Researchers take a step towards a non-invasive test for Down's syndrome
7 March 2011
Down's syndrome is caused by having an extra copy of chromosome 21 (to give three copies, rather than the usual two), known as trisomy-21. Currently, the only way to diagnose Down's syndrome during pregnancy is to perform invasive procedures, such as amniocentesis or chorionic villus sampling, which involve taking samples of the fluid surrounding the unborn baby or cells from the placenta. These procedures are associated with a significant risk of miscarriage of around 1 per cent.
Researchers at the Cyprus Institute of Neurology and Genetics have developed a new method to detect extra copies of the fetal chromosome in a blood sample from the mother. The test takes advantage of differences in patterns of DNA methylation between mother and baby, which allows the researchers to detect the trace quantities of fetal DNA that are present in the mother's blood.
Using a method known as quantitative PCR, the researchers can compare the ratio of chromosome 21 detected in normal and trisomy-21 cases to accurately diagnose Down's syndrome. The new test correctly identified 26 normal and 14 trisomy-21 cases in a blinded trial, with no false positives or negatives.
Dr Nigel Carter from the Wellcome Trust Sanger Institute, who collaborated on the study, said: "The results are extremely promising but we must remember that this is a small study. A much larger-scale study will be required before we can see this test moving into standard clinical practice."
The method is simple, fast and easy to perform in every genetic diagnostic lab worldwide because it does not require expensive equipment, software or any special infrastructure.
Image: PCR reactions ready for analysis. Credit: Wellcome Library, London.
Reference
Papageorgiou EA et al. Fetal-specific DNA methylation ration permits noninvasive prenatal diagnosis of trisomy-21. Nat Med 2011 [epub ahead of print].
