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]

Sandhoff disease comprises a phenotypic continuum encompassing acute infantile, subacute juvenile, and late-onset disease. Although classification into these phenotypes is somewhat arbitrary, it is helpful in understanding the variation observed in the timing of disease onset, presenting manifestations, rate of progression, and life span. Acute infantile Sandhoff disease (onset age <6 months). Infants are generally normal at birth followed by progressive weakness and slowing of developmental progress, then developmental regression and severe neurologic impairment. Seizures are common. Death usually occurs between ages two and three years. Subacute juvenile Sandhoff disease (onset age 2-5 years). After attaining normal developmental milestones, developmental progress slows, followed by developmental regression and neurologic impairment (abnormal gait, dysarthria, and cognitive decline). Death (usually from aspiration) typically occurs in the early to late teens. Late-onset Sandhoff disease (onset older teen years or young adulthood). Nearly normal psychomotor development is followed by a range of neurologic findings (e.g., weakness, spasticity, dysarthria, and deficits in cerebellar function) and psychiatric findings (e.g., deficits in executive function and memory). Life expectancy is not necessarily decreased. [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]

GDAP1-related hereditary motor and sensory neuropathy (GDAP1-HMSN) is a peripheral neuropathy (also known as a subtype of Charcot-Marie-Tooth disease) that typically affects the lower extremities earlier and more severely than the upper extremities. As the neuropathy progresses, the distal upper extremities also become severely affected. Proximal muscles can also become weak. Age at onset ranges from infancy to early childhood. In most cases, disease progression causes disabilities within the first or second decade of life. At the end of the second decade, most individuals are wheelchair bound. Disease progression varies considerably even within the same family. The neuropathy can be either of the demyelinating type with reduced nerve conduction velocities or the axonal type with normal nerve conduction velocities. Vocal cord paresis is common. Intelligence is normal. Life expectancy is usually normal, but on occasion may be reduced because of secondary complications. [from GeneReviews]

Multiple congenital anomalies-hypotonia-seizures syndrome-2 (MCAHS2) is an X-linked recessive neurodevelopmental disorder characterized by dysmorphic features, neonatal hypotonia, early-onset myoclonic seizures, and variable congenital anomalies involving the central nervous, cardiac, and urinary systems. Some affected individuals die in infancy (summary by Johnston et al., 2012). The phenotype shows clinical variability with regard to severity and extraneurologic features. However, most patients present in infancy with early-onset epileptic encephalopathy associated with developmental arrest and subsequent severe neurologic disability; these features are consistent with a form of developmental and epileptic encephalopathy (DEE) (summary by Belet et al., 2014, Kato et al., 2014). The disorder is caused by a defect in glycosylphosphatidylinositol (GPI) biosynthesis. For a discussion of genetic heterogeneity of MCAHS, see MCAHS1 (614080). For a discussion of nomenclature and genetic heterogeneity of DEE, see 308350. For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293). [from OMIM]

Adenylosuccinase deficiency is an autosomal recessive inborn error of metabolism caused by an enzymatic defect in de novo purine synthesis (DNPS) pathway. ADSL deficiency leads to the accumulation of toxic intermediates, including succinyladenosine (S-Ado) and succinylaminoimidazole carboxamide riboside (SAICAr) in body fluids. There are 3 major phenotypic forms of the disorder that correlate with different values of the S-Ado and SAICAr concentration ratios (S-Ado/SAICAr) in the cerebrospinal fluid. These include the most severe fatal neonatal encephalopathy (S-Ado/SAICAr ratio less than 1); childhood form (type I) with severe psychomotor retardation (S-Ado/SAICAr ratio close to 1), and a milder form (type II) with psychomotor retardation or hypotonia (S-Ado/SAICAr ratio greater than 2) (summary by Baresova et al., 2012). [from OMIM]

POLR3-related leukodystrophy, a hypomyelinating leukodystrophy with specific features on brain MRI, is characterized by varying combinations of four major clinical findings: Neurologic dysfunction, typically predominated by motor dysfunction (progressive cerebellar dysfunction, and to a lesser extent extrapyramidal [i.e., dystonia], pyramidal [i.e., spasticity] and cognitive dysfunctions). Abnormal dentition (delayed dentition, hypodontia, oligodontia, and abnormally placed or shaped teeth). Endocrine abnormalities such as short stature (in ~50% of individuals) with or without growth hormone deficiency, and more commonly, hypogonadotropic hypogonadism manifesting as delayed, arrested, or absent puberty. Ocular abnormality in the form of myopia, typically progressing over several years and becoming severe. POLR3-related leukodystrophy and 4H leukodystrophy are the two recognized terms for five previously described overlapping clinical phenotypes (initially described as distinct entities before their molecular basis was known). These include: Hypomyelination, hypodontia, hypogonadotropic hypogonadism (4H syndrome); Ataxia, delayed dentition, and hypomyelination (ADDH); Tremor-ataxia with central hypomyelination (TACH); Leukodystrophy with oligodontia (LO); Hypomyelination with cerebellar atrophy and hypoplasia of the corpus callosum (HCAHC). Age of onset is typically in early childhood but later-onset cases have also been reported. An infant with Wiedemann-Rautenstrauch syndrome (neonatal progeroid syndrome) was recently reported to have pathogenic variants in POLR3A on exome sequencing. Confirmation of this as a very severe form of POLR3-related leukodystrophy awaits replication in other individuals with a clinical diagnosis of Wiedemann-Rautenstrauch syndrome. [from GeneReviews]

