Any hypertrophic cardiomyopathy in which the cause of the disease is a mutation in the MYL2 gene.

Familial hypertrophic cardiomyopathy-28 (CMH28) is characterized by asymmetric septal hypertrophy, atrial fibrillation and nonsustained ventricular tachycardia, and risk of sudden death. Dyspnea is the most common symptom, but more than half of affected individuals are asymptomatic. Hypertrabeculation of the left ventricle with noncompaction has been observed in some patients (Ochoa et al., 2018). For a general phenotypic description and discussion of genetic heterogeneity of familial hypertrophic cardiomyopathy, see CMH1 (192600).

Hypertrophic cardiomyopathy-29 (CMH29) is characterized by recurrent syncope, dyspnea on exertion, and palpitations. The clinical phenotype is associated with a poor prognosis due to lethal arrhythmias and cardiac failure. Cardiac muscle biopsies show intermyofibrillar accumulation of glycogen and polyglucosan bodies within cardiomyocytes, and skeletal muscle accumulation of glycogen has also been observed (Hedberg-Oldfors et al., 2019). For a general phenotypic description and discussion of genetic heterogeneity of hypertrophic cardiomyopathy, see CMH1 (192600).