SCN5A and sick sinus syndrome: In contrast, loss-of-function of Nav1.5 can be associated with Brugada syndrome (BrS) [30], sick sinus syndrome (SSS) [31], atrioventricular conduction block [32] and supraventricular tachyarrhythmias (SVTs) [33,34], and these arrhythmic phenotypes can overlap with a single SCN5A mutation.