It was shown that in both heterozygous and homozygous conditions, the T634S-hERG mutation increased the simulated QT interval, which changed from 354 ms in WT to 409 ms and 463 ms in heterozygous and homozygous mutation conditions (electronic supplementary material, figure S8), demonstrating a causal link between the reduction in IKr due to the T634S-hERG mutation and QT interval prolongation, which is a main feature of an LQTS phenotype. The gene discussed is KCNH2; the disease is familial long QT syndrome.