The masquerade phenotype was discovered among G3 progeny of an ENU mutagenized male mouse. The mutation comprises a G to A transition at nucleotide position 2557 (Genbank: NM_027902), in the last of the gene's 18 exons, that results in substitution of a termination codon for one encoding tryptophan at amino acid position 783 (W783Ter). This truncates the protein by 29 amino acids at its C terminus, near the end of its serine protease domain and outside of the catalytic site. (J:143779)