MedGen

FBXL4-related encephalomyopathic mitochondrial DNA (mtDNA) depletion syndrome is a multi-system disorder characterized primarily by congenital or early-onset lactic acidosis and growth failure, feeding difficulty, hypotonia, and developmental delay. Other neurologic manifestations can include seizures, movement disorders, ataxia, autonomic dysfunction, and stroke-like episodes. All affected individuals alive at the time they were reported (median age: 3.5 years) demonstrated significant developmental delay. Other findings can involve the heart (hypertrophic cardiomyopathy, congenital heart malformations, arrhythmias), liver (mildly elevated transaminases), eyes (cataract, strabismus, nystagmus, optic atrophy), hearing (sensorineural hearing loss), and bone marrow (neutropenia, lymphopenia). Survival varies; the median age of reported deaths was two years (range 2 days – 75 months), although surviving individuals as old as 36 years have been reported. To date FBXL4-related mtDNA depletion syndrome has been reported in 50 individuals. [from GeneReviews]

Developmental and epileptic encephalopathy-9 (DEE9) is an X-linked disorder characterized by seizure onset in infancy and mild to severe intellectual impairment. Autistic and psychiatric features have been reported in some individuals. The disorder affects heterozygous females only; transmitting males are unaffected (summary by Jamal et al., 2010). For a general phenotypic description and a discussion of genetic heterogeneity of developmental and epileptic encephalopathy, see 308350. [from OMIM]

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. [from GeneReviews]

Pontocerebellar hypoplasia type 2E (PCH2E) is an autosomal recessive neurodegenerative disorder characterized by profoundly impaired intellectual development, progressive microcephaly, spasticity, and early-onset epilepsy (summary by Feinstein et al., 2014). For a general phenotypic description and a discussion of genetic heterogeneity of pontocerebellar hypoplasia type 2, see PCH2A (277470). [from OMIM]

Generalized epilepsy-paroxysmal dyskinesia syndrome is characterised by the association of paroxysmal dyskinesia and generalised epilepsy (usually absence or generalised tonic-clonic seizures) in the same individual or family. The prevalence is unknown. Analysis in one of the reported families led to the identification of a causative mutation in the <i>KCNMA1</i> gene (chromosome 10q22), encoding the alpha subunit of the BK channel. Transmission is autosomal dominant. [from ORDO]

CTCF-related disorder is characterized by developmental delay / intellectual disability (ranging from mild to severe), with both speech and motor delays being common; feeding difficulties, including dysphagia, and other gastrointestinal issues (gastroesophageal reflux disease and/or irritable bowel syndrome) that can lead to growth deficiency; hypotonia; eye anomalies (strabismus and/or refractive errors); scoliosis; nonspecific dysmorphic features; sleep disturbance; tooth anomalies (crowded teeth and/or abnormal decay); and, less commonly, other congenital anomalies (cleft palate, gastrointestinal malrotation, genitourinary anomalies, and congenital heart defects, including aortic ectasia). Short stature, seizures, hearing loss, recurrent infections, microcephaly, and autistic features have also been described in a minority of affected individuals. At least four reported individuals with CTCF-related disorder developed Wilms tumor, one of whom had bilateral Wilms tumor. However, there is no clear evidence of a significant predisposition for the development of cancer in individuals with CTCF-related disorder at this time. [from GeneReviews]

Orofaciodigital syndrome V (OFD5) is an autosomal recessive disorder characterized by cleft palate/uvula, lobulated tongue, frontal bossing, hypertelorism, postaxial polydactyly, and impaired intellectual development (summary by Faily et al., 2017). [from OMIM]

Coenzyme Q10 deficiency-9 (COQ10D9) is an autosomal recessive disorder characterized by onset of cerebellar ataxia associated with cerebellar atrophy in the first decade of life. Some patients may have additional neurologic signs and symptoms, including intellectual disability and seizures. Treatment with CoQ10 may offer clinical benefit (summary by Malicdan et al., 2018). For a general phenotypic description and a discussion of genetic heterogeneity of primary coenzyme Q10 deficiency, see COQ10D1 (607426). [from OMIM]

NARS1-related neurologic disorders encompass NARS1-related neurodevelopmental disorder (NARS1-NDD), a neonatal- or childhood-onset phenotype with central nervous system and peripheral nervous system involvement, and NARS1-related hereditary neuropathy, an adolescent- or early adult-onset hereditary neuropathy. NARS1-NDD manifests with global developmental delay, intellectual disability, microcephaly, ataxia, seizures, and, rarely, neurobehavioral/psychiatric manifestations. Change in muscle tone can manifest either as spasticity or as hypotonia. Peripheral neuropathy with atrophy predominantly of the distal lower limbs can be associated. NARS1-related hereditary neuropathy manifests with mostly motor and sensory impairment involving weakness of predominantly the distal lower limbs and foot deformities, without prominent muscle atrophy. A few individuals have been described with isolated hereditary motor neuropathy associated with foot deformities, ankle contractures, kyphosis, hyperlaxity, and brisk reflexes. To date, 54 individuals from 30 families with NARS1 pathogenic variant(s) have been reported. [from GeneReviews]

Developmental and epileptic encephalopathy-89 (DEE89) is a severe autosomal recessive disorder characterized by profound global developmental delay with impaired intellectual development, absent speech, inability to sit or walk due to axial hypotonia and spastic quadriparesis, and onset of seizures in the first days or months of life. EEG shows suppression-burst pattern or hypsarrhythmia, consistent with DEE or a clinical diagnosis of West syndrome. More variable features include joint contractures with foot deformities, dysmorphic facial features with cleft palate, and omphalocele. Affected individuals have poor motor skills, poor eye contact, and lack of language development; some die in infancy or early childhood. Brain imaging may be normal or show nonspecific abnormalities (summary by Chatron et al., 2020). [from OMIM]