POLR3-related leukodystrophy, a hypomyelinating leukodystrophy with specific features on brain MRI, is characterized by varying combinations of four major clinical findings: Neurologic dysfunction, typically predominated by motor dysfunction (progressive cerebellar dysfunction, and to a lesser extent extrapyramidal [i.e., dystonia], pyramidal [i.e., spasticity] and cognitive dysfunctions). Abnormal dentition (delayed dentition, hypodontia, oligodontia, and abnormally placed or shaped teeth). Endocrine abnormalities such as short stature (in ~50% of individuals) with or without growth hormone deficiency, and more commonly, hypogonadotropic hypogonadism manifesting as delayed, arrested, or absent puberty. Ocular abnormality in the form of myopia, typically progressing over several years and becoming severe. POLR3-related leukodystrophy and 4H leukodystrophy are the two recognized terms for five previously described overlapping clinical phenotypes (initially described as distinct entities before their molecular basis was known). These include: Hypomyelination, hypodontia, hypogonadotropic hypogonadism (4H syndrome); Ataxia, delayed dentition, and hypomyelination (ADDH); Tremor-ataxia with central hypomyelination (TACH); Leukodystrophy with oligodontia (LO); Hypomyelination with cerebellar atrophy and hypoplasia of the corpus callosum (HCAHC). Age of onset is typically in early childhood but later-onset cases have also been reported. An infant with Wiedemann-Rautenstrauch syndrome (neonatal progeroid syndrome) was recently reported to have pathogenic variants in POLR3A on exome sequencing. Confirmation of this as a very severe form of POLR3-related leukodystrophy awaits replication in other individuals with a clinical diagnosis of Wiedemann-Rautenstrauch syndrome. [from GeneReviews]

Huppke-Brendel syndrome (HBS) is characterized by bilateral congenital cataracts, sensorineural hearing loss, and severe developmental delay. To date, six individuals with HBS have been reported in the literature. All presented in infancy with axial hypotonia; motor delay was apparent in the first few months of life with lack of head control and paucity of limb movement. Seizures have been reported infrequently. In all individuals described to date serum copper and ceruloplasmin levels were very low or undetectable. Brain MRI examination showed hypomyelination, cerebellar hypoplasia mainly affecting the vermis, and wide subarachnoid spaces. None of the individuals reported to date were able to sit or walk independently. All affected individuals died between age ten months and six years. [from GeneReviews]

Hypomyelination and congenital cataract (HCC) is usually characterized by bilateral congenital cataracts and normal psychomotor or only mildly delayed development in the first year of life, followed by slowly progressive neurologic impairment manifest as ataxia, spasticity (brisk tendon reflexes and bilateral extensor plantar responses), and mild-to-moderate cognitive impairment. Dysarthria and truncal hypotonia are observed. Cerebellar signs (truncal titubation and intention tremor) and peripheral neuropathy (muscle weakness and wasting of the legs) are present in the majority of affected individuals. Seizures can occur. Cataracts may be absent in some individuals. [from GeneReviews]

Zellweger syndrome (ZS) is an autosomal recessive multiple congenital anomaly syndrome resulting from disordered peroxisome biogenesis. 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 13 (CG13, equivalent to CGH) have mutations in the PEX13 gene. For information on the history of PBD complementation groups, see 214100. [from OMIM]

Developmental and epileptic encephalopathy-5 (DEE5) is a neurologic disorder characterized by global developmental delay and the onset of tonic seizures or infantile spasms in the first months of life. The seizures tend to be refractory to treatment, and EEG shows hypsarrhythmia, consistent with a clinical diagnosis of West syndrome. Affected individuals have severely impaired psychomotor development with lack of visual attention, poor head control, feeding difficulties, microcephaly, and spastic quadriplegia. Brain imaging may show cerebral atrophy and hypomyelination (summary by Saitsu et al., 2010). For a general phenotypic description and a discussion of genetic heterogeneity of developmental and epileptic encephalopathy, see 308350. [from OMIM]

Combined oxidative phosphorylation deficiency-24 (COXPD24) is an autosomal recessive mitochondrial disorder with wide phenotypic variability. Most patients present in infancy with delayed neurodevelopment, refractory seizures, hypotonia, and hearing impairment due to auditory neuropathy. Less common features may include cortical blindness, renal dysfunction, and/or liver involvement, suggestive of Alpers syndrome (MTDPS4A; 203700). Patients with the severe phenotype tend to have brain abnormalities on imaging, including cerebral atrophy and hyperintensities in the basal ganglia and brainstem, consistent with Leigh syndrome. Laboratory values may be normal or show increased lactate and evidence of mitochondrial respiratory chain defects, particularly in muscle. Some patients achieve little developmental milestones and may die in infancy or early childhood. However, some patients have a less severe phenotype manifest only by myopathy (summary by Sofou et al., 2015, Vanlander et al., 2015, and Mizuguchi et al., 2017). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060). [from OMIM]

