'Safer' test for Down's Syndrome developed

Invasive procedures currently used risk miscarriage and damage to the foetus. A Stanford University test of DNA evidence in 18 pregnant women's blood correctly identified nine cases of Down's syndrome, reports PNAS journal. The university now wants a larger-scale test. Babies with Down's syndrome have an extra copy of chromosome 21, causing physical and intellectual impairments. "Non-invasive testing will be much safer than current approaches" - Researcher Dr Stephen Quake

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.

In tests on 18 pregnant women, shotgun sequencing correctly identified nine cases of Down's syndrome and two other inherited disorders - aneuploidies - caused by an abnormal number of chromosomes. Dr Stephen Quake and his Stanford team say they need to repeat their study in a larger number of women, but they are confident that it could be used routinely in hospitals a few years from now. "The more informed parents are, the better the position they are in to make the choice that is right for them" - Carol Boys, chief executive of the Down's Syndrome Association