Magic™ Anti-Troponin I monoclonal antibody, clone TPC102

Defined as clinically unexplained hypertrophy of the left ventricle, hypertrophic cardiomyopathy (HCM) is traditionally understood as a disease of the cardiac sarcomere. Mutations in TNNC1-encoded cardiac troponin C (cTnC) are a relatively rare cause of HCM. Here, we report clinical and functional characterization of a novel TNNC1 mutation, A31S, identified in a pediatric HCM proband with multiple episodes of ventricular fibrillation and aborted sudden cardiac death. Diagnosed at age 5, the proband is family history-negative for HCM or sudden cardiac death, suggesting a de novo mutation. TnC-extracted cardiac skinned fibers were reconstituted with the cTnC-A31S mutant, which increased Ca2+ sensitivity with no effect on the maximal contractile force generation. Reconstituted actomyosin ATPase assays with 50% cTnC-A31S:50% cTnC-WT-demonstrated Ca2+ sensitivity that was intermediate between 100% cTnC-A31S and 100% cTnC-WT, whereas the mutant increased the activation of the actomyosin ATPase without affecting the inhibitory qualities of the ATPase. The secondary structure of the cTnC mutant was evaluated by circular dichroism, which did not indicate global changes in structure. Fluorescence studies demonstrated increased Ca2+ affinity in isolated cTnC, the troponin complex, thin filament, and to a lesser degree, thin filament with myosin subfragment 1. These results suggest that this mutation has a direct effect on the Ca2+ sensitivity of the myofilament, which may alter Ca2+ handling and contribute to the arrhythmogenesis observed in the proband. In summary, we report a novel mutation in the TNNC1 gene that is associated with HCM pathogenesis and may predispose to the pathogenesis of a fatal arrhythmogenic subtype of HCM.

Restrictive cardiomyopathy is a rare form of pediatric cardiac disease, for which the known genes include MYH7, TNNT2, TNNI3, ACTC1, and DES. We describe a pediatric proband with fatal restrictive cardiomyopathy associated with septal hypertrophy and compound heterozygosity for TNNC1 mutations (NM_003280: p.A8V [c.C23T] and p.D145E [c.C435A]). This association between restrictive cardiomyopathy and TNNC1 mutations was strengthened by prospective observations on the second pregnancy in the family which revealed, in the presence of the same TNNC1 genotype, prenatally diagnosed hypertrophic cardiomyopathy which evolved into restrictive cardiomyopathy, heart failure and death at the age of 9 months. Contrary to previous reports, family and population analyses showed that each of the TNNC1 variants was not pathogenic when present alone. Our results (i) confirm that genetic backgrounds of hypertrophic cardiomyopathy and restrictive cardiomyopathy overlap and (ii) indicate that TNNC1 is a likely novel gene for autosomal recessive restrictive cardiomyopathy. (C) 2016 Wiley Periodicals, Inc.