SCN5A and sick sinus syndrome: Mutations in SCN5A, the gene that encodes the pore-forming subunit of human cardiac sodium channel Nav1.5, have been associated with a variety of inherited arrhythmogenic syndromes including type 3 long-QT syndrome (LQT3)4, Brugada syndrome (BrS)5, progressive cardiac conduction disease (PCCD)6, sick sinus syndrome (SSS)7, atrial fibrillation (AF)8, dilated cardiomyopathy (DCM)9 and more complex overlapping syndrome10, 11.