What is monosomy X (Turner syndrome)?

Monosomy X, also known as Turner syndrome, occurs when a girl has just one complete copy of the X chromosome in the cells of her body (most females have two copies). Intelligence is normal for the vast majority of people with Turner syndrome. These girls and women are more likely to experience certain challenges with learning, growth, and development. Learning disabilities in math and memory occur more frequently in girls with Turner syndrome, while speech and reading tend to be strengths. Some may experience attention and social difficulties. Differences in appearance are typically subtle and these girls often blend in with their peers. Some common physical features are a wide and short neck, droopy eyelid, and almost all girls with Turner syndrome are short in height. Puberty is often delayed or absent in untreated girls and infertility is common regardless of treatment. Health issues may include hearing loss and heart and kidney defects.

How common is Turner syndrome?

About one in every 2500 girls is born with Turner syndrome. The condition is not related to race, nationality, religion or socioeconomic status. There is usually no family history of Turner syndrome.

How is Turner syndrome treated?

Hormone treatment is often used to achieve puberty at an appropriate age and increase adult height. If learning or social challenges occur they can be addressed in the same way that they are for any other child, with help in school or from other professionals. Birth defects may require surgery. Most girls born with Turner syndrome who receive good medical care have a normal lifespan and lead healthy and productive lives.

Other names for
Monosomy X

  • Turner syndrome


  • Clin Pediatr. 2006 May;45(4):301-313.
  • Gardner, R. J. M., & Sutherland, G. R. (2011). Chromosome abnormalities and genetic counseling (4th ed.). New York: Oxford University Press, Inc.
  • Jones, K. L. (Ed.). (2013). Smith’s recognizable patterns of human malformation (7th ed.). Philadelphia: Elsevier Inc.