The targeting vector was designed to insert a mutation (Q526X) into exon 10. A floxed neo cassette was inserted into exon 10 and was removed via cre-mediated recombination. This mutation is homologous to the nonsense autosomal dominant mutation Q529X in humans with familial restrictive cardiomyopathy. Homozygous mutant mice show impaired mRNA transcription in heart and skeletal muscle relative to wild-type and heterozygous littermates. Western blotting confirmed that no full-length or truncated protein is detectable in skeletal muscle from homozygous mutant mice.