Major Cardiac Events in Patients and Relatives With Hereditary Hypertrophic Cardiomyopathy.

Background: Little evidence is available on the disease expression in relatives of index patients with hypertrophic cardiomyopathy (HCM). This information has important implications for family screening programs, genetic counseling, and management of affected families.

Objectives: The purpose of this study was to investigate the disease expression and penetrance in relatives of index patients carrying pathogenic/likely pathogenic (P/LP) variants in recognized HCM genes.

Methods: A total of 453 consecutive and unrelated HCM index patients underwent clinical and genetic investigations. A total of 903 relatives of genotype-positive index patients were invited for clinical investigations and genetic testing. Penetrance, disease expression, and incidence rates of major adverse cardiac events (MACEs) were investigated in individuals carrying P/LP variants.

Results: Forty percent (183/453) of index patients carried a P/LP variant. Eighty-four percent (757/903) of all relatives of index patients with P/LP variants were available for the investigation, of whom 54% (407/757) carried a P/LP variant. The penetrance of HCM among relatives was 39% (160/407). Relatives with HCM and index patients were diagnosed at a similar age (43 ± 18 years vs 46 ± 15 years;  = 0.11). There were no differences in clinical characteristics or incidence rates of MACE during 8 years of follow-up.

Conclusions: The disease expression of HCM among index patients and affected relatives carrying P/LP variants in recognized disease genes was similar, with an equal risk of experiencing MACE. These findings provide evidence to support family screening and follow-up of genotype-positive HCM families to improve management and diminish the number of adverse disease complications among relatives.