The origins of hypertrophic cardiomyopathy-causing mutations in two South African subpopulations: A unique profile of both independent and founder events
Hypertrophic cardiomyopathy (HCM) is an autosomal dominantly inherited disease of the cardiac sarcomere, caused by numerous mutations in genes encoding protein components of this structure. Mutation carriers are at risk of sudden cardiac death, mostly as adolescents or young adults. The reproductive disadvantage incurred may explain both the global occurrence of diverse independent HCM-associated mutations and the rare reports of founder effects within populations. We have investigated whether this holds true for two south African subpopulations, one of mixed ancestry and one of northern- European descent. Previously, we had detected three novel mutations - Ala797Thr in the β-myosin heavy-chain gene (βMHC), Arg92Trp in the cardiac troponin T gene (cTnT), and Arg645His in the myosin-binding protein C gene (MyBPC) - and two documented βMHC mutations (Arg403Trp and Arg249Gln). Here we report three additional novel mutations - Gln499Lys in βMHC and Va1896Met and Δc756 in MyBPC - and the documented βMHC Arg719Gln mutation. Seven of the nine HCM-causing mutations arose independently; no conclusions can be drawn for the remaining two. However, the βMHC Arg403Trp and Ala797Thr and cTnT Arg92Trp mutations were detected in another one, eight, and four probands, respectively, and haplotype analysis in families carrying these recurring mutations inferred their origin from three common ancestors. The milder phenotype of the βMHC mutations may account for the presence of these founder effects, whereas population dynamics alone may have overridden the reproductive disadvantage incurred by the more lethal, cTnT Arg92Trp mutation.