Blood test for Down’s Syndrome
Prenatal screening for Down’s syndrome could soon consist of a simple blood test for the mother, as reliable as an amniocentesis, but much less of a risk to the foetus. Several competing teams have produced tests with the common idea of analysing foetal genetic material present in the mother’s blood. In this way the extra chromosome characteristic of Down’s syndrome can be detected. The stakes are high: Down’s syndrome affects one in 700 pregnancies, and one in 100 in mothers over forty.
Researchers at Stanford University have just taken the lead by publishing a paper in the prestigious journal, Proceedings of the National Academy of Sciences, the perfect results of the technique which they tested on 18 women at the beginning of the second trimester of pregnancy.
American company Sequenom, which is working on a similar method, announced at the end of September “perfect agreement” between the results of their test and the amniocenteses of more than 200 expectant mothers in their first or second trimesters. They have yet to publish the data, but the firm already plans commercial availability in June 2009.
If the results are validated, these tests will revolutionize prenatal screening for Down’s syndrome, the most widespread chromosomal disorder. Strategies differ between countries, but so far, the only 100% reliable test is via the analysis of foetal chromosomes by amniocentesis during the second trimester (or by CVS – chorionic vilius sampling, biopsy of placental tissue during the first trimester). But these techniques cause miscarriages in 1percent of cases. France, record-holders for amniocentesis (11% of pregnancies) is currently reviewing the screening policy to reduce the numbers using this test.
Non-invasive tests were pioneered about ten years ago by a Hong Kong scientist, Dennis Lo, who showed that foetal DNA was present in the mother’s blood. Since then, many teams have latched on to using this easily accessible source of foetal genetic material to perform prenatal screening. However, it is still necessary to differentiate the genetic material of the foetus from that of the mother.
In this race for non-invasive screening procedures, France is not completely absent. Patricia Peterlini-Brechot (Inserm) and her team have perfected a method for separating foetal cells present in the mother’s blood.
Already proven effective in screening for spinal amyotrophy, another genetic illness, this method has never been clinically tested for Down’s syndrome. Research was blocked in 2006 because of a conflict between the researchers and their industrial associate, Metagenex, over the commercial use of the proceure in oncology.