Health

'Safer' test developed for Down's

by Amitjha | October 6, 2008 at 09:58 pm

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Stanford university says it has developed safer test to diagnose Down's syndrome.

One of the current ways of confirming the syndrome is amniocentesis, in which a needle is used to take a sample of the fluid within the womb. Approximately one in 100 women who have the test will miscarry as a result, A similar invasive procedure that takes a tissue sample from inside the womb, called chorionic villus sampling, carries a miscarriage risk of two in 100. It can be carried out at an early stage of pregnancy than amniocentesis - after 10 weeks gestation compared with after 15 weeks for amniocentesis.

If a foetus has three copies of chromosome 21 rather than the normal two, there will also be a relative increase in the quantity of chromosome 21 in the mother's blood because DNA can cross the placenta from the baby to the mother.

The "shotgun sequencing test" identifies and counts these fragments of DNA and is sensitive enough to detect the very small increase in amount of chromosome 21.

Dr Lyn Chitty, an expert in genetics and foetal medicine at University College London Hospital, said: "This is a potentially exciting development which may take us closer to a safer, non-invasive test for Down's syndrome and the other major aneuploidies, trisomies 13 and 18."

She said other scientists were looking at different genetic markers in maternal blood for Down's. However, these tests would not work in all women, unlike the DNA test.
Carol Boys, chief executive of the Down's Syndrome Association, said: "There is no question that these non-invasive tests will be introduced in the next few years.
"It's therefore incredibly important that potential parents are given accurate information on Down's syndrome before they make a choice about whether to terminate or not.
"We don't consider Down's syndrome a reason for termination, but we recognise that bringing up a child with Down's syndrome isn't right for everyone.
"The more informed parents are, the better the position they are in to make the choice that is right for them."