The genetic cause of Turner syndrome

A girl with Turner syndrome only has one normal X sex chromosome, rather than the usual two (XX).

Everyone is born with 23 pairs of chromosomes. One pair of chromosomes the sex chromosomes determines the baby's gender.

One sex chromosome comes from the father and the other comes from the mother. The mother's contribution is always an X chromosome. The father's contribution can either be an X or a Y chromosome.

A baby girl usually has two X chromosomes (XX), and boys have an X and a Y chromosome (XY). The Y chromosome determines "maleness", so if it is missingas in Turner syndromethe sex of the child will invariably be female.

A female with Turner syndrome is missing part or all of one sex chromosome. This means she has just one complete X chromosome.

Thischromosome variation happens randomly when the baby is conceived in the womb. It is not linked to the mother's age.

The syndrome can either be described as:

  • classic Turner syndrome where one of the X chromosomes is completely missing
  • mosaic Turner syndrome in most cells one X chromosome is complete and the other is partially missing or abnormal in some way, but in some cells there may be just one X chromosome or, rarely, two complete X chromosomes

Content supplied by the NHS Website

Medically Reviewed by a doctor on 30 Nov 2016