Exons 14 and 15, encoding most of the C2C domain of the protein, have been deleted. RT-PCR analysis of cochleae of homozygous mutant mice confirmed the presence of an mRNA lacking the sequence encoded by the deleted exons. Translation of this mRNA would be frame-shifted, leading to a premature termination codon; absence of the expected truncated protein in homozygous mutant cochleae was demonstrated by immunohistolabeling and immunoblot analysis.