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Genetic and Rare Diseases Information Center (GARD)

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Numeric sex chromosome variations

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* Not a rare disease

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Overview

Numeric sex chromosome variations refers to differences in the number of sex chromosomes that may be present in an individual's body cells. Males typically have one X chromosome and one Y chromosome in each body cell with a total of 46 chromosomes (46, XY); females typically have two X chromosomes in each body cell (46, XX). Numeric sex chromosome variations include chromosome findings with extra or missing X or Y chromosomes. Whether there are associated signs or symptoms, as well as severity of features, can vary greatly depending on the variation present. The most common numeric sex chromosome variations include Turner syndrome (45, X); 47, XXY (which usually causes features of Klinefelter syndrome); 47, XYY; and 47, XXX (trisomy X).[1] Most numeric sex chromosome variations are not inherited and occur due to a random error during the formation of reproductive cells (eggs and sperm) in a parent. In some cases, individuals have some cells with the usual 2 sex chromosomes, and some cells with extra or missing sex chromosomes; this is called chromosomal mosaicism.
Last updated: 9/18/2013

References

  1. Carlos A Bacino. Sex chromosome abnormalities. UpToDate. 2013; http://www.uptodate.com/contents/sex-chromosome-abnormalities. Accessed 9/18/2013.
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  • PubMed is a searchable database of medical literature and lists journal articles that discuss Numeric sex chromosome variations. Click on the link to view a sample search on this topic.
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.