Abstract Body (Do not enter title and authors here): Background:
Type 2 Long QT Syndrome (LQT₂), caused by KCNH₂ mutations, is associated with an increased risk of sudden cardiac death (SCD). Clinical severity varies considerably among carriers. We investigated a family harboring the KCNH₂ p.Y427H variant, comprising a symptomatic proband (nine cardiac events), an asymptomatic carrier mother, and a mutation-negative father.
Hypothesis:
We hypothesized that patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) can recapitulate the observed clinical phenotype discordance in vitro.
Methods:
Whole-exome sequencing identified the variant. Peripheral blood mononuclear cells (PBMCs) from all three individuals were reprogrammed into iPSCs and differentiated into cardiomyocytes. Electrophysiological assessment included patch-clamp recordings of I_Kr and I_Ca,L, measurements of action potential duration APD₉₀ and APD₅₀ under pacing, and evaluation of early afterdepolarizations (EADs) and triggered activities (TAs) under spontaneous conditions. Nifedipine, an L-type calcium channel blocker, was used to evaluate arrhythmia suppression.
Results:
I_Kr was markedly reduced in the proband-derived iPSC-CMs (0.26 [0.19–0.29] pA/pF) and mother-derived iPSC-CMs (0.29 [0.27–0.30]) compared to the father-derived iPSC-CMs (1.65 [1.23–2.11], P = 0.001). APD₉₀ was significantly prolonged in the proband-derived iPSC-CMs (824 [691–893] ms) versus the mother-derived iPSC-CMs (559 [491–574] ms, P = 0.010) and father-derived iPSC-CMs (397 [331–403] ms, P < 0.001). Proband-derived iPSC-CMs exhibited a higher incidence of spontaneous EADs and TAs. Notably, I_Ca,L was upregulated in the proband-derived iPSC-CMs (–18.4 [–19.6 to –13.0] pA/pF) compared to the mother-derived iPSC-CMs (–7.23 [–9.5 to –5.9], P = 0.002) and father-derived iPSC-CMs (–7.49 [–8.66 to –5.91], P = 0.001). Nifedipine significantly suppressed EADs and TAs in the proband-derived iPSC-CMs.
Conclusion:
The KCNH₂ p.Y427H variant induces I_Kr loss-of-function. Divergent calcium current responses among family members may reflect a compensatory mechanism modulating phenotypic severity. Patient-specific iPSC-CMs reproduce this variability, providing a platform for mechanistic insights, personalized risk assessment, and therapy in LQT₂.