Autosomal recessive limb-girdle muscular dystrophy-18 (LGMDR18) 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). [from OMIM]

PURA-related neurodevelopmental disorders include PURA syndrome, caused by a heterozygous pathogenic sequence variant in PURA, and 5q31.3 deletion syndrome, caused by a genomic 5q31.3 deletion encompassing all or part of PURA. PURA-related neurodevelopmental disorders are characterized by moderate-to-severe neurodevelopmental delay with absence of speech in most and lack of independent ambulation in many. Early-onset problems can include hypotonia, hypothermia, hypersomnolence, feeding difficulties, excessive hiccups, recurrent central and obstructive apneas, epileptic seizures, abnormal nonepileptic movements (dystonia, dyskinesia, and dysconjugate eye movements), and abnormal vision. Congenital heart defects, urogenital malformations, skeletal abnormalities, and endocrine disorders occur, but are less common. [from GeneReviews]

The defining clinical characteristics of the microcephaly-capillary malformation (MIC-CAP) syndrome are typically present at birth: microcephaly and generalized cutaneous capillary malformations (a few to hundreds of oval/circular macules or patches varying in size from 1-2 mm to several cm), hypoplastic distal phalanges of the hands and/or feet, early-onset intractable epilepsy, and profound developmental delay. Seizures, which can be focal, tonic, and complex partial and can include infantile spasms, appear to stabilize after age two years. Myoclonus of the limbs and eyelids is common; other abnormal movements (dyskinetic, choreiform) may be seen. To date, the diagnosis has been confirmed in 18 individuals from 15 families. [from GeneReviews]

Combined oxidative phosphorylation deficiency-21 (COXPD11) is a severe multisystemic autosomal recessive disorder characterized by neonatal hypotonia and lactic acidosis. Affected individuals may have respiratory insufficiency, foot deformities, or seizures, and all reported patients have died in infancy. Biochemical studies show deficiencies of multiple mitochondrial respiratory enzymes (summary by Garcia-Diaz et al., 2012). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060). [from OMIM]

POLR3-related leukodystrophy, a hypomyelinating leukodystrophy with specific features on brain MRI, is characterized by varying combinations of four major clinical findings: Neurologic dysfunction, typically predominated by motor dysfunction (progressive cerebellar dysfunction, and to a lesser extent extrapyramidal [i.e., dystonia], pyramidal [i.e., spasticity] and cognitive dysfunctions). Abnormal dentition (delayed dentition, hypodontia, oligodontia, and abnormally placed or shaped teeth). Endocrine abnormalities such as short stature (in ~50% of individuals) with or without growth hormone deficiency, and more commonly, hypogonadotropic hypogonadism manifesting as delayed, arrested, or absent puberty. Ocular abnormality in the form of myopia, typically progressing over several years and becoming severe. POLR3-related leukodystrophy and 4H leukodystrophy are the two recognized terms for five previously described overlapping clinical phenotypes (initially described as distinct entities before their molecular basis was known). These include: Hypomyelination, hypodontia, hypogonadotropic hypogonadism (4H syndrome); Ataxia, delayed dentition, and hypomyelination (ADDH); Tremor-ataxia with central hypomyelination (TACH); Leukodystrophy with oligodontia (LO); Hypomyelination with cerebellar atrophy and hypoplasia of the corpus callosum (HCAHC). Age of onset is typically in early childhood but later-onset cases have also been reported. An infant with Wiedemann-Rautenstrauch syndrome (neonatal progeroid syndrome) was recently reported to have pathogenic variants in POLR3A on exome sequencing. Confirmation of this as a very severe form of POLR3-related leukodystrophy awaits replication in other individuals with a clinical diagnosis of Wiedemann-Rautenstrauch syndrome. [from GeneReviews]

A very rare, complex form of hereditary spastic paraplegia characterised by a late-onset, slowly progressive spastic paraplegia associated with mild ataxia and dysarthria, upper extremity involvement (i.e. loss of finger dexterity, dysmetria), and mild cognitive impairment, without the presence of nystagmus. A hypomyelinating leucodystrophy and thin corpus callosum is observed in all cases and psychomotor development is normal or near normal. Caused by mutations in the GJC2 gene (1q41-q42) encoding the gap junction gamma-2 protein. [from SNOMEDCT_US]

Neurodevelopmental disorder with hearing loss, seizures, and brain abnormalities (NEDHSB) is an autosomal recessive disorder characterized by severe neurologic impairment including impaired intellectual development, epilepsy, microcephaly, abnormal muscle tone, and sensorineural hearing loss. Most affected individuals are nonambulatory, cannot sit unassisted, and have no speech development. More variable features include feeding difficulties, poor growth, cortical visual impairment, spasticity, scoliosis, immunodeficiency, and thrombocytopenia (Tanaka et al., 2015). [from OMIM]