Nav1.5 kb. The gene consists of 28 exons, of which exon 1 and in part exon 2 form the 5’ untranslated region (5’UTR) and exon 28 the 3’ untranslated region (3’UTR) of the RNA. SCN5A is part of a family of 10 genes that encode different types of sodium channels, i.e. brain-type (Na1.1, Na1.2, Na1.3, Na1.6), neuronal channels (Na1.7, Na1.8 and Na1.9), skeletal muscle channels (Na1.4) and the cardiac sodium channel Na1.5. SCN5A is mainly expressed in the heart, where expression is abundant in working myocardium and conduction tissue. In contrast, expression is low in the sinoatrial node and atrioventricular node.
Heart block the atrioventricular node ("AV node") which also contains a secondary "pacemaker" that acts as a backup for the SA nodes, then to the bundle of His and then via the bundle branches to the point of the apex of the fascicular branches. Blockages are therefore classified based on where the blockage occurs - namely the SA node ("Sinoatrial block"), AV node ("AV block" or AVB), and at or below the bundle of His ("Intra-Hisian" or "Infra-Hisian block" respectively). Infra-Hisian blocks may occur at the left or right bundle branches ("bundle branch block") or the fascicles of the left bundle branch