title: Mitochondrial myopathies.
abstract: OBJECTIVE
  Our understanding of mitochondrial diseases (defined restrictively as defects of the mitochondrial respiratory chain) is expanding rapidly. In this review, I will give the latest information on disorders affecting predominantly or exclusively skeletal muscle.
  
  
  RESULTS
  The most recently described mitochondrial myopathies are due to defects in nuclear DNA, including coenzyme Q10 deficiency and mutations in genes controlling mitochondrial DNA abundance and structure, such as POLG, TK2, and MPV17. Barth syndrome, an X-linked recessive mitochondrial myopathy/cardiopathy, is associated with decreased amount and altered structure of cardiolipin, the main phospholipid of the inner mitochondrial membrane, but a secondary impairment of respiratory chain function is plausible. The role of mutations in protein-coding genes of mitochondrial DNA in causing isolated myopathies has been confirmed. Mutations in tRNA genes of mitochondrial DNA can also cause predominantly myopathic syndromes and--contrary to conventional wisdom--these mutations can be homoplasmic.
  
  
  CONCLUSIONS
  Defects in the mitochondrial respiratory chain impair energy production and almost invariably involve skeletal muscle, causing exercise intolerance, cramps, recurrent myoglobinuria, or fixed weakness, which often affects extraocular muscles and results in droopy eyelids (ptosis) and progressive external ophthalmoplegia.
authors.affiliation: Department of Neurology, Columbia University Medical Center, New York, NY 10032, USA. sd12@columbia.edu
authors.forename: Salvatore
authors.initials: S
authors.lastname: DiMauro
mesh_terms: D002467:Cell Nucleus / Q000235:genetics; D003067:Coenzymes; D004272:DNA, Mitochondrial / Q000235:genetics; D045222:Electron Transport Chain Complex Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008931:Mitochondria, Muscle / Q000235:genetics / Q000378:metabolism*; D017240:Mitochondrial Myopathies / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D018482:Muscle, Skeletal / Q000378:metabolism / Q000503:physiopathology; D009154:Mutation; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000172:deficiency / Q000235:genetics / Q000378:metabolism
chemical_list: D003067:Coenzymes; D004272:DNA, Mitochondrial; D045222:Electron Transport Chain Complex Proteins; D014451:Ubiquinone; C024989:coenzyme Q10