SCN5A and obesity due to melanocortin 4 receptor deficiency: In this study, we investigated the link between CaMKII-dependent regulation of Nav1.5, pathogenic late current (INa,L), diet-induced obesity, and AF, taking advantage of our phospho-ablated SA knock-in mouse model lacking the CaMKII phosphorylation site on Nav1.5, which attenuates INa,L.