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Turner syndrome

Other Names for this Disease
  • 45, X Syndrome
  • Bonnevie-Ulrich syndrome
  • Chromosome X Monosomy X
  • Gonadal Dysgenesis (45,X)
  • Schereshevkii Turner Syndrome
More Names
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What causes Turner syndrome?

Turner syndrome is a condition caused by partial or complete loss of one of the X chromosomes in females. Females typically have 2 full X chromosome in all of their cells, while males have one X chromosome and one Y chromosome.[1]

Most females with Turner syndrome are missing a full X chromosome in all of their cells (called monosomy X).[2] This is thought to occur due to an error in cell division prior to conception called nondisjunction, which results in egg or sperm cells (germ cells) with an abnormal number of chromosomes. If one of these germ cells is missing an X chromosome and contributes to the genetic makeup of a child, the child will have a single X chromosome in each cell and will be missing the other sex chromosome.[3]

Some females with Turner syndrome have both X chromosomes, but one of the X chromosomes has a deletion.[2] A deletion may occur sporadically (for the first time in the affected individual) or be inherited from a parent. This is sometimes called partial Turner syndrome. The signs and symptoms of partial Turner syndrome can vary widely depending on the size of the missing portion as well as the specific genes that are missing. Generally, larger deletions cause more signs and symptoms than smaller deletions.[1] It is also possible for an individual with Turner syndrome to be missing all or part of one X chromosome in only some of her cells, which is called mosaicism. This may be referred to as mosaic Turner syndrome. Mosaic Turner syndrome is typically caused by a random error in cell division that occurs shortly after conception.[2]
Last updated: 6/25/2012

  1. Genetic Features of Turner Syndrome. National Institute of Child Health and Human Development (NICHD) . September 27, 2004; Accessed 8/8/2008.
  2. Learning About Turner Syndrome. National Human Genome Research Institute (NHGRI). November 27, 2007; Accessed 4/7/2008.
  3. Turner syndrome. Genetics Home Reference. September 2005; Accessed 4/7/2008.