The X chromosome is a large chromosome and contains more than 1000 genes. Some of these genes are important for height and the development of the ovaries, lymph vessels, heart and blood vessels, etc. A lack of these genes will therefore cause problems in various places in the body. Some girls with Turner syndrome have almost no problems except for short stature and/or malfunctioning of the ovaries.
In girls, all the eggs in the ovaries are already present before birth. Girls gradually lose their egg cells until the age of 50, when menopause sets in. This process already starts in the foetus during the last months of pregnancy. The eggs are encased in “vesicles” or “follicles”. The cells of these follicles produce hormones, including female hormones called oestrogens. These hormones are responsible for breast development, uterine growth and menstruation during puberty. In girls and women with Turner syndrome, the eggs disappear much faster than normal. The number of eggs and follicles still present after birth in girls with Turner syndrome varies greatly. Most girls will have no eggs at all by the age of 10-12 and will not have breast development or periods during puberty. In other girls, there are enough eggs to cause some breast development, and sometimes also to menstruate. Two to 5% of adolescents with Turner syndrome (mosaic chromosome pattern) are fertile. In all female Turner patients, the vagina, uterus and fallopian tubes are present.