Scientists Explore New Test for Down Syndrome

TUESDAY Oct. 7, 2008 -- For women worried about the risks of amniocentesis and other currently available tests for chromosomal disorders such as Down syndrome, a new, safer test may be on the horizon, researchers say.

Currently, prenatal genetic tests for Down syndrome, including amniocentesis and chorionic villus sampling, involve insertion of a needle into the uterus. These tests carry a miscarriage risk of about half a percent.

The new technique, described in the Oct. 6 edition of the Proceedings of the National Academy of Sciences, takes advantage of fetal DNA in a pregnant woman's blood. The researchers, from Stanford University, the Howard Hughes Medical Institute and Lucile Packard Children's Hospital, overcame problems other scientists had in the past by determining there was no need to distinguish between maternal DNA and the tiny bits of fetal DNA that accompany it.

The technique scans for fetal aneuploidy, which is an abnormality in the number of fetal chromosomes. Down syndrome is a type of aneuploidy that arises from an extra copy of chromosome 21, the researchers said.

The researchers used samples from 12 women with aneuploid pregnancies and six with normal pregnancies. They found that the women with the Down syndrome pregnancies had more chromosome 21 fragments in their blood than the women with normal pregnancies.

The test has the potential to detect other forms of aneuploidy, too. And since fetal DNA shows up in maternal blood early in pregnancy, the technique could lead to earlier diagnosis of fetal aneuploidy, the researchers said.

"The earlier you know you've got a fetus with Down syndrome, the better able you are to prepare," Stephen Quake, a professor of bioengineering, said in a Stanford news release.

The next step is to repeat the study in a larger number of women.

"This technique is on the leading edge of a flood of different ways that rapid DNA sequencing will be used in medicine," Quake said.

More information

The National Institute of Child Health and Human Development has more about Down syndrome.

Posted: October 2008


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