iPSC Derived Cardiomyocytes Reproduce Divergent Phenotypes Caused by a LQTS Type-1 Likely Pathogenic Mutation

The purpose of this work was to investigate if iPSC derived cardiomyocytes would reproduce the divergent phenotypes observed in a proband and mother that carried the same likely-pathogenic variant in KCNQ1 gene. A 15 years old proband had syncope and cardiac arrest while swimming being diagnosed with LQTS based on a 12 lead ECG. The mother’s ECG showed no abnormalities. Genomic DNA from blood of daughter and mother was extracted using standard procedures. All coding exons and flanking intronic sequences of KCNQ1 (NM_000218) genes were amplified by polymerase chain reaction. Direct sequencing was performed on a 3500XL Genetic Analyzer. Data was analyzed with Geneious software for identification of mutations. For iPSC generation CD71+ CD36+ erythroblasts were reprogrammed using CytoTune™-iPS 2.0 Sendai Reprogramming Kit on irradiated mouse embryonic fibroblast feeder layers. Differentiation into cardiomyocytes was accomplished using the protocol described by Lian et al. (2012). Electrophysiological recordings were obtained from cardiomyocytes after 30–45 days of differentiation. Cells were transferred to acrylic plates pretreated with Matrigel and kept in culture for 3 days before microelectrode action potential (AP) were registered. The ECG recordings showed a corrected QT interval (QTc) of 516 ms for the daughter and 436 ms for the mother. Sequencing showed that both daughter and mother had a c.1763C>T mutation resulting in p.Ile588Thr substitution. iPSC generated from daughter, mother and an unrelated control displayed normal karyotype and expressed pluripotent genes, besides spontaneously differentiating into cells of the three germ layers. Differentiation into cardiomyocytes was ascertained by immunofluorescence and flow cytometry for troponin T. In all differentiations more than 70% of cells were cardiomyocytes. Action potentials recordings showed that ventricular cardiomyocytes from the daughter exhibited significantly longer action potential durations at 90% repolarization than the mother’s or the unrelated control’s cardiomyocytes. Cardiomyocytes derived from iPS cells reproduced the clinical phenotypes exhibited by daughter and mother.