic description and discussion of genetic heterogeneity of autosomal recessive cutis laxa, see ARCL1A (219100).

Growth retardation, developmental delay, and facial dysmorphism (GDFD) is an autosomal recessive multiple congenital anomaly syndrome characterized by severe psychomotor retardation, poor overall growth, and dysmorphic facial features. Additional features may include cardiac malformations and deafness (summary by Daoud et al., 2016).

Three M syndrome is characterized by severe pre- and postnatal growth deficiency (final height 5-6 SD below the mean; i.e., 120-130 cm), characteristic facies, and normal intelligence. Additional features of three M syndrome include short broad neck, prominent trapezii, deformed sternum, short thorax, square shoulders, winged scapulae, hyperlordosis, short fifth fingers, prominent heels, and loose joints. Males with three M syndrome have hypogonadism and occasionally hypospadias.

CDGs, previously called carbohydrate-deficient glycoprotein syndromes, grew from hereditary multisystem disorders first recognized by Jaeken et al. (1980). The characteristic biochemical abnormality of CDGs is the hypoglycosylation of glycoproteins, which is routinely determined by isoelectric focusing of serum transferrin. Type I CDG comprises those disorders in which there is a defect in the assembly of lipid-linked oligosaccharides or their transfer onto nascent glycoproteins, whereas type II CDG comprises defects of trimming, elongation, and processing of protein-bound glycans. For a general discussion of CDGs, see CDG1A (212065). CDG1H is a severe form of CDG. The majority of patients have brain involvement, liver pathology, gastrointestinal symptoms, dysmorphism (including brachydactyly), eye involvement (especially cataract), and skin symptoms. Most patients die within the first year of life (summary by Marques-da-Silva et al., 2017).

Congenital disorders of glycosylation (CDGs) comprise a group of multisystem diseases with mostly severe psychomotor and mental retardation. Type I CDG comprises those disorders in which there are defects that affect biosynthesis of dolichol-linked oligosaccharides in the cytosol or the endoplasmic reticulum (ER), as well as defects involving the transfer of oligosaccharides onto nascent glycoproteins. Type II CDG comprises all defects of further trimming and elongation of N-linked oligosaccharides in the ER and Golgi (Schwarz et al., 2004). CDG1K is a type I CDG characterized by predominant neurologic involvement. Survival ranges from the second day of life to adulthood. The liver is affected in a minority of patients and shows hepatomegaly, edema, ascites, cholestatic jaundice, portal hypertension, and Budd-Chiari syndrome (summary by Marques-da-Silva et al., 2017). For a general discussion of CDGs, see CDG1A (212065).

Congenital disorder of glycosylation type Ix (CDG1X) is a rare autosomal recessive disorder of protein glycosylation. Clinical features include hypotonia, developmental delay, seizures and respiratory difficulties (Shrimal et al., 2013; Kilic and Akkus, 2020).

CDG IIe is caused by a mutation that impairs the integrity of the conserved oligomeric Golgi (COG) complex and alters Golgi trafficking, resulting in the disruption of multiple glycosylation pathways. For a general discussion of CDGs, see CDG1A (212065).

An extremely rare form of carbohydrate deficient glycoprotein syndrome with, in the few cases reported to date, variable signs including microcephaly, growth retardation, psychomotor retardation and facial dysmorphism.

The Catania type of acrofacial dysostosis is characterized by intrauterine growth retardation, short stature, microcephaly, intellectual disability, widow's peak, mandibulofacial dysostosis without cleft palate, ear anomalies, mild pre- and postaxial limb hypoplasia with brachydactyly, mild interdigital webbing, dental anomalies, and cryptorchidism and hypospadias in males (Opitz et al., 1993; Wulfsberg et al., 1996).

6q25 microdeletion syndrome is a recently described syndrome characterized by developmental delay, facial dysmorphism and hearing loss.

HNF1A-MODY and HNF4A-MODY have similar signs and symptoms that develop slowly over time. Early signs and symptoms in these types are caused by high blood glucose and may include frequent urination (polyuria), excessive thirst (polydipsia), fatigue, blurred vision, weight loss, and recurrent skin infections. Over time uncontrolled high blood glucose can damage small blood vessels in the eyes and kidneys. Damage to the light-sensitive tissue at the back of the eye (the retina) causes a condition known as diabetic retinopathy that can lead to vision loss and eventual blindness. Kidney damage (diabetic nephropathy) can lead to kidney failure and end-stage renal disease (ESRD). While these two types of MODY are very similar, certain features are particular to each type. For example, babies with HNF4A-MODY tend to weigh more than average or have abnormally low blood glucose at birth, even though other signs of the condition do not occur until childhood or young adulthood. People with HNF1A-MODY have a higher-than-average risk of developing noncancerous (benign) liver tumors known as hepatocellular adenomas.\n\nThe different types of MODY are distinguished by their genetic causes. The most common types are HNF1A-MODY (also known as MODY3), accounting for 50 to 70 percent of cases, and GCK-MODY (MODY2), accounting for 30 to 50 percent of cases. Less frequent types include HNF4A-MODY (MODY1) and renal cysts and diabetes (RCAD) syndrome (also known as HNF1B-MODY or MODY5), which each account for 5 to 10 percent of cases. At least ten other types have been identified, and these are very rare.\n\nGCK-MODY is a very mild type of the condition. People with this type have slightly elevated blood glucose levels, particularly in the morning before eating (fasting blood glucose). However, affected individuals often have no symptoms related to the disorder, and diabetes-related complications are extremely rare.\n\nRCAD is associated with a combination of diabetes and kidney or urinary tract abnormalities (unrelated to the elevated blood glucose), most commonly fluid-filled sacs (cysts) in the kidneys. However, the signs and symptoms are variable, even within families, and not everyone with RCAD has both features. Affected individuals may have other features unrelated to diabetes, such as abnormalities of the pancreas or liver or a form of arthritis called gout.\n\nMaturity-onset diabetes of the young (MODY) is a group of several conditions characterized by abnormally high levels of blood glucose, also called blood sugar. These forms of diabetes typically begin before age 30, although they can occur later in life. In MODY, elevated blood glucose arises from reduced production of insulin, which is a hormone produced in the pancreas that helps regulate blood glucose levels. Specifically, insulin controls how much glucose (a type of sugar) is passed from the blood into cells, where it is used as an energy source.

Warsaw syndrome is characterized by the clinical triad of severe congenital microcephaly, growth restriction, and sensorineural hearing loss due to cochlear hypoplasia. Intellectual disability is typically in the mild-to-moderate range. Severe speech delay is common. Gross and fine motor milestones are usually attained at the usual time, although a few individuals have mild delays. Additional common features include skeletal anomalies and cardiovascular anomalies. Abnormal skin pigmentation and genitourinary malformations have also been reported. Some individuals have had increased chromosome breakage and radial forms on cytogenetic testing of lymphocytes treated with diepoxybutane and mitomycin C.

Frontonasal dysplasia-2 (FND2) is an autosomal recessive disorder characterized by variable degrees of alopecia, skull defects, hypertelorism, depressed nasal bridge and ridge with notched alae nasi, and abnormal central nervous system findings (summary by Kariminejad et al., 2014).

The chromosome 16p12.2-p11.2 deletion syndrome is characterized phenotypically by dysmorphic facial features, feeding difficulties, recurrent ear infections, developmental delay, and cognitive impairment. Additional features, such as heart defects and short stature, are variable (Ballif et al., 2007; Battaglia et al., 2009). The pericentric region of chromosome 16, specifically involving 16p12-p11, is a structurally complex region enriched in repetitive sequence elements, rendering this region susceptible to deletion or rearrangement (Ballif et al., 2007). There are several phenotypes associated with variation in this region: see 611913 for a deletion or duplication at 16p11.2 associated with autism; see 136570 for discussion of a recurrent 520-kb deletion at 16p12.1 associated with developmental delay and craniofacial dysmorphism; and see 613444 for a 220-kb deletion at 16p11.2 associated with isolated severe early-onset obesity and obesity with developmental delay. Battaglia et al. (2009) emphasized that the region at chromosome 16p11.2 that confers susceptibility to autism (AUTS14; see 611913) is located more centromeric to and is distinct from the 16p12.2-p11.2 region involved in the multiple congenital anomalies and intellectual disability phenotype.

Most people with Meier-Gorlin syndrome have distinctive facial features. In addition to being abnormally small, the ears may be low-set or rotated backward. Additional features can include a small mouth (microstomia), an underdeveloped lower jaw (micrognathia), full lips, and a narrow nose with a high nasal bridge.\n\nSome people with Meier-Gorlin syndrome have other skeletal abnormalities, such as unusually narrow long bones in the arms and legs, a deformity of the knee joint that allows the knee to bend backwards (genu recurvatum), and slowed mineralization of bones (delayed bone age).\n\nMeier-Gorlin syndrome is a condition primarily characterized by short stature. It is considered a form of primordial dwarfism because the growth problems begin before birth (intrauterine growth retardation). After birth, affected individuals continue to grow at a slow rate. Other characteristic features of this condition are underdeveloped or missing kneecaps (patellae), small ears, and, often, an abnormally small head (microcephaly). Despite a small head size, most people with Meier-Gorlin syndrome have normal intellect.\n\nAdditional features of Meier-Gorlin syndrome can include difficulty feeding and a lung condition known as pulmonary emphysema or other breathing problems.\n\nAbnormalities in sexual development may also occur in Meier-Gorlin syndrome. In some males with this condition, the testes are small or undescended (cryptorchidism). Affected females may have unusually small external genital folds (hypoplasia of the labia majora) and small breasts. Both males and females with this condition can have sparse or absent underarm (axillary) hair.

Abnormalities in sexual development may also occur in Meier-Gorlin syndrome. In some males with this condition, the testes are small or undescended (cryptorchidism). Affected females may have unusually small external genital folds (hypoplasia of the labia majora) and small breasts. Both males and females with this condition can have sparse or absent underarm (axillary) hair.\n\nAdditional features of Meier-Gorlin syndrome can include difficulty feeding and a lung condition known as pulmonary emphysema or other breathing problems.\n\nMeier-Gorlin syndrome is a condition primarily characterized by short stature. It is considered a form of primordial dwarfism because the growth problems begin before birth (intrauterine growth retardation). After birth, affected individuals continue to grow at a slow rate. Other characteristic features of this condition are underdeveloped or missing kneecaps (patellae), small ears, and, often, an abnormally small head (microcephaly). Despite a small head size, most people with Meier-Gorlin syndrome have normal intellect.\n\nSome people with Meier-Gorlin syndrome have other skeletal abnormalities, such as unusually narrow long bones in the arms and legs, a deformity of the knee joint that allows the knee to bend backwards (genu recurvatum), and slowed mineralization of bones (delayed bone age).\n\nMost people with Meier-Gorlin syndrome have distinctive facial features. In addition to being abnormally small, the ears may be low-set or rotated backward. Additional features can include a small mouth (microstomia), an underdeveloped lower jaw (micrognathia), full lips, and a narrow nose with a high nasal bridge.

Meier-Gorlin syndrome-4 (MGORS4) is a rare autosomal recessive disorder with the hallmarks of short stature, small external ears, and reduced or absent patellae. Breast hypoplasia is present in females (Guernsey et al., 2011). For a general phenotypic description and a discussion of genetic heterogeneity of Meier-Gorlin syndrome, see 224690.

Abnormalities in sexual development may also occur in Meier-Gorlin syndrome. In some males with this condition, the testes are small or undescended (cryptorchidism). Affected females may have unusually small external genital folds (hypoplasia of the labia majora) and small breasts. Both males and females with this condition can have sparse or absent underarm (axillary) hair.\n\nAdditional features of Meier-Gorlin syndrome can include difficulty feeding and a lung condition known as pulmonary emphysema or other breathing problems.\n\nMeier-Gorlin syndrome is a condition primarily characterized by short stature. It is considered a form of primordial dwarfism because the growth problems begin before birth (intrauterine growth retardation). After birth, affected individuals continue to grow at a slow rate. Other characteristic features of this condition are underdeveloped or missing kneecaps (patellae), small ears, and, often, an abnormally small head (microcephaly). Despite a small head size, most people with Meier-Gorlin syndrome have normal intellect.\n\nSome people with Meier-Gorlin syndrome have other skeletal abnormalities, such as unusually narrow long bones in the arms and legs, a deformity of the knee joint that allows the knee to bend backwards (genu recurvatum), and slowed mineralization of bones (delayed bone age).\n\nMost people with Meier-Gorlin syndrome have distinctive facial features. In addition to being abnormally small, the ears may be low-set or rotated backward. Additional features can include a small mouth (microstomia), an underdeveloped lower jaw (micrognathia), full lips, and a narrow nose with a high nasal bridge.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the DHDDS gene.

Dyskeratosis congenita and related telomere biology disorders (DC/TBD) are caused by impaired telomere maintenance resulting in short or very short telomeres. The phenotypic spectrum of telomere biology disorders is broad and includes individuals with classic dyskeratosis congenita (DC) as well as those with very short telomeres and an isolated physical finding. Classic DC is characterized by a triad of dysplastic nails, lacy reticular pigmentation of the upper chest and/or neck, and oral leukoplakia, although this may not be present in all individuals. People with DC/TBD are at increased risk for progressive bone marrow failure (BMF), myelodysplastic syndrome or acute myelogenous leukemia, solid tumors (usually squamous cell carcinoma of the head/neck or anogenital cancer), and pulmonary fibrosis. Other findings can include eye abnormalities (epiphora, blepharitis, sparse eyelashes, ectropion, entropion, trichiasis), taurodontism, liver disease, gastrointestinal telangiectasias, and avascular necrosis of the hips or shoulders. Although most persons with DC/TBD have normal psychomotor development and normal neurologic function, significant developmental delay is present in both forms; additional findings include cerebellar hypoplasia (Hoyeraal Hreidarsson syndrome) and bilateral exudative retinopathy and intracranial calcifications (Revesz syndrome and Coats plus syndrome). Onset and progression of manifestations of DC/TBD vary: at the mild end of the spectrum are those who have only minimal physical findings with normal bone marrow function, and at the severe end are those who have the diagnostic triad and early-onset BMF.

SUCLG1-related mitochondrial DNA (mtDNA) depletion syndrome, encephalomyopathic form with methylmalonic aciduria is characterized in the majority of affected newborns by hypotonia, muscle atrophy, feeding difficulties, and lactic acidosis. Affected infants commonly manifest developmental delay / cognitive impairment, growth retardation / failure to thrive, hepatopathy, sensorineural hearing impairment, dystonia, and hypertonia. Notable findings in some affected individuals include hypertrophic cardiomyopathy, epilepsy, myoclonus, microcephaly, sleep disturbance, rhabdomyolysis, contractures, hypothermia, and/or hypoglycemia. Life span is shortened, with median survival of 20 months.

Ogden syndrome (OGDNS) is an X-linked neurodevelopmental disorder characterized by postnatal growth failure, severely delayed psychomotor development, variable dysmorphic features, and hypotonia. Many patients also have cardiac malformations or arrhythmias (summary by Popp et al., 2015).

X-linked dominant chondrodysplasia Chassaing-Lacombe type is a rare genetic bone disorder characterized by chondrodysplasia, intrauterine growth retardation (IUGR), hydrocephaly and facial dysmorphism in the affected males.

Kabuki syndrome (KS) is characterized by typical facial features (long palpebral fissures with eversion of the lateral third of the lower eyelid; arched and broad eyebrows; short columella with depressed nasal tip; large, prominent, or cupped ears), minor skeletal anomalies, persistence of fetal fingertip pads, mild-to-moderate intellectual disability, and postnatal growth deficiency. Other findings may include: congenital heart defects, genitourinary anomalies, cleft lip and/or palate, gastrointestinal anomalies including anal atresia, ptosis and strabismus, and widely spaced teeth and hypodontia. Functional differences can include: increased susceptibility to infections and autoimmune disorders, seizures, endocrinologic abnormalities (including isolated premature thelarche in females), feeding problems, and hearing loss.

Chromosome Xq27.3-q28 duplication syndrome is an X-linked recessive neurodevelopmental disorder characterized by mild mental retardation, mild facial dysmorphism, short stature, and primary testicular failure manifest as high-pitched voice, sparse body hair, abdominal obesity, and small testes. Female carriers may have short stature and premature ovarian failure (summary by Rio et al., 2010).

Acrodysostosis-1 (ACRDYS1) is a form of skeletal dysplasia characterized by short stature, severe brachydactyly, facial dysostosis, and nasal hypoplasia. Affected individuals often have advanced bone age and obesity. Laboratory studies show resistance to multiple hormones, including parathyroid, thyrotropin, calcitonin, growth hormone-releasing hormone, and gonadotropin (summary by Linglart et al., 2011). However, not all patients show endocrine abnormalities (Lee et al., 2012). Genetic Heterogeneity of Acrodysostosis See also ACRDYS2 (614613), caused by mutation in the PDE4D gene (600129) on chromosome 5q12.

