Testing for Tay-Sachs disease

Tests can be carried out to check if you're a carrier of Tay-Sachs disease or to diagnosethe condition after birth.

Preconception screening

Screening for the HEXA mutation that causes Tay-Sachs disease is recommended if you're planning to start a family and you're in a high-risk group for developing the disease.

In the UK, two main groups of people are thought to have a high risk of developing the condition:

• people of Ashkenazi Jewish descent this applies to most people of Jewish descent inthe UK
• people with a known history of Tay-Sachs disease in their family

Screening involveschecking yourself and your partner for the HEXA mutation using a Blood tests . If you both test positive, you have a25% chance of conceiving a babywho develops Tay-Sachs disease.

Antenatal screening

It's also possible to test a foetus for Tay-Sachs disease during pregnancy (antenatal screening) using tests such as:

• chorionic villus sampling (between weeks 11 and 14 of pregnancy)where a sample of cells is taken from the placenta to be tested
• amniocentesis (between weeks 15and 20 of pregnancy) where a needle is used to remove amniotic fluid for testing

Ifa diagnosis of Tay-Sachs disease is confirmed, you can choose to terminate or continue the pregnancy.

Tests after birth

A diagnosis of Tay-Sachs disease would be strongly suspected if a young baby develops symptoms closely associated with the condition,such asan exaggerated response to sudden noisesand red spotsat the back ofthe eyes.

Blood tests can also be carried out to check if the body is producing the Hexosaminidase-A (Hex-A) enzyme (see causes of Tay-Sachs disease for more information).

If there's any doubt about the diagnosis, it can usually be confirmed by taking a blood sample and extracting DNA from it to check for the HEXA mutation.

Receiving the diagnosis

Being told your baby has a fatal and incurable condition is a devastating experience, and you will probably experience profound feelings of grief, bereavement andeven guilt.

The National Tay-Sachs & Allied Diseases Association is an American foundation for people affected by Tay-Sachs disease. Its website has information on waysto treat the symptoms, as well as useful advice about coping with the emotional impact of the condition.

The UK-based charity Genetic Alliance UK also provides information and services for people who have been affected by genetic conditions such as Tay-Sachs disease,as do organisations such as Climb .

You may also find it useful to read more about caring for a child with a terminal illness .

Pre-implantation genetic diagnosis

For couples at risk of having a child with Tay-Sachs disease, pre-implantation genetic diagnosis (PGD) may be an option.

PGD involves using in vitro fertilisation (IVF) , where eggs are removed from a woman's ovaries before being fertilised with sperm in a laboratory. After a few days, the resulting embryos can be tested forTay-Sachs diseaseand a maximum of two unaffected embryos are transferred into the uterus.

However, funding for PGD is decided on an individual basis. For example, you may be considered ineligible for PGD on the NHS if you already have unaffected children or if the chances of success are thought to be low. In these cases, you can choose to fund PGD yourself, although it's likely to cost between 6,000 and 10,000.