MedGen

Mucopolysaccharidosis type II (MPS II; also known as Hunter syndrome) is an X-linked multisystem disorder characterized by glycosaminoglycan (GAG) accumulation. The vast majority of affected individuals are male; on rare occasion heterozygous females manifest findings. Age of onset, disease severity, and rate of progression vary significantly among affected males. In those with the neuronopathic phenotype, central nervous system (CNS) involvement (manifesting primarily as progressive cognitive deterioration), progressive airway disease, and cardiac disease usually results in death in the first or second decade of life. In those with the non-neuronopathic phenotype, the CNS is minimally or not affected. However, the effect of GAG accumulation on other organ systems can be severe. Survival into the early adult years with normal intelligence is common in the non-neuronopathic phenotype. Additional findings in neuronopathic and non-neuronopathic MPS II include: short stature, macrocephaly with or without communicating hydrocephalus, macroglossia, hoarse voice, conductive and sensorineural hearing loss, dysostosis multiplex, spinal stenosis, carpal tunnel syndrome, and hepatosplenomegaly. [from GeneReviews]

While the majority of individuals with HRAS-related Costello syndrome (Costello syndrome) share characteristic findings affecting multiple organ systems, the phenotypic spectrum is wide, ranging from a mild or attenuated phenotype to a severe phenotype with early-lethal complications. Costello syndrome is typically characterized by failure to thrive in infancy as a result of severe postnatal feeding difficulties; short stature; developmental delay or intellectual disability; coarse facial features (full lips, large mouth, full nasal tip); curly or sparse, fine hair; loose, soft skin with deep palmar and plantar creases; papillomata of the face and perianal region; diffuse hypotonia and joint laxity with ulnar deviation of the wrists and fingers; tight Achilles tendons; and cardiac involvement including cardiac hypertrophy (usually hypertrophic cardiomyopathy), congenital heart defects (usually valvular pulmonic stenosis), and arrhythmia (usually supraventricular tachycardia, especially abnormal atrial rhythm / multifocal atrial tachycardia or ectopic atrial tachycardia). Relative or absolute macrocephaly is typical, and postnatal cerebellar overgrowth can result in the development of a Chiari I malformation with associated anomalies including hydrocephalus or syringomyelia. Individuals with Costello syndrome have an approximately 15% lifetime risk for malignant tumors including rhabdomyosarcoma and neuroblastoma in young children and transitional cell carcinoma of the bladder in adolescents and young adults. [from GeneReviews]

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

Aspartylglucosaminuria is a lysosomal storage disorder characterized by developmental delay, intellectual disability, behavioral manifestations (hyperactivity in young children, anxiety and restlessness in adolescence, and apathy in adulthood), recurrent infections, musculoskeletal features, and characteristic craniofacial features (prominent supraorbital ridges, hypertelorism, periorbital fullness, short nose with broad nasal bridge, thick vermilion of the upper and lower lips, and macroglossia) that become more prominent with age. Additional neurologic manifestations can include seizures, poor balance and coordination, and progressive cerebral atrophy in adulthood. Macrocephaly is common. Musculoskeletal features include lordosis, scoliosis, and arthritis in adolescents and young adults; vertebral dysplasia and/or rib cage abnormalities; and progressive muscle wasting, joint contractures, bursitis, and osteoporosis in adulthood. Skin manifestations (facial seborrhea, rosacea, and angiofibromas), gastrointestinal manifestations, neutropenia, and thrombocytopenia occur in some individuals. The clinical manifestations of aspartylglucosaminuria worsen with age, and adults have progressive psychomotor decline. [from GeneReviews]

The phenotypic spectrum associated with RPS6KA3 pathogenic variants is a continuum. Coffin-Lowry syndrome (CLS) classically manifests in males with developmental delay, intellectual disability, neurologic manifestations (hypotonia, stimulus-induced drop attacks, spastic paraparesis, and seizures), musculoskeletal manifestations (kyphoscoliosis and pectus deformity), and characteristic craniofacial and hand findings. Dental issues, sensorineural hearing loss, and obstructive sleep apnea also occur. The milder end of the continuum in males includes neurodevelopmental disabilities with or without less pronounced multisystem involvement. Heterozygous females often exhibit clinical manifestations that can be consistent with clinically defined CLS but are typically less severe than those seen in affected males. Developmental delay and intellectual disability comprise the core phenotypic findings, and quality of life and prognosis are variably affected by the presence and severity of neurologic and musculoskeletal involvement. [from GeneReviews]

