The mutation is an intracisternal A-particle (IAP) retrotransposon insertion into a C3H/HeSnJ genomic region. The IAP is inserted into intron 2 of the gene and disrupts the normal splicing of the mRNA transcribed from this gene. Resulting in-frame stop codons from the insertion of IAP sequences resulted in severely reduced protein levels in mutant tissues. The retrotransposition of this IAP is a recent event occurring during, or after, the establishment of the C3H/HeSn substrain. (J:218443)