GJA5 and atrial fibrillation: The human atrium chiefly expresses Cx40 and Cx43, and abnormalities in Cx40 levels and distribution were prevalent in AF.44 Previous pre-clinical work has also shown that Cx40-KO increases the susceptibility to atrial arrhythmias in mice.45 Similarly, Cx43 plays a crucial role in cardiac development and down-regulation of Cx43 triggers sympathetic AF.46 These studies all highlight the contribution of the abundance and distribution of gap junctions to the maintenance of normal electrophysiology.