MedGen

PLP1 disorders of central nervous system myelin formation include a range of phenotypes from Pelizaeus-Merzbacher disease (PMD) to spastic paraplegia 2 (SPG2). PMD typically manifests in infancy or early childhood with nystagmus, hypotonia, and cognitive impairment; the findings progress to severe spasticity and ataxia. Life span is shortened. SPG2 manifests as spastic paraparesis with or without CNS involvement and usually normal life span. Intrafamilial variation of phenotypes can be observed, but the signs are usually fairly consistent within families. Heterozygous females may manifest mild-to-moderate signs of the disease. [from GeneReviews]

Angelman syndrome (AS) is characterized by severe developmental delay or intellectual disability, severe speech impairment, gait ataxia and/or tremulousness of the limbs, and unique behavior with an apparent happy demeanor that includes frequent laughing, smiling, and excitability. Microcephaly and seizures are also common. Developmental delays are first noted at around age six months; however, the unique clinical features of AS do not become manifest until after age one year. [from GeneReviews]

MPV17-related mitochondrial DNA (mtDNA) maintenance defect presents in the vast majority of affected individuals as an early-onset encephalohepatopathic (hepatocerebral) disease that is typically associated with mtDNA depletion, particularly in the liver. A later-onset neuromyopathic disease characterized by myopathy and neuropathy, and associated with multiple mtDNA deletions in muscle, has also rarely been described. MPV17-related mtDNA maintenance defect, encephalohepatopathic form is characterized by: Hepatic manifestations (liver dysfunction that typically progresses to liver failure, cholestasis, hepatomegaly, and steatosis); Neurologic involvement (developmental delay, hypotonia, microcephaly, and motor and sensory peripheral neuropathy); Gastrointestinal manifestations (gastrointestinal dysmotility, feeding difficulties, and failure to thrive); and Metabolic derangements (lactic acidosis and hypoglycemia). Less frequent manifestations include renal tubulopathy, nephrocalcinosis, and hypoparathyroidism. Progressive liver disease often leads to death in infancy or early childhood. Hepatocellular carcinoma has been reported. [from GeneReviews]

The creatine deficiency disorders (CDDs), inborn errors of creatine metabolism and transport, comprise three disorders: the creatine biosynthesis disorders guanidinoacetate methyltransferase (GAMT) deficiency and L-arginine:glycine amidinotransferase (AGAT) deficiency; and creatine transporter (CRTR) deficiency. Developmental delay and cognitive dysfunction or intellectual disability and speech-language disorder are common to all three CDDs. Onset of clinical manifestations of GAMT deficiency (reported in ~130 individuals) is between ages three months and two years; in addition to developmental delays, the majority of individuals have epilepsy and develop a behavior disorder (e.g., hyperactivity, autism, or self-injurious behavior), and about 30% have movement disorder. AGAT deficiency has been reported in 16 individuals; none have had epilepsy or movement disorders. Clinical findings of CRTR deficiency in affected males (reported in ~130 individuals) in addition to developmental delays include epilepsy (variable seizure types and may be intractable) and behavior disorders (e.g., attention deficit and/or hyperactivity, autistic features, impulsivity, social anxiety), hypotonia, and (less commonly) a movement disorder. Poor weight gain with constipation and prolonged QTc on EKG have been reported. While mild-to-moderate intellectual disability is commonly observed up to age four years, the majority of adult males with CRTR deficiency have been reported to have severe intellectual disability. Females heterozygous for CRTR deficiency are typically either asymptomatic or have mild intellectual disability, although a more severe phenotype resembling the male phenotype has been reported. [from GeneReviews]

Dejerine-Sottas neuropathy is a demyelinating peripheral neuropathy with onset in infancy. It can show autosomal dominant or recessive inheritance. Affected individuals have delayed motor development due to severe distal motor and sensory impairment, resulting in difficulties in gait. Some patients have generalized hypotonia in infancy. Other features may include pes cavus, scoliosis, and sensory ataxia. Nerve conduction velocities are severely decreased (sometimes less than 10 m/s), and sural nerve biopsy shows severe loss of myelinated fibers (summary by Baets et al., 2011). [from OMIM]

Spinocerebellar ataxia type 17 (SCA17) is characterized by ataxia, dementia, and involuntary movements, including chorea and dystonia. Psychiatric symptoms, pyramidal signs, and rigidity are common. The age of onset ranges from three to 55 years. Individuals with full-penetrance alleles develop neurologic and/or psychiatric symptoms by age 50 years. Ataxia and psychiatric abnormalities are frequently the initial findings, followed by involuntary movement, parkinsonism, dementia, and pyramidal signs. Brain MRI shows variable atrophy of the cerebrum, brain stem, and cerebellum. The clinical features correlate with the length of the polyglutamine expansion but are not absolutely predictive of the clinical course. [from GeneReviews]

