Three cases of chronic progressive external ophthalmoplegia demonstrated ragged-red fibers. Histochemical stains showed that the ragged-red fiber appearance was produced by abnormal mitochondria in the muscle. Electron microscopic studies demonstrated the ultrastructural origin of the intramitochondrial inclusions seen in ragged-red fibers. The associated abnormalities in lactic acid metabolism possibly represent an underlying generalized defect in metabolism. This evidence suggests that chronic progressive external ophthalmoplegia is a diffuse disease of the mitochondria.
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