CRISPR/Cas9 technology generated a T to G change resulting in a serine to alanine substitution at amino acid 637 (S637A) in the RS (arginine-serine) domain. Western blot analysis shows that phosphorylation at this site is dramatically reduced in heterozygotes and almost undetectable in homozygous mice and also that protein level is elevated in both heterozygotes and homozygotes compared to levels in wild-type mice. This corresponds to the human S635A mutation identified in patients with dilated cardiomyopathy.