Risk-Free Procedure Maps Fetal DNA From Parents’ DNA

Among the main reasons a pregnant woman undergoes prenatal testing is to determine if the baby has genetic abnormalities. These invasive procedures-amniocentesis and chorionic villus sampling (CVS)–involve testing the placental tissue, and they carry a slight (for most people) risk of inducing a miscarriage.

But as widely reported last week, including in a story by the New York Times, for the first time, researchers have mapped the entire genetic profile of a fetus using only a blood sample from the mother and a saliva sample from the father. This could mean that in the not-too-distant future, most prospective parents can know the DNA blueprint of a child long before it is born, and without the risks of an invasive, risky test.

It would enable countless genetic disorders to be detected and possibly treated in the womb.

The new technique, however, also has the potential to present serious ethical questions, possibly increasing abortions for reasons other than medical, such as personal parental preferences for certain traits.

The paper was published in the journal Science Translational Medicine.

The researchers deduced the DNA sequence of the fetus with about 98 percent accuracy, but the technology is not practical, affordable or accurate enough for widespread use currently. The researchers estimated that it would cost as much as $50,000 to map one fetal DNA today.

But as The Times noted, “The cost of DNA sequencing is falling at a blistering pace, and accuracy is improving as well. The researchers estimated that the procedure could be widely available in three to five years. Others said it would take somewhat longer. ”

Parents concerned about passing on a genetic disease sometimes use in vitro fertilization and test the embryo before implanting into the womb. The new technique doesn’t require complete fetal cells, making DNA testing easier and less risky.

The genome was determined 18.5 weeks into the pregnancy; researchers said it might be possible to get accurate results in the first trimester, which is as early or even earlier than some invasive procedures.

It’s possible now to determine a fetus’ gender, paternity and whether it has Down syndrome via analysis of the mother’s blood. But determining the whole genome is more difficult. That enables detection of disorders including cystic fibrosis, Tay-Sachs disease and Marfan syndrome, which are caused by mutations in a single gene.

According to The Times, more than 3,000 such diseases occur collectively in about 1 in 100 births. They can be inherited or occur spontaneously in the fetus.

As described in The Times story by Marcy Darnovsky of the Center for Genetics and Society, a public interest group, the ethical concerns are about “who deserves to be born.”

Parents might opt for abortion if the fetus has a genetic disease, but also if it lacked a favored trait. “Moreover,” the paper said, “a full fetal genome sequence would turn up numerous mutations for which information is lacking as to whether they cause disease, posing a dilemma for expectant parents and their doctors.”

False positives are also a concern.

To learn more about healthy pregnancy and potential problems, read our article on prenatal care.

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