The molecular mutation is a 57 bp deletion in intron 4 of the gene, which alters the splice donor site. This results in retention of the remaining 48 bp of the intron in the expressed mRNA. The insertion converts a cytosine to a guanine at nucleotide position 450 of the ORF and changes codon 150 (TAC) to a stop codon (TAG) (amino acid change: Tyr150Ter). Western blot analysis showed that no detectable protein is expressed from this allele. Because this mutation was found in ICR and CD1 it is carried in many strains, including IRD1 and IRD2.