Turner syndrome


What chromosome changes cause Turner syndrome?

Turner syndrome is caused by the complete or partial loss of one of the two X chromosomes in girls. When all of a chromosome is missing, this can be called a monosomy. When part of a chromosome is missing, this can be called a deletion. In rare instances, Turner syndrome is caused because genetic material on the X chromosome is duplicated or the chromosome forms a ring or also has genetic material from the Y chromosome. The altered or missing X chromosome may occur in all the cells of a girl's body, or may occur only in a percentage of cells with the remaining cells having two unaltered X chromosomes. This is called mosaicism. Generally, more cells that carry the abnormality, the more severe a disorder is. Turner syndrome is usually not inherited; the complete or partial loss (deletion) of the X chromosome usually occurs after the egg has been fertilized and appears to be a random event. There is nothing the parents did to cause the disorder.

Chromosomes are found in the nucleus of every cell. Chromosomes carry the genetic material of a person in the form of genes. They have a long arm called 'q' and a short arm called 'p'. Genes on the X chromosome influence many different systems in the body. It is the loss of these genes that causes the signs and symptoms of Turner syndrome. Most people have 46 chromosomes; 23 inherited from their mother and 23 from their father. Twenty-two chromosomes are the same in girls and boys, but girls have two X chromosomes and boys have one X and one Y chromosome. These are called the sex chromosomes because they determine the sex of a person. Because boys only have one X chromosome, Turner syndrome is not compatible with life in a boy and leads to miscarriage or stillbirth.

About half of the girls with Turner syndrome, have monosomy X, which means that one entire X chromosome is missing in some (mosaicism) or all of their cells. Some girls have a partial loss (deletion) of one X chromosome in some or all of their cells. There are other abnormalities of the X chromosome that can cause Turner syndrome. Ring chromosome X is when both ends of the one of the X chromosomes break off and then the remaining ends combine to form a ring. This can cause severe problems including intellectual disability. Isochromosome Xq is when there is an extra (duplicated) copy of the long arm (q) of the X chromosome. Sometimes, in addition to a partial or complete loss of one X chromosome, there is genetic material from the Y chromosome in some cells of the body.

The genetic changes causing Turner syndrome are complex. Parents and individuals should talk with a medical geneticist or a genetic counselor. To find a medical professional nearby who can discuss information about Turner syndrome, a listing of medical geneticists can be found at the American College of Medical Geneticists website and genetic counselors can be found on the National Society of Genetic Counselors website.

  • Backeljauw P. Clinical manifestations and diagnosis of Turner syndrome. UpToDate Inc. website. http://www.uptodate.com/contents/clinical-manifestations-and-diagnosis-of-turner-syndrome
  • Turner Syndrome. The Genetics Home Reference website. https://ghr.nlm.nih.gov/condition/turner-syndrome
  • Turner Syndrome. The National Organization for Rare Disorders website. https://rarediseases.org/rare-diseases/turner-syndrome/
  • Culen C, Ertl DA, Schubert K, Bartha-Doering L, Haeusler G. Care of girls and women with Turner syndrome: beyond growth and hormones. Endocr Connect. 2017;6(4):R39-R51. http://www.endocrineconnections.com/content/6/4/R39.full.pdf+html

More Causes Content

We use cookies to ensure that we give you the best experience on our website. By continuing to browse this site, you are agreeing to our use of cookies.

Continue Find out more about our use of cookies and similar technology

This content comes from a hidden element on this page.

The inline option preserves bound JavaScript events and changes, and it puts the content back where it came from when it is closed.

Remember Me