RESUMO
Brugada Syndrome (BrS) is an inheritable arrhythmia condition that is associated with rare, loss-of-function variants in the cardiac sodium channel gene, SCN5A. Interpreting the pathogenicity of SCN5A missense variants is challenging and ~79% of SCN5A missense variants in ClinVar are currently classified as Variants of Uncertain Significance (VUS). An in vitro SCN5A-BrS automated patch clamp assay was generated for high-throughput functional studies of NaV1.5. The assay was independently studied at two separate research sites - Vanderbilt University Medical Center and Victor Chang Cardiac Research Institute - revealing strong correlations, including peak INa density (R2=0.86). The assay was calibrated according to ClinGen Sequence Variant Interpretation recommendations using high-confidence variant controls (n=49). Normal and abnormal ranges of function were established based on the distribution of benign variant assay results. The assay accurately distinguished benign controls (24/25) from pathogenic controls (23/24). Odds of Pathogenicity values derived from the experimental results yielded 0.042 for normal function (BS3 criterion) and 24.0 for abnormal function (PS3 criterion), resulting in up to strong evidence for both ACMG criteria. The calibrated assay was then used to study SCN5A VUS observed in four families with BrS and other arrhythmia phenotypes associated with SCN5A loss-of-function. The assay revealed loss-of-function for three of four variants, enabling reclassification to likely pathogenic. This validated APC assay provides clinical-grade functional evidence for the reclassification of current VUS and will aid future SCN5A-BrS variant classification.
RESUMO
BACKGROUND: Common single nucleotide polymorphisms at chromosome 4q25 (rs2200733, rs10033464) are associated with both lone and typical atrial fibrillation (AF). Risk alleles at 4q25 have recently been shown to predict recurrence of AF after ablation in a population of predominately lone AF, but lone AF represents only 5%-30% of AF cases. OBJECTIVE: To test the hypothesis that 4q25 AF risk alleles can predict response to AF ablation in the majority of AF cases. METHODS: Patients enrolled in the Vanderbilt AF Registry underwent 378 catheter-based AF ablations (median age 60 years; 71% men; 89% typical AF) between 2004 and 2011. The primary end point was time to recurrence of any nonsinus atrial tachyarrhythmia (atrial tachycardia, atrial flutter, or AF). RESULTS: Two-hundred atrial tachycardia, atrial flutter, or AF recurrences (53%) were observed. In multivariable analysis, the rs2200733 risk allele predicted a 24% shorter recurrence-free time (survival time ratio 0.76; 95% confidence interval [CI] 0.6-0.95; P = .016) compared with wild type. The heterozygous haplotype demonstrated a 21% shorter recurrence-free time (survival time ratio 0.79; 95% CI 0.62-0.99) and the homozygous risk allele carriers a 39% shorter recurrence-free time (survival time ratio 0.61; 95% CI 0.37-1.0; P = .037). CONCLUSIONS: Risk alleles at the 4q25 loci predict impaired clinical response to AF ablation in a population of patients with predominately typical AF. Our findings suggest that the rs2200733 polymorphism may hold promise as an objectively measured patient characteristic that can be used as a clinical tool for selecting patients for AF ablation.