High prevalence of Arginine to Glutamine substitution at 98, 141 and 162 positions in Troponin I (TNNI3) associated with hypertrophic cardiomyopathy among Indians

Abstract

Background: Troponin I (TNNI3) is the inhibitory subunit of the thin filament regulatory complex Troponin, which confers calcium-sensitivity to striated muscle actomyosin ATPase activity. Mutations (2-7%) in this gene had been reported in hypertrophic cardiomyopathy patients (HCM). However, the frequencies of mutations and associated clinical presentation have not been established in cardiomyopathy patients of Indian origin, hence we have undertaken this study.

Methods: We have sequenced all the exons, including the exon-intron boundaries of TNNI3 gene in 101 hypertrophic cardiomyopathy patients (HCM), along with 160 healthy controls, inhabited in the same geographical region of southern India.

Results: Our study revealed a total of 16 mutations. Interestingly, we have observed Arginine to Glutamine (R to Q) mutation at 3 positions 98, 141 and 162, exclusively in HCM patients with family history of sudden cardiac death. The novel R98Q was observed in a severe hypertrophic obstructive cardiomyopathy patient (HOCM). The R141Q mutation was observed in two familial cases of severe asymmetric septal hypertrophy (ASH++). The R162Q mutation was observed in a ASH++ patient with mean septal thickness of 29 mm, and have also consists of allelic heterogeneity by means of having one more synonymous (E179E) mutation at g.4797: G → A: in the same exon 7, which replaces a very frequent codon (GAG: 85%) with a rare codon (GAA: 14%). Screening for R162Q mutation in all the available family members revealed its presence in 9 individuals, including 7 with allelic heterogeneity (R162Q and E179E) of which 4 were severely affected. We also found 2 novel SNPs, (g.2653; G → A and g.4003 C → T) exclusively in HCM, and in silico analysis of these SNPs have predicted to cause defect in recognition/binding sites for proteins responsible for proper splicing.

Conclusion: Our study has provided valuable information regarding the prevalence of TNNI3 mutations in Indian HCM patients and its risk assessment, these will help in genetic counseling and to adopt appropriate treatment strategies.

Figure 1

(A - F). Sequence electropherograms of TNNI3 gene. Upper panel representing the control sequences, whereas the lower panel showing the mutations observed in the HCM patients. The mutations sites are shown with arrows. A. Novel missense heterozygous mutation at the nucleotide position g.4019 (G > A) that changes the amino acid Arginine (CGA) to Glutamine (CAA) at the residue 98. B. A heterozygous mutation at the nucleotide position g.4682 (G > A) that changes the amino acid Arginine (CGG) to Glutamine (CAG) at residue 141. C. A heterozygous mutation at the nucleotide position g.4745 (G > A) that changes the amino acid Arginine (CGG) to Glutamine (CAG) at residue 162. D. A novel homozygous splice acceptor site SNP at the nucleotide position g.2653 (AA) in intron 5. E. A novel homozygous SNP at the nucleotide position g.4003 (TT) in Intron 6. F. A heterozygous silent mutation (E179E), at the nucleotide position g.4797 (G > A) in exon 7.

Figure 2

A pedigree of a hypertrophic cardiomyopathy (HCM) family with R98Q mutation in the exon 6 of cardiac troponin ITNNI3gene is depicted.

Figure 3

A pedigree of a four-generation hypertrophic cardiomyopathy (HCM) family with R162Q and E179E mutations in the exon 7 of cardiac (TNNI3)Troponin I gene.

Figure 4

Principal components analysis of Indian case/control samples together with Chinese, African and European HapMap samples, based on a panel of 50 ancestry-informative SNP markers (AIMs).