title: The expanding phenotype of mitochondrial myopathy.
abstract: OBJECTIVE
  Our understanding of mitochondrial diseases (defined restrictively as defects in the mitochondrial respiratory chain) continues to progress apace. In this review we provide an update of information regarding disorders that predominantly or exclusively affect skeletal muscle.
  
  
  RESULTS
  Most recently described mitochondrial myopathies are due to defects in nuclear DNA, including coenzyme Q10 deficiency, and mutations in genes that control mitochondrial DNA (mtDNA) abundance and structure such as POLG and TK2. Barth syndrome, an X-linked recessive mitochondrial myopathy/cardiopathy, is associated with altered lipid composition of the inner mitochondrial membrane, but a putative secondary impairment of the respiratory chain remains to be documented. Concerning the 'other genome', the role played by mutations in protein encoding genes of mtDNA in causing isolated myopathies has been confirmed. It has also been confirmed that mutations in tRNA genes of mtDNA can 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, myalgia, cramps, 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, New York, USA. sd12@columbia.edu
authors.forename: Salvatore
authors.initials: S
authors.lastname: DiMauro
authors.forename: Juliana
authors.initials: J
authors.lastname: Gurgel-Giannetti
mesh_terms: D004272:DNA, Mitochondrial / Q000145:classification / Q000235:genetics; D006801:Humans; D017240:Mitochondrial Myopathies / Q000235:genetics* / Q000503:physiopathology; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics; D010641:Phenotype
chemical_list: D004272:DNA, Mitochondrial; D009687:Nuclear Proteins