In a chemical mutagenesis screen, we identified the novel Scn8a8J allele of the gene encoding the neuronal voltage-gated sodium channel Na v 1.6. The missense mutation V929F in this allele alters an evolutionarily conserved residue in the pore loop of domain 2 of Na v 1.6. Electroencephalography (EEG) revealed well-defined spike-wave discharges (SWD), the hallmark of absence epilepsy, in Scn8a8J heterozygotes and in heterozygotes for two classical Scn8a alleles, Scn8amed (null) and Scn8amed-jo (missense). Mouse strain background had a significant effect on SWD, with mutants on the C3HeB/FeJ strain showing a higher incidence than on C57BL/6J. The abnormal EEG patterns in heterozygous mutant mice and the influence of genetic background on SWD make SCN8A an attractive candidate gene for common human absence epilepsy, a genetically complex disorder.

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