p.D1690N Nav1.5 rescues p.G1748D mutation gating defects in a compound heterozygous Brugada syndrome patient

BACKGROUND We identified 2 compound heterozygous mutations (p.D1690N and p.G1748D) in the SCN5A gene encoding cardiac Na+ channels (Nav1.5) in a proband diagnosed with Brugada syndrome type 1. Furthermore, in the allele encoding the p.D1690N mutation, the p.H558R polymorphism was also detected. OBJECTIVE The purpose of this study was to analyze the functional properties of the mutated channels as well as the putative modulator effects produced by the presence of the polymorphism. METHODS Wild-type and mutated human Nav1.5 channels were expressed in Chinese hamster ovary cells and recorded using whole-cell patch-damp technique. RESULTS Separately, both p.D1690N and p.G1748D mutations produced a marked reduction in peak Na+ current density (>80%), mainly due to their limited trafficking toward the membrane. Furthermore, p.G1748D mutation profoundly affected channel gating. Both p.D1690N and p.G1748D produced a marked dominant negative effect when cotransfected with either wild-type or p.H558R channels. Conversely, p.H558R was able to rescue defective trafficking of p.D1690N channels toward the membrane when both polymorphism and mutation were in the same construct. Surprisingly, cotransfection with p.D1690N, either atone or together with the polymorphism (p.H558R-D1690N), completely restored the profound gating defects exhibited by p.G1748D channels but only slightly rescued their trafficking. CONCLUSION Our results add further support to the hypothesis that Nav1.5 subunits interact among them before trafficking toward the membrane and suggest that a missense mutation can rescue the defective gating produced by another missense mutation.