Exercise intolerance due to cytochrome b mutation

Muscle Nerve. 2010 Jul;42(1):136-40. doi: 10.1002/mus.21649.


Cytochrome b mutations are rare causes of exercise intolerance. We report an 18-year-old man with exercise intolerance since childhood, resting lactic acidosis, cytochrome c oxidase (COX)-positive ragged-red fibers, and isolated muscle complex III deficiency due to a heteroplasmic m.14849T>C mutation in cytochrome b. We review previously described patients carrying mutations in the same gene. COX-positive ragged-red fibers together with exercise intolerance and lactic acidemia provide a clue for the diagnosis of this rare mitochondrial disorder.

Publication types

  • Case Reports

MeSH terms

  • Acidosis / metabolism
  • Adolescent
  • Blood Chemical Analysis
  • Cardiomyopathies / genetics
  • Cardiomyopathies / pathology
  • Cytochromes b / genetics*
  • Electron Transport Complex IV / genetics
  • Electron Transport Complex IV / metabolism
  • Exercise Tolerance / genetics*
  • Humans
  • Male
  • Mitochondria, Muscle / enzymology
  • Mitochondrial Myopathies / genetics*
  • Mitochondrial Myopathies / pathology
  • Mutation / physiology


  • Cytochromes b
  • Electron Transport Complex IV