Positional candidate approach for the gene responsible for benign adult familial myoclonic epilepsy.

Benign adult familial myoclonic epilepsy (BAFME) is an autosomal dominant idiopathic epileptic syndrome characterized by adult-onset tremulous finger movement, myoclonus, epileptic seizures, and nonprogressive course, recognized in Japanese families. We recently assigned the gene locus to chromosome 8q23.3-q24.11 by linkage analysis. In this study, we identified the sequence of human cDNA encoding Kv8.1, a neuronal modulatory alpha-subunit of the voltage-gated potassium channel, mapped to human chromosome 8q22.3-8q24.1. Human Kv8.1 cDNA had a 1,500-nucleotide open reading frame encoding a polypeptide of 500 amino acids, in which six hydrophobic transmembrane segments were well conserved, and its overall amino acids homology as compared with those of rat and golden hamster was 95.0% and 95.0%. Tissue-distribution analysis by reverse transcription-polymerase chain reaction (RT-PCR) showed the presence of the Kv 8.1 transcript exclusively in the brain. The analysis of the genomic organization of the human gene revealed consistency of three exons interrupted by two introns each of 1.2 and 3.5 kb. We analyzed the genomic sequence of the patients with BAFME and found no change in the pathogenesis of the disease.