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Biological Chemistry

Fetal genome sequenced at five weeks

Cells from Pap smear carry enough fetal DNA to screen for genetic diseases

by Elizabeth K. Wilson
November 7, 2016 | A version of this story appeared in Volume 94, Issue 44

Just five weeks into gestation, a fetus can have its DNA collected during its mother’s routine Pap smear and accurately genotyped, according to a study (Sci. Transl. Med. 2016, DOI: 10.1126/scitranslmed.aah4661). The development holds promise for early genetic testing for thousands of birth defects. To obtain such information currently, pregnant women must undergo invasive and risky procedures such as chorionic villus sampling (CVS), a tissue analysis technique, at around 10–12 weeks’ gestation or amniocentesis at 16–18 weeks. Progress has also been made in the development of tests that detect snippets of fetal DNA in a mother’s blood. However, it can be difficult to generate an accurate picture of a fetal genome from these methods. Now, a team led by Chandni V. Jain, Sascha Drewlo, and D. Randall Armant of Wayne State University School of Medicine isolated placental cells known as trophoblasts from cervical canal swabs of 20 pregnant women at five to 19 weeks’ gestation. Trophoblasts carry fetal DNA, which the team was able to isolate and distinguish from the mothers’ DNA. They also showed that the fetal DNA quality is on par with DNA obtained through CVS or amniocentesis. The authors say tests can be developed for this source of fetal DNA that could identify single gene mutations, such as those responsible for some metabolic syndromes.


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