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)

Inclusion Criteria: * Participants must be aged 18 to 65 years * A confirmed molecular diagnosis of MELAS or LHON-Plus * Symptomatic participants with MELAS harboring the m.3243A\>G variant or a mitochondrial pathogenic variant solely mapping in a mitochondrial gene encoding a mitochondrial subunit of Complex I * Symptomatic participants with LHON-Plus harboring the m.11778G\>A or a mitochondrial pathogenic variant only mapping in a mitochondrial gene encoding a mitochondrial subunit of Complex I * Normal enzymatic Complex II activity * Participants able to swallow capsules and comply with the requirements of the study according to the opinion of the investigator * Able to give written, informed consent * Participants who are sexually active and/or fertile must use an effective birth control during the study Exclusion Criteria: * • History of another primary mitochondrial disorder * Participants acutely ill * Positive urine pregnancy test for female subjects of childbearing potential within seven days prior to the first dose of the investigational drug * Pregnancy and/or breastfeeding * Participating in another mitochondrial disorder trial * Participated in another mitochondrial disorder trial within the last six months * On a current therapy with other investigational agents * Absence of neurological symptoms, muscle weakness, or exercise intolerance * Presence of any of the following signs or symptoms in the past six months at grade 3 or higher based on the CTCAE version 4.03: nausea, vomiting, diarrhea, hypoglycemia, hyperglycemia, dizziness, blurred vision, or syncope * A known hypersensitivity to any excipient contained in the drug formulation * Current abuse of drugs and/or alcohol * Unable to consent for themselves * Participants with an enteral feeding tube * Inability to travel to the study site