Hypertrophic cardiomyopathy (HCM) is a primary disease of the myocardium (the muscle of the heart) in which a portion of the myocardium is hypertrophied (thickened) without any obvious cause, creating functional impairment of the cardiac muscle. It is a leading cause of sudden cardiac death in young athletes.The occurrence of hypertrophic cardiomyopathy is a significant cause of sudden unexpected cardiac death in any age group and as a cause of disabling cardiac symptoms. Younger people are likely to have a more severe form of hypertrophic cardiomyopathy.HCM is frequently asymptomatic until sudden cardiac death, and for this reason some suggest routinely screening certain populations for this disease.A cardiomyopathy is a disease that affects the muscle of the heart. With HCM, the myocytes (cardiac contractile cells) in the heart increase in size, which results in the thickening of the heart muscle. In addition, the normal alignment of muscle cells is disrupted, a phenomenon known as myocardial disarray. HCM also causes disruptions of the electrical functions of the heart. HCM is most commonly due to a mutation in one of nine sarcomeric genes that results in a mutated protein in the sarcomere, the primary component of the myocyte (the muscle cell of the heart). These are predominantly single-point missense mutations in the genes for beta-myosin heavy chain (MHC), myosin-binding protein C, cardiac troponinT, or tropomyosin. These mutations cause myofibril and myocyte structural abnormalities and possible deficiencies in force generation. Not to be confused with dilated cardiomyopathy or any other cardiomyopathy.While most literature so far focuses on European, American, and Japanese populations, HCM appears in all ethnic groups. The prevalence of HCM is about 0.2% to 0.5% of the general population.