New non-invasive prenatal test shows promise

A new technique could provide an alternative to invasive pregnancy tests, researchers based in the US and Asia have shown. Using small amounts of fetal DNA present in the mother's blood, they have managed to carry out prenatal tests for the inherited blood disorder thalassaemia. The study appeared in the early online edition of the Proceedings of the National Academy of Sciences.

Currently, tests for Down syndrome and genetic conditions such as cystic fibrosis rely on taking fetal cell samples, using either amniocentesis or CVS (chorionic villus sampling). Both techniques involve injecting a needle into the womb, and so carry a small risk of miscarriage. Because of this, researchers have been trying for some time to develop a non-invasive technique for carrying out genetic tests during pregnancy.

It was already known that a small number of cells from the fetus always find their way into the mother's bloodstream, where they are attacked by the maternal immune system. As a result, an estimated 3-5 per cent of the 'free' DNA in the mother's plasma comes from the fetus. However, previous attempts to analyse this DNA have been thwarted by the large amounts of maternal DNA present.

In the latest study, researchers at the Chinese University of Hong Kong and Boston University used mass spectrometry - a powerful technique that can be used to identify specific chemicals present at low concentrations in a chemically complex mixture. The scientists looked for fetal beta-thalassaemia gene mutation in pregnant woman at risk of passing on the disorder, between the seventh and 21st weeks of pregnancy. Their method relied on a new way of selectively 'amplifying' the fetal DNA region of interest, which they used either to examine the mutation directly, or indirectly, by looking at DNA 'markers'close by. In all cases, the team accurately predicted the presence or absence of beta thalassaemia gene mutations in the fetus.

'This development is very exciting and has addressed a long-awaited need in non-invasive prenatal diagnosis', said team leader YM Dennis Lo. He also told the Scientist magazine that the technique could be used for sex selection, but that such a use would be unacceptable to him, and instead should only be used for diagnosing serious disorders.