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Health & Pregnancy

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Prenatal Down Syndrome Blood Test in the Works

Study Shows Test That Checks for Genetic Markers May Offer Safer Alternative to Amniocentesis
WebMD Health News
Reviewed by Laura J. Martin, MD

March 7, 2011 -- A new method of screening for Down syndrome during pregnancy may eventually offer a safer, less invasive alternative to amniocentesis, according to a new study.

The experimental Down syndrome test screens for genetic markers of the developmental disorder in blood samples taken from the mother between the 11th and 14th weeks of pregnancy.

Early testing of the new method showed it correctly distinguished between 14 fetuses with Down syndrome and 26 healthy fetuses with 100% accuracy.

Down syndrome is the most common cause of mental retardation.

Currently, the only way to conclusively diagnose the disorder during pregnancy is to take samples of genetic material from the fetus via amniocentesis or another method. But these methods come with a risk of miscarriage.

Other less invasive prenatal tests, such as nuchal translucency scans, can only estimate the risk of Down syndrome in the fetus.

DNA Differences in Down Syndrome

The new Down syndrome test is based on differences in DNA methylation patterns, which are critical to gene expression, between the mother and the fetus. It screens for extra copies of a fetal chromosome in the mother’s blood.

In Down syndrome, there are three copies of chromosome 21, called trisomy-21, instead of the normal two.

Researchers say the method is fast and easy to perform in any genetic diagnostic lab and does not require special or expensive equipment.

“Such a noninvasive approach will avoid the risk of miscarriages of normal pregnancies caused by current, more invasive procedures,” write researcher Elisavet A. Papageorgiou, of the Cyprus Institute of Neurology and Genetics in Nicosia, Cyprus, and colleagues in Nature Medicine.

“Nevertheless, a larger-scale study will need to be performed to assist in the introduction of the diagnostic strategy into the clinical practice of prenatal diagnostic laboratories.”

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