Last month (October 17), genetic diagnostics manufacturer Sequenom released a new test that can detect whether a baby has Down syndrome from a sample of the mother’s blood. At the time, researchers predicted it would be the first of many such non-invasive fetal tests. Now, with the publication of a similar test for genetic deletions in unborn babies, that prediction appears to be coming true.

David Peters of the University of Pittsburgh Medical Center and his colleagues took blood samples from a pregnant woman whose older child had developmental delay and dysmorphic features. Doctors had previously determined that the older child inherited a 4.2-Megabase deletion on chromosome 12 from its father. Amniocentesis—a procedure involving the extraction of a small amount of fluid from the amniotic sac—and genetic testing had identified the same heterozygous deletion in the new male fetus. The researchers tested the mother’s blood sample to...

Sequencing seven maternal plasma samples, the researchers identified lower DNA copy number of the deleted 4-Mb region on chromosome 12, while all other regions appeared normal. Because the mother carried no such deletion, the results suggest that the fetal DNA did, resulting in lower overall copy numbers of that region.

"We have shown proof of concept that a fetal chromosomal microdeletion can be identified by means of noninvasive analysis of DNA in maternal plasma," the authors wrote. They published their results yesterday (November 10) in the New England Journal of Medicine.

Such non-invasive tests could one day decrease the need for amniocentesis, which carries a small risk of miscarriage.

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