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Pre-natal diagnosis

Introduction

Pre-natal diagnosis is only available to couples who already have a child diagnosed with A-T. When a child develops ataxia-telangiectasia (A-T), it means that the healthy parents both carry a mutated gene and the child has received a mutated gene from each parent. The chance of this occurring is 1 in 4 each time the couple has a pregnancy.

It is possible, however, to detect whether a foetus is affected by A-T. One effective way to do this is by measuring the response of cells from the pregnancy to ionising radiation. The cells required for this test can be collected either by chorionic villus sampling or amniocentesis.

A family wishing to test a foetus would need to check with the laboratory of Prof. Malcolm Taylor at Birmingham University that pre-natal diagnosis was possible. This may mean that blood samples from the whole family need to be analysed. Professor Taylor will then be able to confirm that testing is possible.

Tests in Pregnancy

Chorionic Villus Sampling (CVS)

This test is usually carried out at around 10 weeks into the pregnancy. The procedure takes around half an hour and involves visiting the hospital for no more than a couple of hours. A fine, flexible, plastic tube is passed through the cervix under ultrasound control and a small sample is taken from the edge of the developing placenta, which contains the same chromosome pattern as the foetus. Women who have had this done say the sensation is similar to having a cervical smear test. A result should be available in about two weeks. There is a small chance that the procedure may cause the pregnancy to miscarry (about 1%).

Amniocentesis

This test is carried out later in the pregnancy, at about 16-18 weeks. A sample of the fluid surrounding the baby is taken, again under ultrasound scan control, via a needle through the abdominal wall. It has a slightly lower risk of causing miscarriage than the CVS but the results are not available until about 19 weeks into the pregnancy.

Results

The sample can be taken locally, although it should then be sent to Professor Taylor (arranged in advance). The above tests will give an accurate answer as to whether or not the foetus is affected (although no test is ever 100% certain). If the foetus is affected, parents would then have the choice about whether or not to continue the pregnancy.

For further information on pre-natal diagnosis and for advice please contact us.