Turner syndrome (TS)

Turner syndrome is a combination of abnormalities caused by a genetic defect. It occurs in 1 in 2000-2500 live girls but is much more frequent in spontaneous miscarriages. In Belgium and Luxemburg, approximately 30 girls are born each year with Turner syndrome.  

Genetic material (DNA) is organised in the form of chromosomes in all the cells of the human body. Normally, humans have 46 chromosomes arranged in 23 pairs. From each pair, there is one chromosome from the father and one chromosome from the mother. One pair is responsible for the sex of the individual: these chromosomes are called sex chromosomes. There are two forms of this chromosome: the X and the Y chromosome. Girls have two X chromosomes, while boys have an X and a Y chromosome.  

In girls with Turner syndrome, the entire or a large part of one X chromosome is missing.  

The diagnosis is performed by a genetic test requiring a blood sample. The diagnosis can also be made before birth by chromosome analysis on an amniotic fluid sample or by biopsy of the placental tissue. It can also be detected with a non-invasive prenatal test (NIPT) during which the foetal DNA in the mother’s blood is tested for chromosomal defects.  

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. 

• Growth hormone treatment: Although girls with Turner syndrome are not deficient in growth hormone, the administration of extra growth hormone initially accelerates growth and eventually increases stature as an adult. The length gain on the final height achieved with growth hormone treatment is 5-10 cm and depends, among other things, on the age at which the growth hormone and oestrogen treatment were started.  
• Oestrogen treatment is usually started around the age of 11-12 years. The beginning of treatment is partly determined by the stature and psychological development.  
• Due to the premature disappearance of the eggs in the ovaries, most girls with Turner syndrome are infertile. Because the internal female organs are intact, in vitro fertilisation is possible. If eggs are present in adolescence cryopreservation can be discussed with the patient. However, the follow-up of the pregnancy must be done very carefully in an experienced centre as there is a high risk of complications. 

Dutch – Flemish Turner syndrome guidelines : Turner richtlijn 2022_final