Circ Arrhythm Electrophysiol. 2026 Feb;19(2):e014270. doi: 10.1161/CIRCEP.125.014270. Epub 2026 Jan 26.
ABSTRACT
BACKGROUND: Pathogenic SCN5A variants are associated with inherited arrhythmias such as long-QT syndrome, Brugada syndrome, and sick sinus syndrome. While Nav1.5, an α-subunit of the cardiac sodium channel encoded by SCN5A, has been considered to function as a monomer, recent studies reveal that a reduction of sodium current in wild-type Nav1.5 can be caused by dimerization with loss-of-function mutated Nav1.5 through dominant-negative effects. However, the clinical significance of the dominant-negative effect remains unclear.
METHOD: We genetically screened a family who presented with sick sinus syndrome and sudden cardiac death. Whole-cell patch-clamp study using HEK293 (human embryonic kidney) cells coexpressing wild-type and variant SCN5A was performed. Channel dimerization was assessed by coimmunoprecipitation and proximity ligation assays. Also, the effects of difopein, a high-affinity inhibitor of Nav1.5 interaction via 14-3-3 proteins, were evaluated.
RESULTS: The proband carried compound heterozygous variants p.T1396P and p.G833R. The whole-cell mode patch-clamp techniques demonstrated that the p.T1396P showed a dominant-negative effect on the peak sodium currents (37% decrease in INa) and altered gating properties (5.6-mV shift in steady-state inactivation) when expressed with wild-type SCN5A. These effects were abolished by difopein. p.G833R showed no dominant-negative or coupled gating effect but still formed dimers. The proband developed earlier and more severe bradycardia than the mother, who only carries p.T1396P, suggesting that loss of coupled gating effect contributed to the severe phenotype.
CONCLUSIONS: Our findings suggest that coupled gating may be physiologically important for normal Nav1.5 function, and its loss can exacerbate disease severity.
PMID:41582807 | PMC:PMC12911491 | DOI:10.1161/CIRCEP.125.014270