A mitochondrial myopathy with a defective respiratory chain and carnitine deficiency

A boy presented suffering from generalised weakness, exercise intolerance and lactic acidosis. The weakness became evident at 2 years. A cerebral CT-scan showed cerebellar atrophy and central and peripheral atrophy of both hemispheres. With trichrome staining about 20% of the muscle fibres showed large areas containing red-staining granular material. Electron microscopic examination showed that this material consisted of areas of mitochondrial proliferation, most of the mitochondria having abnormal ultrastructural characteristics. Pyruvate dehydrogenase complex and citric acid cycle activities were determined by measuring 14CO2 production from various labelled substrates. Diminished oxidation rates were found with the patient's muscle homogenate for all substrates tested, indicating a defect in the respiratory chain. The cytochromes were present in normal quantities. Succinate cytochrome c reductase activity was very decreased. Carnitine concentration was decreased in serum and in muscle as well.