This mutation was identified phenotypically in a screen of progeny of ENU-treated mice via MRI examinaton of 15.5 days post-coitum embryos for cardiac malformations. The mutation comprises a T-to-C transition in exon 11 of the gene, resulting in substitution of arginine for cysteine at amino acid position 470 of both isoforms of the protein (C470R). This eliminates a disulfide bond in the P domain, which prevents the protein's export from the endoplasmic reticulum and destroys its proprotein convertase activity.