Mitochondrial encephalo-cardio-myopathy due to <i>TMEM70</i> mutation is characterized by early neonatal onset of hypotonia, hypetrophic cardiomyopathy and apneic spells within hours after birth accompanied by lactic acidosis, hyperammonemia and 3-methylglutaconic aciduria.

Mosaic variegated aneuploidy syndrome is an autosomal recessive disorder characterized by poor growth and variable phenotypic manifestations, such as facial dysmorphism and congenital heart defects, associated with mosaic aneuploidies resulting from defects in cell division (summary by Snape et al., 2011). See also MVA1 (257300), caused by mutation in the BUB1B gene (602860) on chromosome 15q15.

Chromosome 20q11-q12 deletion syndrome is characterized by global developmental delay, poor overall growth, sometimes with severe feeding difficulties, facial dysmorphism, and distal skeletal anomalies. Some patients may have hearing impairment, retinopathy, or cardiac defects. It is a multisystemic disorder with variable features (summary by Loddo et al., 2018).

De Barsy syndrome, also known as autosomal recessive cutis laxa type III (ARCL3), is a rare autosomal recessive disorder characterized by an aged appearance with distinctive facial features, sparse hair, ophthalmologic abnormalities, intrauterine growth retardation (IUGR), and cutis laxa (summary by Lin et al., 2011). For a phenotypic description and a discussion of genetic heterogeneity of de Barsy syndrome, see 219150. For a phenotypic description and a discussion of genetic heterogeneity of autosomal recessive cutis laxa, see 219200.

Coffin-Siris syndrome (CSS) is classically characterized by aplasia or hypoplasia of the distal phalanx or nail of the fifth and additional digits, developmental or cognitive delay of varying degree, distinctive facial features, hypotonia, hirsutism/hypertrichosis, and sparse scalp hair. Congenital anomalies can include malformations of the cardiac, gastrointestinal, genitourinary, and/or central nervous systems. Other findings commonly include feeding difficulties, slow growth, ophthalmologic abnormalities, and hearing impairment.

Trichohepatoenteric syndrome (THES), generally considered to be a neonatal enteropathy, is characterized by intractable diarrhea (seen in almost all affected children), woolly hair (seen in all), intrauterine growth restriction, facial dysmorphism, and short stature. Additional findings include poorly characterized immunodeficiency, recurrent infections, skin abnormalities, and liver disease. Mild intellectual disability (ID) is seen in about 50% of affected individuals. Less common findings include congenital heart defects and platelet anomalies. To date 52 affected individuals have been reported.

Fanconi anemia (FA) is characterized by physical abnormalities, bone marrow failure, and increased risk for malignancy. Physical abnormalities, present in approximately 75% of affected individuals, include one or more of the following: short stature, abnormal skin pigmentation, skeletal malformations of the upper and/or lower limbs, microcephaly, and ophthalmic and genitourinary tract anomalies. Progressive bone marrow failure with pancytopenia typically presents in the first decade, often initially with thrombocytopenia or leukopenia. The incidence of acute myeloid leukemia is 13% by age 50 years. Solid tumors – particularly of the head and neck, skin, and genitourinary tract – are more common in individuals with FA.

Fanconi anemia (FA) is characterized by physical abnormalities, bone marrow failure, and increased risk for malignancy. Physical abnormalities, present in approximately 75% of affected individuals, include one or more of the following: short stature, abnormal skin pigmentation, skeletal malformations of the upper and/or lower limbs, microcephaly, and ophthalmic and genitourinary tract anomalies. Progressive bone marrow failure with pancytopenia typically presents in the first decade, often initially with thrombocytopenia or leukopenia. The incidence of acute myeloid leukemia is 13% by age 50 years. Solid tumors – particularly of the head and neck, skin, and genitourinary tract – are more common in individuals with FA.

Fanconi anemia (FA) is characterized by physical abnormalities, bone marrow failure, and increased risk for malignancy. Physical abnormalities, present in approximately 75% of affected individuals, include one or more of the following: short stature, abnormal skin pigmentation, skeletal malformations of the upper and/or lower limbs, microcephaly, and ophthalmic and genitourinary tract anomalies. Progressive bone marrow failure with pancytopenia typically presents in the first decade, often initially with thrombocytopenia or leukopenia. The incidence of acute myeloid leukemia is 13% by age 50 years. Solid tumors – particularly of the head and neck, skin, and genitourinary tract – are more common in individuals with FA.

Heterotaxy ('heter' meaning 'other' and 'taxy' meaning 'arrangement'), or situs ambiguus, is a developmental condition characterized by randomization of the placement of visceral organs, including the heart, lungs, liver, spleen, and stomach. The organs are oriented randomly with respect to the left-right axis and with respect to one another (Srivastava, 1997). Heterotaxy is a clinically and genetically heterogeneous disorder. For a discussion of genetic heterogeneity of visceral heterotaxy, see HTX1 (306955).

Hereditary sensory and autonomic neuropathy type VI (HSAN6) is a severe autosomal recessive disorder characterized by neonatal hypotonia, respiratory and feeding difficulties, lack of psychomotor development, and autonomic abnormalities including labile cardiovascular function, lack of corneal reflexes leading to corneal scarring, areflexia, and absent axonal flare response after intradermal histamine injection (summary by Edvardson et al., 2012). For a discussion of genetic heterogeneity of hereditary sensory and autonomic neuropathy, see HSAN1 (162400).

Most characteristically, Aicardi-Goutières syndrome (AGS) manifests as an early-onset encephalopathy that usually, but not always, results in severe intellectual and physical disability. A subgroup of infants with AGS present at birth with abnormal neurologic findings, hepatosplenomegaly, elevated liver enzymes, and thrombocytopenia, a picture highly suggestive of congenital infection. Otherwise, most affected infants present at variable times after the first few weeks of life, frequently after a period of apparently normal development. Typically, they demonstrate the subacute onset of a severe encephalopathy characterized by extreme irritability, intermittent sterile pyrexias, loss of skills, and slowing of head growth. Over time, as many as 40% develop chilblain skin lesions on the fingers, toes, and ears. It is becoming apparent that atypical, sometimes milder, cases of AGS exist, and thus the true extent of the phenotype associated with pathogenic variants in the AGS-related genes is not yet known.

The peroxisome biogenesis disorder (PBD) Zellweger syndrome (ZS) is an autosomal recessive multiple congenital anomaly syndrome. Affected children present in the newborn period with profound hypotonia, seizures, and inability to feed. Characteristic craniofacial anomalies, eye abnormalities, neuronal migration defects, hepatomegaly, and chondrodysplasia punctata are present. Children with this condition do not show any significant development and usually die in the first year of life (summary by Steinberg et al., 2006). For a complete phenotypic description and a discussion of genetic heterogeneity of Zellweger syndrome, see 214100. Individuals with PBDs of complementation group 2 (CG2) have mutations in the PEX5 gene. For information on the history of PBD complementation groups, see 214100.

CDG2L is an autosomal recessive multisystem disorder apparent from birth or early infancy. It is characterized by poor growth, gastrointestinal and liver abnormalities, delayed psychomotor development, hypotonia, recurrent infections, hematologic abnormalities, increased bleeding tendency, and hyperhidrosis or hyperkeratosis. More variable features include nonspecific dysmorphic facial features and cardiac septal defects. The disorder often results in death in infancy or the first years of life (summary by Rymen et al., 2015). For a general discussion of CDGs, see CDG1A (212065) and CDG2A (212066).

Coffin-Siris syndrome is a congenital malformation syndrome characterized by developmental delay, intellectual disability, coarse facial features, feeding difficulties, and hypoplastic or absent fifth fingernails and fifth distal phalanges. Other more variable features may also occur. Patients with ARID1A mutations have a wide spectrum of manifestations, from severe intellectual disability and serious internal complications that could result in early death to mild intellectual disability (summary by Kosho et al., 2014). For a general phenotypic description and a discussion of genetic heterogeneity of Coffin-Siris syndrome, see CSS1 (135900). The chromosome 1p36.11 duplication syndrome, in which the ARID1A gene is duplicated, is characterized by impaired intellectual development, microcephaly, dysmorphic facial features, and hand and foot anomalies.

Coffin-Siris syndrome is a congenital malformation syndrome characterized by developmental delay, intellectual disability, coarse facial features, feeding difficulties, and hypoplastic or absent fifth fingernails and fifth distal phalanges. Other more variable features may also occur. Patients with SMARCB1 mutations may have more severe neurodevelopmental deficits including severe intellectual disability, brain structural abnormalities, and no expressive words, as well as scoliosis (summary by Kosho et al., 2014). For a general phenotypic description and a discussion of genetic heterogeneity of Coffin-Siris syndrome, see CSS1 (135900).

Coffin-Siris syndrome is a congenital malformation syndrome characterized by developmental delay, intellectual disability, coarse facial features, feeding difficulties, and hypoplastic or absent fifth fingernails and fifth distal phalanges. Other more variable features may also occur. Patients with SMARCA4 mutations may have less coarse craniofacial appearances and fewer behavioral abnormalities than Coffin-Siris patients with mutations in other genes (summary by Kosho et al., 2014). For a general phenotypic description and a discussion of genetic heterogeneity of Coffin-Siris syndrome, see CSS1 (135900).

Acrodysostosis-2 (ACRDYS2) is a rare skeletal dysplasia characterized by brachydactyly, facial dysostosis, and spinal stenosis. Many patients have intellectual disability and some have hormone resistance (summary by Michot et al., 2012 and Lee et al., 2012). For a discussion of genetic heterogeneity of acrodysostosis, see ACRDYS1 (101800).

Primary coenzyme Q10 (CoQ10) deficiency is usually associated with multisystem involvement, including neurologic manifestations such as fatal neonatal encephalopathy with hypotonia; a late-onset slowly progressive multiple-system atrophy-like phenotype (neurodegeneration with autonomic failure and various combinations of parkinsonism and cerebellar ataxia, and pyramidal dysfunction); and dystonia, spasticity, seizures, and intellectual disability. Steroid-resistant nephrotic syndrome (SRNS), the hallmark renal manifestation, is often the initial manifestation either as isolated renal involvement that progresses to end-stage renal disease (ESRD), or associated with encephalopathy (seizures, stroke-like episodes, severe neurologic impairment) resulting in early death. Hypertrophic cardiomyopathy (HCM), retinopathy or optic atrophy, and sensorineural hearing loss can also be seen.

Classic Joubert syndrome (JS) is characterized by three primary findings: A distinctive cerebellar and brain stem malformation called the molar tooth sign (MTS). Hypotonia. Developmental delays. Often these findings are accompanied by episodic tachypnea or apnea and/or atypical eye movements. In general, the breathing abnormalities improve with age, truncal ataxia develops over time, and acquisition of gross motor milestones is delayed. Cognitive abilities are variable, ranging from severe intellectual disability to normal. Additional findings can include retinal dystrophy, renal disease, ocular colobomas, occipital encephalocele, hepatic fibrosis, polydactyly, oral hamartomas, and endocrine abnormalities. Both intra- and interfamilial variation are seen.

Microcephalic primordial dwarfism, Dauber type is a rare, genetic developmental defect during embryogenesis characterized by severe pre- and postnatal growth retardation, severe microcephaly, severe developmental delay and intelletual disability, severe adult short stature and facial dysmorphism (incl. hypotelorism, small ears, prominent nose). Other reported features include skeletal anomalies (Madelung deformity, clinodactyly, mild lumbar scoliosis, bilateral hip dysplasia) and seizures. Absence of thelarche and menarche is also associated.

The peroxisomal biogenesis disorder (PBD) Zellweger syndrome (ZS) is an autosomal recessive multiple congenital anomaly syndrome. Affected children present in the newborn period with profound hypotonia, seizures, and inability to feed. Characteristic craniofacial anomalies, eye abnormalities, neuronal migration defects, hepatomegaly, and chondrodysplasia punctata are present. Children with this condition do not show any significant development and usually die in the first year of life (summary by Steinberg et al., 2006). For a complete phenotypic description and a discussion of genetic heterogeneity of Zellweger syndrome, see 214100. Individuals with PBDs of complementation group 5 (CG5, equivalent to CG10 and CGF) have mutations in the PEX2 gene. For information on the history of PBD complementation groups, see 214100.

Primary microcephaly-10 (MCPH10) is an autosomal recessive disorder characterized by extremely small head size (-9 SD) at birth and death usually by 1 year of age. Neuropathologic examination shows severe loss of neurons as well as neuronal loss of polarity and abnormal dendritic maturation (summary by Yang et al., 2012). For a general phenotypic description and a discussion of genetic heterogeneity of primary microcephaly, see MCPH1 (251200).

Dyskeratosis congenita and related telomere biology disorders (DC/TBD) are caused by impaired telomere maintenance resulting in short or very short telomeres. The phenotypic spectrum of telomere biology disorders is broad and includes individuals with classic dyskeratosis congenita (DC) as well as those with very short telomeres and an isolated physical finding. Classic DC is characterized by a triad of dysplastic nails, lacy reticular pigmentation of the upper chest and/or neck, and oral leukoplakia, although this may not be present in all individuals. People with DC/TBD are at increased risk for progressive bone marrow failure (BMF), myelodysplastic syndrome or acute myelogenous leukemia, solid tumors (usually squamous cell carcinoma of the head/neck or anogenital cancer), and pulmonary fibrosis. Other findings can include eye abnormalities (epiphora, blepharitis, sparse eyelashes, ectropion, entropion, trichiasis), taurodontism, liver disease, gastrointestinal telangiectasias, and avascular necrosis of the hips or shoulders. Although most persons with DC/TBD have normal psychomotor development and normal neurologic function, significant developmental delay is present in both forms; additional findings include cerebellar hypoplasia (Hoyeraal Hreidarsson syndrome) and bilateral exudative retinopathy and intracranial calcifications (Revesz syndrome and Coats plus syndrome). Onset and progression of manifestations of DC/TBD vary: at the mild end of the spectrum are those who have only minimal physical findings with normal bone marrow function, and at the severe end are those who have the diagnostic triad and early-onset BMF.

A rare multiple congenital anomalies syndrome with characteristics of distinctive facial appearance (low frontal hairline, bilateral ptosis, prominent eyes, flat midface, broad, ?at nares, Cupid''s bow upper lip vermilion and small, low-set, posteriorly rotated ears), cleft palate, conductive hearing loss, heart defects (atrial or ventricular septal defect) and mild developmental delay/intellectual disability.

Meckel syndrome, also known as Meckel-Gruber syndrome, is a severe pleiotropic autosomal recessive developmental disorder caused by dysfunction of primary cilia during early embryogenesis. There is extensive clinical variability and controversy as to the minimum diagnostic criteria. Early reports, including that of Opitz and Howe (1969) and Wright et al. (1994), stated that the classic triad of Meckel syndrome comprises (1) cystic renal disease; (2) a central nervous system malformation, most commonly occipital encephalocele; and (3) polydactyly, most often postaxial. However, based on a study of 67 patients, Salonen (1984) concluded that the minimum diagnostic criteria are (1) cystic renal disease; (2) CNS malformation, and (3) hepatic abnormalities, including portal fibrosis or ductal proliferation. In a review of Meckel syndrome, Logan et al. (2011) stated that the classic triad first described by Meckel (1822) included occipital encephalocele, cystic kidneys, and fibrotic changes to the liver. Genetic Heterogeneity of Meckel Syndrome See also MKS2 (603194), caused by mutation in the TMEM216 gene (613277) on chromosome 11q12; MKS3 (607361), caused by mutation in the TMEM67 gene (609884) on chromosome 8q; MKS4 (611134), caused by mutation in the CEP290 gene (610142) on chromosome 12q; MKS5 (611561), caused by mutation in the RPGRIP1L gene (610937) on chromosome 16q12; MKS6 (612284), caused by mutation in the CC2D2A gene (612013) on chromosome 4p15; MKS7 (267010), caused by mutation in the NPHP3 (608002) gene on chromosome 3q22; MKS8 (613885), caused by mutation in the TCTN2 gene (613846) on chromosome 12q24; MKS9 (614209), caused by mutation in the B9D1 gene (614144) on chromosome 17p11; MKS10 (614175), caused by mutation in the B9D2 gene (611951) on chromosome 19q13; MKS11 (615397), caused by mutation in the TMEM231 gene (614949) on chromosome 16q23; MKS12 (616258), caused by mutation in the KIF14 gene (611279) on chromosome 1q32; MKS13 (617562), caused by mutation in the TMEM107 gene (616183) on chromosome 17p13; and MKS14 (619879), caused by mutation in the TXNDC15 gene (617778) on chromosome 5q31.

