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 theta(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.