The G213D variant in Na_v1.5 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

Variants in SCN5A encoding Na_v1.5 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_v1.5 altered Na⁺ channel function and how flecainide corrected the defect in a family with multifocal ectopic Purkinje-related premature contractions (MEPPC)-like syndrome.

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.

The G213D variant in Na_v1.5 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.