Multifocal atrial and ventricular premature contractions with an increased risk of dilated cardiomyopathy caused by a Na_v1.5 gain-of-function mutation (G213D)

Background: SCN5A mutations can lead to different cardiac diseases. Recently, SCN5A mutations have been linked to the clinical entity multifocal ectopic Purkinje-related premature contractions (MEPPC) characterized by ventricular ectopy and dilated cardiomyopathy. Methods & Results: A family with a uniform MEPPC-like phenotype, associated with complex atrial and ventricular arrhythmias and dilated cardiomyopathy caused by a high frequency of ventricular ectopy was clinically assessed. Screening of the SCN5A gene revealed a missense mutation in the linker between segments 3 and 4 in domain 1 of the Na_v1.5 protein, resulting in a glycine to aspartate substitution at position 213 (G213D). The phenotype co-segregated with the missense mutation. Electrophysiological studies of wild type (WT) hNa_v1.5 and hNa_v1.5_G213D expressed in CHO-K cells showed that the voltage of half-maximal activation (V_½) was significantly more negative for hNa_v1.5_G213D compared to WT (V_½ = −38.7 ± 0.5 mV for WT and V_½ = − 42.4 ± 0.5 mV for G213D; P < 0.001). This suggests activation of Na_v1.5_G231D at more negative potentials. The V_½ of steady-state inactivation was significantly shifted towards more positive values for Na_v1.5_G213D (V_½ = − 86.7 ± 0.2 mV for WT and − 82.2 ± 0.3 mV for G213D; P < 0.001), also contributing to a gain-of-function phenotype. Flecainide and amiodarone markedly reduced premature atrial and ventricular contractions in four patients. Conclusion: The Na_v1.5_G213D mutation is associated with a gain-of-function phenotype, multifocal atrial and ventricular ectopy and dilated cardiomyopathy. Since patients with a MEPPC-like phenotype may specifically benefit from Class-1 antiarrhythmic drugs or amiodarone, clinical identification of this disease entity is important.