Fetal DNA scanned for disease

Scientists have scanned the entire DNA of an unborn child from the mother's blood sample for the first time to safely check for genetic disorders. The new technique, developed by Dr Dennis Lo from the Chinese University of Hong Kong, was tested in a couple being screened for an inherited blood disease called beta-thalassemia, a form of anaemia.

The complex procedure involved sequencing almost four billion DNA molecules from the pregnant mother's blood sample and separating the fetal DNA strands buried deep within it. They were then able to piece together a genome-wide genetic map of the fetus by using the genetic maps of both the parents, which highlighted places where the inherited DNA differed in the fetus.

Finally, the completed fetal genetic map was scanned for genetic disorders and researchers found that the baby had inherited the beta-thalassemia mutation from the father, and was therefore a carrier of the disease. 'Our study suggests the feasibility of using genome-wide scanning to diagnose fetal genetic disorders pre-natally in a non-invasive way', the researchers said.

At the moment, prenatal testing of genetic diseases relies on invasive methods, which require taking a tissue sample from the placenta (CVS) or removing amniotic fluid from the womb (amniocentesis) with an injection. These techniques involve a one percent risk of triggering a miscarriage or infection and are therefore only carried out in cases where the probability of disease is high.

In 1997, it was discovered that some of the fetus' DNA circulates in the mother's blood stream. The researchers of this new study observed that 'uncovering the fetal genome amongst floating DNA is technologically akin to finding a needle in a haystack', because the DNA of the baby makes up only ten percent of the total genetic mixture of the blood.

This study raises the possibility that non-invasive fetal genetic testing may eventually be possible. However, more development and testing of this novel technique will be needed before it could replace existing clinical methods. The new approach also raises a number of ethical, legal and social issues that require active discussion among clinicians, scientists, ethicists and the community.

Dr Christine Patch, Consultant Genetic Counsellor at Guy's Hospital in London, said: 'While this is a potentially interesting approach that may have benefit for some families with serious genetic disorders who are making difficult choices when having children, there are many concerns'.

'Before such a test could be offered in the clinic, a much larger study is required to determine the robustness of the technique, and numerous logistical, economic and ethical issues need to be addressed including how to deal with unexpected or incidental findings', added Dr Caroline Wright, Head of Science at the Public Health Genomics Foundation.

'Tests like this may produce clinically useful information, but they may also be a cause of unnecessary worry and anxiety; or they may offer false reassurance in a pregnancy that has serious non-genetic abnormalities that will not be picked up by the test', explained Dr Patch. 'We do not randomly test pregnancies for a long list of other conditions that may only manifest in adult life on the basis that individuals may not want to know that information when they are older'.

The study was funded by the Hong Kong Research Grants Council, Sequenom Incorporated from the US, the Chinese University of Hong Kong, and the Government of the Hong Kong Special Administrative Region, China. The research was published in the journal Science Translational Medicine.