Coenzyme Q10 deficiency and isolated myopathy.

Three unrelated, sporadic patients with muscle coenzyme Q10 (CoQ10) deficiency presented at 32, 29, and 6 years of age with proximal muscle weakness and elevated serum creatine kinase (CK) and lactate levels, but without myoglobinuria, ataxia, or seizures. Muscle biopsy showed lipid storage myopathy, combined deficiency of respiratory chain complexes I and III, and CoQ10 levels below 50% of normal. Oral high-dose CoQ10 supplementation improved muscle strength dramatically and normalized serum CK.