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Disease Profile

Numeric sex chromosome variations

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.


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Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable



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.


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    In-Depth Information

    • 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.


      1. Carlos A Bacino. Sex chromosome abnormalities. UpToDate. 2013; https://www.uptodate.com/contents/sex-chromosome-abnormalities. Accessed 9/18/2013.