Once the causative genetic change is known within a family it is possible to undertake genetic testing during pregnancy. There are two ways of doing this:
STANDARD PRENATAL DIAGNOSIS
At around 11 to 12 weeks into the pregnancy a small sample is taken from the placenta. Cells removed in this procedure are then analysed looking for the change in the CADASIL gene. If a change is found then we would know that the baby would be at a high risk of developing CADASIL at some stage in their life. Currently there would be no preventative treatment to stop development of the signs and symptoms. At this stage, the couple would have the option of having a termination of the pregnancy if that is what they wish. This test is not undertaken lightly and you would need to speak to the geneticist at your local Clinical Genetic Service to discuss the implications of undertaking the test. The test itself is not without risk and can cause a miscarriage of the pregnancy. This needs to be considered when deciding whether or not to undertake the test.
PREIMPLANTATION GENETIC DIAGNOSIS
This is a more recently developed test that involves in-vitro fertilisation (IVF, also known as test tube pregnancy). Several embryos would be developed until they reach the stage where they contain eight cells. At this stage, one of these cells would be removed and analysed to determine if it carries the CADASIL gene change. If it does then this embryo would not be re-implanted in the mother, thus excluding the chance of the gene change being passed on to subsequent generations. This process is called pre-implantation genetic diagnosis (PGD, also known as embryo screening). Whilst being very good at removing the chance of passing on the CADASIL gene and also removing the need to consider a termination of pregnancy, the chances of having a liveborn child with IVF and PGD is only in the order of 25% per cycle. This technology is expensive, currently costing in the region of £10,000 pounds. Some couples will be able to secure funding from their local health authority, particularly if it is their first child or they do not have an unaffected child. This procedure should not be undertaken lightly as it is complicated and can be particularly arduous for the female partner as she needs to undergo fertility treatment to produce several eggs at the same time. Several of the procedures involved are also very time critical, meaning that visits to hospital have to be made on particular days and at particular times.
If you would like to discuss prenatal diagnosis or pre-implantation genetic diagnosis you should contact your local Genetics Service.