,113,142 The gene variants associated with gain-of-function of the Scn5a gene, which encodes the Nav1.5 sodium channel, can lead to a prolongation of the plateau, in addition to a slower and prolonged repolarization phase, due to an increase in late Na+ current (as seen in long QT syndrome type 3), and therefore, provoke a longer action-potential duration.148. This evidence concerns the gene SCN5A and long QT syndrome 3.