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.

Childhood absence epilepsy (CAE, ECA), a subtype of idiopathic generalized epilepsy (EIG; 600669), is characterized by a sudden and brief impairment of consciousness that is accompanied by a generalized, synchronous, bilateral, 2.5- to 4-Hz spike and slow-wave discharge (SWD) on EEG. Seizure onset occurs between 3 and 8 years of age and seizures generally occur multiple times per day. About 70% of patients experience spontaneous remission of seizures, often around adolescence. There are no structural neuropathologic findings in patients with ECA (Crunelli and Leresche, 2002). Genetic Heterogeneity of Susceptibility to Childhood Absence Epilepsy The ECA1 locus has been mapped to chromosome 8q24; see also EIG1 (see 600669), which also maps to 8q24. Susceptibility to the development of childhood absence epilepsy may be conferred by variation in several genes: ECA2 (see 607681), conferred by variation in the GABRG2 gene (137164) on chromosome 5q31.1; ECA4 (611136), conferred by variation in the GABRA1 gene (137160) on chromosome 5q34; ECA5 (612269), conferred by variation in the GABRB3 gene (137192) on chromosome 15q12; and ECA6 (see 611942), conferred by variation in the CACNA1H gene (607904) on chromosome 16p13. See EIG11 (607628) for discussion of a locus previously designated ECA3 on chromosome 3q26.

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.

Juvenile absence epilepsy is a subtype of idiopathic generalized epilepsy (IGE; see 600669). Manifestations occur around puberty, in contrast to childhood absence epilepsy (CAE; 600131), which begins at age 6 to 7 years. Absence seizures, generalized tonic-clonic seizures (GTCS), GTCS on awakening, and myoclonic seizures are the main features of JAE. (Commission on Classification and Terminology of the International League Against Epilepsy, 1989). Genetic Heterogeneity of Juvenile Absence Epilepsy See also susceptibility to juvenile absence epilepsy-2 (EJA2; see 607628), conferred by variation in the CLCN2 gene (600570) on chromosome 3q26.

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.

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.