MedGen

Any generalized epilepsy in which the cause of the disease is a mutation in the CASR gene. [from MONDO]

Both juvenile myoclonic epilepsy and juvenile absence epilepsy are subtypes of idiopathic generalized epilepsy (EIG). For a general phenotypic description and a discussion of genetic heterogeneity of these disorders, see EIG1 (600669), EJM1 (254770), and EJA1 (607631). [from OMIM]

Progressive myoclonic epilepsy type 1(EPM1) is a neurodegenerative disorder characterized by onset from age six to 15 years, stimulus-sensitive myoclonus, and tonic-clonic epileptic seizures. Some years after the onset, ataxia, incoordination, intentional tremor, and dysarthria develop. Individuals with EPM1 are cognitively mostly within the normal range, but show emotional lability and depression. The epileptic seizures are usually well controlled by anti-seizure medication, but the myoclonic jerks are progressive, action activated, and treatment resistant, and can be severely disabling. [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]

For a general phenotypic description and a discussion of genetic heterogeneity of idiopathic generalized epilepsy, see 600669. Juvenile myoclonic epilepsy is a subtype of idiopathic generalized epilepsy; see 254770 for a general phenotypic description and a discussion of genetic heterogeneity of JME. [from OMIM]

EZH2-related overgrowth includes EZH2-related Weaver syndrome at one end of the spectrum and tall stature at the other. Although most individuals diagnosed with a heterozygous EZH2 pathogenic variant have been identified because of a clinical suspicion of Weaver syndrome, a minority have been identified through molecular genetic testing of family members of probands or individuals with overgrowth who did not have a clinical diagnosis of Weaver syndrome. Thus, the extent of the phenotypic spectrum associated with a heterozygous EZH2 pathogenic variant is not yet known. Weaver syndrome is characterized by tall stature, variable intellect (ranging from normal intellect to severe intellectual disability), characteristic facial appearance, and a range of associated clinical features including advanced bone age, poor coordination, soft doughy skin, camptodactyly of the fingers and/or toes, umbilical hernia, abnormal tone, and hoarse low cry in infancy. Brain MRI has identified abnormalities in a few individuals with EZH2-related overgrowth. Neuroblastoma occurs at a slightly increased frequency in individuals with a heterozygous EZH2 pathogenic variant but data are insufficient to determine absolute risk. There is currently no evidence that additional malignancies (including hematologic malignancies) occur with increased frequency. [from GeneReviews]

Succinic semialdehyde dehydrogenase (SSADH) deficiency is characterized by infantile-onset hypotonia, developmental delay, cognitive impairment, expressive language deficit, and mild ataxia. Epilepsy is present in about half of affected individuals and is more common in adults. Hyperkinetic behavior, aggression, self-injurious behaviors, hallucinations, and sleep disturbances have been reported in nearly half of all affected individuals, more commonly in those who are older. Basal ganglia signs including choreoathetosis, dystonia, and myoclonus have been reported in a few individuals with earlier-onset, more severe disease. Involvement beyond the central nervous system has not been described. Individuals with SSADH deficiency typically have 4-hydroxybutyric aciduria present on urine organic acid analysis. Head MRI reveals T2 hyperintensities in multiple regions, involving the globus pallidi, cerebellar dentate nuclei, subthalamic nuclei, subcortical white matter, and brain stem, as well as cerebral and sometimes cerebellar atrophy. EEG findings include background slowing and spike discharges that are usually generalized. [from GeneReviews]

MECP2 duplication syndrome is a severe neurodevelopmental disorder characterized by early-onset hypotonia, feeding difficulty, gastrointestinal manifestations including gastroesophageal reflux and constipation, delayed psychomotor development leading to severe intellectual disability, poor speech development, progressive spasticity, recurrent respiratory infections (in ~75% of affected individuals), and seizures (in ~50%). MECP2 duplication syndrome is 100% penetrant in males. Occasionally females have been described with a MECP2 duplication and a range of findings from mild intellectual disability to a phenotype similar to that seen in males. In addition to the core features, autistic behaviors, nonspecific neuroradiologic findings on brain MRI, mottled skin, and urogenital anomalies have been observed in several affected boys. [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]

Childhood absence epilepsy is a condition characterized by recurrent seizures (epilepsy). This condition begins in childhood, usually between ages 3 and 8. Affected children have absence seizures (also known as petit mal seizures), which are brief episodes of impaired consciousness that look like staring spells. During seizures, children are not aware of and do not respond to people or activities around them. The seizures usually last several seconds and they occur often, up to 200 times each day.

