A Study to Evaluate Efficacy and Safety of Vatiquinone for Treating Mitochondrial Disease in Participants With Refractory Epilepsy

Inclusion Criteria: * Signed informed consent form. * Participant or parent/legal guardian is able and willing to complete seizure diaries for the duration of the study. * Genetic confirmation of inherited mitochondrial disease with associated epilepsy phenotype (Alpers/polymerase subunit gamma \[POLG\], Leigh syndrome, mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes \[MELAS\]), or other genetically confirmed mitochondrial disease secondary to mitochondrial mutations (Pontocerebellar Hypoplasia Type 6 \[PCH6\], nuclear DNA RARS2 mutation) or myoclonic epilepsy with ragged red fibers (MERRF, mitochondrial DNA \[mtDNA\] mitochondrially encoded tRNA lysine \[MT-TK\] mutation). * Despite ongoing treatment with at least 2 antiepileptic drugs: * have ≥6 observed motor seizures occurring during the 28 days prior to the baseline visit (Day 0). * have ≥2 observed motor seizures in the first 14 days and ≥2 in the second 14 days of the Run-in period (Day -14). * do not have a consecutive 20-day seizure free period. * have at least 80% of seizure diary data. * Documented medical history of epilepsy associated with mitochondrial disease for at least 6 months prior to screening except for participants who are \<2 years of age at the time of screening (participants \<2 years of age can be considered for enrollment if all other screening criteria are met due to the potential for rapid progression in these participants). * Consent to abstain from non-approved…