The new study, published this week by researchers from The Chinese University of Hong Kong in the British Medical Journal, tested the accuracy of a new blood test to detect Downs Syndrome on 753 subjects, of which 86 were found to carry a fetus with Downs Syndrome. The new blood test had no false negatives (i.e. it did not show a negative result when the fetus actually had Downs Syndrome), and 3.1% incidence of false positives (i.e. it diagnosed Downs Syndrome in 3.4% of the subjects when that was not really the case). Today, the actual test procedures for Downs Syndrome carry a 1 to 2% risk of miscarriage. The new test relies on a state-of-the-art DNA technique called multiplexed massively parallel DNA sequencing, and requires only a blood test for the mother. It would dramatically reduce the risk of miscarriage, when compared to traditional techniques.
Downs Syndrome is the most common genetic abnormality in fetuses. The risk of a fetus carrying Downs Syndrome is approximately 0.1% for the general population, but goes up very fast with the mother's age, to reach almost 1% for a 40-year old mother. Downs Syndrome means severe genetic retardation for the child, and 90% of the mothers typically elect to terminate their pregnancy when the diagnostic is made. As the diagnostic is more likely when it becomes harder for the mother to experience pregnancy -due to age,- many parents now have to make very difficult choices between the wish to know if the fetus carries Downs Syndrome, and the risk of miscarriage that the present tests carry.
The new test will radically alter the risk proposition. It takes advantage of the fact that the fetus' DNA can be found in the mother's blood, and requires only a very low risk blood test for the mother. If the test is negative, since it has shown no false negatives so far, no more testing is needed. If the test is positive, meaning in only 1-2% of the cases, to absolutely ascertain the presence of Downs Syndrome, the standard test procedure, which carries higher risk, is required. The risk is therefore decreased, for the general population, by 98%, since only positive blood test results require the riskier traditional test.
Traditional tests with a high certainly of results for Downs Syndrome today require invasive procedures. The most common is amniosynthesis, and involves piercing the amniotic sac with a needle to pick up a sample of amniotic fluid. The other test, chorionic villus sampling, also invasive, requires a small piece of the placenta for testing. Both tests carry a 0.5% to 2% risk of miscarriage.
The new test is technically ready for deployment, but is not commercially ready, and would be expensive today. We expect to see it appear in one to two years in the mainstream, by which time it will be significantly cost reduced. It represents a revolution in testing for Downs Syndrome, which, because of the radical decrease in risk of miscarriage, will clearly become the primary approach to Downs Syndrome testing. When amniosynthesis and chorionic villus sampling are typically restricted today to high risk pregnancies (often those of older mothers), we believe that this new technology will make it possible to test all pregnant women, and may largely eliminate Downs Syndrome altogether in the developed world.
Why are we reporting on a test that is no ready for implementation today? We normally only review commercially available tools and techniques. This test represents a remarkable breakthrough for all pregnant couples - a phase of life common to practically all of us. We believe that it is important to spread awareness of this radically better upcoming choice for pregnant couples.
Want to read more about it? Try New Scientist, PhysOrg, Medical News Today, WebMD, WebMD 2, NHS UK, BBC, TIME Magazine, MedPage Today, ABC News, LA Times, CBS News, CTV.ca, CBC.ca, Boston.com, Science Daily, Third Age, and Globe and Mail
Study Abstract in the British Medical Journal
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