Evaluation of the Efficacy and Safety of THRV-1268 in Participants With Long QT Syndrome Type 2 (LQTS2) and Type 3 (LQTS3)

The goal of this clinical trial is to learn whether the study drug THRV-1268 can safely and effectively shorten the QT interval in people diagnosed with Long QT Syndrome Type 2 (LQTS 2) and Long QT Syndrome Type 3 (LQTS 3). The study will also learn about the safety and tolerability of THRV-1268 at different doses. The main questions this study aims to answer are: Does THRV-1268 reduce the QTc interval (a measure of the heart's electrical recovery time)? What side effects or medical problems occur when participants take THRV-1268? Which dose of THRV-1268 works best and is safest? Participants will: Complete a 3-week observation period with ECG and Holter monitoring to establish baseline QTc measurements Take THRV-1268 twice daily at two dose levels for 6 weeks (Part A) or be randomly assigned to a dose group for 6 weeks (Part B - cohort 1) Have clinic visits and tests to monitor safety and changes in their heart rhythm May continue taking THRV-1268 for up to 1 year for ongoing safety and efficacy evaluation Researchers will compare changes in QTc over time and evaluate side effects to determine whether THRV-1268 can help reduce the risk of abnormal heart rhythms and sudden cardiac events in people with LQTS 2 and LQTS 3.