TNNI3 and cardiomyopathy: Here, we identify the mutation in 5 families from South Lebanon and present phenotypic data on 57 TNNI3 p.Arg21Cys-related cardiomyopathy patients showing that the TNNI3 p.Arg21Cys mutation causes a malignant form of HCM characterized by early SCD in most mutation carriers.