A Basket Clinical Study to Assess Glycerol Tributyrate in Patients With Mitochondrial Encephalopathy, Lactic Acidosis, Stroke-like Episodes (MELAS) or Leber's Hereditary Optic Neuropathy-Plus (LHON-Plus)

This is a parallel arm non-randomized dose-escalation, open-label basket exploratory phase 1 clinical trial where Mitochondrial encephalopathy, lactic acidosis, stroke-like episodes (MELAS) and Leber's hereditary optic neuropathy-Plus (LHON-Plus) participants will undergo simultaneous enrollment in two disease-based arms and receive daily oral doses of glycerol tributyrate to assess its safety and potential for efficacy using clinical, biochemical, and molecular evidence. This study will utilize a two-month baseline lead-in phase to establish and document the clinical baseline for each participant in both arms in order to compare the molecular and clinical parameters. This is clinically relevant in light of the high clinical heterogeneity among subjects affected by the same mitochondrial disease (MELAS or LHON-Plus). For ethical concerns prompted by the lack of treatment for these two intractable and progressive mitochondrial diseases, there will not be a placebo control group. Thus, each participant will act as their own control and receive oral doses of glycerol tributyrate, eliminating the need for a placebo. Considering the high clinical heterogeneity among participants affected by MELAS or LHON-Plus and some clinical divergence between MELAS and LHON-Plus, this strategy is beneficial to every enrolled participants, as each will receive the investigational drug, glycerol tributyrate. In addition, this approach will determine the subject-specific maximal optimized dose in a personalized medicine-based approach. After approval of the IRB protocol from the Institutional Review Board Data and signed consent form from all participants, this investigational basket clinical trial has three phases spanning over 20 months: * A baseline lead-in phase (2 months) to collect participant-specific baseline for clinical, biochemical, molecular and metabolic biomarkers that will be monitored throughout the subsequent dose-escalation and clinical phases. * A dose-escalation phase (6 months) to determine the participant-specific maximum tolerated dose (MTD) during which participant-specific clinical and biochemical biomarkers are collected every month. * A clinical phase at a fixed subject-specific MTD dose (12 months) to collect participant-specific clinical, biochemical, molecular and metabolic biomarkers and to perform three scheduled skin biopsies: at the outset, mid-point, and the end of this clinucal phase. We have planned for a 12-month-long clinical phase at a fixed participant-specific MTD considering the absence of reliable predictors that makes idiosyncratic disease-specific symptoms for MELAS and LHON-Plus impossible to forecast among participant for assessing the potential efficacy of glycerol tributyrate by monitoring clinical symptoms specific for each disease. During the 12-month-long time-frame, disease-specific clinical symptoms will be collected as preliminary evidence of efficacy of glycerol tributyrate using disease-specific biomarkers. Finally, discharge procedure during which the clinical investigator will record non-serious adverse events or serious adverse events for 7 or 30 days, respectively, after the last day of study participation.