SCN5A and long QT syndrome 3: There is a rapid growing interest for clinical diagnosis of the disease genes that underlie genetic heart rhythm disorders since the discovery of the first Long QT type 3 syndrome-associated genes in 19954, 12, As mentioned, a collection of cardiac diseases are caused by a single channelopathy gene SCN5A. Alternatively, 13 distinct disease-causing genes are implicated in a single OMIM entity, the conduction system disease13, suggesting a more complex genetic heterogeneity than previously thought.