Study of Idebenone in the Treatment of Mitochondrial Encephalopathy Lactic Acidosis & Stroke-like Episodes

Inclusion Criteria: * Diagnosis of MELAS with confirmed A3243G mtDNA mutation, or evidence of central nervous system involvement (cognitive problems, migraines, memory loss) * Cerebral lactate level equal to or greater than 5.0 i.u. at baseline * Patients at least 8 and \< 65 years of age at baseline * Patients with a body weight \> 37 kg/82 lbs at baseline * Stable co-medication/vitamins/supplements within 1 month prior to baseline * Patients who in the opinion of the investigator are able to comply with the requirements of the study, including swallowing the study medication * Negative urine pregnancy test at screening and baseline (female patients of childbearing potential) Exclusion Criteria: * Contraindication to MRS (e.g. metal implant, claustrophobia) * Stroke like event within 2 months prior to baseline * Treatment with idebenone at any dose, or coenzyme Q10 at doses above 100mg/d within 1 month prior to baseline * Inadequate contraception use * Pregnancy and/or breast-feeding * Clinically significant abnormalities of clinical hematology or biochemistry including, but not limited to, elevations greater than 1.5 times the upper limit of normal of aspartate aminotransferase (AST), alanine aminotransferase (ALT) or creatinine * Current abuse of drugs or alcohol * Participation in a trial of another investigational drug within the last month * Other factor that, in the investigator's opinion, excludes the patient from entering the study