Mitochondrial encephalomyopathy and partial cytochrome c oxidase deficiency.

A 52-year-old man had slowly progressive weakness and wasting of limb-muscles, sensorineural hearing loss, and complex partial seizures. CT showed cerebral atrophy, but he was not demented. Muscle biopsy showed ragged-red fibers and decreased histochemical stain for cytochrome c oxidase. Biochemical studies showed decreased cytochrome c oxidase activity in crude muscle extracts and in isolated mitochondria (44 and 30% of normal), while other mitochondrial enzymes were normal. A comparable decrease of immunologically reactive enzyme protein was shown by immunotitration with antibodies against human heart cytochrome c oxidase. Partial defects of cytochrome c oxidase may cause adult-onset, slowly progressive mitochondrial encephalomyopathies.