Extremely high levels of mutant mtDNAs co-localize with cytochrome c oxidase-negative ragged-red fibers in patients harboring a point mutation at nt 3243

Hum Mol Genet. 1994 Mar;3(3):449-54. doi: 10.1093/hmg/3.3.449.


A single mtDNA point mutation at nt 3243 has been associated with two different clinical phenotypes: mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes ('MELAS3243') and progressive external ophthalmoplegia ('PEO3243'). It has been shown that there is a much higher proportion of ragged-red fibers (RRF) with cytochrome c oxidase (COX) deficiency in PEO3243 than in MELAS3243. Using PCR/RFLP analysis of isolated individual skeletal muscle fibers from patients with both syndromes, we found a direct correlation between the localized concentration of the nt 3243 mutation and impairment of COX function at the single muscle fiber level: we found relatively low levels of mutant mtDNAs (56 +/- 21%) in 'normal' fibers; high levels (90 +/- 6%) in COX-positive RRF; and an almost complete segregation of mutant mtDNAs (95 +/- 3%) in COX-negative RRF. Thus, the differential distribution of fibers with extremely high concentrations of mutant mtDNAs characterizes, and probably distinguishes, the skeletal muscle of PEO and MELAS patients harboring the same nt-3243 mutation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Analysis of Variance
  • Cytochrome-c Oxidase Deficiency
  • DNA, Mitochondrial / genetics
  • DNA, Mitochondrial / metabolism*
  • Electron Transport Complex IV / metabolism*
  • Humans
  • MELAS Syndrome / enzymology
  • MELAS Syndrome / genetics*
  • MELAS Syndrome / pathology
  • Muscles / enzymology
  • Muscles / pathology*
  • Mutation
  • Ophthalmoplegia, Chronic Progressive External / enzymology
  • Ophthalmoplegia, Chronic Progressive External / genetics*
  • Ophthalmoplegia, Chronic Progressive External / pathology
  • Phenotype
  • Point Mutation*
  • Polymerase Chain Reaction
  • Polymorphism, Restriction Fragment Length


  • DNA, Mitochondrial
  • Electron Transport Complex IV