New Prenatal Blood Tests To Diagnose Down Syndrome Could Replace Existing Invasive Procedures

Main Category: Pregnancy / Obstetrics
Also Included In: Pediatrics / Children's Health
Article Date: 09 Oct 2008 - 5:00 PST

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Two separate research teams each have developed techniques for noninvasive prenatal blood tests for Down syndrome that have yet to produce a false negative or a false positive result, the New York Times reports. The two Down Syndrome test procedures currently available -- amniocentesis and chorionic villus sampling, or CVS -- work by inserting a needle into the uterus to retrieve fetal cells and carry a slight risk of miscarriage estimated at one in 200 to less than one in 1,000, according to the Times. The experimental noninvasive tests require only a blood sample.

According to the Times, Down syndrome occurs when an infant is born with three copies of chromosome 21 instead of two. It is the most common chromosomal disorder, resulting in mild to moderate mental retardation, unusual facial features and a high risk of heart defects. Testing is usually recommended for women 35 or older and others with certain risk factors. The American College of Obstetricians and Gynecologists now recommends that it should be an option for all women.

Sequenom, a biotechnology company in San Diego, developed a test it plans to begin selling next year that has successfully diagnosed about 400 blood samples. The research has not yet been published in a peer-reviewed journal. The test would be given to women at 12 to 14 weeks' gestation but the company hopes to be able to have the test work at 10 weeks' gestation. The Sequenom-developed test initially will be used to screen woman to determine who should subsequently undergo either amniocentesis or CVS, processes that already are conducted by ultrasound and a variety of blood tests, the Times reports. Some experts said that unless a non-invasive test can replace the current diagnostic tests it will not be significant. However, other experts said that even an improvement on existing screening tests would represent a big advance because current screening tests can miss 5% to 30% of Down syndrome cases, the Times reports. Harry Stylli, CEO of Sequenom, said the test could be used as a diagnostic test in the future that would "ultimately replace amnio[centesis] and CVS."

Researchers at Stanford University and the Howard Hughes Medical Institute, led by Stephen Quake of Stanford, developed a different non-invasive test that has been successful in testing 18 different blood samples. The results were published Monday in the Proceedings of the National Academy of Sciences (Pollack, New York Times, 10/7). Quake said the new test could be administered as early as five weeks post-conception and the results could be back within days instead of weeks as with the amniocentesis and CVS. The Stanford test also has been shown to detect other chromosomal conditions such as Edward syndrome, which kills half of infants in the first week of life, and Patau syndrome, which leads to the death of 80% of newborns during infancy, Reuters reports (Dunham, Reuters, 10/6). The test uses recent DNA technology that provides more detailed genetic information, the San Jose Mercury News reports (Krieger, San Jose Mercury News, 10/6).

According to the Times, some advocates for people with Down syndrome have expressed concern that the test will result in more women choosing to have abortions after their fetuses receive a positive Down syndrome diagnosis (New York Times, 10/7).

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