Down syndrome

“Issue of ‘New Prenatal Test For Down Syndrome Less Risky Than Amniocentesis, Scientists Say’ Supporting Ch. 3 Heredity & Environment”

I. Summary of News Article

ScienceDaily (Oct.7, 2008). Pregnant women worried about their babies’ genetic health face a though decision: get prenatal testing and risk miscarriage, or skip the test and miss the chance to learn of genetic defectsbefore birth.
But a new prenatal test could make this dilemma obsolete. The new method, developed by scientists at Stanford University, the Howard Hughes Medical Institute and Lucile PackardChildren’s Hospital, requires only maternal blood sample to spot chromosomal disorders such as Down syndrome.
Current prenatal gene tests, such as amniocentesis and chorionic villus sampling, requireinserting a needle in the uterus and carry a miscarriage risk of around half a percent.
The new method scans for fetal aneuploidy, an abnormality in the number of fetal chromosomes. Humanstypically inherit 46 chromosomes, half from each parent.
The Stanford/Packard team developed a way to count chromosomes using bits of fetal DNA in a pregnant woman’s blood. First, using samples from 12women with aneuploid pregnancies and six with normal pregnancies, the researches separated maternal blood into cells and plasma. They discarded the blood cells, focusing on the liquid plasma’s DNAfragments, which come from both the mom and the fetus. They counted the number of DNA fragments and used DNA sequencing to read each one.
Women with Down syndrome pregnancies had morechromosome-21 fragments in their blood than women with normal pregnancies.
Because fetal DNA shows up in maternal blood quite early in pregnancy, the team says their technique could provide a much earlierdiagnosis for fetal aneuploidy than is now available. “The earlier you know you’ve got a fetus with Down syndrome, the better able you are to prepare,” Quake said, nothing that the benefit holds both...