Deafness, dystonia, and cerebral hypomyelination is an X-linked recessive mental retardation syndrome characterized by almost no psychomotor development, dysmorphic facial features, sensorineural deafness, dystonia, pyramidal signs, and hypomyelination on brain imaging (summary by Cacciagli et al., 2013).

Congenital disorder of glycosylation type IIm, or developmental and epileptic encephalopathy-22 (DEE22), is an X-linked dominant severe neurologic disorder characterized by infantile-onset seizures, hypsarrhythmia on EEG, hypotonia, and developmental delay associated with severe intellectual disability and lack of speech. These features are consistent with developmental and epileptic encephalopathy (DEE). Brain malformations usually include cerebral and cerebellar atrophy. Additionally, some patients may have dysmorphic features or coarse facies (Ng et al., 2013; Kodera et al., 2013). For a general discussion of CDGs, see CDG1A (212065) and CDG2A (212066). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350.

Any non-syndromic X-linked intellectual disability in which the cause of the disease is a mutation in the USP9X gene.

Any complex cortical dysplasia with other brain malformations in which the cause of the disease is a mutation in the KIF5C gene.

Multiple mitochondrial dysfunctions syndrome-3 (MMDS3) is an autosomal recessive severe neurodegenerative disorder characterized by loss of previously acquired developmental milestones in the first months or years of life. Some affected patients have normal development in early infancy before the onset of symptoms, whereas others show delays from birth. Features included loss of motor function, spasticity, pyramidal signs, loss of speech, and cognitive impairment. The disease course is highly variable: some patients die of respiratory failure early in childhood, whereas some survive but may be bedridden with a feeding tube. Less commonly, some patients may survive and have a stable course with motor deficits and mild or even absent cognitive impairment, although there may be fluctuating symptoms, often in response to infection. Other variable features include visual problems and seizures. Brain imaging shows diffuse leukodystrophy in the subcortical region, brainstem, cerebellum, and spinal cord. Laboratory studies tend to show increased lactate and CSF glycine, and decreased activity of mitochondrial complexes I and II, although these findings are also variable. There may be additional biochemical evidence of mitochondrial dysfunction (summary by Liu et al., 2018). For a general description and a discussion of genetic heterogeneity of multiple mitochondrial dysfunctions syndrome, see MMDS1 (605711).

Any complex cortical dysplasia with other brain malformations in which the cause of the disease is a mutation in the KIF2A gene.

Infantile hypotonia with psychomotor retardation and characteristic facies (IHPRF) is a severe autosomal recessive neurologic disorder with onset at birth or in early infancy. Affected individuals show very poor, if any, normal cognitive development. Some patients are never learn to sit or walk independently (summary by Al-Sayed et al., 2013). Genetic Heterogeneity of Infantile Hypotonia with Psychomotor Retardation and Characteristic Facies See also IHPRF2 (616801), caused by mutation in the UNC80 gene (612636) on chromosome 2q34; and IHPRF3 (616900), caused by mutation in the TBCK gene (616899) on chromosome 4q24.

Combined oxidative phosphorylation deficiency-17 (COXPD17) is an autosomal recessive disorder of mitochondrial dysfunction characterized by onset of severe hypertrophic cardiomyopathy in the first year of life. Other features include hypotonia, poor growth, lactic acidosis, and failure to thrive. The disorder may be fatal in early childhood (summary by Haack et al., 2013).

Asparagine synthetase deficiency (ASD) mainly presents as a triad of congenital microcephaly, severe developmental delay, and axial hypotonia followed by spastic quadriplegia. Low cerebrospinal fluid (CSF) asparagine level can help the clinician in differentiating this disorder from others. In most cases age of onset of apnea, excessive irritability, and seizures is soon after birth. Affected individuals typically do not acquire any developmental milestones. Spastic quadriplegia can lead to severe contractures of the limbs and neurogenic scoliosis. Feeding difficulties (gastroesophageal reflux disease, frequent vomiting, swallowing dysfunction, and gastroesophageal incoordination) are a significant problem in most affected individuals. A majority have cortical blindness. MRI findings are nonspecific but may include generalized atrophy and simplified gyral pattern.

Combined oxidative phosphorylation deficiency-18 (COXPD18) is an autosomal recessive disorder of mitochondrial function characterized by intrauterine growth retardation, hypotonia, visual impairment, speech delay, and lactic acidosis associated with decreased mitochondrial respiratory chain activity. Affected patients may also show hematologic abnormalities, mainly macrocytic anemia (summary by Hildick-Smith et al., 2013). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060).

Verheij syndrome is characterized by growth retardation, delayed psychomotor development, dysmorphic facial features, and skeletal, mainly vertebral, abnormalities. Additional variable features may include coloboma, renal defects, and cardiac defects (summary by Verheij et al., 2009 and Dauber et al., 2013).

Classic Joubert syndrome (JS) is characterized by three primary findings: A distinctive cerebellar and brain stem malformation called the molar tooth sign (MTS). Hypotonia. Developmental delays. Often these findings are accompanied by episodic tachypnea or apnea and/or atypical eye movements. In general, the breathing abnormalities improve with age, truncal ataxia develops over time, and acquisition of gross motor milestones is delayed. Cognitive abilities are variable, ranging from severe intellectual disability to normal. Additional findings can include retinal dystrophy, renal disease, ocular colobomas, occipital encephalocele, hepatic fibrosis, polydactyly, oral hamartomas, and endocrine abnormalities. Both intra- and interfamilial variation are seen.

Seckel syndrome is a rare autosomal recessive disorder characterized by severe pre- and postnatal growth retardation, severe microcephaly with mental retardation, and specific dysmorphic features (Faivre et al., 2002). For a general description and a discussion of genetic heterogeneity of Seckel syndrome, see 210600.

Most characteristically, Aicardi-Goutières syndrome (AGS) manifests as an early-onset encephalopathy that usually, but not always, results in severe intellectual and physical disability. A subgroup of infants with AGS present at birth with abnormal neurologic findings, hepatosplenomegaly, elevated liver enzymes, and thrombocytopenia, a picture highly suggestive of congenital infection. Otherwise, most affected infants present at variable times after the first few weeks of life, frequently after a period of apparently normal development. Typically, they demonstrate the subacute onset of a severe encephalopathy characterized by extreme irritability, intermittent sterile pyrexias, loss of skills, and slowing of head growth. Over time, as many as 40% develop chilblain skin lesions on the fingers, toes, and ears. It is becoming apparent that atypical, sometimes milder, cases of AGS exist, and thus the true extent of the phenotype associated with pathogenic variants in the AGS-related genes is not yet known.

In some cases, people with permanent neonatal diabetes mellitus also have certain neurological problems, including developmental delay and recurrent seizures (epilepsy). This combination of developmental delay, epilepsy, and neonatal diabetes is called DEND syndrome. Intermediate DEND syndrome is a similar combination but with milder developmental delay and without epilepsy.\n\nIndividuals with permanent neonatal diabetes mellitus experience slow growth before birth (intrauterine growth retardation). Affected infants have hyperglycemia and an excessive loss of fluids (dehydration) and are unable to gain weight and grow at the expected rate (failure to thrive).\n\nA small number of individuals with permanent neonatal diabetes mellitus have an underdeveloped pancreas. Because the pancreas produces digestive enzymes as well as secreting insulin and other hormones, affected individuals experience digestive problems such as fatty stools and an inability to absorb fat-soluble vitamins.\n\nPermanent neonatal diabetes mellitus is a type of diabetes that first appears within the first 6 months of life and persists throughout the lifespan. This form of diabetes is characterized by high blood sugar levels (hyperglycemia) resulting from a shortage of the hormone insulin. Insulin controls how much glucose (a type of sugar) is passed from the blood into cells for conversion to energy.

Desbuquois dysplasia (DBQD) is an autosomal recessive chondrodysplasia belonging to the multiple dislocation group and characterized by severe prenatal and postnatal growth retardation (stature less than -5 SD), joint laxity, short extremities, and progressive scoliosis. The main radiologic features are short long bones with metaphyseal splay, a 'Swedish key' appearance of the proximal femur (exaggerated trochanter), and advanced carpal and tarsal bone age with a delta phalanx (summary by Huber et al., 2009). Desbuquois dysplasia is clinically and radiographically heterogeneous, and had been classified into 2 types based on the presence (type 1) or absence (type 2) of characteristic hand anomalies, including an extra ossification center distal to the second metacarpal, delta phalanx, bifid distal thumb phalanx, and dislocation of the interphalangeal joints (Faivre et al., 2004). However, patients with and without these additional hand anomalies have been reported to have mutations in the same gene (see, e.g., CANT1); thus, these features are not distinctive criteria to predict the molecular basis of DBQD (Furuichi et al., 2011). In addition, Kim et al. (2010) described another milder variant of DBQD with almost normal outwardly appearing hands, but significant radiographic changes, including short metacarpals, elongated phalanges, and remarkably advanced carpal bone age. However, there is no accessory ossification center distal to the second metacarpal, and patients do not have thumb anomalies. Similar changes occur in the feet. These patients also tend to develop precocious osteoarthritis of the hand and spine with age. This phenotype is sometimes referred to as the 'Kim variant' of DBQD (Furuichi et al., 2011). Genetic Heterogeneity of Desbuquois Dysplasia DBQD2 (615777) is caused by mutation in the XYLT1 gene (608124) on chromosome 16p12. Two unrelated patients with immunodeficiency-23 (IMD23; 615816), due to mutation in the PGM3 gene (172100), were reported to have skeletal features reminiscent of DBQD.

A rare, syndromic diabetes mellitus characterized by partial pancreatic agenesis, diabetes mellitus, and heart anomalies (including transposition of the great vessels, ventricular or atrial septal defects, pulmonary stenosis, or patent ductus arteriosis).

Desbuquois dysplasia, which belongs to the multiple dislocation group of disorders, is characterized by dislocations of large joints, severe pre- and postnatal growth retardation, joint laxity, and flat face with prominent eyes. Radiologic features include short long bones with an exaggerated trochanter that gives a 'monkey wrench' appearance to the proximal femur, and advanced carpal and tarsal ossification (summary by Bui et al., 2014). For a discussion of genetic heterogeneity of Desbuquois dysplasia, see DBQD1 (251450).

Any mitochondrial complex III deficiency in which the cause of the disease is a mutation in the UQCC2 gene.

A rare genetic syndromic intellectual disability characterized by global developmental delay and borderline to severe intellectual disability, autism spectrum disorder with obsessive behavior, stereotypies, hyperactivity but frequently friendly and affable personality, feeding difficulties, short stature, muscular hypotonia, microcephaly, characteristic dysmorphic features (hypertelorism, high arched eyebrows, ptosis, deep and/or broad nasal bridge, broad/prominent nasal tip, short and/or upturned philtrum, narrow mouth, and micrognathia), and skeletal anomalies (kyphosis and/or scoliosis, arthrogryposis, slender habitus and extremities). Other clinical features may include hernias, congenital heart defects, cryptorchidism and seizures.

Intellectual developmental disorder with microcephaly and with or without ocular malformations or hypogonadotropic hypogonadism (IDDMOH) is characterized by mildly impaired intellectual development and microcephaly. Patients may also have ocular malformations, ocular apraxia, or hypogonadotropic hypogonadism. The disorder shows a unique DNA methylation signature (summary by Al-Jawahiri et al., 2022).

ADNP-related disorder is characterized by hypotonia, severe speech and motor delay, mild-to-severe intellectual disability, and characteristic facial features (prominent forehead, high anterior hairline, wide and depressed nasal bridge, and short nose with full, upturned nasal tip) based on a cohort of 78 individuals. Features of autism spectrum disorder are common (stereotypic behavior, impaired social interaction). Other common findings include additional behavioral problems, sleep disturbance, brain abnormalities, seizures, feeding issues, gastrointestinal problems, visual dysfunction (hypermetropia, strabismus, cortical visual impairment), musculoskeletal anomalies, endocrine issues including short stature and hormonal deficiencies, cardiac and urinary tract anomalies, and hearing loss.

Severe combined immunodeficiency (SCID) due to DNA-PKcs deficiency is an extremely rare type of SCID (see this term) characterized by the classical signs of SCID (severe and recurrent infections, diarrhea, failure to thrive), absence of T and B lymphocytes, and cell sensitivity to ionizing radiation.

Neu-Laxova syndrome-2 (NLS2) is a rare autosomal recessive disorder characterized by a recognizable pattern of severe congenital malformations leading to prenatal or early postnatal lethality. Affected individuals have abnormal craniofacial features, microcephaly, intrauterine growth retardation, ichthyosis, flexion deformities, limb malformations, and edema of the hands and feet. Some patients have malformations of the central nervous system, such as abnormal gyration (summary by Acuna-Hidalgo et al., 2014). For a discussion of genetic heterogeneity of Neu-Laxova syndrome, see NLS1 (256520).

Any autosomal recessive primary microcephaly in which the cause of the disease is a mutation in the CENPE gene.

Microcephaly and chorioretinopathy-2 is an autosomal recessive developmental disorder characterized by delayed psychomotor development, visual impairment, and short stature (summary by Martin et al., 2014). For a discussion of genetic heterogeneity of microcephaly and chorioretinopathy, see MCCRP1 (251270).

Temple syndrome is a short stature disorder of imprinting. The cardinal features are low birth weight, hypotonia and motor delay, feeding problems early in life, early puberty, and significantly reduced final height. Facial features include a broad forehead and short nose with a wide nasal tip, and the majority of patients have small hands and feet. However, many of the clinical features are nonspecific, making diagnosis difficult. In addition, isodisomy may uncover recessive disorders, which may influence the phenotype in maternal uniparental disomy of chromosome 14 (UPD14mat) cases (summary by Ioannides et al., 2014).

A rare genetic developmental defect during embryogenesis malformation syndrome with characteristics of intrauterine growth restriction, flexion arthrogryposis of all joints, severe microcephaly, renal cystic dysplasia/agenesis/hypoplasia and complex malformations of the brain (cerebral and cerebellar hypoplasia, vermis, corpus callosum and/or occipital lobe agenesis, with or without arhinencephaly), as well as of the genitourinary tract (ureteral agenesis/hypoplasia, uterine hypoplasia and/or vaginal atresia), leading to fetal demise.

Trichothiodystrophy is a rare autosomal recessive disorder in which patients have brittle, sulfur-deficient hair that displays a diagnostic alternating light and dark banding pattern, called 'tiger tail banding,' under polarizing microscopy. TTD patients display a wide variety of clinical features, including cutaneous, neurologic, and growth abnormalities. Common additional clinical features are ichthyosis, intellectual/developmental disabilities, decreased fertility, abnormal characteristics at birth, ocular abnormalities, short stature, and infections. There are both photosensitive and nonphotosensitive forms of the disorder. Patients with TTD have not been reported to have a predisposition to cancer (summary by Faghri et al., 2008). For a discussion of genetic heterogeneity of TTD, see 601675.

Complex lethal osteochondrodysplasia of the Symoens-Barnes-Gistelinck type is characterized by severe skeletal osteopenia, microcephaly, multiple fractures, and congenital anomalies including ascites, pleural effusion, and intracranial ventriculomegaly (Symoens et al., 2015).

Microcephaly, short stature, and impaired glucose metabolism-2 (MSSGM2) is an autosomal recessive syndrome characterized by microcephaly associated with impaired intellectual development, and short stature. Patients develop diabetes in the second or third decade of life, and hypothyroidism and delayed puberty have also been reported (Abdulkarim et al., 2015; Kernohan et al., 2015). For a discussion of genetic heterogeneity of microcephaly, short stature, and impaired glucose metabolism, see MSSGM1 (616033).

UNC80 deficiency is characterized by hypotonia, strabismus, oral motor dysfunction, postnatal growth deficiency, and developmental delay. The majority of individuals do not learn to walk. All individuals lack expressive language; however, many have expressive body language, and a few have used signs to communicate. Seizures may develop during infancy or childhood. Additional features can include nystagmus, extremity hypertonia, a high-pitched cry, repetitive and self-stimulatory behaviors, constipation, clubfeet, joint contractures, and scoliosis. For most individuals the UNC80 deficiency syndrome is not progressive. Individuals have slow acquisition of skills and do not have a loss of skills suggestive of neurodegeneration.

Any Seckel syndrome in which the cause of the disease is a mutation in the TRAIP gene.

Primary coenzyme Q10 (CoQ10) deficiency is usually associated with multisystem involvement, including neurologic manifestations such as fatal neonatal encephalopathy with hypotonia; a late-onset slowly progressive multiple-system atrophy-like phenotype (neurodegeneration with autonomic failure and various combinations of parkinsonism and cerebellar ataxia, and pyramidal dysfunction); and dystonia, spasticity, seizures, and intellectual disability. Steroid-resistant nephrotic syndrome (SRNS), the hallmark renal manifestation, is often the initial manifestation either as isolated renal involvement that progresses to end-stage renal disease (ESRD), or associated with encephalopathy (seizures, stroke-like episodes, severe neurologic impairment) resulting in early death. Hypertrophic cardiomyopathy (HCM), retinopathy or optic atrophy, and sensorineural hearing loss can also be seen.

