Identification of rare variants in TNNI3 with atrial fibrillation in a Chinese GeneID population

Abstract

Despite advances by genome-wide association studies (GWAS), much of heritability of common human diseases remains missing, a phenomenon referred to as 'missing heritability'. One potential cause for 'missing heritability' is the rare susceptibility variants overlooked by GWAS. Atrial fibrillation (AF) is the most common arrhythmia seen at hospitals and increases risk of stroke by fivefold and doubles risk of heart failure and sudden death. Here, we studied one large Chinese family with AF and hypertrophic cardiomyopathy (HCM). Whole-exome sequencing analysis identified a mutation in TNNI3, R186Q, that co-segregated with the disease in the family, but did not exist in >1583 controls, suggesting that R186Q causes AF and HCM. High-resolution melting curve analysis and direct DNA sequence analysis were then used to screen mutations in all exons and exon-intron boundaries of TNNI3 in a panel of 1127 unrelated AF patients and 1583 non-AF subjects. Four novel missense variants were identified in TNNI3, including E64G, M154L, E187G and D196G in four independent AF patients, but no variant was found in 1583 non-AF subjects. All variants were not found in public databases, including the ExAC Browser database with 60,706 exomes. These data suggest that rare TNNI3 variants are associated with AF (P = 0.03). TNNI3 encodes troponin I, a key regulator of the contraction-relaxation function of cardiac muscle and was not previously implicated in AF. Thus, this study may identify a new biological pathway for the pathogenesis of AF and provides evidence to support the rare variant hypothesis for missing heritability.

Keywords: Atrial fibrillation (AF); Cardiac troponin I; Hypertrophic cardiomyopathy; TNNI3 mutations; Whole exome sequencing.

Figure 1

An electrocardiogram from patient II:2 in the Chinese family with both HCM and AF. Typical electrocardiographic features with a diagnosis of AF were observed in patient II:2.

Figure 2

The pedigree structure of the Chinese with both HCM and AF. Males and females are shown with squares and circles, respectively. Filled symbols indicate ‘affected’, and open symbols are ‘un-affected’. A symbol with a question mark shows a family member without a definitive diagnosis of AF. The genotype for TNNI3 mutation c.G557A (p.R186Q) is indicated below each symbol with DNA available for genotyping.

Figure 3

Sequencing data for mutations of TNNI3 identified in four different AF patients.

Figure 4

Schematic structure of cardiac troponin I. A: Structure of cardiac troponin I with the location of the mutations identified in this study indicated. B: Schematic structure showing interactions among troponin I, troponin T, and troponin C in the calcium saturated thin filament. Cardiac troponin I is marked in red. α-helices are shown with cylinders (Wang et al. 2012).

Figure 5

All five AF mutations in cardiac troponin I occur on amino acid residues that are highly conserved among different species during evolution. The location of each mutated amino acid residue is marked in red.