This mutation was identified by IgM+ B-cell proliferation and flow cytometry screening of progeny of an ENU treated mouse. The mutation is an A to T substitution at nucleotide position 925 of the cDNA sequence (NCBI m37, Ensembl build 62), in a region corresponding to exon 5 of the gene. It results in replacement of aspartic acid by valine at amino acid position 215 of the protein.