MedGen

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]

SCN1A seizure disorders encompass a spectrum that ranges from simple febrile seizures and generalized epilepsy with febrile seizures plus (GEFS+) at the mild end to Dravet syndrome and intractable childhood epilepsy with generalized tonic-clonic seizures (ICE-GTC) at the severe end. Phenotypes with intractable seizures including Dravet syndrome are often associated with cognitive decline. Less commonly observed phenotypes include myoclonic astatic epilepsy (MAE), Lennox-Gastaut syndrome, infantile spasms, epilepsy with focal seizures, and vaccine-related encephalopathy and seizures. The phenotype of SCN1A seizure disorders can vary even within the same family. [from GeneReviews]

Developmental and epileptic encephalopathy-36 (DEE36) is an X-linked neurodevelopmental disorder characterized by the onset of seizures at a mean age of 6.5 months. Most patients present with infantile spasms associated with hypsarrhythmia on EEG, consistent with a clinical diagnosis of West syndrome. The seizures tend to be refractory to treatment, although some patients may respond to benzodiazepines or a ketogenic diet. Affected individuals have severely delayed psychomotor development with poor motor function, severe intellectual disability, poor or absent speech, and limited eye contact. More variable features include feeding difficulties sometimes requiring tube feeding, ocular defects including cortical visual impairment, dysmorphic facial features, and scoliosis or osteopenia. The vast majority of patients reported have been females, although rare affected males with a similar phenotype have been described. Most patients show normal N-glycosylation on transferrin isoelectric focusing, but some show abnormal N-glycosylation consistent with CDG type I (summary by Ng et al., 2020). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350. For a discussion of the classification of CDGs, see CDG1A (212065). [from OMIM]

Microcephaly with or without chorioretinopathy, lymphedema, or impaired intellectual development (MCLMR) is an autosomal dominant disorder that involves an overlapping but variable spectrum of central nervous system and ocular developmental anomalies. Microcephaly ranges from mild to severe and is often associated with mild to moderate developmental delay and a characteristic facial phenotype with upslanting palpebral fissures, broad nose with rounded tip, long philtrum with thin upper lip, prominent chin, and prominent ears. Chorioretinopathy is the most common eye abnormality, but retinal folds, microphthalmia, and myopic and hypermetropic astigmatism have also been reported, and some individuals have no overt ocular phenotype. Congenital lymphedema, when present, is typically confined to the dorsa of the feet, and lymphoscintigraphy reveals the absence of radioactive isotope uptake from the webspaces between the toes (summary by Ostergaard et al., 2012). Robitaille et al. (2014) found that MCLMR includes a broader spectrum of ocular disease, including retinal detachment with avascularity of the peripheral retina, and noted phenotypic overlap with familial exudative vitreoretinopathy (FEVR; see EVR1, 133780). Birtel et al. (2017) observed intrafamilial and intraindividual variability in retinal phenotype, and noted that syndromic manifestations in some patients are too subtle to be detected during a routine ophthalmologic evaluation. Variable expressivity and reduced penetrance have also been observed in some families (Jones et al., 2014; Li et al., 2016). Autosomal recessive forms of microcephaly with chorioretinopathy have been reported (see 251270). See also Mirhosseini-Holmes-Walton syndrome (autosomal recessive microcephaly with pigmentary retinopathy and impaired intellectual development; 268050). [from OMIM]

The spectrum of FARS2 deficiency ranges from the infantile-onset phenotype, characterized by epileptic encephalopathy with lactic acidosis and poor prognosis (70% of affected individuals), to the later-onset phenotype, characterized by spastic paraplegia, less severe neurologic manifestations, and longer survival (30% of affected individuals). To date FARS2 deficiency has been reported in 37 individuals from 25 families. Infantile-onset phenotype. Seizures are difficult to control and may progress quickly at an early age to intractable seizures with frequent status epilepticus; some children have hypsarrhythmia on EEG. All have developmental delay; most are nonverbal and unable to walk. Feeding difficulties are common. More than half of affected children die in early childhood. Later-onset phenotype. All affected individuals have spastic paraplegia manifested by weakness, spasticity, and exaggerated reflexes of the lower extremities associated with walking difficulties; some have developmental delay/intellectual disability; some have brief seizures that resolve over time. [from GeneReviews]

The neuronal ceroid lipofuscinoses (NCL; CLN) are a clinically and genetically heterogeneous group of neurodegenerative disorders characterized by the intracellular accumulation of autofluorescent lipopigment storage material in different patterns ultrastructurally. The clinical course includes progressive dementia, seizures, and progressive visual failure (Mole et al., 2005). For a discussion of genetic heterogeneity of neuronal ceroid lipofuscinosis, see CLN1 (256730). [from OMIM]