Some affected individuals have febrile seizures before they develop childhood absence epilepsy. Febrile seizures are involuntary muscle contractions (convulsions) brought on by a high body temperature (fever).

In most people with childhood absence epilepsy, the absence seizures disappear in adolescence. However, some affected individuals continue to have absence seizures into adulthood, or they may develop generalized tonic-clonic seizures, which cause muscle rigidity, convulsions, and loss of consciousness, or myoclonic seizures, which are characterized by rapid, uncontrolled muscle jerks. [from MedlinePlus Genetics]

CHD2-related neurodevelopmental disorders are characterized by early-onset epileptic encephalopathy (i.e., refractory seizures and cognitive slowing or regression associated with frequent ongoing epileptiform activity). Seizure onset is typically between ages six months and four years. Seizure types typically include drop attacks, myoclonus, and rapid onset of multiple seizure types associated with generalized spike-wave on EEG, atonic-myoclonic-absence seizures, and clinical photosensitivity. Intellectual disability and/or autism spectrum disorders are common. [from GeneReviews]

SCN8A-related epilepsy with encephalopathy is characterized by developmental delay, seizure onset in the first 18 months of life (mean 4 months), and intractable epilepsy characterized by multiple seizure types (generalized tonic-clonic seizures, infantile spasms, and absence and focal seizures). Epilepsy syndromes can include Lennox-Gastaut syndrome, West syndrome, and epileptic encephalopathies (e.g., Dravet syndrome). Hypotonia and movement disorders including dystonia, ataxia, and choreoathetosis are common. Psychomotor development varies from normal prior to seizure onset (with subsequent slowing or regression after seizure onset) to abnormal from birth. Intellectual disability, present in all, ranges from mild to severe (in ~50% of affected individuals). Autistic features are noted in some. Sudden unexpected death in epilepsy (SUDEP) of unknown cause has been reported in approximately 10% of published cases. To date SCN8A-related epilepsy with encephalopathy has been reported in the literature in about 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]

Mutations in the GABRG2 gene cause a spectrum of seizure disorders, ranging from early-onset isolated febrile seizures (FS) to childhood absence epilepsy (CAE) to generalized epilepsy with febrile seizures plus, type 3 (GEFS+3), which tends to represent a more severe phenotype. Patients with isolated febrile seizures usually have onset in the first year of life and show spontaneous remission by age 6 years. Many of these patients may later develop absence seizures, which may also spontaneously remit, whereas a few may continue to have various types of febrile and afebrile seizures that persist beyond childhood, consistent with GEFS+. There is phenotypic variability in the seizure type, even within a family carrying the same mutation, suggesting that other loci may be involved (summary by Singh et al., 1999 and Marini et al., 2003). For a phenotypic description and a discussion of genetic heterogeneity of familial febrile seizures, see 121210. For a general phenotypic description and a discussion of genetic heterogeneity of GEFS+, see 604233. For a phenotypic description and discussion of genetic heterogeneity of childhood absence epilepsy, see 600131. [from OMIM]

Idiopathic generalized epilepsy (EIG) is a broad term that encompasses several common seizure phenotypes, classically including childhood absence epilepsy (CAE, ECA), juvenile absence epilepsy (JAE), and juvenile myoclonic epilepsy (JME, EJM) (Commission on Classification and Terminology of the International League Against Epilepsy, 1989). Generalized epilepsy with febrile seizures plus (GEFS+) shows phenotypic overlap with IGE, and includes patients with early-onset febrile seizures who later develop various types of febrile and afebrile seizures, such as those observed in EIG (summary by Singh et al., 1999). For a general phenotypic description and a discussion of genetic heterogeneity of EIG, see 600669. For a general phenotypic description and a discussion of genetic heterogeneity of GEFS+, see 604233. For a general phenotypic description and a discussion of genetic heterogeneity of EJM, see 254770. [from OMIM]

