MYH7 is a gene encoding a myosin heavy chain beta (MHC-β) isoform (slow twitch) expressed primarily in the heart, but also in skeletal muscles (type I fibers).
Changes in the relative abundance of MHC-β and MHC-α (MYH6, the fast isoform of cardiac myosin heavy chain) correlate with the contractile velocity of cardiac muscle. In early fetal development, MHC-β is predominately expressed in the ventricles, while MHC-α is predominantly expressed in the atria. In healthy adult hearts, MHC-α is predominantly expressed in the atria (>90%), while MHC-β (~50%) is expressed in the atria of failing adult hearts. In vitro studies have demonstrated that newly formed cardiac myocytes express MHC-β, and after prolonged (1-5 weeks) contractile activity MHC-α becomes detectable. An allelic variant of this gene is associated with approximately 40% of the cases of Hypertrophic cardiomyopathy (HCM). This condition is an autosomal-dominant disease, in which a single copy of the variant gene causes enlargement of the left ventricle of the heart. Disease onset usually occurs later in life, perhaps triggered by changes in thyroid hormone function and/or physical stress.
Another condition associated to mutations in this gene is paraspinal and proximal muscle atrophy (doi: 10.1016/j.nmd.2013.04.003).
Jääskeläinen P, Miettinen R, Kärkkäinen P et al. (2004). "Genetics of hypertrophic cardiomyopathy in eastern Finland: few founder mutations with benign or intermediary phenotypes". Ann. Med.36 (1): 23–32. doi:10.1080/07853890310017161. PMID15000344.
Kamisago M, Schmitt JP, McNamara D et al. (2007). "Sarcomere protein gene mutations and inherited heart disease: a beta-cardiac myosin heavy chain mutation causing endocardial fibroelastosis and heart failure". Novartis Found. Symp.274: 176–89; discussion 189–95, 272–6. PMID17019812.