Developmental and epileptic encephalopathy-35 (DEE35) is an autosomal recessive neurodegenerative disorder characterized by onset of seizures in the first months of life associated with essentially no normal development. Brain imaging shows a characteristic pattern consistent with lack of myelination of early structures, including the posterior limb of the internal capsule, brainstem tracts, and tracts to the primary visual and motor cortices. Many patients die in early childhood (summary by Kevelam et al., 2015) For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350.

Autosomal dominant cutis laxa-3 is characterized by thin skin with visible veins and wrinkles, cataract or corneal clouding, clenched fingers, pre- and postnatal growth retardation, and moderate intellectual disability. In addition, patients exhibit a combination of muscular hypotonia with brisk muscle reflexes (Fischer-Zirnsak et al., 2015). For a general phenotypic description and discussion of genetic heterogeneity of autosomal dominant cutis laxa, see ARCL1 (123700).

Dyskeratosis congenita and related telomere biology disorders (DC/TBD) are caused by impaired telomere maintenance resulting in short or very short telomeres. The phenotypic spectrum of telomere biology disorders is broad and includes individuals with classic dyskeratosis congenita (DC) as well as those with very short telomeres and an isolated physical finding. Classic DC is characterized by a triad of dysplastic nails, lacy reticular pigmentation of the upper chest and/or neck, and oral leukoplakia, although this may not be present in all individuals. People with DC/TBD are at increased risk for progressive bone marrow failure (BMF), myelodysplastic syndrome or acute myelogenous leukemia, solid tumors (usually squamous cell carcinoma of the head/neck or anogenital cancer), and pulmonary fibrosis. Other findings can include eye abnormalities (epiphora, blepharitis, sparse eyelashes, ectropion, entropion, trichiasis), taurodontism, liver disease, gastrointestinal telangiectasias, and avascular necrosis of the hips or shoulders. Although most persons with DC/TBD have normal psychomotor development and normal neurologic function, significant developmental delay is present in both forms; additional findings include cerebellar hypoplasia (Hoyeraal Hreidarsson syndrome) and bilateral exudative retinopathy and intracranial calcifications (Revesz syndrome and Coats plus syndrome). Onset and progression of manifestations of DC/TBD vary: at the mild end of the spectrum are those who have only minimal physical findings with normal bone marrow function, and at the severe end are those who have the diagnostic triad and early-onset BMF.

In patients with SSMED, short stature and microcephaly are apparent at birth, and there is progressive postnatal growth failure. Endocrine dysfunction, including hypergonadotropic hypogonadism, multinodular goiter, and diabetes mellitus, is present in affected adults. Progressive ataxia has been reported in some patients, with onset ranging from the second to fifth decade of life. In addition, a few patients have developed tumors, suggesting that there may be a predisposition to tumorigenesis. In contrast to syndromes involving defects in other components of the nonhomologous end-joining (NHEJ) complex (see, e.g., 606593), no clinically overt immunodeficiency has been observed in SSMED, although laboratory analysis has revealed lymphopenia or borderline leukopenia in some patients (Murray et al., 2015; Bee et al., 2015; de Bruin et al., 2015; Guo et al., 2015).

Any lethal congenital contracture syndrome in which the cause of the disease is a mutation in the ADGRG6 gene.

White-Sutton syndrome is a neurodevelopmental disorder characterized by a wide spectrum of cognitive dysfunction, developmental delays (particularly in speech and language acquisition), hypotonia, autism spectrum disorder, and other behavioral problems. Additional features commonly reported include seizures, refractive errors and strabismus, hearing loss, sleep disturbance (particularly sleep apnea), feeding and gastrointestinal problems, mild genital abnormalities in males, and urinary tract involvement in both males and females.

Dyskeratosis congenita and related telomere biology disorders (DC/TBD) are caused by impaired telomere maintenance resulting in short or very short telomeres. The phenotypic spectrum of telomere biology disorders is broad and includes individuals with classic dyskeratosis congenita (DC) as well as those with very short telomeres and an isolated physical finding. Classic DC is characterized by a triad of dysplastic nails, lacy reticular pigmentation of the upper chest and/or neck, and oral leukoplakia, although this may not be present in all individuals. People with DC/TBD are at increased risk for progressive bone marrow failure (BMF), myelodysplastic syndrome or acute myelogenous leukemia, solid tumors (usually squamous cell carcinoma of the head/neck or anogenital cancer), and pulmonary fibrosis. Other findings can include eye abnormalities (epiphora, blepharitis, sparse eyelashes, ectropion, entropion, trichiasis), taurodontism, liver disease, gastrointestinal telangiectasias, and avascular necrosis of the hips or shoulders. Although most persons with DC/TBD have normal psychomotor development and normal neurologic function, significant developmental delay is present in both forms; additional findings include cerebellar hypoplasia (Hoyeraal Hreidarsson syndrome) and bilateral exudative retinopathy and intracranial calcifications (Revesz syndrome and Coats plus syndrome). Onset and progression of manifestations of DC/TBD vary: at the mild end of the spectrum are those who have only minimal physical findings with normal bone marrow function, and at the severe end are those who have the diagnostic triad and early-onset BMF.

Developmental and epileptic encephalopathy-29 (DEE29) is an autosomal recessive neurologic disorder characterized by the onset of refractory myoclonic seizures in the first months of life. Affected individuals have poor overall growth, congenital microcephaly with cerebral atrophy and impaired myelination on brain imaging, spasticity with abnormal movements, peripheral neuropathy, and poor visual fixation (summary by Simons et al., 2015). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350.

Arboleda-Tham syndrome (ARTHS) is an autosomal dominant disorder with the core features of impaired intellectual development, speech delay, microcephaly, cardiac anomalies, and gastrointestinal complications (summary by Kennedy et al., 2019).

X-linked syndromic intellectual developmental disorder-33 (MRXS33) is an X-linked recessive neurodevelopmental disorder characterized by delayed psychomotor development, intellectual disability, and characteristic facial features (summary by O'Rawe et al., 2015).

Trichothiodystrophy-5 (TTD5) is an X-linked disorder characterized by sparse and brittle hair, facial dysmorphism, global developmental delays, growth deficiency, hypogonadism, and structural brain abnormalities (summary by Mendelsohn et al., 2020). For a general phenotypic description and a discussion of genetic heterogeneity of trichothiodystrophy, see TTD1 (601675).

VATER is a mnemonically useful acronym for the nonrandom association of vertebral defects (V), anal atresia (A), tracheoesophageal fistula with esophageal atresia (TE), and radial or renal dysplasia (R). This combination of associated defects was pointed out by Quan and Smith (1972). Nearly all cases have been sporadic. VACTERL is an acronym for an expanded definition of the association that includes cardiac malformations (C) and limb anomalies (L). The VACTERL association is a spectrum of various combinations of its 6 components, which can be a manifestation of several recognized disorders rather than a distinct anatomic or etiologic entity (Khoury et al., 1983). Also see VATER/VACTERL association with hydrocephalus (VACTERL-H; 276950) and VACTERL with or without hydrocephalus (VACTERLX; 314390).

The Mulchandani-Bhoj-Conlin syndrome (MBCS) is characterized by prenatal growth restriction, severe short stature with proportional head circumference, and profound feeding difficulty (Mulchandani et al., 2016).

MIRAGE syndrome is an acronym for the major findings of myelodysplasia, infection, restriction of growth, adrenal hypoplasia, genital phenotypes, and enteropathy. Cytopenias are typically seen soon after birth; thrombocytopenia is the most common followed by anemia and pancytopenia. Recurrent infections from early infancy include pneumonia, urinary tract infection, gastroenteritis, meningitis, otitis media, dermatitis, subcutaneous abscess, and sepsis. Reported genital phenotypes in those with 46,XY karyotype included hypospadias, microphallus, bifid shawl scrotum, ambiguous genitalia, or complete female genitalia. Hypoplastic or dysgenetic ovaries have been reported in females. Gastrointestinal complications include chronic diarrhea and esophageal dysfunction. Moderate-to-severe developmental delay is reported in most affected individuals. Autonomic dysfunction and renal dysfunction are also reported.

Van Esch-O'Driscoll syndrome (VEODS) is characterized by varying degrees of intellectual disability, moderate to severe short stature, microcephaly, hypogonadism, and variable congenital malformations (Van Esch et al., 2019).

Intellectual developmental disorder with dysmorphic facies and ptosis (IDDDFP) is an autosomal dominant neurodevelopmental disorder characterized by delayed psychomotor development, intellectual disability, delayed language, and dysmorphic facial features, most notably ptosis/blepharophimosis. Additional features may include poor growth, hypotonia, and seizures (summary by Mattioli et al., 2017). See also chromosome 3p deletion syndrome (613792).

Any lethal congenital contracture syndrome in which the cause of the disease is a mutation in the GLDN gene.

Shashi-Pena syndrome is a neurodevelopmental syndrome characterized by delayed psychomotor development, variable intellectual disability, hypotonia, facial dysmorphism, and some unusual features, including enlarged head circumference, glabellar nevus flammeus, and deep palmar creases. Some patients may also have atrial septal defect, episodic hypoglycemia, changes in bone mineral density, and/or seizures (summary by Shashi et al., 2016).

The core features of short stature-micrognathia syndrome (SSMG) are intrauterine growth restriction (IUGR), postnatal short stature that is often rhizomelic, and micrognathia. Other common features include preterm birth, microcephaly, developmental delay, and genitourinary malformations in males. Transient liver dysfunction and glycosylation abnormalities during illness, giant cell hepatitis, hepatoblastoma, and cataracts have also been observed. Inter- and intrafamilial phenotypic severity varies greatly, from a relatively mild disorder to intrauterine death or stillbirth (Ritter et al., 2022).

A rare genetic, multiple congenital anomalies syndrome characterized by short stature, hand brachydactyly with hypoplastic distal phalanges, global development delay, intellectual disability, and more variably seizures, obesity, and craniofacial dysmorphism that includes microcephaly, high forehead, flat face, hypertelorism, deep set eyes, flat nasal bridge, averted nostrils, long philtrum, thin lip vermilion, and short neck.

Any mitochondrial DNA depletion syndrome in which the cause of the disease is a mutation in the TFAM gene.

ZTTK syndrome (ZTTKS) is a severe multisystem developmental disorder characterized by delayed psychomotor development and intellectual disability. Affected individuals have characteristic dysmorphic facial features, hypotonia, poor feeding, poor overall growth, and eye or visual abnormalities. Most patients also have musculoskeletal abnormalities, and some have congenital defects of the heart and urogenital system. Brain imaging usually shows developmental abnormalities such as gyral changes, cortical and/or cerebellar atrophy, and thin corpus callosum (summary by Kim et al., 2016).

GRIDHH is an autosomal recessive multisystem disorder characterized by poor overall growth, impaired intellectual development, hypotonia, and variable liver dysfunction. Additional features, such as seizures and hearing loss, may also be present (summary by Kopajtich et al., 2016).

Developmental and epileptic encephalopathy-40 (DEE40) is an autosomal recessive neurologic disorder characterized by the onset of refractory infantile spasms within the first 6 months of life. Affected infants may have normal or mildly delayed development before the onset of seizures, but thereafter show developmental stagnation and severe neurologic impairment. EEG typically shows hypsarrhythmia, consistent with a clinical diagnosis of West syndrome. Additional features include poor feeding, axial hypotonia with peripheral spasticity, limited eye contact, profoundly impaired intellectual development with absent language, and poor fine motor skills (summary by Alfaiz et al., 2016). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350.

Autosomal dominant tubulointerstitial kidney disease-5 (ADTKD5) is characterized by the onset of progressive chronic renal disease in the first decades of life. Mild hyperuricemia may be present, but gout, hypertension, and proteinuria are usually absent. The disease may be associated with anemia or neutropenia. Some patients may have additional findings, including poor overall growth and impaired cognitive function. Renal biopsy shows tubulointerstitial abnormalities with atrophic tubules and fibrosis; secondary glomerular abnormalities and simple cysts may also be present (summary by Bolar et al., 2016). For a discussion of genetic heterogeneity and revised nomenclature of ADTKD, see ADTKD1 (162000).

Bone marrow failure syndrome-3 is an autosomal recessive disorder characterized by onset of pancytopenia in early childhood. Patients may have additional variable nonspecific somatic abnormalities, including poor growth, microcephaly, and skin anomalies (summary by Tummala et al., 2016). BMFS3 has a distinct phenotype and may include features that overlap with Shwachman-Diamond syndrome (SDS1; 260400), such as pancreatic insufficiency and short stature, and with dyskeratosis congenita (see, e.g., DKCA1, 127550), such as dental and hair abnormalities and shortened telomeres. In addition, some patients may have joint and skeletal abnormalities, impaired development, and retinal dysplasia (summary by D'Amours et al., 2018). For a discussion of genetic heterogeneity of BMFS, see BMFS1 (614675).

Hydrops, lactic acidosis, and sideroblastic anemia (HLASA) is an autosomal recessive multisystem disorder characterized by the onset of hydrops in utero. The severity of the hydrops and the disorder in general is highly variable. At birth, affected infants usually show poor growth, lactic acidosis, pulmonary hypertension with hypoxic respiratory insufficiency, and sideroblastic anemia. More variable features may include hepatosplenomegaly or cholestasis, hypoglycemia, pancreatic insufficiency, and micropenis or hypospadias. Death in infancy may occur. Those who survive tend to have resolution of lactic acidosis and anemia, but may show developmental delay and sensorineural deafness (summary by Riley et al., 2020).

RERE-related disorders are characterized by neurodevelopmental problems with or without structural anomalies of the eyes, heart, kidneys, and genitourinary tract and mild sensorineural hearing loss. Hypotonia and feeding problems are common among affected individuals. Developmental delay and intellectual disability range from mild to profound. Behavior problems may include attention-deficit/hyperactivity disorder, self-injurious behavior, and autism spectrum disorder. A variety of eye anomalies (coloboma, optic nerve anomalies, microphthalmia, and/or Peter's anomaly) and vision issues (myopia, anisometropia, astigmatism, exotropia, esotropia) have been reported. Congenital heart defects, most commonly septal defects, have also been described. Genitourinary abnormalities include vesicoureteral reflux, and cryptorchidism and hypospadias in males. Sensorineural hearing loss can be unilateral or bilateral.

Coffin-Siris syndrome is a rare congenital disorder characterized by delayed psychomotor development, intellectual disability, coarse facial features, and hypoplasia of the distal phalanges, particularly the fifth digit. Other features may also be observed, including congenital heart defects, hypoplasia of the corpus callosum, and poor overall growth with short stature and microcephaly (summary by Wieczorek et al., 2013). Patients with SMARCE1 mutations have a wide spectrum of manifestations, including severe to moderate intellectual disability and heart defects (summary by Kosho et al., 2014). For a general phenotypic description and a discussion of genetic heterogeneity of Coffin-Siris syndrome, see CSS1 (135900).

Neurodevelopmental disorder with or without hypotonia, seizures, and cerebellar atrophy (NEDHSCA) is an autosomal recessive disorder characterized by severely delayed psychomotor development, hypotonia apparent since infancy, and early-onset seizures in most patients. Some patients may have additional features, such as cerebellar atrophy, ataxia, and nonspecific dysmorphic features. NEDHSCA is one of a group of similar neurologic disorders resulting from biochemical defects in the glycosylphosphatidylinositol (GPI) biosynthetic pathway. Some patients with NEDHSCA may have the Emm-null blood group phenotype (see 619812) (summary by Makrythanasis et al., 2016; Duval et al., 2021). For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293).

The marfanoid-progeroid-lipodystrophy syndrome (MFLS) is characterized by congenital lipodystrophy, premature birth with an accelerated linear growth disproportionate to weight gain, and progeroid appearance with distinct facial features, including proptosis, downslanting palpebral fissures, and retrognathia. Other characteristic features include arachnodactyly, digital hyperextensibility, myopia, dural ectasia, and normal psychomotor development (Takenouchi et al., 2013). Takenouchi et al. (2013) noted phenotypic overlap with Marfan syndrome (154700) and Shprintzen-Goldberg craniosynostosis syndrome (182212).

Immunodeficiency-centromeric instability-facial anomalies syndrome-3 is an autosomal recessive disorder characterized by recurrent infections in childhood and variable dysmorphic facial features. Laboratory studies show hypomethylation of certain chromosomal regions. Additional features, including delayed development, are variable (summary by Thijssen et al., 2015). For a discussion of genetic heterogeneity of immunodeficiency-centromeric instability-facial anomalies syndrome, see ICF1 (242860).

Witteveen-Kolk syndrome (WITKOS) is an autosomal dominant disorder with characteristic distinctive facial features, microcephaly, short stature, and mildly impaired intellectual development with delayed cognitive and motor development and subtle anomalies on MRI-brain imaging (summary by Balasubramanian et al., 2021).

