Hypertrophic cardiomyopathy in identical twins: a case report with mismatch between genotype and phenotype

Hypertrophic cardiomyopathy (HCM) is the most common genetic cardiomyopathy; however, it is a very rare condition among twins. A mismatch between the phenotype and clinical course has been identified, even in the presence of apparently identical genotypes.

A pair of male monozygotic-diamniotic twins of 17 years old with a mismatch in HCM clinical expression is informed. Both twins have the same pathogenic variant [c.1816G>A (p.Val606Met)] located in MYH7, a gene that encodes an essential component in the contraction of cardiac muscle. The twins presented obstructive basal anteroseptal vs. non-obstructive medium apical HCM and different clinical courses (non-fatal sudden cardiac death vs. asymptomatic). It is hypothesized that twin-to-twin transfusion syndrome could be implied in the different phenotypes due to prenatal history, but other genetic and epigenetic factors can be implied.

Despite carrying the same pathogenic variant, the phenotypical presentation and clinical course vary widely, despite a similar risk profile, suggesting the influence of genetic/epigenetic and environmental factors on disease progression.