Multiple endocrine neoplasia type 2 (MEN2) includes the following phenotypes: MEN2A, familial medullary thyroid carcinoma (FMTC, which may be a variant of MEN2A), and MEN2B. All three phenotypes involve high risk for development of medullary carcinoma of the thyroid (MTC); MEN2A and MEN2B involve an increased risk for pheochromocytoma; MEN2A involves an increased risk for parathyroid adenoma or hyperplasia. Additional features of MEN2B include mucosal neuromas of the lips and tongue, distinctive facies with enlarged lips, ganglioneuromatosis of the gastrointestinal tract, and a marfanoid habitus. MTC typically occurs in early childhood in MEN2B, early adulthood in MEN2A, and middle age in FMTC. [from GeneReviews]

Alpha-thalassemia X-linked intellectual disability (ATR-X) syndrome is characterized by distinctive craniofacial features, genital anomalies, hypotonia, and mild-to-profound developmental delay / intellectual disability (DD/ID). Craniofacial abnormalities include small head circumference, telecanthus or widely spaced eyes, short triangular nose, tented upper lip, and thick or everted lower lip with coarsening of the facial features over time. While all affected individuals have a normal 46,XY karyotype, genital anomalies comprise a range from hypospadias and undescended testicles, to severe hypospadias and ambiguous genitalia, to normal-appearing female external genitalia. Alpha-thalassemia, observed in about 75% of affected individuals, is mild and typically does not require treatment. Osteosarcoma has been reported in a few males with germline pathogenic variants. [from GeneReviews]

MED12-related disorders include the phenotypes of FG syndrome type 1 (FGS1), Lujan syndrome (LS), X-linked Ohdo syndrome (XLOS), Hardikar syndrome (HS), and nonspecific intellectual disability (NSID). FGS1 and LS share the clinical findings of cognitive impairment, hypotonia, and abnormalities of the corpus callosum. FGS1 is further characterized by absolute or relative macrocephaly, tall forehead, downslanted palpebral fissures, small and simple ears, constipation and/or anal anomalies, broad thumbs and halluces, and characteristic behavior. LS is further characterized by large head, tall thin body habitus, long thin face, prominent nasal bridge, high narrow palate, and short philtrum. Carrier females in families with FGS1 and LS are typically unaffected. XLOS is characterized by intellectual disability, blepharophimosis, and facial coarsening. HS has been described in females with cleft lip and/or cleft palate, biliary and liver anomalies, intestinal malrotation, pigmentary retinopathy, and coarctation of the aorta. Developmental and cognitive concerns have not been reported in females with HS. Pathogenic variants in MED12 have been reported in an increasing number of males and females with NSID, with affected individuals often having clinical features identified in other MED12-related disorders. [from GeneReviews]

Classically, Coffin-Siris syndrome (CSS) was characterized by specific dysmorphic features (coarse facies, sparse scalp hair, thick eyebrows with long lashes, wide nasal bridge with broad nasal tip, anteverted nares with thick ala nasi, wide mouth with thick, everted vermilion of the upper and lower lips, and hypertrichosis), the absence or underdevelopment of the fifth digit finger/toe or nail, learning and developmental differences, and various organ system-related anomalies. As genetic technology has evolved, more individuals with subtle physical exam findings are being diagnosed with CSS. The vast majority of affected individuals have developmental delay / intellectual disability, typically in the moderate-to-severe range, although those with mild cognitive impairment or even normal intelligence have more rarely been described. Most affected individuals have feeding difficulties (with ~25%-50% requiring a feeding tube in childhood, some of whom then outgrow it), hypotonia, and frequent infections. About half of affected individuals have epilepsy. Other findings may include skeletal features (joint laxity, scoliosis), hearing impairment (both conductive and sensorineural), eye issues (ptosis, strabismus), congenital heart defects, genitourinary malformations, and behavioral issues (including hyperactivity and/or aggressiveness). [from GeneReviews]

