Prevalence and Clinical Implication of Double Mutations in Hypertrophic Cardiomyopathy

Background—Available data suggests that double mutations in patients with hypertrophic cardiomyopathy are not rare and are associated with a more severe phenotype. Most of this data, however, is based on noncontemporary variant classification. Methods and Results—Clinical data of all hypertrophic cardiomyopathy patients with 2 rare genetic variants were retrospectively reviewed and compared with a group of patients with a single disease-causing variant. Furthermore, a literature search was performed for all studies with information on prevalence and outcome of patients with double mutations. Classification of genetic variants was reanalyzed according to current guidelines. In our cohort (n=1411), 9% of gene-positive patients had 2 rare variants in sarcomeric genes but only in 1 case (0.4%) were both variants classified as pathogenic. Patients with 2 rare variants had a trend toward younger age at presentation when compared with patients with a single mutation. All other clinical variables were similar. In...