American
scientists have reported in the New England Journal of Medicine that Down’s
syndrome can now be reliably tested for in a pregnant mother’s blood. The current method for testing is an assessment
based on age and an ultrasound scan, with further tests performed on patients
deemed “high-risk”. These additional
tests require a sample of placenta fluid obtained using a needle. This procedure has a risk of miscarriage.
The new approach
looks for DNA fragments from the placenta, which float around in the mother’s
bloodstream. Down’s syndrome is the
result of an extra chromosome, and this excess of genetic information can be
detected from the DNA in the blood.
Research has demonstrated the effectiveness of the test in high-risk
women, but now a team at the University of California, San Francisco, proposes
that this blood test could replace current testing for all women.
In a study
conducted with 16,000 women, the new test correctly identified 38 cases of Down’s
syndrome, while the basic test only found 30 and had a higher incidence of
false positives. The UK’s national
screening committee will evaluate this new test in a couple of months. Although they do not envision that every woman’s
blood will be tested in this manner, it will broaden access to testing by
offering a less invasive and less risky option.
Similar blood tests will soon become available for other genetic
disorders, such as cystic fibrosis.
Meghan
Harrington (Group B)
Very interesting post, it's encouraging to hear that there is a safer and more effective test to determine down's syndrome. How do they obtain these DNA fragments from the placenta? Do they just take a sample of blood from the mother and test it? Are these fragments hard to find in the blood?
ReplyDeleteDavid Rains,
All they have to do is sample the blood, which, in a pregnant female, contains some fluid from the placenta. A blood test is typically a routine procedure, so the fragments are not too hard to find.
Delete-Meghan Harrington
Great Blog! It was clear, concise and well organized. I am sure a lot of mothers will be on board with this new approach. I was also wondering, are there any set backs of obtaining a blood sample over the previous more invasive method? For example, will this new method take longer to yield results?
ReplyDelete-Posted by Amanda Okpoebo
Great post, Meghan. After reading your blog and the study linked above, I've learnt that there's cell-free DNA of the fetus(es) in a mother's bloodstream, which can be used directly to detect Down's syndrome. I have a few questions for you: 1. Would this test still be effective if the mother carries semi-identical or fraternal twins or triplets? 2. Can this test be executed any time during pregnancy? 3. Do you think the effectiveness of this test would increase the abortion rate?
ReplyDelete-Posted by Phi Duong
Since the research is still new, there is not yet information regarding testing for twins. I would think that the test could be performed, but in the case in which identical twins share a placenta, it may be difficult to differentiate which fetus has the extra chromosome. With fraternal twins, the general differences in their DNA sequences may enhance the ability to identify which fetus is affected. This test can be executed as early as the first trimester. I think the effectiveness of this test could very likely increase abortion rate; the less invasive nature and better accuracy of this test will probably increase the number of women who ultimately find out that their baby has Down's syndrome. Consequently, this knowledge gives them the opportunity to make that choice, which they wouldn't have had without this form of detection.
Delete-Meghan Harrington