Open-Label, Dose-Escalating Study Assessing Safety, Tolerability, Efficacy, of RP103 in Mitochondrial Disease

This is an open-label, dose-escalation study to assess the safety, tolerability, efficacy, pharmacokinetics and pharmacodynamics of cysteamine bitartrate delayed-release capsules (RP103) for treatment of children with inherited mitochondrial disease. Prior to treatment, patients will undergo a Screening Visit. If eligible, each participant will return for the Day 1 study visit and begin dosing. Every 2 weeks over the subsequent 8 weeks, participants will alternate between returning to the clinic for detailed assessments (Weeks 4 and 8) and receiving a telephone call from the Investigator team to assess safety and RP103 dose (Weeks 2 and 6) and the potential need for an immediate unscheduled study visit. Thereafter, participants will continue to return to the clinic every 4 weeks for detailed assessments at Weeks 12, 16, 20, and 24 (the Study Exit visit). The Study Exit visit will occur at Week 24, and participants will be offered the opportunity to continue on to an extension study (RP103-MITO-002 \[NCT02473445\]) until results of the present study are known. Study with completed results acquired from Horizon in 2024.