Meta-analysis of cardiomyopathy-associated variants in troponin genes identifies loci and intragenic hot spots that are associated with worse clinical outcomes

Abstract

Introduction: Troponin (TNN)-encoded cardiac troponins (Tn) are critical for sensing calcium and triggering myofilament contraction. TNN variants are associated with development of cardiomyopathy; however, recent advances in genetic analysis have identified rare population variants. It is unclear how certain variants are associated with disease while others are tolerated.

Objective: To compare probands with TNNT2, TNNI3, and TNNC1 variants and utilize high-resolution variant comparison mapping of pathologic and rare population variants to identify loci associated with disease pathogenesis.

Methods: Cardiomyopathy-associated TNN variants were identified in the literature and topology mapping conducted. Clinical features were compiled and compared. Rare population variants were obtained from the gnomAD database. Signal-to-noise (S:N) normalized pathologic variant frequency against population variant frequency. Abstract review of clinical phenotypes was applied to "significant" hot spots.

Results: Probands were compiled (N = 70 studies, 224 probands) as were rare variants (N = 125,748 exomes; 15,708 genomes, MAF <0.001). TNNC1-positive probands demonstrated the youngest age of presentation (20.0 years; P = .016 vs TNNT2; P = .004 vs TNNI3) and the highest death, transplant, or ventricular fibrillation events (P = .093 vs TNNT2; P = .024 vs TNNI3; Kaplan Meir: P = .025). S:N analysis yielded hot spots of diagnostic significance within the tropomyosin-binding domains, α-helix 1, and the N-Terminus in TNNT2 with increased sudden cardiac death and ventricular fibrillation (P = .004). The inhibitory region and C-terminal region in TNNI3 exhibited increased restrictive cardiomyopathy (P =.008). HCM and RCM models tended to have increased calcium sensitivity and DCM decreased sensitivity (P < .001). DCM and HCM studies typically showed no differences in Hill coefficient which was decreased in RCM models (P < .001). CM models typically demonstrated no changes to F_max (P = .239).

Conclusion: TNNC1-positive probands had younger ages of diagnosis and poorer clinical outcomes. Mapping of TNN variants identified locations in TNNT2 and TNNI3 associated with heightened pathogenicity, RCM diagnosis, and increased risk of sudden death.

Keywords: Cardiomyopathy; Signal-to-noise analysis; TNNC1; TNNI3; TNNT2; Troponin; Troponin C; Troponin I; Troponin T.

Figure 1:. A.

Study methodology and inclusion and exclusion criteria. B. Variant frequencies in variants and the gnomAD database. *P=0.0001

Figure 2:. A.

Histogram exhibiting distribution of ages of diagnoses in TNNT2 (red), TNNI3 (blue), and TNNC1 (green) probands. B. Histogram exhibiting average proband age in TNNT2, TNNI3, and TNNC1. C. Survival curve for TNNT2 (red), TNNI3 (blue), and TNNC1 (green) probands; * TNNC1 vs TNNI3: P=0.008; TNNC1 vs TNNT2: P=0.019. D. Histogram exhibiting the distribution of hypertrophic cardiomyopathy (HCM; orange), dilated cardiomyopathy (DCM; blue), restrictive cardiomyopathy (RCM; grey), and left ventricular noncompaction cardiomyopathy (LVNC; purple) in TNNT2, TNNI3, and TNNC1 probands. *indicates significance

Figure 3:. A.

Histogram exhibiting distribution of ages of diagnoses in probands with compound heterozygosity and probands with heterozygosity. B. Histogram exhibiting distribution of ages of diagnoses in probands with double heterozygosity and probands with heterozygosity. *indicates significance

Figure 4:

Signal-to-noise ratio analysis of TNNT2 probands mapped against TnT amino acid location and domain: N-Terminus, tropomyosin (Tm) binding domains, actin-activation region, the Tm, TnI, and TnC binding domain, and alpha helix (AH) 1 and 2. Arrows point to significant hotspots with outcome relevance.

Figure 5:

Signal-to-noise ratio analysis of TNNI3 probands mapped against TnI amino acid location and domains: N-terminal extension, I-T arm, inhibitory region (IR), switch-peptide domain (SP), and C-terminus/mobile domain. Arrows point to significant hotspots with outcome relevance.