Fetuses can be screened for Down's syndrome using amniocentesis and other invasive methods, which all carry a risk of inducing miscarriage. A non-invasive test that analyses fetal DNA extracted from the mother's blood might one day replace current methods.

Philippos Patsalis at the Cyprus Institute of Neurology and Genetics in Nicosia and his colleagues used an antibody-based method to examine patterns of fetal DNA methylation on chromosome 21, of which Down's patients have an extra copy.

The researchers chose eight regions in which methylation levels differed most between people with and without Down's. They calculated a score for each case and used this to classify samples as unaffected or as Down's syndrome. The researchers accurately identified all 14 cases of Down's out of a pool of 40 samples.

Nature Med. doi:10.1038/nm.2312 (2011)