Characterization of a novel missense mutation in the pore of HERG in a patient with long QT Syndrome

HERG Mutation and Long QT Syndrome. Introduction: A new strategy to elucida te the molecular mechanisms underlying the long QT syndrome (LQTS) is now a vailable with genetic mutational analyses and characterization of ion chann el mutations. Methods and Results: In a 26-year-old woman with LQTS, we identified a nove l missense mutation in the pore of HERG by using polymerase chain reaction/ single-strand conformation polymorphism (PCR/SSCP) and sequencing of her ge nomic DNA. The mutation resulted in an amino acid substitution of a positiv ely charged lysine for a highly conserved uncharged asparagine at codon 629 (N629K). Whole cell, patch clamp studies were conducted in COS7 cells by t ransfecting with wild-type (WT) and/or the mutant N629K HERG, The WT HERG p roduced an I-Kr-like, E-4031-sensitive conductance with an inward rectifica tion, In contrast, the cells transfected with the N629K HERG did not displa y any time-dependent current. Cotransfection of WT and N629K HERG (at a rat io of 1:1) produced a significantly smaller conductance when compared with WT HERG (WT 59.9 +/- 7.3 pA/pF [n = 22] vs WT+N629K 5.5 +/- 2.3 pA/pF [n = 11]; P < 0.01), but did not alter K+ ion selectivity and tail current-volta ge dependence. Because aprindine hydrochloride was effective in preventing ventricular tachycardias, we also tested the effect of the drug on WT HERG (I-Kr) and KvLQT1/KCNE1 (I-Ks) currents expressed in COS7. Conclusion: Functional analyses of a novel missense mutation in the pore of HERG suggest that the mutation causes marked reduction of I-Kr via a domin ant negative effect.