Mutation Analysis of KCNQ1, KCNH2 and SCN5A Genes in Taiwanese Long QT Syndrome Patients.

Long QT syndrome (LQTS) is a genetic cardiac disease. Gene mutation affects the structure or function of ion channels that are associated with a high risk of sudden death. The goal of this study was to determine the frequency of KCNQ1, KCNH2, and SCN5A mutations in LQTS in a Taiwanese population. Genomic DNA was extracted from peripheral blood samples obtained from 5 patients with LQTS and the family members of 3 LQTS patients. High resolution melting (HRM) analysis and direct DNA sequencing were used to characterize the KCNQ1, KCNH2, and SCN5A genetic variations. HRM analysis was successfully optimized for 14 of the 16 exons of the KCNQ1, 5 of the 15 exons of the KCNH2, and 23 of the 27 exons of the SCN5A. HRM and direct DNA sequencing was applied to the cohort of 5 cases and some of their family. The genetic testing revealed two pathogenic mutations (p.T309I in KCNQ1 and p.R744fs in KCNH2) and all of the mutational frequencies in KCNQ1 and KCNH2 were 20%. In the two patients who carry the pathogenic mutation presenting with recurrent syncope due to ventricular fibrillation, an implantable cardioverter defibrillator was implanted. We also discovered 11 polymorphisms in KCNQ1, 3 in KCNH2, and 5 in SCN5A. Two-fifths of cases (40%) presented with one of the three major LQTS-causing gene mutations.