Antenatal screening for Fragile X: time to proceed?

This week, a small team of experts recommended the establishment of a national antenatal screening programme for Fragile X syndrome. The report, commissioned by the NHS Health Technology Assessment programme, examined the public health aspects of screening for Fragile X and suggested that a screening programme aimed at all pregnant women would be 'feasible and acceptable'.]

Fragile X is the most common cause of inherited learning disability and affects about 1 in 4000 boys and 1 in 8000 girls. The method currently used to detect those at high risk of having a baby with the condition is through cascade screening. When an individual suffering from Fragile X is diagnosed, counselling and genetic testing is offered to family members in order to calculate their risk. This is a very effective method of screening because it minimises the chance of people at very low risk of being falsely alarmed.

The nature of the inheritance of Fragile X means that many women at raised risk don't have an obvious family history of learning difficulties. As a result, such women will be unaware of their risk of having a child with Fragile X. However, an antenatal screening programme, offered to all pregnant women, could be used to determine whether or not such women are at high risk of having a child with the condition. If they are shown to be at high risk, the woman can use the information to make a decision about whether to have an amniocentesis test to determine the fetus' risk and whether to have a termination of pregnancy should the fetus' risk be shown to be high.

The authors of the Health Technology Assessment report, suggested that an antenatal screening programme for Fragile X in England and Wales would be 'feasible and acceptable'. Whether this advice is acted upon remains to be seen. In October, a subgroup of the National Screening Committee will examine the study and make its own recommendations. If antenatal screening for Fragile X were to go ahead, how might such a service be offered?

The important question to ask is whether an adequate system is in place to handle those who are identified as being at high risk of Fragile X. For instance, besides the risk to the fetus, a woman who is identified as being at raised risk of Fragile X is likely to have a network of relatives whose own risk needs to be assessed. A good referral system, through which such individuals are quickly sent to a clinical genetics centre for accurate information and careful counselling, is a vital component of an antenatal screening programme. In busy NHS antenatal clinics, there is neither the time nor the expertise to provide the kind of follow-up care which individuals identified as being at high risk really need.