Fucosidosis is an autosomal recessive lysosomal storage disease caused by defective alpha-L-fucosidase with accumulation of fucose in the tissues. Clinical features include angiokeratoma, progressive psychomotor retardation, neurologic signs, coarse facial features, and dysostosis multiplex. Fucosidosis has been classified into 2 major types. Type 1 is characterized by rapid psychomotor regression and severe neurologic deterioration beginning at about 6 months of age, elevated sweat sodium chloride, and death within the first decade of life. Type 2 is characterized by milder psychomotor retardation and neurologic signs, the development of angiokeratoma corporis diffusum, normal sweat salinity, and longer survival (Kousseff et al., 1976). [from OMIM]

Alpha-thalassemia X-linked intellectual disability (ATR-X) syndrome is characterized by distinctive craniofacial features, genital anomalies, hypotonia, and mild-to-profound developmental delay / intellectual disability (DD/ID). Craniofacial abnormalities include small head circumference, telecanthus or widely spaced eyes, short triangular nose, tented upper lip, and thick or everted lower lip with coarsening of the facial features over time. While all affected individuals have a normal 46,XY karyotype, genital anomalies comprise a range from hypospadias and undescended testicles, to severe hypospadias and ambiguous genitalia, to normal-appearing female external genitalia. Alpha-thalassemia, observed in about 75% of affected individuals, is mild and typically does not require treatment. Osteosarcoma has been reported in a few males with germline pathogenic variants. [from GeneReviews]

Mucopolysaccharidosis type III (MPS III) is a multisystem lysosomal storage disease characterized by progressive central nervous system degeneration manifest as severe intellectual disability (ID), developmental regression, and other neurologic manifestations including autism spectrum disorder (ASD), behavioral problems, and sleep disturbances. Disease onset is typically before age ten years. Disease course may be rapidly or slowly progressive; some individuals with an extremely attenuated disease course present in mid-to-late adulthood with early-onset dementia with or without a history of ID. Systemic manifestations can include musculoskeletal problems (joint stiffness, contractures, scoliosis, and hip dysplasia), hearing loss, respiratory tract and sinopulmonary infections, and cardiac disease (valvular thickening, defects in the cardiac conduction system). Neurologic decline is seen in all affected individuals; however, clinical severity varies within and among the four MPS III subtypes (defined by the enzyme involved) and even among members of the same family. Death usually occurs in the second or third decade of life secondary to neurologic regression or respiratory tract infections. [from GeneReviews]

CDKL5 deficiency disorder (CDD) is a developmental and epileptic encephalopathy (DEE) characterized by severe early-onset intractable epilepsy and motor, cognitive, visual, and autonomic disturbances. Movement disorders include chorea, dystonia, and stereotypical hand and leg movements. Although females are more commonly affected than males (female-to-male ratio is approximately 4:1), the severity of manifestations in heterozygous females and hemizygous males can be equivalent. However, the severity of the phenotype can vary depending on the type and position of the CDKL5 pathogenic variant, pattern of X-chromosome inactivation in females, and presence of postzygotic mosaicism in males or females, who can have mild manifestations. [from GeneReviews]

Cri-du-chat syndrome was first described by Lejeune et al. (1963) as a hereditary congenital syndrome associated with deletion of part of the short arm of chromosome 5. The deletions can vary in size from extremely small and involving only band 5p15.2 to the entire short arm. Although the majority of deletions arise as new mutations, approximately 12% result from unbalanced segregation of translocations or recombination involving a pericentric inversion in one of the parents. [from OMIM]

Noonan syndrome with multiple lentigines (NSML) is a condition in which the cardinal features consist of lentigines, hypertrophic cardiomyopathy, short stature, pectus deformity, and dysmorphic facial features including widely spaced eyes and ptosis. Multiple lentigines present as dispersed flat, black-brown macules, mostly on the face, neck, and upper part of the trunk with sparing of the mucosa. In general, lentigines do not appear until age four to five years but then increase to the thousands by puberty. Some individuals with NSML do not exhibit lentigines. Approximately 85% of affected individuals have heart defects, including hypertrophic cardiomyopathy (typically appearing during infancy and sometimes progressive) and pulmonary valve stenosis. Postnatal growth restriction resulting in short stature occurs in fewer than 50% of affected persons, although most affected individuals have a height that is less than the 25th centile for age. Sensorineural hearing deficits, present in approximately 20% of affected individuals, are poorly characterized. Intellectual disability, typically mild, is observed in approximately 30% of persons with NSML. [from GeneReviews]

