MITOCHONDRIAL ENCEPHALOMYOPATHY WITH COENZYME Q(10) DEFICIENCY

Coenzyme Q(10) (CoQ(10)) transfers electrons from complexes I and II o f the mitochondrial respiratory chain to complex III. There is one pub lished report of human CoQ(10) deficiency describing two sisters with encephalopathy, proximal weakness, myoglobinuria, and lactic acidosis. We report a patient who had delayed motor milestones, proximal weakne ss, premature exertional fatigue, and episodes of exercise-induced pig menturia. She also developed partial-complex seizures. Serum creatine kinase was approximately four times the upper limit of normal and veno us lactate was mildly elevated. Skeletal muscle biopsy revealed many r agged-red fibers, cytochrome c oxidase-deficient fibers, and excess li pid. In isolated muscle mitochondria, impaired oxygen consumption was corrected by the addition of decylubiquinone. During standardized exer cise, ventilatory and circulatory responses were compatible with a def ect of oxidation-phosphorylation, which was confirmed by near-infrared spectroscopy analysis. Biochemical analysis of muscle extracts reveal ed decreased activities of complexes I+II and I+III, while CoQ(10) con centration was less than 25% of normal. With a brief course of CoQ(10) (150 mg daily), the patient reported subjective improvement. The tria d of CNS involvement, recurrent myoglobinuria, and ragged-red fibers s hould alert clinicians to the possibility of CoQ(10) deficiency.