New Test "Promising" for Prenatal Diagnosis of Down Syndrome

Down Syndrome, also known as Trisomy 21, is a spectrum of both physical and intellectual abnormalities that are related to a known, specific, genetic condition: the presence of an "extra" chromosome (hence the word "trisomy," meaning "third") at position 21 of the human genome. Although there are certain fetal abnormalities that can be detected by a prenatal ultrasound exam and a specific maternal blood test ("Maternal AFP level") that are known to be associated with Down Syndrome, no specific non-invasive test or combination of such tests is capable of making an acceptably-accurate diagnosis of Down Syndrome prior to the birth of an affected infant.

However, if the initial results of a study published in the early access edition of The British Medical Journal can be confirmed, a reliable prenatal test for detection of that condition may be forthcoming relatively soon.

A multinational team of biochemists, geneticists, and physicians report that, using a sophisticated series of biochemical processes and recent techniques in DNA technology, they have developed a laboratory test that promises to make the prenatal diagnosis of Down Syndrome a matter as simple as taking a blood sample from the expectant mother.

The new test is based on the well-known fact that some fetal blood cells will normally enter the mother's circulation. Although these "escaped" fetal cells are always relatively small in number, the researchers were able to selectively remove those fetal cells from a sample of the mother's blood and then subject ed the cells to DNA analysis.

The researchers found that in women who were considered to be at highest risk of carrying a fetus with Down Syndrome, the new blood test was able to detect Down Syndrome with an overall accuracy of greater than 90 %, which is far greater than the accuracy reported for the currently-recommended combination of ultrasound and and blood testing. In fact, the researches suggested that if the new testing protocol can be validated in larger clinical trials, the new test could foreseeably greatly reduce the number of "Genetic" Amniocentesis and Chorionic Villus Sampling tests that are currently being done to establish the presence or absence of Trisomy 21 and related conditions

Although the reported results would, if validated in more extensive clinical trials, be considered as equivalent to the "Holy Grail" of prenatal genetic testing, I cannot help but to suggest that we should pause to consider our responses to the ethical issues that such testing will certainly raise. Is there anything that would prevent this test from becoming used as a "gender selection tool" to decide elective termination of some pregnancies in those societies that place a higher "value" on one sex over the other? Or, as writer Bonnie Roachman stated in today's issue of "Time Online:"

"What if new tests for Down syndrome could one day mean no more affected babies are born? Is that cause to celebrate medical advances or reason to worry we are callously weeding out the less-than-perfect in our midst?"

Even the most superficial of consideration involving the potential issues of morality versus technology that will be raised by this, and other related medical testing, should alert us to the serious issues that we, as a society will one day have to face. Since I am approaching the end of my life, the answer to the above questions are not mine to give. Instead, I can only hope that the darker forces of the old Eugenics Movement has long since passed into extinction.

See Also

For a more detailed review of Trisomy 21 / Down Syndrome, see either the WebMD article "Down Syndrome" or the Mayo Clinic's Down Syndrome pages. For medical professionals and / or those readers with a few semesters of coursework in genetics and molecular biology, the Online Mendelian In Man web site has an excellent compendium regarding this condition..

The study mentioned in this post can be found online as: RWK Chieu et al. "Non-invasive Prenatal Assessment of Trisomy 21 by Multiplexed Maternal Plasma DNA Sequencing: Large Scale Validity Study." British Medical Journal: DOI 2011; 342: c7401 (HTMLPDF).

Bonnie Roachman. "Can a New Blood Test Make Babies with Down Syndrome Disappear?" Time Magazine Online Edition. January 13, 2011.