Neuronal ceroid lipofuscinosis-4 (CLN4) is an autosomal dominant neurodegenerative disorder characterized by onset of symptoms in adulthood. It belongs to a group of progressive neurodegenerative diseases characterized by accumulation of intracellular autofluorescent lipopigment storage material in the brain and other tissues. Several different forms have been described according to age of onset (see, e.g., CLN3, 204200). Individuals with the adult form, sometimes referred to as Kufs disease, develop psychiatric manifestations, seizures, cerebellar ataxia, and cognitive decline. Retinal degeneration is usually not present (summary by Benitez et al., 2011 and Velinov et al., 2012). For a general phenotypic description and a discussion of genetic heterogeneity of CLN, see CLN1 (256730). [from OMIM]

TSEN54 pontocerebellar hypoplasia (TSEN54-PCH) comprises three PCH phenotypes (PCH2, 4, and 5) that share characteristic neuroradiologic and neurologic findings. The three PCH phenotypes (which differ mainly in life expectancy) were considered to be distinct entities before their molecular basis was known. PCH2. Children usually succumb before age ten years (those with PCH4 and 5 usually succumb as neonates). Children with PCH2 have generalized clonus, uncoordinated sucking and swallowing, impaired cognitive development, lack of voluntary motor development, cortical blindness, and an increased risk for rhabdomyolysis during severe infections. Epilepsy is present in approximately 50%. PCH4. Neonates often have seizures, multiple joint contractures ("arthrogryposis"), generalized clonus, and central respiratory impairment. PCH5 resembles PCH4 and has been described in one family. [from GeneReviews]

RAB18 deficiency is the molecular deficit underlying both Warburg micro syndrome (characterized by eye, nervous system, and endocrine abnormalities) and Martsolf syndrome (characterized by similar – but milder – findings). To date Warburg micro syndrome comprises >96% of reported individuals with genetically defined RAB18 deficiency. The hallmark ophthalmologic findings are bilateral congenital cataracts, usually accompanied by microphthalmia, microcornea (diameter <10), and small atonic pupils. Poor vision despite early cataract surgery likely results from progressive optic atrophy and cortical visual impairment. Individuals with Warburg micro syndrome have severe to profound intellectual disability (ID); those with Martsolf syndrome have mild to moderate ID. Some individuals with RAB18 deficiency also have epilepsy. In Warburg micro syndrome, a progressive ascending spastic paraplegia typically begins with spastic diplegia and contractures during the first year, followed by upper-limb involvement leading to spastic quadriplegia after about age five years, often eventually causing breathing difficulties. In Martsolf syndrome infantile hypotonia is followed primarily by slowly progressive lower-limb spasticity. Hypogonadism – when present – manifests in both syndromes, in males as micropenis and/or cryptorchidism and in females as hypoplastic labia minora, clitoral hypoplasia, and small introitus. [from GeneReviews]

Acute infantile GM2 activator deficiency is a neurodegenerative disorder in which infants, who are generally normal at birth, have progressive weakness and slowing of developmental progress between ages four and 12 months. An ensuing developmental plateau is followed by progressively rapid developmental regression. By the second year of life decerebrate posturing, difficulty in swallowing, and worsening seizures lead to an unresponsive vegetative state. Death usually occurs between ages two and three years. [from GeneReviews]

D-2-hydroxyglutaric aciduria is a neurometabolic disorder first described by Chalmers et al. (1980). Clinical symptoms include developmental delay, epilepsy, hypotonia, and dysmorphic features. Mild and severe phenotypes were characterized (van der Knaap et al., 1999). The severe phenotype is homogeneous and is characterized by early infantile-onset epileptic encephalopathy and, often, cardiomyopathy. The mild phenotype has a more variable clinical presentation. Genetic Heterogeneity of D-2-Hydroxyglutaric Aciduria D-2-hydroxyglutaric aciduria-2 (D2HGA2; 613657) is caused by heterozygous mutation in the mitochondrial isocitrate dehydrogenase-2 gene (IDH2; 147650) on chromosome 15q26. [from OMIM]

GRIN2B-related neurodevelopmental disorder is characterized by mild to profound developmental delay / intellectual disability (DD/ID) in all affected individuals. Muscle tone abnormalities (spasticity and/or hypotonia, occasionally associated with feeding difficulties), as well as epilepsy and autism spectrum disorder (ASD) / behavioral issues, are common. Other infantile- or childhood-onset findings include microcephaly; dystonic, dyskinetic, or choreiform movement disorder; and/or cortical visual impairment. Brain MRI reveals a malformation of cortical development in a minority of affected individuals. To date, fewer than 100 individuals with GRIN2B-related neurodevelopmental disorder have been reported. [from GeneReviews]

