Aims: The purpose of this study is to review different aspects of mitochondrial myopathies.
Development: Mitochondrial DNA is different to that found in the nucleus and is generally inherited through the mother. There are from 2 to 10 copies per mitochondrion and hundreds or thousands of mitochondria per cell. It contains 37 genes. The oxidative phosphorylation system consists of five enzymatic complexes. Mitochondrial diseases can affect many organs but somewhat more frequent in tissues that are physiologically more demanding as regards oxidative phosphorylation, such as the nervous system, the heart and skeletal muscle. Diagnosis of mitochondrial disease is performed by studying skeletal muscle because it is easily accessible and because of its dependence on oxidative metabolism; moreover, deficits in the respiratory chain are often not expressed in cultivated fibroblasts.
Conclusions: The bioptic muscle specimen must be frozen using isopentane for later histochemical examination. For study under the electron microscope, a small sample must be set in glutaraldehyde or a similar fixative. A 150 mg (5 mm3) fragment which has been frozen without isopentane should be used for the study of the respiratory chain, although fresh muscle tissue is needed for the examination of the complex V. About 50 mg of frozen tissue are required for the study of the mitochondrial mutations.