This mutation, whose phenotype was first observed among G3 progeny of an ENU-mutagenized male mouse, has been identified as a T to C transition at nucleotide 503 of this gene, in the third of its 9 exons. This substitution is predicted to result in replacement of leucine by proline at amino acid position 168 of the standard form of the protein, which corresponds to amino acid position 443 of the long protein isoform, in the second transmembrane helix. Expression has not been analyzed.