Familial Dilated Cardiomyopathy Caused by an Alpha-Tropomyosin Mutation : The Distinctive Natural History of Sarcomeric Dilated Cardiomyopathy

ObjectivesWe sought to further define the role of sarcomere mutations in dilated cardiomyopathy (DCM) and associated clinical phenotypes.BackgroundMutations in several contractile proteins contribute to DCM, but definitive evidence for the roles of most sarcomere genes remains limited by the lack of robust genetic support.MethodsDirect sequencing of 6 sarcomere genes was performed on 334 probands with DCM. A novel D230N missense mutation in the gene encoding alpha-tropomyosin (TPM1) was identified. Functional assessment was performed by the use of an in vitro reconstituted sarcomere complex to evaluate ATPase regulation and Ca2+affinity as correlates of contractility.ResultsTPM1D230N segregated with DCM in 2 large unrelated families. This mutation altered an evolutionarily conserved residue and was absent in >1,000 control chromosomes. In vitro studies demonstrated major inhibitory effects on sarcomere function with reduced Ca2+sensitivity, maximum activation, and Ca2+affinity compared with wild-type TPM1. Clinical manifestations ranged from decompensated heart failure or sudden death in those presenting early in life to asymptomatic left ventricular dysfunction in those diagnosed during adulthood. Notably, several affected infants had remarkable improvement.ConclusionsGenetic segregation in 2 unrelated families and functional analyses conclusively establish a pathogenic role for TPM1mutations in DCM. In vitro results demonstrate contrasting effects of DCM and hypertrophic cardiomyopathy mutations in TPM1, suggesting that specific functional consequences shape cardiac remodeling. Along with previous reports, our data support a distinctive, age-dependent phenotype with sarcomere-associated DCM where presentation early in life is associated with severe, sometimes lethal, disease. These observations have implications for the management of familial DCM.