Genetic variation in exon 5 of troponin - I gene in hypertrophic cardiomyopathy cases

Background: Cardiomyopathies are a heterogeneous group of heart muscle disorders and are classified as 1) Hypertrophic Cardiomyopathy (HCM) 2) Dilated cardiomyopathy (DCM) 3) Restrictive cardiomyopathy (RCM) and 4) Arrhythmogenic right ventricular dysplasia (ARVD) as per WHO classification, of which HCM and DCM are common. HCM is a complex but relatively common form of inherited heart muscle disease with prevalence of 1 in 500 individuals and is commonly associated with sarcomeric gene mutations. Cardiac muscle troponin I (TNNI-3) is one such sarcomeric protein and is a subunit of the thin filament-associated troponin-tropomyosin complex involved in calcium regulation of skeletal and cardiac muscle contraction. Mutations in this gene were found to be associated with a history of sudden cardiac death in HCM patients.
Aim: Therefore the present study aims to identify for mutations associated with troponin I gene in a set of HCM patients from Indian population.
Materials and Methods: Mutational analyses of 92 HCM cases were carried out following PCR based SSCP analysis.
Results: The study revealed band pattern variation in 3 cases from a group of 92 HCM patients. This band pattern variation, on sequencing revealed base changes, one at nt 2560 with G>T transversion in exon-5 region with a wobble and others at nt 2479 and nt 2478 with G>C and C>G transversions in the intronic region upstream of the exon 5 on sequencing. Further analysis showed that one of the probands showed apical form of hypertrophy, two others showing asymmetric septal hypertrophy. Two of these probands showed family history of the condition.
Conclusions: Hence, the study supports earlier reports of involvement of TNNI-3 in the causation of apical and asymmetrical forms of hypertrophy.

Keywords
Genetic variation, hypertrophic cardiomyopathy, sudden cardiac death, troponin-I