Electrophysiological Study of V535M hERG Mutation of LQT2

This study examined the current changes of human ether-a-go-go-related gene （hERG） mutation derived from a LQT2 Chinese family with a highly penetrating phenotype. Mutation was identi-fied and site-directed mutagenesis was performed to induce the mutation in wild-type （WT） hERG. WT hERG and mutated V535M were cloned and transiently expressed in HEK293 cells. At the 48th and 72nd h after transfection, membrane currents were recorded using whole cell patch-clamp procedures. An A〉G transition at 1605 resulting in replacement of V535M was identified. Compared to WT, V535M mutation significantly decreased tail currents of hERG. At test potential of-40 mV after depolarizing at ＋50 mV, tail current densities were 83.354-7.06 pA/pF in WT and 50.38-4-7.74 pA/pF in V535M respectively （n=20, P〈0.01）. Gating kinetics of bERG revealed that Vl/2 of steady-state inactivation shifted to negative potential in the mutant （V1/2,v535M： -61.814-1.7 mV vs. V1/2, wx： -43.1q-0.71 mV）. The time constant of recovery from inactivation was markedly prolonged in the mutant compared to WT among test potentials. V535M hERG mutation demonstrated markedly decreased tail current densities, which suggests that V535M is a new loss-of-function mutation of hERG channel responsible for LQT2.

Mutation analysis of potassium channel genes KCNQ1 and KCNH2 in patients with long QT syndrome

Objective To determine mutations of two common potassium channel subunit genes KCNQ1, KCNH2 causing long QT syndrome (LQTS) in the Chinese.Methods Thirty-one Chinese LQTS pedigrees were characterized for mutations in the two LQTS genes, KCNQ1 and KCNH2, by sequencing.Results Two novel KCNQ1 mutations, S277L in the S5 domain and G306V in the channel pore, and two novel KCNH2 mutations, L413P in the transmembrane domain S1 and L559H in the transmembrane domain S5 were identified. The triggering factors for cardiac events developed in these mutation carriers included physical exercise and excitation. Mutation L413P in KCNH2 was associated with the notched T wave on ECGs. Mutation L559H in KCNH2 was associated with the typical bifid T wave on ECGs. Mutation S277L in KCNQ1 was associated with a high-amplitude T wave and G306V was associated with a low-amplitude T wave. Two likely polymorphisms, IVS11 +18C >T in KCNQ1 and L520V in KCNH2 were also identified in two LQTS patients.Conclusions The mutation rates for both KCNQ1 (6.4%) and KCNH2 (6.4%) are lower in the Chinese population than those from North America or Europe.