Sudden death due to troponin T mutations
Objectives. This study was designed to verify initial observations of the clinical and prognostic features of hypertrophic cardiomyopathy caused by cardiac troponin T gene mutations. Background. The most common cause of sudden cardiac death in the young is hypertrophic cardiomyopathy, which is usually familial. Mutations causing familial hypertrophic cardiomyopathy have been identified in a number of contractile protein genes, raising the possibility of genetic screening for subjects at risk. A previous report suggested that mutations in the cardiac troponin T gene were notable because they were associated with a particularly poor prognosis but only mild hypertrophy. Given the variability of some genotype:phenotype correlations, further analysis of cardiac troponin T mutations has been a priority. Methods. Deoxyribonucleic acid from subjects with hypertrophic cardiomyopathy was screened for cardiac troponin T mutations using a ribonuclease protection assay. Polymerase chain reaction-based detection of a novel mutation was used to genotype members of two affected pedigrees. Gene carriers were examined by echocardiography and electrocardiology, and a family history was obtained. Results. A novel cardiac troponin T gene mutation, arginine 92 tryptophan, was identified in 19 of 48 members of two affected pedigrees. The clinical phenotype was characterized by minimal hypertrophy (mean [± SD] maximal ventricular wall thickness 11.3 ± 5.4 mm) and low disease penetrance by clinical criteria (40% by echocardiography) but a high incidence of sudden cardiac death (mean age 17 ± 9 years). Conclusions. These data support the observation that apparently diverse cardiac troponin T gene mutations produce a consistent disease phenotype. Because this is one of poor prognosis, despite deceptively mild or undetectable hypertrophy, genotyping at this locus may be particularly informative in patient management and counseling.