Dear John
Turner syndrome is caused by the loss of one X chromosome ( usually paternal) in fetal cells, producing a females conceptus with 45 chromosomes. This results in early spontaneous loss of the fetus in over 95% of cases.
Severely affected fetuses who survive to the second trimester can be detected by ultrasonography, which shows cystic hygroma, chylothorax, ascites and hydrops. Fetal mortality is very high in these cases.
The incidence of Turner syndrome in liveborn females infants is 1 in 2.500.
Phenotypic abnormalities vary considerably but are usually mild. In some infants the only detectable abnormality is lymphoedema of the hands and feet. The most consistent features of the syndrome are short stature and infertllity from streak gonads, but neck webbing, broad chest, cubitus valgus, coarctation of the aorta, renal anomalies and visual problems may also occur.
Intelligence is usually within the normal range, but a few girls have educational or behavioural problems.
Associations with autoimmune thyroiditis, hypertension, obesity and non insulin dependent diabetes have been reported.
Growth can be stimulated with androgens or growth hormone, and oestrogen replacement treatment is necessary for pubertal development.
A proportion of girls with Turner syndrome have a mosaic 46XX/45X karyotype and some of these have a normal gonadal development and are fertile, although they have an increased risk of early miscarriage and of premature ovarian failure.
Other X chromosomal abnormalities including deletions or rearrangements can also result in Turner syndrome.
Maite Sole
Clinical geneticist
