The same variants in sarcomeric genes can lead to different cardiomyopathies within the same family. This gave rise to the concept of a continuum of sarcomeric cardiomyopathies. However, the manifestations and evolution of these cardiomyopathies in pathogenic variant carriers, including members of the same family, remains poorly understood. We present a case of familial sarcomeric cardiomyopathy caused by heterozygous truncating pathogenic variant p.Q1233* in cardiac myosin-binding protein C (MyBPC3) gene. The proband was first diagnosed with restrictive cardiomyopathy combined with left ventricular noncompaction (LVNC) and sarcoidosis at the age of 64. The predominantly restrictive phenotype of cardiomyopathy is considered to be a result of interaction between LVNC and sarcoid myocarditis. His 39-year-old son and 35-year-old daughter have identical non-obstructive asymmetric hypertrophic cardiomyopathy. The risk of sudden cardiac death in the son is high due to myocardial fibrosis, ischemia and nonsustained VT. We assume that both phenotypes in the family may have originally been different or there may have been a gradual transformation of the hypertrophic phenotype into LVNC. Myocarditis is regarded as an important epigenomic modifier of sarcomeric cardiomyopathy. In the proband and his son, cardioverter-defibrillators were implanted, and the proband experienced appropriate shocks due to ventricular tachycardia/fibrillation. The proband was also treated with corticosteroids. His death at the age of 69 years occurred due to acute gastric hemorrhage accompanied by progressive heart failure. This report confirms the concept of the phenotypic continuum of sarcomeric cardiomyopathies and describes possible phenotypic patterns and their transformation over time.
Keywords: MyBPC3; hypertrophic cardiomyopathy; left ventricular noncompaction; restrictive cardiomyopathy; sarcoidosis; truncating pathogenic variants.