A neomycin resistance cassette replaced approximately 1.3 kb of sequence, including exon 14. RT-PCR analysis of muscle using primers in exons 13 and 15 detected a low level of a truncated transcript in homozygous mutant mice, whereas RT-PCR studies using primers in exons 13 and 14 did not detect transcript in these mice. Western blot analysis of liver did not detect protein in homozygous mutant mice. (J:76435)