A G-to-T transversion at coding cDNA nucleotide 4189 (c.4189G>T in GenBank NM_007578) leads to an arginine-to-leucine substitution at amino acid position 1303 (p.R1303L), in the highly conserved, positively charged transmembrane segment S4 of repeat III of the encoded protein. Levels of transcript and protein encoded by the gene are similar in brains of mutant and wild-type mice.