Scientists at the Chinese University of Hong Kong have developed an accurate, non-invasive test to identify Down's syndrome, using fetal cells present in the mother's blood. The researchers, who reported their results in last week's issue of The Lancet, successfully used the new technique to identify three fetuses affected by the chromosomal condition.
Down's syndrome is usually caused by an extra copy of chromosome 21, the smallest human chromosome. Currently, the only certain way to detect the extra genetic material is to examine fetal cells present in the amniotic fluid (amniocentesis), a procedure that carries a small risk of miscarriage. Although blood tests are also available, they only measure hormone levels, and only have a success rate of 60 per cent.
The Chinese team successfully obtained fetal cells from maternal blood by looking in the liquid of the blood sample (plasma) rather than the cellular element, as previous researchers had done. They then used a technique known as fluorescent in situ hybridisation (FISH) to detect the presence of three chromosome 21s. The test is 'a direct measure of Down's syndrome' says team leader Dennis Lo. 'There's no reason to think it could not be used to detect all cases', he added, although he stressed the need for many more trials.
The new test could potentially be used to detect any condition involving an abnormal number of chromosomes, providing a faster, safer alternative to amniocentesis. 'If it can be shown to be a reliable test, it means people aren't going to be subjecting healthy babies to the risk of miscarriage' said Cynthia Clarkson of the National Childbirth Trust.