SCN5A and long QT syndrome 12: In the myocardial deletion mutants, downregulated ion transport genes included Snta1 and Fxyd1. SNTA1 associates with the cardiac sodium channel SCN5A and the plasma membrane Ca2+-ATPase PMCA4B (also known as ATP2B4), and mutations in SNTA1 are associated with long QT syndrome 12 (Ueda et al., 2008).