EOI-743 is a promising new drug for the treatment of hereditary respiratory chain disease, known as mitochondrial disease. EPI-743 is a small molecule of polyphenylquinone whose primary mechanism of action is to restore already reduced intracellular glutathione levels in patients with mitochondrial disease. The U.S. Food and Drug Administration has approved EPI-743 for clinical trials in genetically confirmed hereditary respiratory chain diseases. Completed Phase I and Phase IIa clinical trials have demonstrated that patients with Leigh syndrome taking the drug have stopped progressing, have improved clinical symptoms and imaging, and have had no serious adverse events. A Phase IIb trial is currently underway in which 30 children with mitochondrial disease will be randomized into two groups: a treatment group taking EPI-743 and a control group taking placebo. 6 months after the end of the trial, the treatment group will be allowed to continue taking EPI-743 for 6 months and the placebo group will be allowed to take EPI-743 for 6 months. EPI-743 Phase IIb clinical trial enrollment criteria 1. Age 1-12 years. 2, cranial MRI consistent with leigh syndrome. 3, Moderate disease severity, with disease progression in the past year. 4, Patient informed consent, and permission from an authorized treatment center.