Juvenile myoclonic epilepsy is a subtype of idiopathic generalized epilepsy (EIG; see 600669) affecting up to 26% of all individuals with EIG. Individuals with JME have afebrile seizures only, with onset in adolescence of myoclonic jerks. Myoclonic jerks ... Juvenile myoclonic epilepsy is a subtype of idiopathic generalized epilepsy (EIG; see 600669) affecting up to 26% of all individuals with EIG. Individuals with JME have afebrile seizures only, with onset in adolescence of myoclonic jerks. Myoclonic jerks occur usually 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-q35; EJM6 (see 607682), by variation in the CACNB4 gene (601949) on 2q22-q23; EJM7 (see 613060), by variation in the GABRD gene (137163) on 1p36; and EJM8 (see 607628), by variation in the CLCN2 gene (600570) on 3q26. 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.
Dreifuss (1989) gave a clinical review. He reported the case of a young college woman who sought medical treatment after experiencing her first generalized convulsive seizure, which occurred after a period of sleep deprivation and alcohol consumption. She ... Dreifuss (1989) gave a clinical review. He reported the case of a young college woman who sought medical treatment after experiencing her first generalized convulsive seizure, which occurred after a period of sleep deprivation and alcohol consumption. She had recalled occasional myoclonic jerks when she awoke in the morning. The ictal EEG shows a typical 4- to 6-Hz multispike and wave complex; the interictal EEG may be normal. Valproate controls seizures in most JME patients. JME is said to account for between 5.4 and 10.2% of epilepsy, but despite clinical and EEG features that should enable its easy identification, the rate of misdiagnosis remains high (Grunewald et al., 1992). Liu et al. (1995) stated that juvenile myoclonic epilepsy is the most frequent form of hereditary grand mal epilepsy. In the EEG, 15- to 30-Hz multispikes are associated with myoclonic and tonic-clonic convulsions beginning at 8 to 20 years of age. Moreover, EEG 3.5- to 6-Hz multispike wave complexes appear in clinically asymptomatic family members. Medina et al. (2008) reported a 4-generation family from Honduras in which 4 individuals had clinical features of juvenile myoclonic epilepsy. The proband had childhood absence epilepsy (see, e.g., ECA1; 600131) evolving to JME, and his sister had JME. Two affected relatives had febrile seizures and grand mal seizures, respectively. Seven additional family members with the mutation were clinically asymptomatic but had epileptiform-EEG patterns consisting of spontaneous and frequent 3 to 6-Hz diffuse and bilateral multispike wave complexes or bifrontal 5 to 7-Hz spikes. Camfield and Camfield (2009) performed a questionnaire-based review of 23 patients with JME after a mean disease duration of 25.8 years. The mean age at onset of first seizure was 10.4 years. All patients had myoclonic and generalized tonic-clonic seizures, and 14 (60%) had a history of absence seizures. At the time of follow-up, 11 (48%) had discontinued antiepileptic medication: 6 were seizure-free, 3 had myoclonic seizures only, and 2 continued to have rare seizures. Status epilepticus occurred in 8 (36%) and intractable epilepsy in 3. About 65 to 77% reported they were 'very satisfied' with work, health, friendships, and social life, but 17 (74%) of 23 had at least 1 major unfavorable social outcome, such as unemployment, living alone, or unplanned pregnancy.
In affected members of 6 unrelated families with juvenile myoclonic epilepsy, Suzuki et al. (2004) identified several heterozygous mutations in the EFHC1 gene (608815.0001-608815.0005). Several unaffected family members carried mutations, indicating reduced penetrance. The affected families included the ... In affected members of 6 unrelated families with juvenile myoclonic epilepsy, Suzuki et al. (2004) identified several heterozygous mutations in the EFHC1 gene (608815.0001-608815.0005). Several unaffected family members carried mutations, indicating reduced penetrance. The affected families included the Belize kindred reported by Liu et al. (1995) and several of the Mexican families reported by Bai et al. (2002). Medina et al. (2008) identified 5 novel mutations in transcripts A and B of the EFHC1 gene (see, e.g., 608815.0008) in 4 (9%) of 44 Hispanic patients from Mexico and Honduras and in 2 (3%) of 67 Japanese patients with juvenile myoclonic epilepsy. Clinically unaffected mutation carriers had abnormal EEG patterns.