Functional characterization and allele-specific RNA interference-based rescue of KCNH2 p.F68C variant associated with...

Long QT syndrome (LQTS) is an inherited life-threatening cardiac disorder characterized by delayed ventricular repolarization and increased risk of malignant arrhythmias. Among its subtypes, long QT syndrome type 2 (LQT2) is primarily caused by pathogenic variants in KCNH2, which encodes the human ether-à-go-go-related gene (hERG) potassium channel responsible for the rapid delayed rectifier current (I_Kr). However, the substantial functional heterogeneity among KCNH2 variants poses a major challenge for clinical interpretation and precision intervention. In this study, we sought to functionally characterize KCNH2 p.F68C variant (c.203T > G) identified in a Chinese LQT2 patient and to evaluate the feasibility of RNA interference-based modulation of its functional impact on the hERG channel. Using biochemical and electrophysiological analyses in HEK293T cells, we show that variant p.F68C causes a severe trafficking defect and exerts a dominant-negative effect on wild-type hERG channels, leading to markedly reduced rapid delayed rectifier potassium current (I_Kr). In contrast to several previously reported Per-Arnt-Sim (PAS) domain variants, the trafficking defect of p.F68C was resistant to reduced culture temperature, chemical chaperones, and pharmacological chaperones. Notably, allele-specific RNA interference selectively suppressed mutant hERG expression, alleviated dominant-negative interference, and partially restored hERG current density without detectable cytotoxicity. Together, these findings establish p.F68C as a loss-of-function KCNH2 variant and highlight allele-specific RNA interference as a variant-directed strategy that may serve as an alternative to suppression-replacement approaches, providing a basis for functional interpretation and precision therapeutic exploration of individual KCNH2 variants.