Characterization of a NaV1.5 Gain-of-Function Mutation (G213D) causing Multifocal Atrial and Ventricular Premature Ectopies and an Increased Risk of Dilated Cardiomyopathy

Background: Mutations in SCN5A have been linked to different cardiac diseases including multifocal ectopic Purkinje-related premature contractions (MEPPC) characterized by ventricular ectopy and dilated cardiomyopathy (DCM). Here we characterize the Nav1.5 G213D variant found in a large Danish family with frequent premature ventricular and atrial contractions, frequent nonsustained ventricular tachycardia and DCM. Methods and Results: The family was clinically assessed and an MEPPC-like phenotype including complex atrial and ventricular arrhythmias and dilated cardiomyopathy was found. Genetic screening revealed a G213D Nav1.5 missense mutation in the link of segment 3 and 4 in domain 1 of the Nav1.5 protein. The MEPPC-like phenotype co-segregated with G213D. Electrophysiological studies of wild type (WT) hNav1.5 and hNav1.5_G213D expressed in CHO-K cells was performed using conventional patch clamp and a SynchoPatch 384PE (Nanion Technologies) high throughput automatic patch clamp. The half-maximal inactivation (V½) was significantly more negative for hNav1.5_G213D compared to WT and the V½ of steady-state inactivation was shifted towards more positive values for hNav1.5_G213D, resulting in increased window-currents. This suggests that hNav1.5_G213D activates at more negative potentials and a larger fraction of channels will recover from inactivation during the diastole resulting in a gain-of-function phenotype. A combination of wild type and G213D mimicking the heterozygote state exhibited an intermediate phenotype. Flecainide or amiodarone resulted in a markedly reduced number of premature atrial and ventricular contractions in patients. Conclusions: The G213D Nav1.5 variant is associated with a gain-of-function and is associated with multifocal atrial and ventricular ectopy and dilated cardiomyopathy.