Most GoF conditions in Nav1.5 result in Long-QT syndromes that often degenerate into more lethal forms of arrhythmias, including torsade-de-pointes or ventricular tachycardia and ventricular fibrillation (Gimrikh et al., 1985; Antzelevitch et al., 1996). Here, SCN5A is linked to cardiac arrhythmia.