Clinical and Genetic Analysis of a Large Pedigree with Juvenile Myoclonic Epilepsy.

Juvenile myoclonic epilepsy is a common type of idiopathic generalized epilepsy characterized by myoclonic, generalized tonic‐clonic, and in 30% of patients, absence seizures. We studied a three‐generation pedigree of 33 members, 10 of whom were clinically affected with juvenile myoclonic epilepsy or presented with subclinical electroencephalographic (EEG) 3.5‐ to 6.0‐Hz diffuse polyspike‐wave or spike‐wave complexes. Juvenile myoclonic epilepsy and the EEG trait segregated as an autosomal dominant trait with 70% penetrance. Linkage analysis using this model showed significant linkage to four microsatellite markers centromeric to human leukocyte antigen (HLA) in chromosome 6p. Maximum lod scores of 3.43 at θ m=f = 0.00 for D6S272, D6S466, D6S257, and D6S402 were obtained. Recombinant events in 2 affected members defined the gene region to a 43‐cM interval flanked by D6S258 (HLA region) and D6S313 (centromere). Our results in this large family provide evidence that a gene responsible for juvenile myoclonic epilepsy and the subclinical, 3.5‐ to 6.0‐Hz, polyspike‐wave or spike‐wave EEG pattern is located in chromosome 6p.