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