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Genetic and Rare Diseases Information Center (GARD)

Other Names for this Disease
  • 48 XXXX
  • 48 XXXX syndrome
  • Tetra X
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Tetrasomy X is a chromosome disorder that only affects females and is caused by having four copies of the X chromosome instead of two. Females with tetrasomy X have a total of 48 chromosomes in their cells, so this condition is sometimes written as 48, XXXX. The signs and symptoms of tetrasomy X vary, but can include mild to moderate speech and learning difficulties; developmental delay; distinctive facial features; dental abnormalities; hypotonia and joint laxity; radioulnar synostosis; heart defects; hip dysplasia; and problems with ovarian function. An increased risk of childhood infections has also been reported. Tetrasomy X is caused by a random error that occurs during the development of an egg cell and is not caused by anything a mother does during her pregnancy.[1][2]
Last updated: 2/19/2014


  1. Tetrasomy X. Unique. 2005; Accessed 9/11/2012.
  2. N Ayari, A Berge, Susan Howell, and Nicole Tartaglia. Tetrasomy X. Orphanet. January, 2010; Accessed 2/19/2014.
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Basic Information

  • Genetics Home Reference (GHR) contains information on Tetrasomy X. This website is maintained by the National Library of Medicine.
  • Unique is a source of information and support to families and individuals affected by rare chromosome disorders. Click on the link to view information about tetrasomy X.

In Depth Information

  • Orphanet is a European reference portal for information on rare diseases and orphan drugs.  Access to this database is free of charge.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Tetrasomy X. Click on the link to view a sample search on this topic.