Inclusion Criteria:  Participants with inherited mitochondrial disease including Leigh syndrome, Alpers syndrome, mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS), myoclonic epilepsy with ragged-red fibers (MERRF), pontocerebellar hypoplasia type 6 (PCH6), or other mitochondrial disease who participated in a previous vatiquinone clinical study or treatment plan. Women of childbearing potential must have a negative pregnancy test at screening/baseline and agree to abstinence or the use of at least 1 of the highly effective forms of contraception as specified in the protocol (with a failure rate of <1% per year when used consistently and correctly). Highly effective contraception or abstinence must be continued for the duration of the study, and for up to 50 days after the last dose of study drug. Fertile men who are sexually active with women of childbearing potential and who have not had a vasectomy, must agree to use a barrier method of birth control during the study and for up to 50 days after the last dose of study drug.  Exclusion Criteria:  Current participation in any other interventional study. Pregnancy or breast feeding.