Distal chromosome 19q13.11 deletion syndrome is an autosomal dominant neurodevelopmental disorder characterized by poor overall growth, slender habitus, microcephaly, delayed development, intellectual disability with poor or absent speech, and feeding difficulties. Additional features include dysmorphic facies, signs of ectodermal dysplasia, hand and foot anomalies, and genitourinary anomalies, particularly in males (summary by Chowdhury et al., 2014).

Dyskeratosis congenita and related telomere biology disorders (DC/TBD) are caused by impaired telomere maintenance resulting in short or very short telomeres. The phenotypic spectrum of telomere biology disorders is broad and includes individuals with classic dyskeratosis congenita (DC) as well as those with very short telomeres and an isolated physical finding. Classic DC is characterized by a triad of dysplastic nails, lacy reticular pigmentation of the upper chest and/or neck, and oral leukoplakia, although this may not be present in all individuals. People with DC/TBD are at increased risk for progressive bone marrow failure (BMF), myelodysplastic syndrome or acute myelogenous leukemia, solid tumors (usually squamous cell carcinoma of the head/neck or anogenital cancer), and pulmonary fibrosis. Other findings can include eye abnormalities (epiphora, blepharitis, sparse eyelashes, ectropion, entropion, trichiasis), taurodontism, liver disease, gastrointestinal telangiectasias, and avascular necrosis of the hips or shoulders. Although most persons with DC/TBD have normal psychomotor development and normal neurologic function, significant developmental delay is present in both forms; additional findings include cerebellar hypoplasia (Hoyeraal Hreidarsson syndrome) and bilateral exudative retinopathy and intracranial calcifications (Revesz syndrome and Coats plus syndrome). Onset and progression of manifestations of DC/TBD vary: at the mild end of the spectrum are those who have only minimal physical findings with normal bone marrow function, and at the severe end are those who have the diagnostic triad and early-onset BMF.

CDK13-related disorder, reported in 43 individuals to date, is characterized in all individuals by developmental delay / intellectual disability (DD/ID); nearly all individuals older than age one year display impaired verbal language skills (either absent or restricted speech). Other common findings are recognizable facial features in some individuals, behavioral problems (autism spectrum disorder or autistic traits/stereotypies, attention-deficit/hyperactivity disorder), feeding difficulties in infancy, structural cardiac defects, and seizures.

Anauxetic dysplasia is a spondyloepimetaphyseal dysplasia characterized by severe short stature of prenatal onset, very short adult height (less than 1 meter), hypodontia, midface hypoplasia, and mild intellectual disability. Vertebrae are ovoid with concave dorsal surfaces in the lumbar region and show delayed bone maturation. Femoral heads and necks are hypoplastic, as are the iliac bodies. Long bones show irregular mineralization of the metaphyses. The first and fifth metacarpals are short and wide with small, late-ossifying epiphyses and bullet-shaped middle phalanges (summary by Barraza-Garcia et al., 2017). For a discussion of genetic heterogeneity of anauxetic dysplasia, see ANXD1 (607095).

IDDFSDA is an autosomal recessive severe multisystem disorder characterized by poor overall growth, developmental delay, early-onset seizures, intellectual disability, and dysmorphic features. There is phenotypic variability. The most severely affected patients have a neurodevelopmental disorder with microcephaly, absent speech, and inability to walk, and they require feeding tubes. Some patients have congenital heart defects or nonspecific abnormalities on brain imaging. Less severely affected individuals have mild to moderate intellectual disability with normal speech and motor development (summary by Santiago-Sim et al., 2017).

Gabriele-de Vries syndrome is characterized by mild-to-profound developmental delay / intellectual disability (DD/ID) in all affected individuals and a wide spectrum of functional and morphologic abnormalities. Intrauterine growth restriction or low birth weight and feeding difficulties are common. Congenital brain, eye, heart, kidney, genital, and/or skeletal system anomalies have also been reported. About half of affected individuals have neurologic manifestations, including hypotonia and gait abnormalities. Behavioral issues can include attention-deficit/hyperactivity disorder, anxiety, autism or autistic behavior, and schizoaffective disorder.

Autosomal recessive limb-girdle muscular dystrophy-18 (LGMD18) is characterized by childhood-onset of proximal muscle weakness resulting in gait abnormalities and scapular winging. Serum creatine kinase is increased. A subset of patients may show a hyperkinetic movement disorder with chorea, ataxia, or dystonia and global developmental delay (summary by Bogershausen et al., 2013). Additional more variable features include alacrima, achalasia, cataracts, or hepatic steatosis (Liang et al., 2015; Koehler et al., 2017). For a discussion of genetic heterogeneity of autosomal recessive limb-girdle muscular dystrophy, see LGMDR1 (253600).

Fanconi anemia (FA) is characterized by physical abnormalities, bone marrow failure, and increased risk for malignancy. Physical abnormalities, present in approximately 75% of affected individuals, include one or more of the following: short stature, abnormal skin pigmentation, skeletal malformations of the upper and/or lower limbs, microcephaly, and ophthalmic and genitourinary tract anomalies. Progressive bone marrow failure with pancytopenia typically presents in the first decade, often initially with thrombocytopenia or leukopenia. The incidence of acute myeloid leukemia is 13% by age 50 years. Solid tumors – particularly of the head and neck, skin, and genitourinary tract – are more common in individuals with FA.

Diencephalic-mesencephalic junction dysplasia syndrome-1 (DMJDS1) is an autosomal recessive neurodevelopmental disorder characterized by progressive microcephaly, severely delayed or even absent psychomotor development with profound intellectual disability, and spasticity or dystonia. Some patients may have seizures and/or visual impairment. Brain imaging shows a characteristic developmental malformation of the midbrain; subtle intracranial calcifications may also be present (summary by Aran et al., 2016 and Guemez-Gamboa et al., 2018). Genetic Heterogeneity of Diencephalic-Mesencephalic Junction Dysplasia Syndrome See also DMJDS2 (618646), caused by mutation in the GSX2 gene (616253) on chromosome 4q12.

Galloway-Mowat syndrome is a renal-neurologic disease characterized by early-onset nephrotic syndrome associated with microcephaly, gyral abnormalities of the brain, and delayed psychomotor development. Most patients have dysmorphic facial features, often including hypertelorism, ear abnormalities, and micrognathia. Other features, such as arachnodactyly and visual impairment, are more variable. Most patients die in the first years of life (summary by Braun et al., 2017). For a general phenotypic description and a discussion of genetic heterogeneity of GAMOS, see GAMOS1 (251300).

Birk-Landau-Perez syndrome (BILAPES) is an autosomal recessive syndromic developmental disorder characterized by global developmental delay apparent from infancy or early childhood. Some patients have developmental regression with loss of speech and motor skills, whereas other patients never achieve these milestones. More variable features may include hypotonia, poor overall growth, ataxia, dystonia, abnormal eye movements, and renal insufficiency (Perez et al., 2017; Kleyner et al., 2022).

Congenital heart defects and skeletal malformations syndrome (CHDSKM) is characterized by atrial and ventricular septal defects, with aortic root dilation in adulthood. Skeletal defects are variable and include pectus excavatum, scoliosis, and finger contractures, and some patients exhibit joint laxity. Failure to thrive is observed during infancy and early childhood (Wang et al., 2017).

MISSLA is an autosomal recessive disorder characterized by intrauterine growth retardation, microcephaly, variable short stature, and limb abnormalities mainly affecting the upper limb and radial ray. Affected individuals typically have mild intellectual disability, but may have normal development (summary by Reynolds et al., 2017).

A rare genetic multiple congenital anomalies/dysmorphic syndrome characterized by global developmental delay, variable degrees of intellectual disability, and facial dysmorphism (including high nasal bridge, deep-set eyes, and wide mouth), often associated with feeding difficulties and/or gastroesophageal reflux. Additional reported manifestations are seizures, hypotonia, autistic features, and joint laxity. Brain imaging may show non-specific features (such as cerebral atrophy).

Al Kaissi syndrome (ALKAS) is an autosomal recessive developmental disorder characterized by growth retardation, spine malformation, particularly of the cervical spine, dysmorphic facial features, and delayed psychomotor development with moderate to severe intellectual disability (summary by Windpassinger et al., 2017).

NEMMLAS is an autosomal recessive multisystemic disorder characterized by delayed psychomotor development, intellectual disability, and abnormal motor function, including hypotonia, dystonia, ataxia, and spasticity. Patient tissues may show deficiencies in one or more of the mitochondrial oxidative phosphorylation (OXPHOS) enzymes, but this is not a constant finding (summary by Wortmann et al., 2017).

COXPD33 is an autosomal recessive multisystem disorder resulting from a defect in mitochondrial energy metabolism. The phenotype is highly variable, ranging from death in infancy to adult-onset progressive external ophthalmoplegia (PEO) and myopathy. A common finding is cardiomyopathy and increased serum lactate (summary by Feichtinger et al., 2017). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060).

Galloway-Mowat syndrome is a renal-neurologic disease characterized by early-onset nephrotic syndrome associated with microcephaly, gyral abnormalities of the brain, and delayed psychomotor development. Most patients have dysmorphic facial features, often including hypertelorism, ear abnormalities, and micrognathia. Other features, such as arachnodactyly and visual impairment, are more variable. Most patients die in the first years of life (summary by Braun et al., 2017). For a general phenotypic description and a discussion of genetic heterogeneity of GAMOS, see GAMOS1 (251300).

IMDDHH is a multisystem disorder characterized by immunodeficiency, mildly delayed psychomotor development, poor overall growth from infancy, and hypohomocysteinemia. Additional features, such as congenital heart defects and liver involvement, are more variable (summary by Huppke et al., 2017).

A rare genetic multiple congenital anomalies/dysmorphic syndrome characterized by global developmental delay and moderate to severe intellectual disability, as well as variable other manifestations, such as macro- or microcephaly, epilepsy, hypotonia, behavioral problems, stereotypic movements, and facial dysmorphism (including arched eyebrows, long palpebral fissures, prominent nasal bridge, upturned nose, dysplastic ears, and broad mouth), among others. Brain imaging may show cerebellar anomalies, hypoplastic corpus callosum, enlarged ventricles, polymicrogyria, or white matter abnormalities.

Seckel syndrome is a rare autosomal recessive disorder characterized by intrauterine growth retardation, dwarfism, microcephaly with mental retardation, and a characteristic 'bird-headed' facial appearance (Shanske et al., 1997). Genetic Heterogeneity of Seckel Syndrome Other forms of Seckel syndrome include SCKL2 (606744), caused by mutation in the RBBP8 gene (604124) on chromosome 18q11; SCKL4 (613676), caused by mutation in the CENPJ gene (609279) on chromosome 13q12; SCKL5 (613823), caused by mutation in the CEP152 gene (613529) on chromosome 15q21; SCKL6 (614728), caused by mutation in the CEP63 gene (614724) on chromosome 3q22; SCKL7 (614851), caused by mutation in the NIN gene (608684) on chromosome 14q22; SCKL8 (615807), caused by mutation in the DNA2 gene (601810) on chromosome 10q21; SCKL9 (616777), caused by mutation in the TRAIP gene (605958) on chromosome 3p21; SCKL10 (617253), caused by mutation in the NSMCE2 gene (617246) on chromosome 8q24; and SCKL11 (620767), caused by mutation in the CEP295 gene (617728) on chromosome 11q21. The report of a Seckel syndrome locus on chromosome 14q, designated SCKL3, by Kilinc et al. (2003) was found to be in error; see History section.

Any Neu-Laxova syndrome in which the cause of the disease is a mutation in the PHGDH gene.

Ritscher-Schinzel syndrome (RSS) is a clinically recognizable condition that includes the cardinal findings of craniofacial features, cerebellar defects, and cardiovascular malformations resulting in the alternate diagnostic name of 3C syndrome. Dysmorphic facial features may include brachycephaly, hypotonic face with protruding tongue, flat appearance of the face on profile view, short midface, widely spaced eyes, downslanted palpebral fissures, low-set ears with overfolding of the upper helix, smooth or short philtrum, and high or cleft palate. Affected individuals also typically have a characteristic metacarpal phalangeal profile showing a consistent wavy pattern on hand radiographs. RSS is associated with variable degrees of developmental delay and intellectual disability. Eye anomalies and hypercholesterolemia may be variably present.

Cornelia de Lange syndrome (CdLS) encompasses a spectrum of findings from mild to severe. Severe (classic) CdLS is characterized by distinctive facial features, growth restriction (prenatal onset; <5th centile throughout life), hypertrichosis, and upper-limb reduction defects that range from subtle phalangeal abnormalities to oligodactyly (missing digits). Craniofacial features include synophrys, highly arched and/or thick eyebrows, long eyelashes, short nasal bridge with anteverted nares, small widely spaced teeth, and microcephaly. Individuals with a milder phenotype have less severe growth, cognitive, and limb involvement, but often have facial features consistent with CdLS. Across the CdLS spectrum IQ ranges from below 30 to 102 (mean: 53). Many individuals demonstrate autistic and self-destructive tendencies. Other frequent findings include cardiac septal defects, gastrointestinal dysfunction, hearing loss, myopia, and cryptorchidism or hypoplastic genitalia.

The cartilage-hair hypoplasia – anauxetic dysplasia (CHH-AD) spectrum disorders are a continuum that includes the following phenotypes: Metaphyseal dysplasia without hypotrichosis (MDWH). Cartilage-hair hypoplasia (CHH). Anauxetic dysplasia (AD). CHH-AD spectrum disorders are characterized by severe disproportionate (short-limb) short stature that is usually recognized in the newborn, and occasionally prenatally because of the short extremities. Other findings include joint hypermobility, fine silky hair, immunodeficiency, anemia, increased risk for malignancy, gastrointestinal dysfunction, and impaired spermatogenesis. The most severe phenotype, AD, has the most pronounced skeletal phenotype, may be associated with atlantoaxial subluxation in the newborn, and may include cognitive deficiency. The clinical manifestations of the CHH-AD spectrum disorders are variable, even within the same family.

Trichohepatoenteric syndrome (THES), generally considered to be a neonatal enteropathy, is characterized by intractable diarrhea (seen in almost all affected children), woolly hair (seen in all), intrauterine growth restriction, facial dysmorphism, and short stature. Additional findings include poorly characterized immunodeficiency, recurrent infections, skin abnormalities, and liver disease. Mild intellectual disability (ID) is seen in about 50% of affected individuals. Less common findings include congenital heart defects and platelet anomalies. To date 52 affected individuals have been reported.

The Meier-Gorlin syndrome is a rare disorder characterized by severe intrauterine and postnatal growth retardation, microcephaly, bilateral microtia, and aplasia or hypoplasia of the patellae (summary by Shalev and Hall, 2003). While almost all cases have primordial dwarfism with substantial prenatal and postnatal growth retardation, not all cases have microcephaly, and microtia and absent/hypoplastic patella are absent in some. Despite the presence of microcephaly, intellect is usually normal (Bicknell et al., 2011). Genetic Heterogeneity of Meier-Gorlin Syndrome Most forms of Meier-Gorlin syndrome are autosomal recessive disorders, including Meier-Gorlin syndrome-1; Meier-Gorlin syndrome-2 (613800), caused by mutation in the ORC4 gene (603056) on chromosome 2q23; Meier-Gorlin syndrome-3 (613803), caused by mutation in the ORC6 gene (607213) on chromosome 16q11; Meier-Gorlin syndrome-4 (613804), caused by mutation in the CDT1 gene (605525) on chromosome 16q24; Meier-Gorlin syndrome-5 (613805), caused by mutation in the CDC6 gene (602627) on chromosome 17q21; Meier-Gorlin syndrome-7 (617063), caused by mutation in the CDC45L gene (603465) on chromosome 22q11; and Meier-Gorlin syndrome-8 (617564), caused by mutation in the MCM5 gene (602696) on chromosome 22q12. An autosomal dominant form of the disorder, Meier-Gorlin syndrome-6 (616835), is caused by mutation in the GMNN gene (602842) on chromosome 6p22.

Dyskeratosis congenita and related telomere biology disorders (DC/TBD) are caused by impaired telomere maintenance resulting in short or very short telomeres. The phenotypic spectrum of telomere biology disorders is broad and includes individuals with classic dyskeratosis congenita (DC) as well as those with very short telomeres and an isolated physical finding. Classic DC is characterized by a triad of dysplastic nails, lacy reticular pigmentation of the upper chest and/or neck, and oral leukoplakia, although this may not be present in all individuals. People with DC/TBD are at increased risk for progressive bone marrow failure (BMF), myelodysplastic syndrome or acute myelogenous leukemia, solid tumors (usually squamous cell carcinoma of the head/neck or anogenital cancer), and pulmonary fibrosis. Other findings can include eye abnormalities (epiphora, blepharitis, sparse eyelashes, ectropion, entropion, trichiasis), taurodontism, liver disease, gastrointestinal telangiectasias, and avascular necrosis of the hips or shoulders. Although most persons with DC/TBD have normal psychomotor development and normal neurologic function, significant developmental delay is present in both forms; additional findings include cerebellar hypoplasia (Hoyeraal Hreidarsson syndrome) and bilateral exudative retinopathy and intracranial calcifications (Revesz syndrome and Coats plus syndrome). Onset and progression of manifestations of DC/TBD vary: at the mild end of the spectrum are those who have only minimal physical findings with normal bone marrow function, and at the severe end are those who have the diagnostic triad and early-onset BMF.