Marshall syndrome (MRSHS) is characterized by midfacial hypoplasia, cleft palate, ocular anomalies including high myopia and cataracts, sensorineural hearing loss, short stature with spondyloepiphyseal dysplasia, and arthropathy. In contrast to Stickler syndrome type II, it has less severe eye findings but striking ocular hypertelorism, more pronounced maxillary hypoplasia, and ectodermal abnormalities (summary by Shanske et al., 1997 and Ala-Kokko and Shanske, 2009). [from OMIM]

Serine deficiency disorders include a spectrum of disease ranging from lethal prenatal-onset Neu-Laxova syndrome to serine deficiency with infantile, juvenile, or adult onset. Neu-Laxova syndrome is characterized by severe intrauterine growth deficiency, microcephaly, congenital bilateral cataracts, characteristic dysmorphic features, limb anomalies, and collodion-like ichthyosis. Infants are typically stillborn or die in early infancy. Infantile-onset serine deficiency is characterized by seizures, microcephaly, developmental delay, intellectual disability, and spastic quadriplegia. Individuals that present with juvenile-onset serine deficiency have seizures and many develop spastic quadriplegia. Adult-onset serine deficiency is characterized by progressive axonal polyneuropathy with ataxia and possible cognitive impairment. [from GeneReviews]

Most females with osteopathia striata with cranial sclerosis (OS-CS) present with macrocephaly and characteristic facial features (frontal bossing, hypertelorism, epicanthal folds, depressed nasal bridge, and prominent jaw). Approximately half have associated features including orofacial clefting and hearing loss, and a minority have some degree of developmental delay (usually mild). Radiographic findings of cranial sclerosis, sclerosis of long bones, and metaphyseal striations (in combination with macrocephaly) can be considered pathognomonic. Males can present with a mild or severe phenotype. Mildly affected males have clinical features similar to affected females, including macrocephaly, characteristic facial features, orofacial clefting, hearing loss, and mild-to-moderate learning delays. Mildly affected males are more likely than females to have congenital or musculoskeletal anomalies. Radiographic findings include cranial sclerosis and sclerosis of the long bones; Metaphyseal striations are more common in males who are mosaic for an AMER1 pathogenic variant. The severe phenotype manifests in males as a multiple-malformation syndrome, lethal in mid-to-late gestation, or in the neonatal period. Congenital malformations include skeletal defects (e.g., polysyndactyly, absent or hypoplastic fibulae), congenital heart disease, and brain, genitourinary, and gastrointestinal anomalies. Macrocephaly is not always present and longitudinal metaphyseal striations have not been observed in severely affected males, except for those who are mosaic for the AMER1 pathogenic variant. [from GeneReviews]

Cantú syndrome is characterized by congenital hypertrichosis; distinctive coarse facial features (including broad nasal bridge, wide mouth with full lips and macroglossia); enlarged heart with enhanced systolic function or pericardial effusion and in many, a large patent ductus arteriosus (PDA) requiring repair; and skeletal abnormalities (thickening of the calvaria, broad ribs, scoliosis, and flaring of the metaphyses). Other cardiovascular abnormalities may include dilated aortic root and ascending aorta with rare aortic aneurysm, tortuous vascularity involving brain and retinal vasculature, and pulmonary arteriovenous communications. Generalized edema (which may be present at birth) spontaneously resolves; peripheral edema of the lower extremities (and sometimes arms and hands) may develop at adolescence. Developmental delays are common, but intellect is typically normal; behavioral problems can include attention-deficit/hyperactivity disorder, autism spectrum disorder, obsessive-compulsive disorder, anxiety, and depression. [from GeneReviews]

INSR-related severe insulin resistance syndrome (INSR-SIRS) comprises a phenotypic spectrum that is a continuum from the severe phenotype of Donohue syndrome to the milder phenotype of Rabson-Mendenhall syndrome (RMS). Donohue syndrome is characterized by severe insulin resistance (hyperinsulinemia with associated fasting hypoglycemia and postprandial hyperglycemia), severe prenatal growth restriction, postnatal growth failure, hypotonia, developmental delay, characteristic facies (proptosis, infraorbital folds, large, low-set, posteriorly rotated ears, thick vermilion of the upper and lower lips, and gingival hypertrophy), and organomegaly involving the 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 Donohue syndrome, 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 Donohue syndrome. Complications of longstanding hyperglycemia are the most common cause of death. While death usually occurs in the second decade, some affected individuals live longer. [from GeneReviews]