Genetic testing & pre-natal treatment

Genetic testing isn’t routinely used in the diagnosis of CAH. It can, however, be used for the purposes of family planning where the prospective parents are either carriers or sufferers of CAH. In this case, genetic counselling and testing may be offered prior to undertaking a new pregnancy. The testing compares abnormal adrenal gland genes to normal ones, and looks for differences which would indicate mutations. This means that only known abnormalities can be searched for, and indeed sometimes the searches are restricted to the most common mutations.

There is no pre-natal treatment that can ‘cure’ CAH. However, in the case of girls with virilising forms of CAH, there is a pre-natal treatment that can, in some cases, prevent or minimise the masculinisation of the genitals.

The treatment involves the mother-to-be starting a course of dexamethasone as soon as she knows she is pregnant (preferably before 6 weeks gestation). Once the pregnancy reaches 7-8 weeks gestation, it is now possible for the sex of the foetus to be determined with FISH analysis (fluorescent in situ hybridization), a test using fluorescent DNA probes on maternal blood. This is obviously a big advantage to mothers who have chosen to take dexamethasone treatment, as if the foetus is male, the medication can be stopped (slowly).

If the FISH test shows the baby is female, once the pregnancy reaches the 10th-15th week, a test can then be carried out to determine, whether she is affected by CAH. In the case of an affected girl, the course of dexamethasone is continued through the pregnancy but if she is unaffected, the treatment will have no benefits so (as with male the male foetus) the mother can be weaned off the treatment.

The pre-natal treatment of CAH is a relatively recent development, and many doctors still regard it as experimental. The long term effects of foetal exposure to dexamethasone are unknown and there are still concerns about the unknown risks of the treatment. Dexamethasone is a strong steroid and it can have nasty side-affects for the mother – excessive weight gain, moodiness, insomnia, acne and the development of severe stretch marks. Other potential problems such as high blood pressure mean that close monitoring of the mothers during pregnancy is essential.

The foetus is tested for CAH by either chorionic villus sampling (CVS) or amniocentesis. These tests in themselves carry risks. The chance of a miscarriage is slightly increased by having either of these tests.

A number of Support Group members have undergone pre-natal treatment and will be happy to discuss it further.