Deletion in the cardiac troponin I gene in a family from Northern Sweden with hypertrophic cardiomyopathy

The cardiac troponin I gene has been described to be associated with hypertrophic cardiomyopathy. Until now, mutations in this gene have been found only in the Japanese population. We now present the first non-Japanese family, from northern Sweden, with a mutation in the cardiac troponin I gene. Clinical diagnose was based on echocardiography, with a maximum left ventricular wall thickness of >13 mm. or major electrocardiographic abnormalities, excluding subjects with other known causes of cardiac hypertrophy. Mutation screening was performed with a single-strand conformation polymorphism analysis and identification of mutation by direct DNA sequencing. We have identified a 33-bp deletion in exon 8 encompassing the stop codon. Nine individuals in three generations were tested, and four were carriers of this deletion. The mother was genetically affected and died of heart failure aged 90. Echocardiography at 71 years of age revealed no hypertrophy, but the electrocardiogram showed signs of left ventricular hypertrophy. Her two sons, also genetically affected, had left ventricular hypertrophy, with maximum wall thickness of 15 and 16 mm. respectively. One daughter and four grandchildren were clinically unaffected, but one of them, a 27-year-old woman with maximum wall thickness of 8 mm and normal electrocardiogram, was found to be genetically affected. In conclusion, we describe a non-Japanese family in which hypertrophic cardiomyopathy is due to a genetic defect in the cardiac troponin I gene. This mutation is a deletion of 33 bp in the last exon, whereas the previously described mutations in this gene are single nucleotide changes and a single codon deletion. The deletion of the C-terminal part of the cardiac troponin I protein, seems in this particular family to be associated with a mild phenotypic expression of familial hypertrophic cardiomyopathy. (C) 2000 Academic Press.