CHARACTERIZATION OF COMPOUND HETEROZYGOSITY FOR MUTATIONS R269W IN KCNH2 AND P1824A IN SCN5A ASSOCIATED WITH LONG QT SYNDROME AND SINUS NODE DYSFUNCTION

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Methods: The functional consequence of the mutations were assessed by whole-cell patch clamp recording of mutant channels in a cultured cell lines. With mathematical models of human ventricular myocytes and peripheral sinoatrial node (SAN) cells, we evaluated the changes in kinetic behavior of IKr and INa on the action potential configuration and pacemaker activity. Results: From genetic analysis for 20 probands who presented bradyarrhythmia and had a family history (e.g. implantation of a pacemaker), we identified two heterozygous missense mutations in the KCNH2 and SCN5A genes (R269W in KCNH2 and P1824A in SCN5A) in a patient with both sinoatrial and atrioventricular block, and marked QT prolongation. Electrophysiological study revealed that the outward tail current density at -50mV after a depolarization to +40mV in CHO cells expressing KCNH2 R269W was 51% of wild type (WT) (p<0.05). V1/2 of steady-state inactivation curve in KCNH2 R269W shifted by 30.7 mV in the negative direction compared to WT (p<0.05). On the other hand, peak sodium current amplitude at -40mV in HEK293 cells expressing SCN5A P1824A was 54% of WT (p<0.05). SCN5A P1824A produced a positive shift in the voltage dependence of activation (+5.0 mV, p<0.05) compared to WT. Simulation study showed that these mutational changes consequently prolonged the midmyocardial action potential duration by 58 % in mutant model of human ventricular myocytes. The study also showed that INa and IKr of the patient peripheral SAN model were much smaller, and increasing gap junction conductance caused arrhythmic dynamics (skipped-beat runs). Conclusions: These results demonstrate that KCNH2 R269W may mainly contribute to QT prolongation, and SCN5A P1824A may contribute to sinus node dysfunction and conduction disease as clinical phenotype expressions.