The G213D variant in Nav1.5 alters sodium current and causes an arrhythmogenic phenotype resulting in a multifocal ectopic Purkinje-related premature contraction phenotype in human-induced pluripotent stem cell-derived cardiomyocytes

Aims Variants in SCN5A encoding Na(v)1.5 are associated with cardiac arrhythmias. We aimed to determine the mechanism by which c.638G.A in SCNA5 resulting in p.Gly213Asp (G213D) in Na(v)1.5 altered Na+ channel function and how flecainide corrected the defect in a family with multifocal ectopic Purkinje-related premature contractions (MEPPC)-like syndrome. Methods and results Five patients carrying the G213D variant were treated with flecainide. Gating pore currents were evaluated in Xenopus laevis oocytes. The 638G.A SCN5A variant was introduced to human-induced pluripotent stem cell (hiPSC) by CRISPR-Cas9 gene editing and subsequently differentiated to cardiomyocytes (hiPSC-CM). Action potentials and sodium currents were measured in the absence and presence of flecainide. Ca2+ transients were measured by confocal microscopy. The five patients exhibited premature atrial and ventricular contractions which were suppressed by flecainide treatment. G213D induced gating pore current at potentials negative to -50 mV. Voltage-clamp analysis in hiPSC-CM revealed the activation threshold of I-Na was shifted in the hyperpolarizing direction resulting in a larger I-Na window current. The G213D hiPSC-CMs had faster beating rates compared with wild-type and frequently showed Ca2+ waves and alternans. Flecainide applied to G213D hiPSC-CMs decreased window current by shifting the steady-state inactivation curve and slowed the beating rate. Conclusion The G213D variant in Na(v)1.5 induced gating pore currents and increased window current. The changes in I-Na resulted in a faster beating rate and Ca2+ transient dysfunction. Flecainide decreased window current and inhibited I-Na, which is likely responsible for the therapeutic effectiveness of flecainide in MEPPC patients carrying the G213D variant.

Automated summary

This study identified that the G213D variant in the SCN5A gene results in abnormal function of Na(v)1.5, causing gating pore currents and increased window currents, leading to abnormal cardiac cell activity. Treatment with flecainide can reduce window currents and inhibit I-Na, effectively treating patients with MEPPC-like syndrome.