Genetics of hypertrophic cardiomyopathy in eastern Finland: few founder mutations with benign or intermediary phenotypes

Hypertrophic cardiomyopathy (HCM) is a genetically and clinically heterogeneous myocardial disease caused by mutations in genes encoding sarcomeric proteins. To assess the genetic background and phenotypic expression of HCM in eastern Finland, we screened 35 unrelated patients with HCM from the Kuopio University Hospital area for variants in 9 genes encoding sarcomeric proteins with the PCR-SSCP method. We herewith describe our previous findings in five sarcomeric genes and also report hitherto unpublished data on four additional sarcomeric genes. Mutations in the cardiac myosin-binding protein C gene (MYBPC3) were most frequent, accounting for 26% of cases. A novel mutation (Gln1061X) in this gene was the most common mutation, found in 6 of 35 families and accounting for 17% of all cases. Other novel mutations in MYBPC3 (IVS5-2A --> C, IVS14-13G --> A, and Ex25DeltaLys) were found in one family each. A previously described a-tropomyosin (TPM1) mutation (Asp175Asn) was found in 11% of cases. Haplotype analysis suggested that the two most common variants (MYBPC3-Gln1061X and TPM1-Aspl75Asn) were founder mutations. Only one mutation (Arg719Trp) in the P-myosin heavy chain gene (MYH7) was found in one family, and no disease-causing mutations were found in the genes encoding a-actin, cardiac troponin 1, T, C, or myosin essential and regulatory light chains. Altogether, the aforementioned 6 mutations found in MYBPC3. TPM1, and MYH7 accounted for 61% of familial and 40% of all HCM cases. The mutations were associated mostly with benign or intermediary phenotypes with only few HCM-related deaths. We conclude that the genetic profile of HCM in eastern Finland is unique, characterized by few founder mutations with benign or intermediary phenotypes.