Bonnevie-Ullrich syndrome - Causes of Turner syndrome

Turner syndrome is a genetic condition caused by abnormal sex chromosomes.

One of the female sex chromosomes (see below) is either missing or incomplete. This causes abnormalities as the baby develops in the womb, as well as developmental problems following birth, such as short height, ovarian that do not work properly and learning disabilities.

Chromosomes

Chromosomes are made up of strands of DNA. Each cell in the human body contains 23 pairs of chromosomes.

Chromosomes carry genes (genetic material) that are inherited from your parents and determine your physical appearance and behavioural characteristics. Medical conditions can also be inherited through faulty chromosomes.

The sex chromosomes determine whether a baby will be male or female. They can either be X or Y chromosomes. You inherit one chromosome from each parent, with a female usually having two X chromosomes (XX), and a male having one X and one Y chromosome (XY).

Read more about genetics, chromosomes and genetic inheritance.

Missing or incomplete X chromosome

Turner syndrome occurs when a baby is conceived. It only affects females who have a missing or incomplete X chromosome. If a baby is conceived with a missing X chromosome, the pregnancy will not usually develop and an early miscarriage occurs.

Approximately 95% of pregnancies conceived with Turner syndrome will end in miscarriage. However, there are many reasons for miscarriages. Overall, Turner syndrome is thought to be responsible for around 15% of miscarriages. 

Who is at risk?

Turner syndrome is a fairly rare condition, affecting about 1 in every 2,000 baby girls.

Females of all races, nationalities and regions of the world can get Turner syndrome. It appears to occur randomly and is not linked to the mother’s age. It is also very rare to have a second child with Turner syndrome.

There are no known poisonous chemicals or environmental factors that cause Turner syndrome or increase the likelihood of a baby having it.