Exon 26 was replaced with an frt flanked neo cassette and a modified exon 26 in which nucleotide substitution results in the amino acid substitution of histidine for arginine at position 1648 (R1648H), mimicking a mutation found in human generalized epilepsy with febrile seizures plus (GEFS+) patients. Flp mediated recombination removed the neo cassette.