Novel Loss-of-Function Variant, Cys1384Phe, in SCN5A Is Associated With an Overlapping Phenotype of Brugada Syndrome, Sick Sinus Syndrome, and Dilated Cardiomyopathy

BACKGROUND: Loss-of-function SCN5A variants are primarily associated with Brugada syndrome (BrS), but can also present with overlapping phenotypes. We investigated Cys1384Phe of SCN5A, a novel missense variant associated with BrS, sick sinus syndrome (SSS), and dilated cardiomyopathy (DCM). METHODS AND RESULTS: This study included a large 4-generation Japanese family consisting of 15 individuals (1 proband and 14 family members). Among them, the proband, a cousin, a second cousin and the second cousin's father were diagnosed with BrS. Two of these 4 BrS patients experienced VF events, while the other 2 remained asymptomatic. Another cousin was diagnosed with DCM, and 3 additional family members exhibited complete right bundle branch block and/or SSS. Comprehensive genetic analysis using a target panel sequencing identified a novel missense variant, Cys1384Phe in SCN5A, in the proband and affected family members; however, the phenotypes were different. Whole-cell patch-clamp experiments using HEK293 cells transfected wild-type or Cys1384Phe plasmid demonstrated a complete loss-of-function in the sodium current of the Cys1384Phe cells. Furthermore, the heterozygous expression of Cys1384Phe and wild-type (WT) channels showed a significant reduction of peak sodium current compared with the WT, suggesting a dominant-negative suppression, but no trafficking defect was observed. CONCLUSIONS: The novel Cys1384Phe variant in SCN5A is a complete loss-of-function mutation with dominant-negative suppression, and associated with overlapping phenotypes of BrS, SSS, and DCM.