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Friday, July 3, 1998 Published at 12:13 GMT 13:13 UK


Safe blood test for Down's Syndrome under development

A simple blood test may soon diagnose Down's Syndrome

A safe and simple blood test may in future be able to determine quickly whether a woman is pregnant with a Down's Syndrome baby.

Researchers from Birmingham have developed a DNA test for the condition that cuts the normal diagnosis time from about 15 days to just one day, and removes the need for risky amniocentesis techniques.

Common disorder

Down's syndrome is one of the most common genetic disorders, affecting about one in every 600 newborn babies.

Children born with the disorder have short stature, small heads and mild to severe mental retardation.

The most common pre-natal test for Down's syndrome involves amniocentesis, in which a sample of the fluid that surrounds the foetus is collected.

To do this the amniotic sac must be pierced, which can be risky. Cells in the fluid must then be cultured in a laboratory, which takes about 15 days and requires considerable expertise.

Amplified DNA

The new test uses a technique for copying very small amounts of DNA called polymerase chain reaction (PCA). The process allows DNA to be "amplified" so tell-tale genetic markers can be recognised.

[ image: Results could be known in one day]
Results could be known in one day
Investigators, led by Loveena Verma at Birmingham Heartlands Hospital, tested 2,083 amniotic samples for a set of markers associated with Down's syndrome.

The test correctly showed that 2,053 foetuses were normal and 30 had the disorder and had an accuracy rate of almost 100%.

The technique was automated, with the potential for up to 96 samples to be processed simultaneously and provide results within the same day.

Problems to be overcome

Since only very small amounts of DNA were needed, the doctors predicted that it might be possible to dispense with amniocentesis and use a blood sample instead. But there were still problems to be overcome before this could be achieved.

Writing in the Lancet medical journal, the researchers said: "PCR diagnosis could in future become the method of choice for non-invasive pre-natal diagnosis, on foetal cells isolated from maternal blood.

"Adequate isolation of these foetal cells from a maternal blood sample has, however, proved very difficult."

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