Ververi-Brady syndrome (VEBRAS) is characterized by mild developmental delay, mildly impaired intellectual development and speech delay, and mild dysmorphic facial features. Affected individuals can usually attend mainstream schools with support, and may also show autistic features (summary by Ververi et al., 2018).

Congenital disorder of glycosylation with defective fucosylation is an autosomal recessive multisystem disorder apparent from birth. Affected infants have poor growth, failure to thrive, hypotonia, skeletal anomalies, and delayed psychomotor development with intellectual disability. Additional highly variable congenital defects may be observed (summary by Ng et al., 2018). Genetic Heterogeneity of Congenital Disorders of Glycosylation with Defective Fucosylation See also CDGF2 (618323), caused by mutation in the FCSK gene (608675) on chromosome 16q22. For an overview of congenital disorders of glycosylation (CDG), see CDG1A (212065) and CDG2A (212066).

Characteristic features of the distal 3p- syndrome include low birth weight, microcephaly, trigonocephaly, hypotonia, psychomotor and growth retardation, ptosis, telecanthus, downslanting palpebral fissures, and micrognathia. Postaxial polydactyly, renal anomalies, cleft palate, congenital heart defects (especially atrioventricular septal defects), preauricular pits, sacral dimple, and gastrointestinal anomalies are variable features. Although intellectual deficits are almost invariably associated with cytogenetically visible 3p deletions, rare patients with a 3p26-p25 deletion and normal intelligence or only mild abnormalities have been described (summary by Shuib et al., 2009).

Pontocerebellar hypoplasia type 1D (PCH1D) is a severe autosomal recessive neurologic disorder characterized by severe hypotonia and a motor neuronopathy apparent at birth or in infancy. Patients have respiratory insufficiency, feeding difficulties, and severely delayed or minimal gross motor development. Other features may include eye movement abnormalities, poor overall growth, contractures. Brain imaging shows progressive cerebellar atrophy with relative sparing of the brainstem (summary by Burns et al., 2018). For a general phenotypic description and a discussion of genetic heterogeneity of PCH, see PCH1A (607596).

MGRISCE2 is an autosomal recessive disorder characterized by intrauterine growth restriction, poor postnatal growth with short stature and microcephaly, and increased sister chromatid exchange on cell studies. The disorder results from defective DNA decatenation. The pathogenesis of the disorder is similar to that of Bloom syndrome (BLM; 210900), but patients with mutations in the TOP3A gene do not have a malar rash (summary by Martin et al., 2018). For a discussion of genetic heterogeneity of MGRISCE, see Bloom syndrome (BLM; MGRISCE1; 210900)

MFRG is an autosomal recessive syndrome in which microcephaly, unilateral renal agenesis, ambiguous genitalia, and facial dysmorphisms, including severe micrognathia, are observed in most patients. Variable brain, cardiac, and skeletal anomalies are present, including corpus callosum agenesis or dysgenesis, lissencephaly, atrial and ventricular septal defects, patent ductus arteriosus, hypoplastic right ventricle, and joint contractures (Shaheen et al., 2016).

Squalene synthase deficiency (SQSD) is a rare inborn error of cholesterol biosynthesis with multisystem clinical manifestations similar to Smith-Lemli-Optiz syndrome. Key clinical features include facial dysmorphism, a generalized seizure disorder presenting in the neonatal period, nonspecific structural brain malformations, cortical visual impairment, optic nerve hypoplasia, profound developmental delay / intellectual disability, dry skin with photosensitivity, and genital malformations in males.

CAFDADD is a multisystemic developmental disorder with variable cardiac and digital anomalies and facial dysmorphism. Some patients may have seizures and ocular/aural abnormalities (Tokita et al., 2018).

Combined oxidative phosphorylation deficiency-10 (COXPD10) is an autosomal recessive disorder resulting in variable defects of mitochondrial oxidative respiration. Affected individuals present in infancy with hypertrophic cardiomyopathy and lactic acidosis. The severity is variable, but can be fatal in the most severe cases (summary by Ghezzi et al., 2012). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060).

ASXL3-related disorder is characterized by developmental delay or intellectual disability, typically in the moderate to severe range, with speech and language delay and/or absent speech. Affected individuals may also display autistic features. There may be issues with feeding. While dysmorphic facial features have been described, they are typically nonspecific. Affected individuals may also have hypotonia that can transition to spasticity resulting in unusual posture with flexion contractions of the elbows, wrists, and fingers. Other findings may include poor postnatal growth, strabismus, seizures, sleep disturbance, and dental anomalies.

IMAGEI is an autosomal recessive disorder characterized by intrauterine growth retardation, metaphyseal dysplasia, adrenal hypoplasia congenita, genital anomalies, and immunodeficiency. Patients exhibit distinctive facial features and variable immune dysfunction with evidence of lymphocyte deficiency (Logan et al., 2018). An autosomal dominant form of the disorder, without immunodeficiency (IMAGE; 614732), is caused by mutation in the CDKN1C gene (600856) on chromosome 11p15.

Microcephaly, growth deficiency, seizures, and brain malformations (MIGSB) is a severe autosomal recessive disorder characterized by intrauterine growth retardation, postnatal growth deficiency with severe microcephaly, and poor or absent psychomotor development. Additional features include optic atrophy, early-onset seizures, dysmorphic facial features, and brain malformations, such as partial agenesis of the corpus callosum and simplified gyration (summary by Shaheen et al., 2015).

Galloway-Mowat syndrome is a phenotypically heterogeneous disorder characterized by neurodevelopmental defects combined with renal-glomerular disease manifest as nephrotic syndrome and proteinuria. Most patients with GAMOS6 also have growth deficiency with variable microcephaly, and the renal disease may be age-dependent. Additional variable endocrine abnormalities have also been reported (summary by Braun et al., 2018). For a general phenotypic description and a discussion of genetic heterogeneity of GAMOS, see GAMOS1 (251300).

Turnpenny-Fry syndrome (TPFS) is characterized by developmental delay, impaired intellectual development, impaired growth, and recognizable facial features that include frontal bossing, sparse hair, malar hypoplasia, small palpebral fissures and oral stoma, and dysplastic 'satyr' ears. Other common findings include feeding problems, constipation, and a range of brain, cardiac, vascular, and skeletal malformations (Turnpenny et al., 2018).

Combined oxidative phosphorylation deficiency-39 (COXPD39) is an autosomal recessive multisystem disorder resulting from a defect in mitochondrial energy metabolism. Affected individuals show global developmental delay, sometimes with regression after normal early development, axial hypotonia with limb spasticity or abnormal involuntary movements, and impaired intellectual development with poor speech. More variable features may include hypotonia, seizures, and features of Leigh syndrome (256000) on brain imaging. There are variable deficiencies of the mitochondrial respiratory chain enzyme complexes in patient tissues (summary by Glasgow et al., 2017). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060).

Khan-Khan-Katsanis syndrome (3KS) is an autosomal recessive neurodevelopmental disorder with variable involvement of the ocular, renal, skeletal, and sometimes cardiac systems. Affected individuals present at birth with multiple congenital anomalies, defects in urogenital and limb morphogenesis, poor overall growth with microcephaly, and global developmental delay (summary by Khan et al., 2019).

Holoprosencephaly-12 with or without pancreatic agenesis (HPE12) is a developmental disorder characterized by abnormal separation of the embryonic forebrain (HPE) resulting in dysmorphic facial features and often, but not always, impaired neurologic development. Most patients with this form of HPE also have congenital absence of the pancreas, resulting in early-onset type 1 diabetes mellitus and requiring pancreatic enzyme replacement. Other features may include hearing loss and absence of the gallbladder (summary by De Franco et al., 2019 and Kruszka et al., 2019). For a phenotypic description and a discussion of genetic heterogeneity of holoprosencephaly, see HPE1 (236100).

Hypopigmentation, organomegaly, and delayed myelination and development (HOD) is characterized by hypopigmented skin and hair with normally pigmented irides; organomegaly including enlargement of liver, kidney, and spleen; and delayed myelination on brain MRI accompanied by developmental delay in both gross and fine motor skills. Biopsy findings from skin and other organs are consistent with a lysosomal storage disorder (Nicoli et al., 2019).

Neurodevelopmental disorder with microcephaly, arthrogryposis, and structural brain anomalies (NEDMABA) is an autosomal recessive disorder characterized by severe global developmental delay, usually with hypotonia and absence of spontaneous movements other than head control, impaired intellectual development with absent speech, distal contractures, progressive microcephaly, dysmorphic features, and distal skeletal abnormalities, such as rocker-bottom feet and clenched hands with camptodactyly. Brain imaging tends to show a simplified gyral pattern of the cerebral cortex, delayed myelination, thin corpus callosum, and hypoplasia of the brainstem and cerebellum. The disorder may be complicated by feeding and/or breathing difficulties, often resulting in death in infancy (summary by Magini et al., 2019).

Osteogenesis imperfecta type XX (OI20) is a progressive deforming bone disorder characterized by osteopenia, skeletal deformity, and both healed and new fractures on radiography. Several patients have died due to respiratory failure (Moosa et al., 2019).

Halperin-Birk syndrome (HLBKS) is an autosomal recessive neurodevelopmental disorder characterized by structural brain defects, spastic quadriplegia with multiple contractures, profound developmental delay, seizures, dysmorphism, cataract, and optic nerve atrophy. Death occurs in early childhood (Halperin et al., 2019).

Heyn-Sproul-Jackson syndrome (HESJAS) is characterized by microcephalic dwarfism and global developmental delay (Heyn et al., 2019).

De Barsy syndrome, or autosomal recessive cutis laxa type III (ARCL3), is characterized by cutis laxa, a progeria-like appearance, and ophthalmologic abnormalities (summary by Kivuva et al., 2008). For a phenotypic description and a discussion of genetic heterogeneity of autosomal recessive cutis laxa, see 219100. Genetic Heterogeneity of de Barsy Syndrome Also see ARCL3B (614438), caused by mutation in the PYCR1 gene (179035) on chromosome 17q25.

Silver-Russell Syndrome (SRS) is typically characterized by asymmetric gestational growth restriction resulting in affected individuals being born small for gestational age, with relative macrocephaly at birth (head circumference =1.5 SD above birth weight and/or length), prominent forehead usually with frontal bossing, and frequently body asymmetry. This is followed by postnatal growth failure, and in some cases progressive limb length discrepancy and feeding difficulties. Additional clinical features include triangular facies, fifth-finger clinodactyly, and micrognathia with narrow chin. Except for the limb length asymmetry, the growth failure is proportionate and head growth normal. The average adult height in untreated individuals is ~3.1±1.4 SD below the mean. The Netchine-Harbison Clinical Scoring System (NH-CSS) is a sensitive diagnostic scoring system. Clinical diagnosis can be established in an individual who meets at least four of the NH-CSS clinical criteria – prominent forehead/frontal bossing and relative macrocephaly at birth plus two additional findings – and in whom other disorders have been ruled out.

Developmental and epileptic encephalopathy-85 with or without midline brain defects (DEE85) is an X-linked neurologic disorder characterized by onset of severe refractory seizures in the first year of life, global developmental delay with impaired intellectual development and poor or absent speech, and dysmorphic facial features. The seizures tend to show a cyclic pattern with clustering. Many patients have midline brain defects on brain imaging, including thin corpus callosum and/or variable forms of holoprosencephaly (HPE). The severity and clinical manifestations are variable. Almost all reported patients are females with de novo mutations predicted to result in a loss of function (LOF). However, some patients may show skewed X inactivation, and the pathogenic mechanism may be due to a dominant-negative effect. The SMC1A protein is part of the multiprotein cohesin complex involved in chromatid cohesion during DNA replication and transcriptional regulation; DEE85 can thus be classified as a 'cohesinopathy' (summary by Symonds et al., 2017 and Kruszka et al., 2019). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350.

Permanent neonatal diabetes mellitus (PNDM) is characterized by the onset of hyperglycemia within the first six months of life (mean age: 7 weeks; range: birth to 26 weeks). The diabetes mellitus is associated with partial or complete insulin deficiency. Clinical manifestations at the time of diagnosis include intrauterine growth retardation, hyperglycemia, glycosuria, osmotic polyuria, severe dehydration, and failure to thrive. Therapy with insulin corrects the hyperglycemia and results in dramatic catch-up growth. The course of PNDM varies by genotype.

Sandestig-Stefanova syndrome (SANDSTEF) is an autosomal recessive developmental syndrome characterized by pre- and postnatal microcephaly, trigonocephaly, congenital cataract, microphthalmia, facial gestalt, camptodactyly, loss of periventricular white matter, thin corpus callosum, delayed myelinization, and poor prognosis (Sandestig et al., 2019).

Combined oxidative phosphorylation deficiency-40 (COXPD40) is an autosomal recessive mitochondrial disorder with onset in utero or soon after birth. Affected individuals have severe hypertrophic cardiomyopathy, poor growth, and sensorineural hearing loss. Laboratory studies show evidence of mitochondrial dysfunction, such as lactic acidosis. Patient-derived tissues and cells show variably decreased activities of mitochondrial respiratory complexes I, III, IV, and V. The disorder is lethal, with no reported patients surviving past infancy (summary by Friederich et al., 2018). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060).

Combined oxidative phosphorylation deficiency-42 (COXPD42) is an autosomal recessive metabolic disorder characterized by onset of cardiomyopathy, respiratory insufficiency, lactic metabolic acidosis, and anemia in the first months of life. Patient tissue shows variable impairment of mitochondrial oxidative phosphorylation affecting mtDNA-encoded subunits I, III, and IV. All reported affected infants have died in the first year of life (summary by Friederich et al., 2018). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060).

Microcephaly, developmental delay, and brittle hair syndrome (MDBH) is a multisystem disorder with clinical variability. Affected individuals show cognitive and motor disabilities, as well as some degree of fine, brittle hair with microscopic shaft abnormalities. Other shared features include failure to thrive in early childhood and short stature, with some patients exhibiting feeding difficulties and hepatic steatosis (Kuo et al., 2019).

Silver-Russell Syndrome (SRS) is typically characterized by asymmetric gestational growth restriction resulting in affected individuals being born small for gestational age, with relative macrocephaly at birth (head circumference =1.5 SD above birth weight and/or length), prominent forehead usually with frontal bossing, and frequently body asymmetry. This is followed by postnatal growth failure, and in some cases progressive limb length discrepancy and feeding difficulties. Additional clinical features include triangular facies, fifth-finger clinodactyly, and micrognathia with narrow chin. Except for the limb length asymmetry, the growth failure is proportionate and head growth normal. The average adult height in untreated individuals is ~3.1±1.4 SD below the mean. The Netchine-Harbison Clinical Scoring System (NH-CSS) is a sensitive diagnostic scoring system. Clinical diagnosis can be established in an individual who meets at least four of the NH-CSS clinical criteria – prominent forehead/frontal bossing and relative macrocephaly at birth plus two additional findings – and in whom other disorders have been ruled out.

Silver-Russell Syndrome (SRS) is typically characterized by asymmetric gestational growth restriction resulting in affected individuals being born small for gestational age, with relative macrocephaly at birth (head circumference =1.5 SD above birth weight and/or length), prominent forehead usually with frontal bossing, and frequently body asymmetry. This is followed by postnatal growth failure, and in some cases progressive limb length discrepancy and feeding difficulties. Additional clinical features include triangular facies, fifth-finger clinodactyly, and micrognathia with narrow chin. Except for the limb length asymmetry, the growth failure is proportionate and head growth normal. The average adult height in untreated individuals is ~3.1±1.4 SD below the mean. The Netchine-Harbison Clinical Scoring System (NH-CSS) is a sensitive diagnostic scoring system. Clinical diagnosis can be established in an individual who meets at least four of the NH-CSS clinical criteria – prominent forehead/frontal bossing and relative macrocephaly at birth plus two additional findings – and in whom other disorders have been ruled out.

Rajab interstitial lung disease with brain calcifications-1 (RILCBC1) is an autosomal recessive multisystem disorder with a highly variable phenotype. Most patients present in infancy or early childhood with poor growth and interstitial lung disease, which may lead to death. Some may also have liver, skeletal, and renal abnormalities, and most have intracranial calcifications on brain imaging. Some may have early impaired motor development, but most have normal cognitive development (summary by Xu et al., 2018). Genetic Heterogeneity of Rajab Interstitial Lung Disease with Brain Calcifications Also see Rajab interstitial disease with brain calcifications-2 (RILDBC2; 619013), caused by mutation in the FARSA gene (602918).