Generalized epilepsy with febrile seizures plus type 1 (GEFSP1) is an autosomal dominant neurologic disorder characterized by onset of seizures associated with fever in infancy or early childhood. There is wide phenotypic variability, even within families. In contrast to classic febrile seizures (see, e.g., FEB1, 121210), which affect approximately 3% of children under 6 years of age and typically spontaneously remit by age 6 years, patients with GEFSP1 either have febrile seizures extending beyond age 6 years or develop epilepsy with afebrile seizures. Other seizure types include absence seizures, partial seizures, myoclonic seizures, and atonic seizures. Some patients may have developmental delay after the onset of seizures (summary by Wallace et al., 1998 and Singh et al., 1999). Deprez et al. (2009) reviewed the genetics of epilepsy syndromes starting in the first year of life, and included a diagnostic algorithm. Genetic Heterogeneity of GEFS+ GEFS+ is a genetically heterogeneous disorder. See also GEFS+2 (604403), caused by mutation in the SCN1A gene (182389) on chromosome 2q24; GEFS+3 (see 607681), caused by mutation in the GABRG2 gene (137164) on chromosome 5q34; GEFS+5 (613060), associated with variation in the GABRD (137163) gene on chromosome 1p36; GEFS+9 (616172), caused by mutation in the STX1B gene (601485) on chromosome 16p11; GEFS+10 (618482), caused by mutation in the HCN1 gene (602780) on chromosome 5p12; GEFS+11 (602477), caused by mutation in the HCN2 gene (602781) on chromosome 19p13; and GEFS+12 (620755), caused by mutation in the SLC32A1 gene (616440) on chromosome 20q11. Several putative loci have also been identified; see GEFS+4 (609800), mapped to chromosome 2p24; GEFS+6 (612279), mapped to chromosome 8p23-p21; GEFS+7 (613863), mapped to chromosome 2q24; and GEFS+8 (613828), mapped to chromosome 6q16.3-q22.31. [from OMIM]

The 1q21.1 recurrent microdeletion itself does not appear to lead to a clinically recognizable syndrome as some persons with the deletion have no obvious clinical findings and others have variable findings that most commonly include microcephaly (50%), mild intellectual disability (30%), mildly dysmorphic facial features, and eye abnormalities (26%). Other findings can include cardiac defects, genitourinary anomalies, skeletal malformations, and seizures (~15%). Psychiatric and behavioral abnormalities can include autism spectrum disorders, attention deficit hyperactivity disorder, autistic features, and sleep disturbances. [from GeneReviews]

Idiopathic generalized epilepsy is a broad term that encompasses several common seizure phenotypes, classically including childhood absence epilepsy (CAE, ECA; see 600131), juvenile absence epilepsy (JAE, EJA; see 607631), juvenile myoclonic epilepsy (JME, EJM; see 254770), and epilepsy with grand mal seizures on awakening (Commission on Classification and Terminology of the International League Against Epilepsy, 1989). These recurrent seizures occur in the absence of detectable brain lesions and/or metabolic abnormalities. Seizures are initially generalized with a bilateral, synchronous, generalized, symmetrical EEG discharge (Zara et al., 1995; Lu and Wang, 2009). See also childhood absence epilepsy (ECA1; 600131), which has also been mapped to 8q24. Of note, benign neonatal epilepsy 2 (EBN2; 121201) is caused by mutation in the KCNQ3 gene (602232) on 8q24. Genetic Heterogeneity of Idiopathic Generalized Epilepsy EIG1 has been mapped to chromosome 8q24. Other loci or genes associated with EIG include EIG2 (606972) on 14q23; EIG3 (608762) on 9q32; EIG4 (609750) on 10q25; EIG5 (611934) on 10p11; EIG6 (611942), caused by mutation in the CACNA1H gene (607904) on 16p; EIG7 (604827) on 15q14; EIG8 (612899), caused by mutation in the CASR gene (601199) on 3q13.3-q21; EIG9 (607682), caused by mutation in the CACNB4 gene (601949) on 2q23; EIG10 (613060), caused by mutation in the GABRD gene (137163) on 1p36; EIG11 (607628), caused by variation in the CLCN2 gene (600570) on 3q36; EIG12 (614847), caused by mutation in the SLC2A1 gene (138140) on 1p34; EIG13 (611136), caused by mutation in the GABRA1 gene (137160) on 5q34; EIG14 (616685), caused by mutation in the SLC12A5 gene (606726) on 20q12; EIG15 (618357), caused by mutation in the RORB gene (601972) on 9q22; EIG16 (618596), caused by mutation in the KCNMA1 gene (600150) on chromosome 10q22; EIG17 (602477), caused by mutation in the HCN2 gene (602781) on chromosome 19p13.3; and EIG18 (619521) caused by mutation in the HCN4 gene (605206) on chromosome 15q24. [from OMIM]

Patients with isolated febrile seizures (FEB3B) usually have onset between ages 5 months to 4 years and show spontaneous remission by age 6 years (summary by Singh et al., 2009), whereas patients with GEFS+ continue to have various types of febrile and afebrile seizures later in life (summary by Singh et al., 1999). For a general phenotypic description and a discussion of genetic heterogeneity of GEFS+, see 604233. For a phenotypic description and a discussion of genetic heterogeneity of familial febrile seizures, see 121210. [from OMIM]