Analysis of the trinucleotide CAG repeat from the human mitochondrial DNA polymerase gene in healthy and diseased individuals

Eur J Hum Genet. 1999 Feb-Mar;7(2):140-6. doi: 10.1038/sj.ejhg.5200244.


The human nuclear gene (POLG) for the catalytic subunit of mitochondrial DNA polymerase (DNA polymerase gamma) contains a trinucleotide CAG microsatellite repeat within the coding sequence. We have investigated the frequency of different repeat-length alleles in populations of diseased and healthy individuals. The predominant allele of 10 CAG repeats was found at a very similar frequency (approximately 88%) in both Finnish and ethnically mixed population samples, with homozygosity close to the equilibrium prediction. Other alleles of between 5 and 13 repeat units were detected, but no larger, expanded alleles were found. A series of 51 British myotonic dystrophy patients showed no significant variation from controls, indicating an absence of generalised CAG repeat instability. Patients with a variety of molecular lesions in mtDNA, including sporadic, clonal deletions, maternally inherited point mutations, autosomally transmitted mtDNA depletion and autosomal dominant multiple deletions showed no differences in POLG trinucleotide repeat-length distribution from controls. These findings rule out POLG repeat expansion as a common pathogenic mechanism in disorders characterised by mitochondrial genome instability.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alleles
  • Amino Acid Sequence
  • Base Sequence
  • DNA Polymerase gamma
  • DNA, Complementary
  • DNA, Mitochondrial*
  • DNA-Directed DNA Polymerase / genetics*
  • Humans
  • Mitochondria / enzymology*
  • Molecular Sequence Data
  • Trinucleotide Repeats*


  • DNA, Complementary
  • DNA, Mitochondrial
  • DNA Polymerase gamma
  • DNA-Directed DNA Polymerase

Associated data

  • GENBANK/X98093