Pathogenic KCNH2-G53S variant in the PAS domain influences the electrophysiological phenotype in long QT syndrome type 2

Background: Long QT syndrome type 2 (LQT2) is an arrythmia caused by loss-of-function mutations in KCNH2, leading to impaired Kv11.1 channel function. Objective: To better understand LQT2, we examined the electrophysiological differences related to the G53S variant, which is located within the PAS domain of KCNH2, using patient-specific human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (hiPSC-CMs). Methods: We generated hiPSC-CMs from a patient harboring the KCNH2^G53S variant and a healthy control using non-integrative Sendai virus-mediated reprogramming. Their electrophysiological properties were assessed using microelectrode arrays (MEA), and Ca²⁺ dynamics were characterized using Fluo-4 dye. Results: The patient harboring KCNH2^G53S experienced aborted sudden cardiac death at 22 years of age, was diagnosed with LQT, and had an implantable cardioverter-defibrillator (ICD) implanted. KCNH2^G53S hiPSC-CMs expressed less KCNH2 than normal CMs. Transcriptomic analysis of KCNH2^G53S hiPSC-CMs revealed 3,857 differentially expressed genes, highlighting significant changes in pathways related to LQT2 development. Action potential duration was significantly longer in KCNH2^G53S hiPSC-CMs than in control (545.3 ± 176.3 ms vs. 339.9 ± 44.5 ms; P = 0.019). Corrected field potential duration was significantly longer in KCNH2^G53S hiPSC-CMs than in control (318.0 ± 66.3 ms vs. 234.5 ± 21.0 ms; P = 0.015), indicating altered electrophysiology. KCNH2^G53S hiPSC-CMs exhibited significantly increased calcium transient amplitude and prolonged calcium wave duration under isoproterenol stimulation, indicating exacerbated abnormal calcium handling. Conclusion: Our analysis of hiPSC-CMs carrying a heterozygous KCNH2^G53S mutation, which showed abnormal electrophysiology and impaired calcium handling, provides a basis for developing improved management strategies for patients with LQT2.