Copyright © 2000 The American Society of Human Genetics. All rights reserved.
The American Journal of Human Genetics, Volume 67, Issue 6, 1400-1410, 1 December 2000
doi:10.1086/316900
Mitochondrial Encephalomyopathy and Complex III Deficiency Associated with a Stop-Codon Mutation in the Cytochrome b Gene
J. Andrew Keightley1, *, Roberto Anitori1, †, Miriam D. Burton1, ‡, Franklin Quan1, §, Neil R.M. Buist1, 2 and Nancy G. Kennaway1, 
, 
1 Departments of Molecular and Medical Genetics Oregon Health Sciences University, Portland
2 Pediatrics, Oregon Health Sciences University, Portland
Address for reprints and correspondence: Nancy G. Kennaway, Department of Molecular and Medical Genetics, MP-350, Oregon Health Sciences University, 3181 SW Sam Jackson Park Road, Portland, OR 97201* Present affiliation: Department of Immunology, The Cleveland Clinic, Cleveland.
† Present affiliation: School of Biological Sciences, Macquarie University, North Ryde, New South Wales, Australia.
‡ Present affiliation: Central Institute for the Deaf, St. Louis.
§ Present affiliation: Department of Pediatrics, University of Illinois at Chicago, Chicago.
Abstract
We have reinvestigated a young woman, originally reported by us in 1983, who presented with exercise intolerance and lactic acidosis associated with severe deficiency of complex III and who responded to therapy with menadione and ascorbate. Gradually, she developed symptoms of a mitochondrial encephalomyopathy. Immunocytochemistry of serial sections of muscle showed a mosaic of fibers that reacted poorly with antibodies to subunits of complex III but reacted normally with antibodies to subunits of complexes I, II, or IV, suggesting a mutation of mtDNA. These findings demonstrate the diagnostic value of immunocytochemistry in identifying specific respiratory-chain deficiencies and, potentially, distinguishing between nuclear- or mtDNA-encoded defects. Sequence analysis revealed a stop-codon mutation (G15242A) in the mtDNA-encoded cytochrome b gene, resulting in loss of the last 215 amino acids of cytochrome b. PCR-RFLP analysis indicated that the G15242A mutation was heteroplasmic and was present in a high percentage (87%) of affected tissue (skeletal muscle) and a low percentage (0.7%) of unaffected tissue (blood) but was not detected in controls. Analysis of microdissected muscle fibers showed a significant correlation between the immunoreactivity toward the Rieske protein of complex III and the percentage of mutant mtDNA: immunopositive fibers had a median value of 33% of the G15242A mutation, whereas immunonegative, ragged-red fibers had a median value of 89%, indicating that the stop-codon mutation was pathogenic in this patient. The G15242A mutation was also present in several other tissues, including hair roots, indicating that it must have arisen either very early in embryogenesis, before separation of the primary germ layers, or in the maternal germ line. The findings in this patient are contrasted with other recently described patients who have mutations in the cytochrome b gene.
Article Information
PubMed
Related Articles
- Cytochrome c Oxidase Deficiency Associated with the First St...Cytochrome c Oxidase Deficiency Associated with the First Stop-Codon Point Mutation in Human mtDNA
The American Journal of Human Genetics, Volume 63, Issue 1, 1 July 1998, Pages 29-36
M.G. Hanna, I.P. Nelson, S. Rahman, R.J.M. Lane, J. Land, S. Heales, M.J. Cooper, A.H.V. Schapira, J.A. Morgan-Hughes and N.W. Wood
AbstractSummary: We have identified the first stop-codon point mutation in mtDNA to be reported in association with human disease. A 36-year-old woman experienced episodes of encephalopathy accompanied by lactic acidemia and had exercise intolerance and proximal myopathy. Histochemical analysis showed that 90% of muscle fibers exhibited decreased or absent cytochrome c oxidase (COX) activity. Biochemical studies confirmed a severe isolated reduction in COX activity. Muscle immunocytochemistry revealed a pattern suggestive of a primary mtDNA defect in the COX-deficient fibers and was consistent with either reduced stability or impaired assembly of the holoenzyme. Sequence analysis of mtDNA identified a novel heteroplasmic G→A point mutation at position 9952 in the patient's skeletal muscle, which was not detected in her leukocyte mtDNA or in that of 120 healthy controls or 60 additional patients with mitochondrial disease. This point mutation is located in the 3′ end of the gene for subunit III of COX and is predicted to result in the loss of the last 13 amino acids of the highly conserved C-terminal region of this subunit. It was not detected in mtDNA extracted from leukocytes, skeletal muscle, or myoblasts of the patient's mother or her two sons, indicating that this mutation is not maternally transmitted. Single-fiber PCR studies provided direct evidence for an association between this point mutation and COX deficiency and indicated that the proportion of mutant mtDNA required to induce COX deficiency is lower than that reported for tRNA-gene point mutations. The findings reported here represent only the second case of isolated COX deficiency to be defined at the molecular genetic level and reveal a new mutational mechanism in mitochondrial disease.
Abstract | | - Normal Levels of Wild-Type Mitochondrial DNA Maintain Cytoch...Normal Levels of Wild-Type Mitochondrial DNA Maintain Cytochrome c Oxidase Activity for Two Pathogenic Mitochondrial DNA Mutations but Not for m.3243A→G
The American Journal of Human Genetics, Volume 81, Issue 1, 1 July 2007, Pages 189-195
Steve E. Durham, David C. Samuels, Lynsey M. Cree and Patrick F. Chinnery
AbstractMitochondrial DNA (mtDNA) mutations are a common cause of human disease and accumulate as part of normal ageing and in common neurodegenerative disorders. Cells express a biochemical defect only when the proportion of mutated mtDNA exceeds a critical threshold, but it is not clear whether the actual cause of this defect is a loss of wild-type mtDNA, an excess of mutated mtDNA, or a combination of the two. Here, we show that segments of human skeletal muscle fibers harboring two pathogenic mtDNA mutations retain normal cytochrome c oxidase (COX) activity by maintaining a minimum amount of wild-type mtDNA. For these mutations, direct measurements of mutated and wild-type mtDNA molecules within the same skeletal muscle fiber are consistent with the “maintenance of wild type” hypothesis, which predicts that there is nonselective proliferation of mutated and wild-type mtDNA in response to the molecular defect. However, for the m.3243A→G mutation, a superabundance of wild-type mtDNA was found in many muscle-fiber sections with negligible COX activity, indicating that the pathogenic mechanism for this particular mutation involves interference with the function of the wild-type mtDNA or wild-type gene products.
Abstract | | - Intragenic Inversion of mtDNA: A New Type of Pathogenic Muta...Intragenic Inversion of mtDNA: A New Type of Pathogenic Mutation in a Patient with Mitochondrial Myopathy
The American Journal of Human Genetics, Volume 66, Issue 6, 1 June 2000, Pages 1900-1904
Olimpia Musumeci, Antoni L. Andreu, Sara Shanske, Nereo Bresolin, Giacomo P. Comi, Rodney Rothstein, Eric A. Schon and Salvatore DiMauro
AbstractWe report an unusual molecular defect in the mitochondrially encoded ND1 subunit of NADH ubiquinone oxidoreductase (complex I) in a patient with mitochondrial myopathy and isolated complex I deficiency. The mutation is an inversion of seven nucleotides within the ND1 gene, which maintains the reading frame. The inversion, which alters three highly conserved amino acids in the polypeptide, was heteroplasmic in the patient's muscle but was not detectable in blood. This is the first report of a pathogenic inversion mutation in human mtDNA.
Abstract | | - …more