Arthrogryposis multiplex congenita-5 (AMC5) is an autosomal recessive disorder characterized by severe joint contractures apparent at birth. Affected individuals usually have hypertonia and abnormal movements suggestive of dystonia, as well as feeding and/or breathing difficulties. More variable features may include poor overall growth, strabismus, dysmorphic facies, and global developmental delay with impaired speech (summary by Kariminejad et al., 2017).

DEEAH syndrome is an autosomal recessive multisystemic disorder with onset in early infancy. Affected individuals usually present in the perinatal period with respiratory insufficiency, apneic episodes, and generalized hypotonia. The patients have failure to thrive and severely impaired global development with poor acquisition of motor, cognitive, and language skills. Other common features include endocrine, pancreatic exocrine, and autonomic dysfunction, as well as hematologic disturbances, mainly low hemoglobin. Patients also have dysmorphic and myopathic facial features. Additional more variable features include seizures, undescended testes, and distal skeletal anomalies. Death in early childhood may occur (summary by Schneeberger et al., 2020).

Neurodevelopmental disorder with dysmorphic facies, impaired speech, and hypotonia (NEDDISH) is an autosomal recessive disorder characterized by global developmental delay and mildly to severely impaired intellectual development with poor speech and language acquisition. Some patients may have early normal development with onset of the disorder in the first years of life. More variable neurologic abnormalities include hypotonia, seizures, apnea, mild signs of autonomic or peripheral neuropathy, and autism. Aside from dysmorphic facial features and occasional findings such as scoliosis or undescended testes, other organ systems are not involved (summary by Schneeberger et al., 2020).

Vissers-Bodmer syndrome (VIBOS) is characterized by global developmental delay with variably impaired intellectual development, speech delay, motor delay, and behavioral abnormalities apparent from infancy. The phenotype is highly variable: some individuals have only mild learning difficulties, whereas others have severe cognitive impairment with IQ in the 50s. Many patients have behavioral abnormalities, including autism spectrum disorder, ADD, ADHD, obsessive-compulsive disorder, and impulsivity. Other common features include growth impairment abnormalities, hypotonia, and distal skeletal defects, such as foot and hand deformities. Less common features include seizures, brain abnormalities on MRI, feeding problems, and joint hypermobility. Most individuals have dysmorphic facial features, but there is no recognizable gestalt (summary by Vissers et al., 2020).

Mitochondrial complex IV deficiency nuclear type 4 (MC4DN4) is an autosomal recessive multisystem metabolic disorder characterized by the onset of symptoms in infancy. Affected individuals show hypotonia, failure to thrive, and neurologic distress. Additional features include hepatomegaly, hepatic steatosis, increased serum lactate, and metabolic acidosis. Some patients may develop hypertrophic cardiomyopathy. Patient tissues show decreased levels and activity of mitochondrial respiratory complex IV. Death usually occurs in infancy (summary by Valnot et al., 2000 and Stiburek et al., 2009). For a discussion of genetic heterogeneity of mitochondrial complex IV (cytochrome c oxidase) deficiency, see 220110.

Mitochondrial complex IV deficiency nuclear type 7 (MC4DN7) is an autosomal recessive metabolic encephalomyopathic disorder with highly variable manifestations. Only a few patients have been reported. Some patients have normal early development then show rapid neurodegeneration with progressive muscle weakness, gait disturbances, and cognitive decline in mid to late childhood. Other features may include seizures and visual impairment. Brain imaging shows progressive leukodystrophy with cystic lesions. In contrast, at least 1 patient has been reported who presented in the neonatal period with metabolic acidosis, hydrocephalus, hypotonia, and cortical blindness. This patient developed hypertrophic cardiomyopathy resulting in early death. All patients had increased serum lactate and decreased levels and activity of mitochondrial respiratory complex IV (summary by Massa et al., 2008 and Abdulhag et al., 2015). For a discussion of genetic heterogeneity of mitochondrial complex IV (cytochrome c oxidase) deficiency, see 220110.

Mitochondrial complex IV deficiency nuclear type 12 (MC4DN12) is an autosomal recessive metabolic disorder characterized by the onset of neurologic dysfunction in early infancy. Affected individuals demonstrate hypotonia with poor head control, profoundly delayed global development with inability to fix and follow, poor overall growth, abnormal spasms or myoclonus, and seizures. Most patients die in the first years of life; those that survive have spastic quadriplegia, feeding difficulties necessitating tube feeding, and profoundly impaired intellectual development with poor or absent communication. More variable features include cortical blindness, nystagmus, scoliosis, and hearing impairment. Brain imaging shows abnormalities consistent with Leigh syndrome (see 256000), as well as cystic cavitation. Laboratory studies show lactic acidosis, increased serum creatine kinase, and decreased levels and activity of mitochondrial respiratory complex IV (summary by Lim et al., 2014). For a discussion of genetic heterogeneity of mitochondrial complex IV (cytochrome c oxidase) deficiency, see 220110.

Combined oxidative phosphorylation deficiency-51 (COXPD51) is an autosomal recessive disorder characterized by a Leigh syndrome phenotype (see 256000). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060).

Cleft palate, proliferative retinopathy, and developmental delay (CPPRDD) is characterized by motor and speech delay, with intellectual disability ranging from mild to severe. Brain imaging shows ventriculomegaly as well as other malformations (Harel et al., 2019).

Kaya-Barakat-Masson syndrome (KABAMAS) is a severe autosomal recessive neurodevelopmental disorder characterized by profoundly impaired global development with variable motor abnormalities, such as axial hypotonia, peripheral spasticity, dystonia, and poor coordination, resulting in the inability to sit or walk. Affected individuals have impaired intellectual development with absent speech, poor eye contact, and feeding difficulties, resulting in poor overall growth, sometimes with microcephaly. Dysmorphic features are generally not present. Additional more variable features include early-onset seizures, ocular anomalies, foot deformities, and nonspecific brain imaging findings, such as thin corpus callosum and cerebral, cerebellar, or pontine atrophy. Some patients may die in infancy or early childhood (summary by AlMuhaizea et al., 2020 and Diaz et al., 2020).

X-linked multiple congenital anomalies-neurodevelopmental syndrome (MCAND) is an X-linked recessive congenital multisystemic disorder characterized by poor growth, global developmental delay with impaired intellectual development, and variable abnormalities of the cardiac, skeletal, and genitourinary systems. Most affected individuals also have hypotonia and dysmorphic craniofacial features. Brain imaging typically shows enlarged ventricles and thin corpus callosum; some have microcephaly, whereas others have hydrocephalus. The severity of the disorder is highly variable, ranging from death in early infancy to survival into the second or third decade. Pathogenetically, the disorder results from disrupted gene expression and signaling during embryogenesis, thus affecting multiple systems (summary by Tripolszki et al., 2021 and Beck et al., 2021). Beck et al. (2021) referred to the disorder as LINKED syndrome (LINKage-specific deubiquitylation deficiency-induced Embryonic Defects).

Short stature, facial dysmorphism, and skeletal anomalies with or without cardiac anomalies-2 (SSFSC2) is characterized by thin and short long bones, distinctive facial dysmorphism, and dental and skeletal abnormalities, in the absence of developmental delay or intellectual disability. Cardiac anomalies have been reported in some patients (Lin et al., 2021). For a discussion of genetic heterogeneity of SSFSC, see SSFSC1 (617877).

Den Hoed-de Boer-Voisin syndrome (DHDBV) is characterized by global developmental delay with moderately to severely impaired intellectual development, poor or absent speech, and delayed motor skills. Although the severity of the disorder varies, many patients are nonverbal and have hypotonia with inability to sit or walk. Early-onset epilepsy is common and may be refractory to treatment, leading to epileptic encephalopathy and further interruption of developmental progress. Most patients have feeding difficulties with poor overall growth and dysmorphic facial features, as well as significant dental anomalies resembling amelogenesis imperfecta. The phenotype is reminiscent of Kohlschutter-Tonz syndrome (KTZS; 226750). More variable features of DHDBV include visual defects, behavioral abnormalities, and nonspecific involvement of other organ systems (summary by den Hoed et al., 2021).

Growth restriction, hypoplastic kidneys, alopecia, and distinctive facies (GKAF) is characterized by microcephaly, congenital alopecia, distinctive craniofacial features, severe congenital sensorineural hearing loss, global developmental delay, hydrocephalus, hypoplastic kidneys with renal insufficiency, genital hypoplasia, and early mortality (Ito et al., 2018).

Marbach-Rustad progeroid syndrome (MARUPS) is characterized by progeroid appearance with little subcutaneous fat and triangular facies, growth retardation with short stature, hypoplastic mandible crowded with unerupted supernumerary teeth, and cerebellar intention tremor. Psychomotor development is normal. Although features are reminiscent of Hutchinson-Gilford progeria syndrome (HGPS; 176670), MARUPS is less severe, with a relatively good prognosis. Two patients have been reported (Marbach et al., 2019).

Mitochondrial complex IV deficiency nuclear type 22 (MC4DN22) is an autosomal recessive metabolic disorder characterized by neonatal hypertrophic cardiomyopathy, encephalopathy, and severe lactic acidosis with fatal outcome (Wintjes et al., 2021). For a discussion of genetic heterogeneity of mitochondrial complex IV (cytochrome c oxidase) deficiency, see 220110.

Faundes-Banka syndrome (FABAS) is an autosomal dominant disorder characterized by variable combinations of developmental delay and microcephaly, as well as micrognathia and other dysmorphic features (Faundes et al., 2021).

Susceptibility to acute infection (viral)-induced encephalitis-11 (IIAE11) is an autosomal recessive disorder characterized by increased susceptibility to viral encephalitis with neurotropic viruses, such as herpes simplex virus-1 (HSV-1), influenza B virus (IBV), or norovirus (NV), beginning in the first decade of life. The brainstem is specifically affected, suggesting a defect in tissue-specific and cell-intrinsic immunity. The disease is often fatal (summary by Zhang et al., 2018). For a discussion of genetic heterogeneity of susceptibility to acute infection (viral)-induced encephalitis or encephalopathy, see 610551.

Luo-Schoch-Yamamoto syndrome (LUSYAM) is a neurodevelopmental disorder characterized by global developmental delay and impaired intellectual development apparent from infancy. Affected individuals have delayed walking, early-onset seizures, hypotonia, dysmorphic facial features, and white matter abnormalities on brain imaging (Luo et al., 2021).

Developmental delay, impaired speech, and behavioral abnormalities (DDISBA) is characterized by global developmental delay apparent from early childhood. Intellectual disability can range from mild to severe. Additional variable features may include dysmorphic facial features, seizures, hypotonia, motor abnormalities such as Tourette syndrome or dystonia, and hearing loss (summary by Cousin et al., 2021).

Aicardi-Goutieres syndrome-9 (AGS9) is a type I interferonopathy characterized by severe developmental delay and progressive neurologic deterioration. Patients present in infancy with irritability and spasticity. Brain imaging shows diffusely abnormal white matter, cerebral atrophy, and intracranial calcification. Premature death has been associated with renal and/or hepatic failure (Uggenti et al., 2020). For a general phenotypic description and discussion of genetic heterogeneity of Aicardi-Goutieres syndrome, see AGS1 (225750).

DEGCAGS syndrome is an autosomal recessive syndromic neurodevelopmental disorder characterized by global developmental delay, coarse and dysmorphic facial features, and poor growth and feeding apparent from infancy. Affected individuals have variable systemic manifestations often with significant structural defects of the cardiovascular, genitourinary, gastrointestinal, and/or skeletal systems. Additional features may include sensorineural hearing loss, hypotonia, anemia or pancytopenia, and immunodeficiency with recurrent infections. Death in childhood may occur (summary by Bertoli-Avella et al., 2021).

Neurodevelopmental-craniofacial syndrome with variable renal and cardiac abnormalities (NECRC) is an autosomal dominant disorder characterized by dysmorphic craniofacial features associated with mild developmental delay, mildly impaired intellectual development or learning difficulties, speech delay, and behavioral abnormalities. About half of patients have congenital anomalies of the kidney and urinary tract (CAKUT) and/or congenital cardiac defects, including septal defects (Connaughton et al., 2020).

Rauch-Steindl syndrome (RAUST) is characterized by poor pre- and postnatal growth, sometimes with short stature and small head circumference, characteristic dysmorphic facial features, and variable developmental delay with delayed motor and speech acquisition and impaired intellectual function that can be mild. Other features may include hypotonia and behavioral abnormalities. The phenotype represents a mild form of Wolf-Hirschhorn syndrome (WHS; 194190), which is a contiguous gene deletion syndrome caused by heterozygous deletion of several genes on chromosome 4p16. The clinical features of RAUST are similar to but milder than those of WHS, with less severe dysmorphic facial features, less severe developmental disabilities in general, and absence of a seizure disorder. The phenotype and expressivity of RAUST is highly variable (summary by Rauch et al., 2001; Zanoni et al., 2021).

Autosomal dominant congenital disorder of glycosylation type Iw (CDG1WAD) is characterized by variable skeletal anomalies, short stature, macrocephaly, and dysmorphic features; about half of patients have impaired intellectual development. Additional features include increased muscle tone and muscle cramps (Wilson et al., 2021).

Immunodeficiency-87 and autoimmunity (IMD87) is an autosomal recessive immunologic disorder with wide phenotypic variation and severity. Affected individuals usually present in infancy or early childhood with increased susceptibility to infections, often Epstein-Barr virus (EBV), as well as with lymphadenopathy or autoimmune manifestations, predominantly hemolytic anemia. Laboratory studies may show low or normal lymphocyte numbers, often with skewed T-cell subset ratios. The disorder results primarily from defects in T-cell function, which causes both immunodeficiency and overall immune dysregulation (summary by Serwas et al., 2019 and Fournier et al., 2021).

Combined oxidative phosphorylation deficiency-23 (COXPD23) is an autosomal recessive disorder characterized by early childhood onset of hypertrophic cardiomyopathy and/or neurologic symptoms, including hypotonia and delayed psychomotor development. Laboratory investigations are consistent with a defect in mitochondrial function resulting in lactic acidosis, impaired activities of respiratory complexes I and IV, and defective translation of mitochondrial proteins. Brain imaging shows abnormal lesions in the basal ganglia, thalamus, and brainstem. The severity of the disorder is variable, ranging from death in early infancy to survival into the second decade (summary by Kopajtich et al., 2014). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060).

Immunodeficiency-55 is an autosomal recessive primary immunodeficiency characterized by intrauterine growth retardation, natural killer (NK) cell deficiency, and chronic neutropenia. Most patients also have postnatal growth retardation. Other clinical manifestations include mild facial dysmorphism, dry or eczematous skin, and recurrent infections with both viruses and bacteria. The disorder appears to result from a defect in DNA replication causing blockade of immune cell differentiation in the bone marrow, particularly affecting NK cells (summary by Cottineau et al., 2017).

A rare lethal primary bone dysplasia with characteristics of fetal akinesia, multiple contractures, shortening of all long bones, short, broad ribs, narrow chest and thorax, pulmonary hypoplasia and a protruding abdomen. Short bowed femurs may also be associated.

DYRK1A syndrome is characterized by intellectual disability including impaired speech development, autism spectrum disorder including anxious and/or stereotypic behavior problems, and microcephaly. Affected individuals often have a clinically recognizable phenotype including a typical facial gestalt, feeding problems, seizures, hypertonia, gait disturbances, and foot anomalies. The majority of affected individuals function in the moderate-to-severe range of intellectual disability; however, individuals with mild intellectual disability have also been reported. Other medical concerns relate to febrile seizures in infancy; the development of epilepsy with seizures of the atonic, absence, and generalized myoclonic types; short stature; and gastrointestinal problems. Ophthalmologic, urogenital, cardiac, and/or dental anomalies have been reported.

Primary coenzyme Q10 (CoQ10) deficiency is usually associated with multisystem involvement, including neurologic manifestations such as fatal neonatal encephalopathy with hypotonia; a late-onset slowly progressive multiple-system atrophy-like phenotype (neurodegeneration with autonomic failure and various combinations of parkinsonism and cerebellar ataxia, and pyramidal dysfunction); and dystonia, spasticity, seizures, and intellectual disability. Steroid-resistant nephrotic syndrome (SRNS), the hallmark renal manifestation, is often the initial manifestation either as isolated renal involvement that progresses to end-stage renal disease (ESRD), or associated with encephalopathy (seizures, stroke-like episodes, severe neurologic impairment) resulting in early death. Hypertrophic cardiomyopathy (HCM), retinopathy or optic atrophy, and sensorineural hearing loss can also be seen.