Mutations in the KCTD7 gene cause a severe neurodegenerative phenotype characterized by onset of intractable myoclonic seizures before age 2 years and accompanied by developmental regression. The initial description was consistent with a form of progressive myoclonic epilepsy (designated here as EPM3), whereas a later report identified intracellular accumulation of autofluorescent lipopigment storage material, consistent with neuronal ceroid lipofuscinosis (designated CLN14). Ultrastructural findings on skin biopsies thus appear to be variable. However, clinical features are generally consistent between reports (summary by Staropoli et al., 2012). For a general phenotypic description and a discussion of genetic heterogeneity of progressive myoclonic epilepsy, see EPM1A (254800). For a general phenotypic description and a discussion of genetic heterogeneity of neuronal ceroid lipofuscinosis, see CLN1 (256730). [from OMIM]

Developmental and epileptic encephalopathy-24 (DEE24) is a neurologic disorder characterized by onset of refractory seizures in infancy, severely impaired global development, intellectual disability, and behavioral abnormalities. Most patients have onset of variable types of seizures between 4 and 13 months of age, but earlier onset in the first days of life has also been reported. Seizures are often triggered by fever, at least initially; status epilepticus may occur (summary by Nava et al., 2014 and Marini et al., 2018). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350. [from OMIM]

GRIN1-related neurodevelopmental disorder (GRIN1-NDD) is characterized by mild-to-profound developmental delay / intellectual disability (DD/ID) in all affected individuals. Other common manifestations are epilepsy, muscular hypotonia, movement disorders, spasticity, feeding difficulties, and behavior problems. A subset of individuals show a malformation of cortical development consisting of extensive and diffuse bilateral polymicrogyria. To date, 72 individuals with GRIN1-NDD have been reported. [from GeneReviews]

Kohlschutter-Tonz syndrome (KTZS) is an autosomal recessive disorder characterized by severe global developmental delay, early-onset intractable seizures, spasticity, and amelogenesis imperfecta affecting both primary and secondary teeth and causing yellow or brown discoloration of the teeth. Although the phenotype is consistent, there is variability. Impaired intellectual development is related to the severity of seizures, and the disorder can thus be considered an epileptic encephalopathy. Some infants show normal development until seizure onset, whereas others are delayed from birth. The most severely affected individuals have profound mental retardation, never acquire speech, and become bedridden early in life (summary by Schossig et al., 2012 and Mory et al., 2012). See also Kohlschutter-Tonz syndrome-like (KTZSL; 619229), caused by heterozygous mutation in the SATB1 gene (602075) on chromosome 3p23. [from OMIM]

Individuals with NGLY1-related congenital disorder of deglycosylation (NGLY1-CDDG) typically display a clinical tetrad of developmental delay / intellectual disability in the mild to profound range, hypo- or alacrima, elevated liver transaminases that may spontaneously resolve in childhood, and a complex hyperkinetic movement disorder that can include choreiform, athetoid, dystonic, myoclonic, action tremor, and dysmetric movements. About half of affected individuals will develop clinical seizures. Other findings may include obstructive and/or central sleep apnea, oral motor defects that affect feeding ability, auditory neuropathy, constipation, scoliosis, and peripheral neuropathy. [from GeneReviews]

Developmental and epileptic encephalopathy-42 (DEE42) is a neurologic disorder characterized by the onset of various types of seizures in the first hours or days of life, although rare patients may have onset in the first weeks of life. The seizures tend to be refractory and associated with EEG abnormalities, including multifocal spikes and generalized spike-wave complexes. Affected infants show global developmental delay with severely impaired intellectual development. Other features may include axial hypotonia, peripheral hypertonia with hyperreflexia, tremor, ataxia, and abnormal eye movements (summary by the Epi4K Consortium, 2016). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350. [from OMIM]

The Lafora type of progressive myoclonic epilepsy is an autosomal recessive disorder characterized by insidious onset of progressive neurodegeneration between 8 and 18 years of age. Initial features can include headache, difficulties in school work, myoclonic jerks, generalized seizures, and often visual hallucination. The myoclonus, seizures, and hallucinations gradually worsen and become intractable. This is accompanied by progressive cognitive decline, resulting in dementia. About 10 years after onset, affected individuals are in near-continuous myoclonus with absence seizures, frequent generalized seizures, and profound dementia or a vegetative state. Histologic studies of multiple tissues, including brain, muscle, liver, and heart show intracellular Lafora bodies, which are dense accumulations of malformed and insoluble glycogen molecules, termed polyglucosans (review by Ramachandran et al., 2009). There is a slower progression of disease and later age at death in Lafora disease-2 than in Lafora disease-1 (MELF1, EPM2A; 254780); see Genotype/Phenotype Correlations. Myoclonic epilepsy of Lafora-1 is caused by mutation in the EPM2A gene (608072), which encodes laforin, on chromosome 6q24. For a discussion of genetic heterogeneity of progressive myoclonic epilepsy, see EPM1A (254800). [from OMIM]