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Causes
By Mayo Clinic staffMost people are born with two sex chromosomes. A boy inherits the X chromosome from his mother and the Y chromosome from his father. A girl inherits one X chromosome from each parent. If a girl has Turner syndrome, one copy of the X chromosome is missing or significantly altered. The genetic alterations of Turner syndrome may be one of the following:
- Monosomy. The complete absence of an X chromosome generally occurs because of an error in the father's sperm or in the mother's egg. This results in every cell in the body having only one X chromosome — a condition called monosomy.
- Mosaicism. In some cases, an error occurs in cell division during early stages of fetal development. This results in some cells in the body having two complete copies of the X chromosome. Other cells have only one copy of the X chromosome, or they have one complete and one altered copy. This condition is called mosaicism.
- Y chromosome material. In a small percentage of cases of Turner syndrome, some cells have one copy of the X chromosome and other cells have one copy of the X chromosome and some Y chromosome material. These individuals develop biologically as girls, but the presence of Y chromosome material increases the risk of developing a type of cancer called gonadoblastoma.
Effect of the chromosomal errors
The missing or altered X chromosome of Turner syndrome causes errors during fetal development and other developmental problems after birth — short stature, ovarian failure and learning disabilities.
References
- Learning about Turner syndrome. Genetics Home Reference. http://ghr.nlm.nih.gov/condition/turner-syndrome. Accessed June 28, 2011.
- Davenport ML. Approach to the patient with Turner syndrome. Journal of Clinical Endocrinology and Metabolism. 2010;95:1487.
- Saenger P. Clinical manifestations and diagnosis of Turner syndrome (gonadal dysgenesis). http://www.uptodate.com/home/index.html. Accessed June 28, 2011.
- Bondy CA. Turner syndrome 2008. Hormone Research. 2009;71(suppl):52.
- Clinical features of Turner syndrome. National Institute of Child Health and Human Development. http://turners.nichd.nih.gov/clinical.html. Accessed June 28, 2011.
- Loscalzo ML. Turner syndrome. Pediatrics in Review. 2008;29:219.
- Genetic features of Turner syndrome. National Institute of Child Health and Human Development. http://turners.nichd.nih.gov/genetic.html. Accessed June 28, 2011.
- Ross JL, et al. Growth hormone plus childhood low-dose estrogen in Turner's syndrome. New England Journal of Medicine. 2011;364:1230.
- Saenger P. Management of Turner syndrome (gonadal dysgenesis). http://www.uptodate.com/home/index.html. Accessed June 28, 2011.
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