MODELING LONG QT SYNDROME IN IPS-DERIVED CARDIOMYOCYTES FROM A PATIENT HARBORING THE KCNQ1- I588T MUTATION

Background Human induced pluripotent stem (iPS) cell-derived cardiomyocytes (hiPSC‐CMs) technology offers an unprecedented tool to study cardiac diseases. Long QT syndrome type 1 (LQT1) is an inherited cardiac channelopathy caused by mutations in KCNQ1, which encodes the main subunit of the potassium channel Kv 7.1, leading to delayed repolarizations and imposing potentially fatal arrhythmias on patients. Therefore, the in vitro patient-specific modeling of LQT1 is crucial to test the pathogenicity of the KCNQ1- I588T mutation. Objective The purpose of this study was to test a cellular model of LQT1 based on a KCNQ1-I588T mutation using hiPSC‐CMs. Methods Peripheral blood was collected from a proband (a 15-year-old LQT1 symptomatic patient carrying KCNQ1-I588T mutation), a carrier donor (non-symptomatic familial carrying KCNQ1 mutation), and an unrelated control donor. The erythroblast enriched fraction was reprogrammed into iPS using Sendai virus vector. iPS were characterized for pluripotency markers by RT-PCR and flow cytometry, in vitro spontaneous differentiation, and karyotype stability. iPS were differentiated into cardiomyocytes and electrophysiological studies were performed. Results The proband was clinically diagnosed with LQT1 with resting corrected QT interval equal to 516 ms. The KCNQ1 mutation (c.1763T>C; p.I588T) was identified by NGS in the proband DNA sample. By Sanger, the same mutation was identified in the familial carrier while it was absent in the control subject. Erythroblasts were successfully reprogrammed into iPS. All iPS expressed the 13 different pluripotent markers evaluated, differentiated into three germ layers and presented a normal chromosomic profile. The differentiation protocol generated cells positive for cardiac troponin T. As expected, proband hiPSC‐CMs exhibited prolongation of action potential duration (APD90 = 312 ± 79 ms) when compared to carrier donor and control donor hiPS-CMs (APD90 = 177 ± 68 and 271 ± 71 ms, respectively). Since the mutation is the same in both the proband and the carrier, a protective/damaging molecular regulation must be involved. We speculate that a polymorphism identified only in the proband (SCN5A c.1673A>G; p.H558R) may be involved in this mechanism. Conclusions We identified an LQT1 causative variant that successfully recapitulated LQT1 proband phenotype by in vitro modeling. We also propose the existence of a second variant with a damaging effect on LQT1 symptom development.