Key result
SCN5A p.T1396P variant decreases peak sodium currents by ~37% through a dominant-negative effect.
Why the study?
Pathogenic SCN5A variants cause inherited arrhythmias and mutated Nav1.5 can reduce wild-type sodium current via dominant-negative dimerization, but its clinical significance remains unclear.
Physical interaction (dimerization) of Nav1.5 channels is functionally independent of coupled gating, and the loss of coupled gating can exacerbate the clinical severity of inherited bradyarrhythmias.
Answers are grounded in this paper and cite their sources.
May refine SCN5A variant interpretation in bradyarrhythmias; leaves open dimerization as a therapeutic target pending validation.
BACKGROUND: Pathogenic SCN5A variants are associated with inherited arrhythmias such as long-QT syndrome, Brugada syndrome, and sick sinus syndrome. While Na v 1.5, 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 Na v 1.5 can be caused by dimerization with loss-of-function mutated Na v 1.5 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 Na v 1.5 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 I Na ) 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 Na v 1.5 function, and its loss can exacerbate disease severity.
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Tano et al. (2026) studied SCN5A-Related Bradycardia and Sick Sinus Syndrome. Compound heterozygous SCN5A variants (p.T1396P and p.G833R) vs. Wild-type SCN5A was evaluated on Peak sodium current (INa) and gating properties. The SCN5A p.T1396P variant showed a dominant-negative effect that decreased peak sodium currents by 37% when coexpressed with wild-type channels, whereas p.G833R exhibited no coupled gating effect but retained physical dimerization, indicating that channel dimerization is functionally independent of coupled gating.
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