SATB2-associated syndrome (SAS) is a multisystem disorder in which all affected individuals have developmental delay / intellectual disability that can range from mild to profound but is most commonly moderate to profound. Speech delay and/or absent speech is observed in all affected individuals. Other neurobehavioral manifestations can include jovial or friendly personality, autistic tendencies, agitation or aggressive outbursts, self-injury, impulsivity, hyperactivity, anxiety, difficulty falling asleep or maintaining sleep, and sensory issues. Most affected individuals have hypotonia. EEG abnormalities are frequent but may be without clinically recognizable seizures. While only about 20% of affected individuals have clinical seizures, a subset of affected individuals have electrical status epilepticus in sleep. Craniofacial findings can include nonspecific dysmorphic features, palatal anomalies (cleft palate, high-arched palate, velopharyngeal insufficiency, bifid uvula), and dental anomalies (abnormal shape or size or the upper central incisors, dental crowding, hypodontia, and delayed teeth eruption, among others). Skeletal anomalies can include scoliosis, tibial bowing, and joint contractures. At least one third of individuals have a history of previous fractures and about one quarter of affected individuals have documented low bone mineral density. Other finding can include pre- and postnatal growth restriction, feeding issues, and eye anomalies (strabismus, refractive error). In those with a larger deletion involving SATB2 and adjacent genes, cardiovascular, genitourinary, and ectodermal findings may also be present. [from GeneReviews]

Phelan-McDermid syndrome-SHANK3 related (PMS-SHANK3 related) is characterized by neonatal hypotonia, absent to severely delayed speech, developmental delay, and minor dysmorphic facial features. Most affected individuals have moderate-to-profound intellectual disability. Other features include relatively large fleshy hands, dysplastic toenails, and decreased perspiration that results in a tendency to overheat. Normal stature and normal head size distinguish PMS-SHANK3 related from other autosomal chromosome disorders. Neurobehavioral characteristics include mouthing or chewing non-food items, decreased perception of pain, and autism spectrum disorder or autistic-like affect and behavior. Some individuals experience regression / loss of skills, epilepsy, ataxic/abnormal gait, and sleep disturbance (difficulty falling asleep and staying asleep, hypersomnia, and parasomnias). Less commonly, affected individuals may have strabismus, vision problems (hyperopia or myopia), cardiac anomalies, renal anomalies, and lymphedema. Those who have PMS-SHANK3 related due to a ring chromosome 22 also have a high risk of developing features of NF2-related schwannomatosis (NF2). [from GeneReviews]

Autosomal dominant multiple epiphyseal dysplasia (MED) presents in early childhood, usually with pain in the hips and/or knees after exercise. Affected children report fatigue with long-distance walking. Waddling gait may be present. Adult height is either in the lower range of normal or mildly shortened. The limbs are relatively short in comparison to the trunk. Pain and joint deformity progress, resulting in early-onset osteoarthritis, particularly of the large weight-bearing joints. [from GeneReviews]

POLG-related disorders comprise a continuum of overlapping phenotypes that were clinically defined before the molecular basis was known. POLG-related disorders can therefore be considered an overlapping spectrum of disease presenting from early childhood to late adulthood. The age of onset broadly correlates with the clinical phenotype. In individuals with early-onset disease (prior to age 12 years), liver involvement, feeding difficulties, seizures, hypotonia, and muscle weakness are the most common clinical features. This group has the worst prognosis. In the juvenile/adult-onset form (age 12-40 years), disease is typically characterized by peripheral neuropathy, ataxia, seizures, stroke-like episodes, and, in individuals with longer survival, progressive external ophthalmoplegia (PEO). This group generally has a better prognosis than the early-onset group. Late-onset disease (after age 40 years) is characterized by ptosis and PEO, with additional features such as peripheral neuropathy, ataxia, and muscle weakness. This group overall has the best prognosis. [from GeneReviews]

Charcot-Marie-Tooth disease type 4F (CMT4F) is an autosomal recessive demyelinating neuropathy characterized by distal sensory impairment and distal muscle weakness and atrophy affecting the lower more than the upper limbs. Nerve conduction velocities are decreased and sural nerve biopsy shows loss of myelinated fibers. The age at onset is variable and can range from childhood to adult years. When the onset is in infancy, the phenotype is characterized as Dejerine-Sottas syndrome (DSS; 145900). For a phenotypic description and a discussion of genetic heterogeneity of autosomal recessive demyelinating Charcot-Marie-Tooth disease, see CMT4A (214400). [from OMIM]

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. [from GeneReviews]

Complex cortical dysplasia with other brain malformations-14A (CDCBM14A) is an autosomal recessive neurologic disorder characterized by global developmental delay with impaired intellectual development, motor delay, poor speech development, and early-onset seizures, often focal or atypical absence. Additional features may include strabismus, nystagmus, exo- or esotropia, axial hypotonia, and spasticity. Brain imaging shows bilateral frontoparietal polymicrogyria, a frontal-predominant cobblestone malformation of the cortex, scalloping of the cortical/white matter junction, enlarged ventricles, and hypoplasia of the pons, brainstem, and cerebellum. The disorder can be classified as a malformation of cortical development (summary by Parrini et al., 2009; Luo et al., 2011; Zulfiqar et al., 2021). For a discussion of genetic heterogeneity of CDCBM, see CDCBM1 (614039). [from OMIM]

