Dominant negative effects ofSCN5Amissense variants

Introduction Up to 30% of patients with Brugada Syndrome (BrS) carry loss-of-function (LoF) variants in the cardiac sodium channel gene SCN5A . Recent studies have suggested that the SCN5A protein product Na V 1.5 can form dimers and exert dominant negative effects. Methods We identified 35 LoF variants (<10% peak current compared to wild type (WT)) and 15 partial LoF variants (10-50% peak current compared to WT) that we assessed for dominant negative behavior. SCN5A variants were studied in HEK293T cells alone or in heterozygous co-expression with WT SCN5A using automated patch clamp. To assess clinical risk, we compared the prevalence of dominant negative vs. putative haploinsufficient (frameshift/splice site) variants in a BrS case consortium and the gnomAD population database. Results In heterozygous expression with WT, 32/35 LoF variants and 6/15 partial LoF showed reduction to <75% of WT-alone peak I Na , demonstrating a dominant negative effect. Carriers of dominant negative LoF missense variants had an enriched disease burden compared to putative haploinsufficient variant carriers (2.7-fold enrichment in BrS cases, p=0.019). Conclusions Most SCN5A missense LoF variants exert a dominant negative effect. Cohort analyses reveal that this class of variant confers an especially high burden of BrS.