[Mitochondrial cytopathies].

Mitochondrial cytopathies are diseases due to a defect of mitochondrial respiratory chain and are characterized by the presence of morphological abnormalities of mitochondria (ragged red fibers). The clinical manifestations can be polymorphic as various organs may be involved; but in general, these disorders affect either muscle alone (progressive external ophtalmoplegia, myopathy with weakness) or muscle and brain (encephalomyopathies). Some of these diseases may be due to alterations of the mitochondrial genome. Diagnosis can be achieved through the following steps: measurement of lactate, pyruvate and ketone bodies after fasting followed by a carbohydrate rich meal and/or exercise; histological examination and biochemical investigation of a skeletal muscle biopsy; study of possible mitochondrial genome alterations.