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Cell-free fetal DNA: testing the waters

29 September 2008
By Ailsa Stevens
Science Information Officer, Progress Educational Trust
Appeared in BioNews 477
A decade ago, it was found that the blood of pregnant women contains DNA from the fetus. The discovery of this 'free fetal DNA' (ffDNA) has led to the development of non-invasive prenatal diagnosis, where genetic characteristics of the fetus can be analysed a mere few weeks into pregnancy by studying a sample of the mother's blood.

Many experts believe ffDNA testing will put an end to the anguish couples experience when making the very difficult decision of whether or not to test their unborn child for a genetic condition, by providing a safe alternative to invasive procedures, such as amniocentesis, which carries a risk of miscarriage. An added benefit of ffDNA testing is that it can be carried out much earlier in the pregnancy, giving the couple longer to decide whether or not to terminate an affected pregnancy or to gather more information on the implications of bringing an affected child into the world.

However, there is still much concern that the emergence of a test with no negative repercussions for mother or baby will lead to an increase in abortions, with some parents deciding to terminate for trivial reasons, such as gender or minor disability. The Daily Mail reported last week that '[ffDNA testing] has raised fresh fears over 'designer babies'' (1), though what evidence there is to suggest it will inevitably lead to parents wanting anything more than a 'healthy' baby is open to scrutiny.

These issues were the focus of a debate jointly organised by the Progress Educational Trust and the Royal Society of Medicine. Held on 23 September at the Royal Society of Medicine, the event attracted a diverse audience, including members of the public, health professionals, scientists and policy makers, who gathered to witness three experts - Lynn Chitty, Senior Lecturer in Genetics and Fetal Medicine at the Institute of Child Health, Jane Fisher, Director of Antenatal Results and Choices, and Ainsley Newson, Lecturer in Biomedical Ethics at the University of Bristol - explain the science, explore the ethics and consider the future of free fetal DNA testing.

The debate was expertly chaired by Tessa Homfray, Consultant in Clinical Genetics at St George's Hospital Medical School.

Lyn Chitty opened the debate with an explanation of the technology behind ffDNA testing. She presented data, collected with colleagues from University College Hospital, showing that this can now reliably be used to determine the sex and blood type of the fetus, making it easier to anticipate sex-linked genetic disorders and Rhesus disease. Although, at present, the technology is only suitable for detecting genetic markers not present in the mother, she told the audience that in the future it could be possible to offer ffDNA testing for the diagnosis of a wide-range of single gene disorders, for which the baby's genetic makeup may differ only slightly from the mother's.

Jane Fisher highlighted that, unlike other non-invasive prenatal tests such as ultrasound and serum screening, ffDNA testing can offer a definitive diagnosis which is available to the parents very early on in pregnancy. She emphasised that the delivery of a positive diagnosis has an enormous impact at any time in pregnancy, but that if couples undergo the test at an early stage, without really considering the implications, they may not be fully prepared to make an informed decision about what they would do in the event that the test is positive. Given that such information might be gleaned from something as simple as a blood test, set into motion by little more than a prick on the woman's finger at a stage when she is physically and emotionally new to the pregnancy, she questioned what impact this might have on how a couple might react to positive results.

Finally, Ainsley Newson presented the ethical aspects of the debate, weighing up the advantages of safe accurate testing at an earlier stage in pregnancy, against the disadvantages of having less time to ensure that the couple are able to make an informed decision about what to do in the event of a positive result and whether or not this raises the prospect of increased terminations on the grounds of disability, sex or non-paternity. She also questioned how ffDNA testing should be regulated, raising concerns about the possibility of patients accessing the test over the Internet, without proper clinical oversight.

The talks provoked much debate, with a wide range of thought-provoking comments from the floor and panel.

Several commentators deliberated how the technology might be regulated when, in theory at least, the test could be provided 'direct-to-consumer' using just a tiny pinprick of blood sent through the post. While there was wide agreement that the testing should not be offered without extensive pre- and post-test counselling to ensure that couples fully understand its implications, speakers acknowledged that the simplicity of the test did indeed create a problem for its regulation. One commentator, a UK lawyer, suggested that the US model could be adopted, where laboratories are under obligation to insist that patients have undergone rigorous counselling, though it is not their responsibility to police nor monitor this practice.

Another person expressed concern that ffDNA testing might increase the incidence of terminations and questioned whether it was in fact ethically sound to distinguish between social sex selection and selecting against, for example, a child with Down syndrome. In response, Ainsley Newson emphasised that, given the complexity of cases, each should be evaluated in the context of the parent's own values and solely on a case by case basis. Tessa Homfray pointed out that, despite the introduction of prenatal testing, the number of babies being born with Down syndrome is still increasing, probably partly due to increased parental age.

Another hotly debated topic was the concern that selecting against certain disabilities could negatively impact members of society currently living with such conditions. Ainsley Newson felt that an increase in the number of terminations for certain disabilities could indeed decrease the value of members of society living with that disability, by making them less visible and therefore less likely to be granted necessary resources. Elaborating on this point, Jane Fisher explained that even when faced with a potentially devastating diagnosis, parents still sometimes choose to go ahead with the pregnancy, suggesting that they are unlikely to entertain the opportunity to test for more and more trivial reasons, just because it becomes safe and feasible for them to do so.

Overall, most participants agreed that ffDNA testing offers tremendous benefit to patients and medical practitioners alike, and holds considerable future promise. Nonetheless concerns over the technique, including its accuracy, its potential applications and its regulation, must be fully evaluated before allowing it to enter routine clinical care. In the meantime, it will be the responsibility of health professionals to manage patient expectations, by stressing that, despite media hype, ffDNA testing will not be ready for the clinic for some five years or more.

1) New Blood test to spot Down's syndrome at seven weeks leads to designer babies fear The Daily Mail, 24/09/2008.
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