SCN5A Mutation Type and a Genetic Risk Score Associate Variably with Brugada Syndrome Phenotype in SCN5A Families.

Background - Brugada syndrome (BrS) is characterized by the type 1 Brugada ECG pattern. Pathogenic rare variants in SCN5A (mutations) are identified in 20% of BrS families in whom incomplete penetrance and genotype-negative phenotype-positive individuals are observed. E1784K-SCN5A is the most common SCN5A mutation identified. We determined the association of a BrS genetic risk score (BrS-GRS) and SCN5A mutation type on BrS phenotype in BrS families with SCN5A mutations. Methods - Subjects with a spontaneous type 1 pattern or positive/negative drug challenge from cohorts harboring SCN5A mutations were recruited from 16 centers (n=312). Single nucleotide polymorphisms (SNP) previously associated with BrS at genome-wide significance were studied in both cohorts: rs11708996, rs10428132 and rs9388451. An additive linear genetic model for the BrS-GRS was assumed (6 SNP risk alleles). Results - In the total population (n=312), BrS-GRS ≥4 risk alleles yielded an odds ratio (OR) of 4.15 for BrS phenotype (95%CI:1.45-11.85, p=0.0078). Amongst SCN5A-positive individuals (n=258), BrS-GRS ≥4 risk alleles yielded an odds ratio (OR) of 2.35 (95%CI:0.89-6.22, p=0.0846). In SCN5A-negative relatives (n=54), BrS-GRS ≥4 alleles yielded and OR of 22.29 (95%CI:1.84-269.30, p=0.0146). Among E1784K-SCN5A positive family members (n=79), hosting ≥4 risk alleles gave an OR=5.12 (95%CI:1.93-13.62, p=0.0011). Conclusions - Common genetic variation is associated with variable expressivity of BrS phenotype in SCN5A families, explaining in part incomplete penetrance and genotype-negative phenotype-positive individuals. SCN5A mutation genotype and a BrS-GRS associate with BrS phenotype but the strength of association varies according to presence of a SCN5A mutation and severity of loss of function.