Among the genetic modifiers, the nitric oxide synthase 1 adaptor protein (NOS1AP) gene, also known as the carboxyl- terminal PDZ ligand of neuronal nitric oxide synthase (CAPON) [4] gene, has emerged as a significant genetic marker of QT interval prolongation and arrhythmia risk in the general population [5–12], as well as in LQTS [13, 14]. The gene discussed is NOS1AP; the disease is familial long QT syndrome.