Mitochondrial myopathy

Mitochondrial myopathy
Other names	Mitochondrial muscle disease; muscle mitochondrinopathy; muscle mitochondrial dysfunction
Simplified structure of a typical mitochondrion
Specialty	Neuromuscular medicine

Mitochondrial myopathies are types of myopathies associated with mitochondrial disease.^[1] Adenosine triphosphate (ATP), the chemical used to provide energy for the cell, cannot be produced sufficiently by oxidative phosphorylation when the mitochondrion is either damaged or missing necessary enzymes or transport proteins. With ATP production deficient in mitochondria, there is an over-reliance on anaerobic glycolysis which leads to lactic acidosis either at rest or exercise-induced.^[2]

Primary mitochondrial myopathies are inherited, while secondary mitochondrial myopathies may be inherited (e.g. Duchenne's muscular dystrophy)^[3] or environmental (e.g. alcoholic myopathy^[4][5]). When it is an inherited primary disease, it is one of the metabolic myopathies.^[6][4]

On biopsy, the muscle tissue of patients with these diseases usually demonstrate "ragged red" muscle fibers on Gomori trichrome staining. The ragged-red appearance is due to a buildup of abnormal mitochondria underneath the plasma membrane.^[7] These ragged-red fibres may contain normal or abnormally increased accumulations of glycogen and neutral lipids, with histochemical staining showing abnormal respiratory chain involvement, such as decreased succinate dehydrogenase or cytochrome c oxidase.^[8] Inheritance was believed to be maternal (non-Mendelian extranuclear). It is now known that certain nuclear DNA deletions can also cause mitochondrial myopathy such as the OPA1 gene deletion.^[6]