Juvenile myoclonic epilepsy (EJM, JME) is a subtype of idiopathic generalized epilepsy (EIG; see 600669), affecting up to 26% of all individuals with EIG. Individuals with EJM have afebrile seizures only, with onset in adolescence of myoclonic jerks. Myoclonic jerks usually occur in the morning (Janz and Durner, 1997). Genetic Heterogeneity of Juvenile Myoclonic Seizures Susceptibility to EJM can be conferred by variation in several other genes: EJM5 (611136), by variation in the GABRA1 gene (137160) on 5q34; EJM6 (see 607682), by variation in the CACNB4 gene (601949) on 2q23; EJM8 (see 607628), by variation in the CLCN2 gene (600570) on 3q27; and EJM10 (617924), by variation in the ICK gene (612325) on chromosome 6p12. In addition, EJM loci have been identified by linkage analysis: EJM2 (see 604827) on 15q14, EJM3 (608816) on 6p21, EJM4 (611364) on 5q12-q14, and EJM9 (614280) on 2q33-q36. EJM7 (see 613060) was thought to be caused by variation in the GABRD gene (137163.0002) on 1p36, but the variant was reclassified as a polymorphism.

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.