NKX2-1-related disorders range from benign hereditary chorea (BHC) to choreoathetosis, congenital hypothyroidism, and neonatal respiratory distress syndrome (also known as brain-lung-thyroid syndrome). Childhood-onset chorea, the hallmark feature of NKX2-1-related disorders, may or may not be associated with pulmonary disease or congenital hypothyroidism. Age of onset of chorea varies from early infancy (most commonly) to late childhood or adolescence and may progress into the second decade, after which it remains static or (rarely) remits. Pulmonary disease, the second most common manifestation, can include respiratory distress syndrome in neonates, interstitial lung disease in young children, and pulmonary fibrosis in older individuals. The risk for pulmonary carcinoma is increased in young adults with NKX2-1-related disorders. Thyroid dysfunction, occurring as a result of thyroid dysgenesis, can present as congenital or compensated hypothyroidism. In one review, 50% of affected individuals had the full brain-lung-thyroid syndrome, 30% had brain and thyroid involvement only, and 13% had chorea only. [from GeneReviews]

VLDLR cerebellar hypoplasia (VLDLR-CH) is characterized by non-progressive congenital ataxia that is predominantly truncal and results in delayed ambulation, moderate-to-profound intellectual disability, dysarthria, strabismus, and seizures. Children either learn to walk very late (often after age 6 years) or never achieve independent ambulation. Brain MRI findings include hypoplasia of the inferior portion of the cerebellar vermis and hemispheres, simplified gyration of the cerebral hemispheres, and small brain stem – particularly the pons. [from GeneReviews]

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. [from GeneReviews]

Snyder-Robinson syndrome (SRS) is an X-linked intellectual disability syndrome characterized by asthenic build, facial dysmorphism with a prominent lower lip, kyphoscoliosis, osteoporosis, speech abnormalities, and seizures. Developmental delay usually presents as failure to meet early developmental milestones and then evolves to moderate to profound intellectual disability (which appears to remain stable over time) and variable motor disability. Asthenic habitus and low muscle mass usually develop during the first year, even in males who are ambulatory. During the first decade, males with SRS develop osteoporosis, resulting in fractures in the absence of trauma. [from GeneReviews]

Spinocerebellar ataxia-15 (SCA15) is an autosomal dominant, adult-onset, slowly progressive form of cerebellar ataxia. Most patients also have disabling action and postural tremor, and some have pyramidal tract affection, dorsal column involvement, and gaze palsy. Brain imaging shows cerebellar atrophy mainly affecting the vermis (summary by Synofzik et al., 2011). Autosomal dominant 'pure' cerebellar ataxia, classified as ADCA type III by Harding (1983, 1993), is a genetically heterogeneous disorder (see, e.g., 117210). For a general discussion of autosomal dominant spinocerebellar ataxia, see SCA1 (164400). [from OMIM]

The autosomal dominant TRPV4 disorders (previously considered to be clinically distinct phenotypes before their molecular basis was discovered) are now grouped into neuromuscular disorders and skeletal dysplasias; however, the overlap within each group is considerable. Affected individuals typically have either neuromuscular or skeletal manifestations alone, and in only rare instances an overlap syndrome has been reported. The three autosomal dominant neuromuscular disorders (mildest to most severe) are: Charcot-Marie-Tooth disease type 2C. Scapuloperoneal spinal muscular atrophy. Congenital distal spinal muscular atrophy. The autosomal dominant neuromuscular disorders are characterized by a congenital-onset, static, or later-onset progressive peripheral neuropathy with variable combinations of laryngeal dysfunction (i.e., vocal fold paresis), respiratory dysfunction, and joint contractures. The six autosomal dominant skeletal dysplasias (mildest to most severe) are: Familial digital arthropathy-brachydactyly. Autosomal dominant brachyolmia. Spondylometaphyseal dysplasia, Kozlowski type. Spondyloepiphyseal dysplasia, Maroteaux type. Parastremmatic dysplasia. Metatropic dysplasia. The skeletal dysplasia is characterized by brachydactyly (in all 6); the five that are more severe have short stature that varies from mild to severe with progressive spinal deformity and involvement of the long bones and pelvis. In the mildest of the autosomal dominant TRPV4 disorders life span is normal; in the most severe it is shortened. Bilateral progressive sensorineural hearing loss (SNHL) can occur with both autosomal dominant neuromuscular disorders and skeletal dysplasias. [from GeneReviews]

Any Pitt-Hopkins-like syndrome in which the cause of the disease is a mutation in the NRXN1 gene. [from MONDO]