We obtained high-quality DNA from 70 cases, which were then sequenced for a custom panel of 35 genes, 12 for inherited long- and short-QT syndrome genes (LQT1-LQT12 and SQT1-3), and 23 additional candidate genes derived from genome-wide association studies.
PCR and bidirectional Sanger sequencing of genes important for long QT syndrome (LQTS), short QT syndrome (SQTS), Brugada syndrome type 1 (BrS1), and catecholaminergic polymorphic ventricular tachycardia (CPVT) (KCNQ1, KCNH2, SCN5A, KCNE1, KCNE2, and RYR2) was performed.
Mutations in either KCNQ1 or KCNE1 are responsible for at least four channelopathies that lead to cardiac dysfunction and one that leads to congenital deafness: the Romano-Ward syndrome, the short QT syndrome, atrial fibrillation, and the Jervell and Lange-Nielsen syndrome (cardioauditory syndrome).
A gain-of-function <i>KCNJ2</i> D172N mutation in KCNJ2-encoded Kir2.1 channels underlies one form of short QT syndrome (SQT3), which is associated with increased susceptibility to arrhythmias and sudden death.
The SQTS variant 3 is linked to D172N mutation to the KCNJ2 gene that causes a gain-of-function to the inward rectifier potassium channel current (I <sub>K1</sub>), which shortens the ventricular action potential duration (APD) and effective refractory period (ERP).
Three different gain-of-function mutations in genes encoding for cardiac potassium channels (KCNH2, KCNQ1, and KCNJ2) have been identified up to now to cause short QT syndrome.
A benign variety of the disease has been observed in children with atrial fibrillation and a KCNH2-V141M mutation, and recently a mutation in the cardiac Cl/HCO<sub>3</sub> exchanger AE3 was found to cause SQTS.
Areas covered: The genetic basis for genotyped SQTS variants (SQT1-SQT8) and evidence for arrhythmia substrates from experimental and simulation studies are discussed.
We obtained high-quality DNA from 70 cases, which were then sequenced for a custom panel of 35 genes, 12 for inherited long- and short-QT syndrome genes (LQT1-LQT12 and SQT1-3), and 23 additional candidate genes derived from genome-wide association studies.
SQT1 variant (linked to the rapid delayed rectifier potassium channel current, IKr) of SQTS, results from an inactivation-attenuated, gain-of-function mutation (N588K) in the KCNH2-encoded potassium channels.
The LQT2 was produced by intravenous infusion with dofetilide (n = 6), quinidine (n = 6) and sotalol (n = 6) whereas the SQTS was induced by intravenous escalating concentrations of nicorandil (n = 7), pinacidil (n = 5) and cromakalim (n = 5).
Gain-of-function mutations to potassium channels mediating the rapid delayed rectifier current, <i>I</i><sub>Kr</sub>, underlie SQTS variant 1 (SQT1), in which treatment with Na<sup>+</sup> and K<sup>+</sup> channel blocking class Ia anti-arrhythmic agents has demonstrated some efficacy.