NARS1-related neurologic disorders encompass NARS1-related neurodevelopmental disorder (NARS1-NDD), a neonatal- or childhood-onset phenotype with central nervous system and peripheral nervous system involvement, and NARS1-related hereditary neuropathy, an adolescent- or early adult-onset hereditary neuropathy. NARS1-NDD manifests with global developmental delay, intellectual disability, microcephaly, ataxia, seizures, and, rarely, neurobehavioral/psychiatric manifestations. Change in muscle tone can manifest either as spasticity or as hypotonia. Peripheral neuropathy with atrophy predominantly of the distal lower limbs can be associated. NARS1-related hereditary neuropathy manifests with mostly motor and sensory impairment involving weakness of predominantly the distal lower limbs and foot deformities, without prominent muscle atrophy. A few individuals have been described with isolated hereditary motor neuropathy associated with foot deformities, ankle contractures, kyphosis, hyperlaxity, and brisk reflexes. To date, 54 individuals from 30 families with NARS1 pathogenic variant(s) have been reported. [from GeneReviews]

Early-onset neurodegeneration with choreoathetoid movements and microcytic anemia (NDCAMA) is an autosomal recessive disorder characterized by severe psychomotor developmental abnormalities, abnormal movements, and functional iron deficiency (Costain et al., 2019). [from OMIM]

Neurodevelopmental disorder with microcephaly, cortical malformations, and spasticity (NEDMCMS) is an autosomal recessive disorder characterized by severe to profound global developmental delay, early-onset seizures, microcephaly, and polymicrogyria and/or cerebral atrophy on brain imaging. Most affected individuals are unable to walk or speak and have profoundly impaired intellectual development, as well as axial hypotonia and peripheral spasticity. Rare individuals may be less severely affected (summary by Vandervore et al., 2019). [from OMIM]

Autosomal recessive spastic paraplegia-82 (SPG82) is a progressive neurologic disorder characterized by global developmental delay apparent from infancy, significant motor impairment, and progressive spasticity mainly affecting the lower limbs. Some patients never achieve walking, whereas others lose the ability to walk or walk with an unsteady gait. Additional features include variably impaired intellectual development with language difficulties, ocular anomalies, such as nystagmus and visual impairment, and seizures. Brain imaging shows progressive cerebral and cerebellar atrophy, as well as white matter hyperintensities. Based on the additional abnormalities, the disorder can be classified as a type of complicated SPG (summary by Vaz et al., 2019). For a discussion of genetic heterogeneity of autosomal recessive spastic paraplegia, see SPG5A (270800). [from OMIM]

Developmental and epileptic encephalopathy-79 (DEE79) is a severe neurologic disorder characterized by onset of refractory seizures in the first months of life. Affected individuals have severely impaired psychomotor development and may show hypotonia or spasticity. Brain imaging may show hypomyelination, cerebral atrophy, and thinning of the corpus callosum (summary by Butler et al., 2018 and Hernandez et al., 2019). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350. [from OMIM]

Mitochondrial complex IV deficiency nuclear type 15 (MC4DN15) is an autosomal recessive multisystem metabolic disorder characterized by the onset of symptoms in infancy. Affected individuals show global developmental delay, poor feeding, short stature with microcephaly, proximal muscle weakness, and distal spasticity. Other manifestations include scoliosis, primary pulmonary hypertension, childhood-onset refractory seizures, and inability to walk. Brain imaging shows features consistent with Leigh syndrome (see 256000) and enlarged ventricles. Laboratory studies show increased serum and CSF lactate, as well as decreased levels and activity of mitochondrial respiratory complex IV (summary by Hallmann et al., 2016). For a discussion of genetic heterogeneity of mitochondrial complex IV (cytochrome c oxidase) deficiency, see 220110. [from OMIM]

Developmental and epileptic encephalopathy-108 (DEE108) is characterized by the onset of multiple types of seizures in the first 2 years of life. Affected individuals often have normal early development before the onset of seizures, after which they show developmental regression with loss of skills, particularly language; most are nonverbal or speak only a few words. Other features included mildly delayed walking, unsteady gait, hypotonia, and behavioral abnormalities, such as ADHD or autism (Spinelli et al., 2021). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350. [from OMIM]

Jeffries-Lakhani neurodevelopmental syndrome (JELANS) is an autosomal recessive disorder characterized by hypotonia, early-onset seizures, and global developmental delay apparent from infancy. Affected individuals have motor delay, speech delay, and impaired intellectual development, and about half of patients are nonambulatory and/or nonverbal. Some patients have cardiac arrhythmia, but congenital cardiac septal defects are only rarely observed. Additional features may include feeding difficulties, recurrent infections, ocular defects, and nonspecific dysmorphic features. Premature death due to cardiac arrhythmia or epilepsy may occur (Jeffries et al., 2024). [from OMIM]

Neurodevelopmental disorder with hypotonia and characteristic brain abnormalities (NEDHBA) is an autosomal recessive disorder characterized by impaired intellectual development with striking radiologic abnormalities of the lateral ventricles (Fasham et al., 2023). [from OMIM]

Neurodevelopmental disorder with microcephaly, seizures, and brain atrophy (NEDMISB) is an autosomal recessive disorder characterized by severe global developmental delay, developmental regression with loss of milestones, severe microcephaly, and brain abnormalities, primarily cerebral atrophy and hypoplasia of the corpus callosum. Affected individuals develop seizures in the first year of life; eventually they are unable to sit, feed, or communicate, and may be unresponsive to stimuli. Other features include muscle weakness, spasticity with hyperreflexia, irritability, and contractures (Coulter et al., 2020). [from OMIM]