X chromosome-inactivation patterns of 1,005 phenotypically unaffected females

Am J Hum Genet. 2006 Sep;79(3):493-9. doi: 10.1086/507565. Epub 2006 Jul 27.


X-chromosome inactivation is widely believed to be random in early female development and to result in a mosaic distribution of cells, approximately half with the paternally derived X chromosome inactive and half with the maternally derived X chromosome inactive. Significant departures from such a random pattern are hallmarks of a variety of clinical states, including being carriers for severe X-linked diseases or X-chromosome cytogenetic abnormalities. To evaluate the significance of skewed patterns of X inactivation, we examined patterns of X inactivation in a population of >1,000 phenotypically unaffected females. The data demonstrate that only a very small proportion of unaffected females show significantly skewed inactivation, especially during the neonatal period. By comparison with this data set, the degree of skewed inactivation in a given individual can now be quantified and evaluated for its potential clinical significance.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adult
  • Cell Count
  • Female
  • Humans
  • Infant, Newborn
  • Phenotype
  • Stem Cells / cytology
  • X Chromosome Inactivation / genetics*