Le Turner syndrome (sometimes called gonadal dysgenesis) is a genetic disease which only affects women. The abnormality concerns one of the X chromosomes (the sex chromosomes). Turner syndrome affects approximately 1 in 2 women and is often diagnosed several years after birth, during adolescence. The major symptoms are short stature and abnormal functioning of the ovaries. Turner syndrome is named after the American doctor who discovered it in 1938, Henri Turner.

Men have 46 chromosomes including two so-called sex chromosomes called XY. The genetic formula for a man is 46 XY. Women also have 46 chromosomes including two sex chromosomes called 46 XX. The genetic formula of a woman is therefore 46 XX. In women with Turner syndrome, the genetic combination contains a single X chromosome, so the genetic formula of a woman with Turner syndrome is 45 X0. Either these women are missing an X chromosome or the X chromosome exists, but has an abnormality called a deletion. There is therefore always a chromosomal lack.