Preeclampsia, which along with chronic hypertension and gestational hypertension comprise the hypertensive disorders of pregnancy, is characterized by new hypertension (blood pressure 140/90 or greater) presenting after 20 weeks' gestation with clinically relevant proteinuria. Preeclampsia is 1 of the top 4 causes of maternal mortality and morbidity worldwide (summary by Payne et al., 2011). Preeclampsia is otherwise known as gestational proteinuric hypertension (Davey and MacGillivray, 1988). A high proportion of patients with preeclampsia have glomerular endotheliosis, the unique histopathologic feature of the condition (Fisher et al., 1981). A distinct form of severe preeclampsia is characterized by hemolysis, elevated liver enzymes, and low platelets (HELLP syndrome) (Brown et al., 2000). Genetic Heterogeneity of Preeclampsia/Eclampsia Susceptibility loci for preeclampsia/eclampsia include PEE1 on chromosome 2p13, PEE2 (609402) on chromosome 2p25, and PEE3 (609403) on chromosome 9p13. PEE4 (609404) is caused by mutation in the STOX1 gene (609397) on chromosome 10q22. PEE5 (614595) is caused by mutation in the CORIN gene (605236) on chromosome 4p12. An association with PEE has been found with the EPHX1 gene (132810) on chromosome 1q.

A restrictive dermopathy that has material basis in homozygous or compound heterozygous mutation in the ZMPSTE24 gene on chromosome 1p34.

Stuve-Wiedemann syndrome is an autosomal recessive disorder characterized by bowing of the long bones and other skeletal anomalies, episodic hyperthermia, respiratory distress, and feeding difficulties usually resulting in early death (Dagoneau et al., 2004). See also 'classic' Schwartz-Jampel syndrome type 1 (SJS1; 255800), a phenotypically similar but genetically distinct disorder caused by mutation in the HSPG2 gene (142461) on chromosome 1p36. Genetic Heterogeneity of Stuve-Wiedemann Syndrome Stuve-Wiedemann syndrome-2 (STWS2; 619751) is caused by mutation in the IL6ST gene (600694) on chromosome 5q11.

CLPB (caseinolytic peptidase B) deficiency is characterized by neurologic involvement and neutropenia, which can range from severe to mild. In severe CLPB deficiency, death usually occurs at a few months of age due to significant neonatal neurologic involvement (hyperekplexia or absence of voluntary movements, hypotonia or hypertonia, swallowing problems, respiratory insufficiency, and epilepsy) and severe neutropenia associated with life-threatening infections. Individuals with moderate CLPB deficiency present with neurologic abnormalities in infancy including hypotonia and feeding problems, and develop spasticity, a progressive movement disorder (ataxia, dystonia, and/or dyskinesia), epilepsy, and intellectual disability. Neutropenia is variable, but not life threatening. In those with mild CLPB deficiency there is no neurologic involvement, intellect is normal, neutropenia is mild and intermittent, and life expectancy is normal.

Combined oxidative phosphorylation deficiency-54 (COXPD54) is an autosomal recessive disorder with pleiotropic multisystem presentations resulting from a disruption in mitochondrial transcription and translation. The phenotype is highly variable. Many patients have early-onset sensorineural hearing loss, sometimes in isolation, and sometimes associated with global developmental delay or primary ovarian failure. Other features may include peripheral hypertonia, seizures, muscle weakness, behavioral abnormalities, and leukoencephalopathy on brain imaging. Serum lactate may or may not be elevated (summary by Hochberg et al., 2021). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060).

Stuve-Wiedemann syndrome-2 (STWS2) is an autosomal recessive lethal skeletal dysplasia characterized by short stature, small chest, bowing of the long bones, and neonatal cardiopulmonary and autonomous dysfunction. Additional variable features include congenital thrombocytopenia, eczematoid dermatitis, renal anomalies, and defective acute-phase response (Chen et al., 2020). For a general phenotypic description and discussion of genetic heterogeneity of Stuve-Wiedemann syndrome, see STWS1 (601559).

Cerebellar dysfunction, impaired intellectual development, and hypogonadotropic hypogonadism (CDIDHH) is characterized by delayed motor development, ataxia, severe progressive scoliosis, moderate to severe intellectual disability, and delayed sexual development. Cerebellar hypoplasia has been observed in some patients (Whittaker et al., 2021).

Restrictive dermopathy is a rare genodermatosis characterized mainly by intrauterine growth retardation, tight and rigid skin with erosions, prominent superficial vasculature and epidermal hyperkeratosis, facial dysmorphism (small mouth, small pinched nose and micrognathia), sparse/absent eyelashes and eyebrows, mineralization defects of the skull, thin dysplastic clavicles, pulmonary hypoplasia, multiple joint contractures, and an early neonatal lethal course. Liveborn children usually die within the first week of life (summary by Navarro et al., 2004). For a discussion of genetic heterogeneity of restrictive dermopathy, see RSDM1 (275210).

Osteogenesis imperfecta comprises a group of connective tissue disorders characterized clinically by bone fragility, low bone mass, and increased susceptibility to fractures. Osteogenesis imperfecta type XXII (OI22) is a severe recessive form of the disease (Dubail et al., 2020).

Neurodevelopmental disorder with neuromuscular and skeletal abnormalities (NEDNMS) is an autosomal recessive disorder characterized by global developmental delay apparent from infancy or early childhood. The severity of the disorder is highly variable. Affected individuals show impaired intellectual development and motor delay associated with either severe hypotonia or hypertonia and spasticity. Most affected individuals have skeletal defects and dysmorphic facial features. Some may have ocular or auditory problems, peripheral neuropathy, behavioral abnormalities, and nonspecific findings on brain imaging (Kurolap et al., 2022).

Pontocerebellar hypoplasia type 17 (PCH17) is a severe autosomal recessive developmental disorder characterized by neonatal hypotonia, severe feeding difficulties, and respiratory insufficiency. Brain imaging shows cerebellar and brainstem hypoplasia. Most affected individuals die in infancy. Those who survive show variable developmental delay. Other features of the disorder include distal hypertonia, poor overall growth, visual defects, autonomic problems, dysmorphic features, and seizures (Coolen et al., 2022). For a phenotypic description and a discussion of genetic heterogeneity of PCH, see PCH1A (607596).

Neurodevelopmental disorder with dystonia and seizures (NEDDS) is a severe autosomal recessive disorder characterized by hypotonia and dystonic posturing apparent from early infancy. Affected individuals show global developmental delay with inability to walk or speak and have profoundly impaired intellectual development, often with behavioral abnormalities. Additional features may include other extrapyramidal movements, seizures or seizure-like activity, and cerebellar hypoplasia on brain imaging (Sleiman et al., 2022).

Autosomal dominant intellectual developmental disorder-68 (MRD68) is characterized by developmental delay/intellectual disability, microcephaly, poor growth, feeding difficulties, and dysmorphic features. Some patients may have autism spectrum disorder or attention deficit-hyperactivity disorder (ADHD) (Cif et al., 2020).

Chilton-Okur-Chung neurodevelopmental syndrome (CHOCNS) is characterized mainly by global developmental delay with variably impaired intellectual development and occasional speech delay. Most patients have behavioral abnormalities, including autism spectrum disorder, ADHD, and aggression. About half of patients have dysmorphic facial features, and about half have nonspecific brain abnormalities, including thin corpus callosum. Rare involvement of other organ systems may be present. At least 1 child with normal development at age 2.5 years has been reported (Chilton et al., 2020).

Gastrointestinal defects and immunodeficiency syndrome-1 (GIDID1) is characterized by multiple intestinal atresia, in which atresia occurs at various levels throughout the small and large intestines. Surgical outcomes are poor, and the condition is usually fatal within the first month of life. Some patients exhibit inflammatory bowel disease (IBD), with or without intestinal atresia, and in some cases, the intestinal features are associated with either mild or severe combined immunodeficiency (Samuels et al., 2013; Avitzur et al., 2014; Lemoine et al., 2014). Genetic Heterogeneity of GIDID See also GIDID2 (619708), caused by mutation in the PI4KA gene (600286) on chromosome 22q11.

Severe congenital liver disease (SCOLIV) is an autosomal recessive disorder characterized by the onset of progressive hepatic dysfunction usually in the first years of life. Affected individuals show feeding difficulties with failure to thrive and features such as jaundice, hepatomegaly, and abdominal distension. Laboratory workup is consistent with hepatic insufficiency and may also show coagulation defects, anemia, or metabolic disturbances. Cirrhosis and hypernodularity are commonly observed on liver biopsy. Many patients die of liver failure in early childhood (Moreno Traspas et al., 2022).

Primordial dwarfism-immunodeficiency-lipodystrophy syndrome (PDIL) is characterized by pre- and postnatal growth restriction, with extreme microcephaly, short stature, and absence of subcutaneous fat. There is also significant hematologic/immune dysfunction, with hypo- or agammaglobulinemia, as well as lymphopenia, anemia, and thrombocytopenia, and most affected individuals succumb to infection in early childhood (Parry et al., 2020).

Digenic dyskeratosis congenita (DKCD) is characterized clinically by a combination of mucocutaneous features including abnormal skin pigmentation, nail dystrophy, thin hair, and oral leukoplakia. Some patients may have evidence of bone marrow failure, manifest as immune defects such as recurrent infections or hypogammaglobulinemia. Telomeres are shortened in patient cells. Individuals with DKCD may show severe adverse reactions to treatment with 5-FU (Tummala et al., 2022). For a discussion of genetic heterogeneity of dyskeratosis congenita, see DKCA1 (127550).

Bent bone dysplasia syndrome-2 (BBDS2) is characterized by defects in both the axial and appendicular skeleton, with radiographic findings of undermineralized bone and a distinct angulation of the mid femoral shaft. Extraskeletal features include facial dysmorphisms, abnormally formed ears with tags, widely spaced nipples, and atrial septal defects. Abnormalities of muscle function are suggested by the presence of elbow fusions, ulnar flexion contractions at the wrist, and bilateral talipes equinovarus, as well as failure to mount a respiratory effort at birth (Barad et al., 2020). For a general phenotypic description and discussion of genetic heterogeneity of bent bone dysplasia syndrome, see BBDS1 (614592).

Neurodevelopmental disorder with growth retardation, dysmorphic facies, and corpus callosum abnormalities (NEDGFC) is an autosomal recessive disorder characterized by these cardinal features apparent from infancy. There is phenotypic variability both in disease manifestations and severity. More severely affected individuals are unable to walk independently, are nonverbal, and may have other anomalies, including congenital heart defects, feeding difficulties, or skeletal defects, whereas others show mildly delayed motor and speech acquisition with mild or borderline intellectual disability (summary by von Elsner et al., 2022).

Autosomal recessive dyskeratosis congenita-8 (DKCB8) is characterized by progressive bone marrow failure affecting all lineages apparent from infancy or early childhood. More variable features may include poor growth, mild developmental delay, immunodeficiency, and gastrointestinal manifestations, such as esophageal stricture or inflammatory bowel disease. Some patients may have mucocutaneous features, including oral leukoplakia, nail dystrophy, or pigmentary skin abnormalities, although these features may be absent. Unlike patients with other forms of DKC, those with DKCB8 do not have shortened telomeres, although there is evidence of telomere instability. Hematopoietic stem cell transplant may be curative (Kermasson et al., 2022). For a discussion of genetic heterogeneity of dyskeratosis congenita, see DKCA1 (127550).

Mitochondrial complex I deficiency nuclear type 39 (MC1DN39) is an autosomal recessive nuclear disorder of mitochondrial respiratory chain complex I characterized by intrauterine growth retardation and anemia and postpartum hypertrophic cardiomyopathy, lactic acidosis, encephalopathy, and a severe complex I defect with a fatal outcome (Correia et al., 2021)

Developmental and epileptic encephalopathy-109 (DEE109) is characterized by the onset of various types of seizures in the first months or years of life. Affected individuals show developmental delay before and concurrent with the onset of seizures. Features include impaired intellectual development with poor speech, ataxic gait, coordination problems, and behavioral abnormalities (Manivannan et al., 2022). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350.

Autosomal recessive primary microcephaly-30 (MCPH30) is characterized by small head circumference, poor overall growth, and global developmental delay with variably impaired intellectual development. Affected individuals have been reported to have variable additional congenital anomalies, including atrial septal defect, dysmorphic facial features, tracheal stenosis, and anomalies of the skin and teeth (Carvalhal et al., 2022). For a general phenotypic description and a discussion of genetic heterogeneity of primary microcephaly, see MCPH1 (251200).

Branchial arch abnormalities, choanal atresia, athelia, hearing loss, and hypothyroidism syndrome (BCAHH) is an autosomal dominant disorder characterized by choanal atresia, athelia or hypoplastic nipples, branchial sinus abnormalities, neck pits, lacrimal duct anomalies, hearing loss, external ear malformations, and thyroid abnormalities. Additional features may include developmental delay, impaired intellectual development, and growth failure/retardation (summary by Cuvertino et al., 2020 and Baldridge et al., 2020).

PPP2R5D-related neurodevelopmental disorder is characterized by mild to severe neurodevelopmental delay. Pronounced hypotonia with delay in gross motor skills is common. Onset of independent walking varies widely and ataxia is reported. All reported individuals have speech impairment, with a wide range of abilities. Autism spectrum disorder is reported in six individuals. Macrocephaly is common. Seizures and ophthalmologic abnormalities are reported in fewer than half of individuals. Additional anomalies include skeletal, endocrine, and cardiac malformations, each reported in a few individuals. To date, 23 individuals with PPP2R5D-related neurodevelopmental disorder have been reported.

Neurodevelopmental disorder with absent speech and movement and behavioral abnormalities (NEDSMB) is an autosomal recessive disorder characterized by global developmental delay and severely impaired intellectual development with aggressive behavior. Mild dysmorphic features and hypodontia are also present (Faqeih et al., 2023).

Mitochondrial complex IV deficiency nuclear type 23 (MC4DN23) is an autosomal recessive disorder characterized by infantile-onset encephalopathy (Rius et al., 2022). For a discussion of genetic heterogeneity of mitochondrial complex IV (cytochrome c oxidase) deficiency, see 220110.

Multiple types of congenital heart defects-9 (CHTD9) is characterized by common arterial trunk (truncus arteriosus communis) in most patients, associated with other cardiac defects, including tetralogy of Fallot, interrupted aortic arch, right aortic arch, ventricular hypoplasia, and hypoplastic left heart, as well as other vascular and valvular anomalies (Ta-Shma et al., 2013; Guimier et al., 2023). For a general phenotypic description and discussion of genetic heterogeneity of multiple types of congenital heart defects, see CHTD1 (see 306955).

Congenital myopathy-21 with early respiratory failure (CMYP21) is an autosomal recessive muscle disorder associated with diaphragmatic weakness and spinal rigidity. The age at symptom onset is highly variable, ranging from infancy to adulthood; the severity of the respiratory impairment, which can lead to death in the most severe cases, is also variable. Additional features, including developmental delay and hypertrophic cardiomyopathy, have been observed in one patient each (Weihl et al., 2023; Al-Kasbi et al., 2022). For a discussion of genetic heterogeneity of congenital myopathy, see CMYP1A (117000).

Neurodegeneration with developmental delay, early respiratory failure, myoclonic seizures, and brain abnormalities (NDDRSB) is a severe autosomal recessive disorder characterized by onset of these features in infancy. Affected individuals present with respiratory failure requiring intubation soon after birth; some die due to cardiorespiratory insufficiency. Those that survive show severe global developmental delay, refractory myoclonic seizures, hyperkinetic movements with exaggerated startle response, and microcephaly with dysmorphic features. Additional findings may include sensorineural hearing loss and ocular defects. Brain imaging shows variable abnormalities consistent with progressive neurodegeneration (Cali et al., 2022).

Hatipoglu immunodeficiency syndrome (HATIS) is an autosomal recessive immunologic disorder characterized by childhood onset of failure to thrive, skin manifestations, pancytopenia, and susceptibility to recurrent infections (Harapas et al., 2022).

Cerebroretinal microangiopathy with calcifications and cysts-3 (CRMCC3) is an autosomal recessive disorder characterized by intrauterine growth retardation, retinal exudates, intracranial calcifications, and leukoencephalopathy. Additional features may include global developmental delay and gastrointestinal ectasias. Telomeres may be elongated, but truncated shortened telomeres are present in some tissues (Takai et al., 2016). For a discussion of genetic heterogeneity of CRMCC, see CRMCC1 (612199).

Autosomal recessive spastic paraplegia-89 (SPG89) is characterized by symptom onset in the first years of life. Affected individuals show delayed motor development with abnormal spastic gait and hyperreflexia of the lower limbs. Some patients may have mildly impaired intellectual development or learning difficulties (Deng et al., 2023). For a discussion of genetic heterogeneity of autosomal recessive SPG, see SPG5A (270800).