Mitochondrial myopathies: defects in mitochondrial metabolism in human skeletal muscle.

An uncommon but increasingly diagnosed clinical situation in humans is mitochondrial myopathy, a condition in which muscle function is impaired by defective mitochondrial metabolism in the generation of energy for muscle contraction. It is also now clear that abnormalities of mitochondrial function are not limited to muscle, but may also underlie multisystem disease, in which other tissues are involved and vision and cerebral function may be impaired (Morgan-Hughes, 1982; Morgan-Hughes et al., 1977, 1979, 1983). The clinical picture is therefore variable, but most patients show a marked fatiguability and lacticacidosis even after relatively limited exercise. The spectrum