Exon 21 was replaced with a loxP site and a modified exon in which nucleotide substitutions (CGG to TGA) result in the amino acid substitution of a stop codon for arginine, mimicking a mutation found in human severe myoclonic epilepsy in infancy (SMEI) patients. Flp-mediated recombination removed an FRT-flanked neomycin resistance cassette with a 3' loxP site inserted downstream of exon 23 and left the modified exon 21 through exon 23 floxed. Absence of protein product was confirmed by western blot analysis using C-terminal and N-terminal anti-Nav1.1 antibodies. (J:121969)