Coenzyme Q10 (
CoQ10) transfers electrons from complexes I and II of the mitochondrial respiratory chain to
complex III. There is one published report of human
CoQ10 deficiency describing two sisters with
encephalopathy, proximal weakness,
myoglobinuria, and
lactic acidosis. We report a patient who had delayed motor milestones, proximal weakness, premature exertional
fatigue, and episodes of exercise-induced pigmenturia. She also developed partial-complex
seizures. Serum
creatine kinase was approximately four times the upper limit of normal and venous
lactate was mildly elevated. Skeletal muscle biopsy revealed many ragged-red fibers,
cytochrome c oxidase-deficient fibers, and excess
lipid. In isolated muscle mitochondria, impaired oxygen consumption was corrected by the addition of
decylubiquinone. During standardized exercise, ventilatory and circulatory responses were compatible with a defect of oxidation-phosphorylation, which was confirmed by near-infrared spectroscopy analysis. Biochemical analysis of muscle extracts revealed decreased activities of complexes I+II and I+III, while
CoQ10 concentration was less than 25% of normal. With a brief course of
CoQ10 (150 mg daily), the patient reported subjective improvement. The triad of CNS involvement,
recurrent myoglobinuria, and ragged-red fibers should alert clinicians to the possibility of
CoQ10 deficiency.