Progressive exercise intolerance associated with a new muscle-restricted nonsense mutation (G142X) in the mitochondrial cytochrome b gene

Muscle Nerve. 2003 Oct;28(4):508-11. doi: 10.1002/mus.10429.


We report a novel nonsense mitochondrial cytochrome b mutation (G15170A) in a 40-year-old woman with progressive exercise intolerance and lactic acidosis. Muscle biopsy showed several cytochrome c oxidase-positive ragged-red fibers, and reduced activities of respiratory chain complexes I and III. This mutation, resulting in the loss of 228 amino acids of the protein, was very abundant in the patient's muscle, but undetectable in lymphocytes and fibroblasts. Clinical and laboratory data indicate that this defect is the primary cause of the disease, thus adding a new mutation in the cytochrome b gene among the growing number of patients with exercise intolerance and lactic acidosis.

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acidosis, Lactic / genetics
  • Adult
  • Base Sequence / genetics
  • Codon, Nonsense*
  • Cytochrome b Group / genetics*
  • DNA, Mitochondrial / genetics*
  • DNA, Mitochondrial / metabolism*
  • Electron Transport Complex I
  • Electron Transport Complex III / metabolism
  • Electron Transport Complex IV / metabolism
  • Exercise / physiology*
  • Female
  • Humans
  • Muscle Cramp / genetics
  • Muscle Fibers, Skeletal / enzymology
  • Muscle Fibers, Skeletal / pathology
  • Muscle, Skeletal / metabolism*
  • Muscle, Skeletal / pathology
  • NADH, NADPH Oxidoreductases / metabolism


  • Codon, Nonsense
  • Cytochrome b Group
  • DNA, Mitochondrial
  • NADH, NADPH Oxidoreductases
  • Electron Transport Complex IV
  • Electron Transport Complex I
  • Electron Transport Complex III