H558R, a common SCN5A polymorphism, modifies the clinical phenotype of Brugada syndrome by modulating DNA methylation of SCN5A promoters

Abstract

Background: A common SCN5A polymorphism H558R (c.1673 A > G, rs1805124) improves sodium channel activity in mutated channels and known to be a genetic modifier of Brugada syndrome patients (BrS). We investigated clinical manifestations and underlying mechanisms of H558R in BrS.

Methods and results: We genotyped H558R in 100 BrS (mean age 45 ± 14 years; 91 men) and 1875 controls (mean age 54 ± 18 years; 1546 men). We compared clinical parameters in BrS with and without H558R (H558R+ vs. H558R- group, N = 9 vs. 91). We also obtained right atrial sections from 30 patients during aortic aneurysm operations and compared SCN5A expression and methylation with or without H558R. H558R was less frequent in BrS than controls (9.0% vs. 19.2%, P = 0.028). The VF occurrence ratio was significantly lower (0% vs. 29.7%, P = 0.03) and spontaneous type 1 ECG was less observed in H558R+ than H558R- group (33.3% vs. 74.7%, P = 0.01). The SCN5A expression level was significantly higher and the methylation rate was significantly lower in sections with H558R (N = 10) than those without (0.98 ± 0.14 vs. 0.83 ± 0.19, P = 0.04; 0.7 ± 0.2% vs. 1.6 ± 0.1%, P = 0.004, respectively). In BrS with heterozygous H558R, the A allele mRNA expression was 1.38 fold higher than G allele expression.

Conclusion: The SCN5A polymorphism H558R may be a modifier that protects against VF occurrence in BrS. The H558R decreased the SCN5A promoter methylation and increased the expression level in cardiac tissue. An allelic expression imbalance in BrS with a heterozygous H558R may also contribute to the protective effects in heterozygous mutations.

Keywords: Brugada syndrome; SCN5A; Single nucleotide polymorphism; Ventricular fibrillation.

Fig. 1

Frequency of H558R in the BrS cases and controls, The minor G allele of rs1805124 was less frequent in BrS patients than in normal control cases (P = 0.028, odds ratio (OR) 1.97)

Fig. 2

Frequency of H558R in the BrS cases with or without VF history, The G allele (H558R) was not observed in BrS patients with a history of VF (P = 0.03)

Fig. 3

Kaplan–Meier analysis of cumulative survival from VF in 100 BrS patients. The occurrence ratio of VF was significantly lower in the H558R+ group than in the H558R- group according to a log-rank test (P = 0.03). VF: ventricular fibrillation; blue line: H558R+ group; red line: H558R- group

Fig. 4

Expression levels of the SCN5A gene (using GAPDH as a reference gene), according to the presence or absence of H558R. The expression level of SCN5A was significantly higher in patients with H558R than in those without

Fig. 5

a The rate of methylation was lower in 13 of 16 methylation site. The methylation ratio of the SCN5A gene, according to the presence or not of H558R. b The rate of methylation was lower in patients with H558R than in those without (0.7 ± 0.2% vs. 1.6 ± 0.1%, P = 0.004). All data are indicated by box plots and mean ± standard error

Fig. 6

The correlation of mRNA expression and the rate of methylation in SCN5A. There is mild inverse correlation between the mRNA expression and the rate of methylation in SCN5A (r = −0.38, P = 0.04)

Fig. 7

The expression ratio of the A allele and G allele in patients with heterozygous H558R. The expression levels of G allele and A allele was similar in genome DNA but the A allele (wild) expression was 1.38 fold higher than G allele (pathogenic) expression in mRNA. Allelic imbalance existed in mRNA in patients with heterozygous H558R. (P = 0.004 vs. genome DNA)