Childhood mitochondrial myopathy with ophthalmoplegia.

A 14-year-old boy with mitochondrial myopathy is described, and the findings on muscle biopsy shown. He presented with mild weakness, and severe exercise intolerance; examination showed ptosis, external ophthalmoplegia and severe muscle wasting. There was a possible family history of a similar disorder. Metabolic study demonstrated severe lactic acidosis on exercise. Oxygen consumption was measured and found abnormally high at rest and on exercise. Biochemical study of extracted muscle mitochondria showed decreased respiratory rates with NAD-linked substrates. These and other results suggest the site of the defect to be in the electron transport chain. The possible significance of abnormally high oxygen consumption in the presence of such a defect is discussed.