This mutation, discovered by its visible phenotype among the G3 progeny of an ENU mutagenized male mouse, comprises a C to A transversion at nucleotide position 1866 (Genbank: NM_177431), in the eleventh of the gene's 39 exons. It replaces a codon specifying serine at amino acid position 566 with a termination codon (S566Ter), truncating the encoded protein by 1340 amino acids at its C terminus.