Safe test for Down's syndrome

Scientists are working on a simple blood test

Scientists are developing a simple test to identify Down's syndrome from a sample of the mother's blood.

They have successfully found a way to analyse the blood of a pregnant woman for tell-tale signs of the genetic abnormalities associated with Down's syndrome.

If the test is successfully developed it would provide doctors for the first time with a way to diagnose Down's syndrome without having to carry out a potentially dangerous internal procedure.

At present, techniques such as amniocentesis and chorionic villus sampling, which both involve removal of tissue from the developing foetus for analysis, pose a significant risk both to the developing child and to the mother.

The breakthrough has been made by a team from the Chinese University of Hong Kong using a technique called fluorescence in-situ hybridisation (FISH).

This involves using coloured markers to identify the presence of genetic material called chromosomes.

Normal individuals have two copies of chromosome 21, whereas people with Down's syndrome have three.

Plasma samples

The researchers used the technique to test plasma samples obtained from three women carrying foetuses affected by Down's syndrome.

They were able to identify foetal cells with three chromosome-21 signals.

The results were compared to samples taken from seven foetuses who did not have Down's syndrome.

The researchers are confident that their results show that it should be feasible to develop a non-invasive test.

They recommend that future large-scale trials should be initiated to assess the diagnostic accuracy of this method.

Sarah Waights, from the Down's Syndrome Association, said the test might help some prospective parents, but only if accompanied by sufficient counselling.

She said: "The problem with pre-natal testing is that it is so often carried out without proper counselling and support for the parents and therefore often leads to big grief."

The research is published in The Lancet medical journal.