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Fetal genome blood test: Lots of issues, scientists say

July 06, 2012|By Rosie Mestel | Los Angeles Times
  • A pregnant woman's blood permits scientists to figure out the genome of a fetus. But how will the technology be used?
A pregnant woman's blood permits scientists to figure out the genome… (Hannah Johnston / Getty…)

Scientists can now sequence the entire genome of a fetus from samples of a pregnant woman’s blood, several recent studies have shown. It will come as no surprise that bioethicists are plenty interested in these developments and the benefits and thorny issues they will raise.

The technology -- and the issues -- are discussed at length in a commentary this week in the journal Nature Medicine by Diana Bianchi of the Mother Infant Research Institute at Tufts Medical Center.

Because a pregnant woman's blood carries pieces of fetal DNA, researchers can devise tests to tell with a high degree of certainty whether the fetus carries extra chromosomes (as an extra chromosome 21 in Down syndrome, for example). They can also test for versions of genes that cause or raise the risk for a disease, potentially screening for a whole slew of genetic disorders in one fell swoop.

And as geneticists learn more about the genetics behind traits such as eye color or hair color, these noninvasive fetal tests will be to pick up on those characteristics as well.

“Prenatal genetic diagnostic technology is advancing at an astonishingly rapid pace,” Bianchi writes. She cites 117 research reports in her paper -- and notes that 53 of them were published in the last two years alone.  

The developments hold a lot of promise for personalized fetal medicine, she says, but “time is of the essence”  for scientists, bioethicists, physicians, parents and government officials to do some serious thinking and decision-making about how the new advances should be applied and regulated.

Already, noninvasive tests for Down syndrome are on the market in the U.S and several thousand of such tests have been performed. The companies marketing them are tussling with each other over patent rights: One of them, San Diego's Sequenom, Inc., was just denied a request to a California court to block sales of another test, by rival Ariosa Diagnostics of San Jose. 

The new tests could soon replace the two-pronged approach currently used, in which a blood test is done first, measuring for abnormal levels of certain proteins. If the protein levels are abnormal, that’s followed by either amniocentesis or chorionic villus sampling, to obtain fetal cells and count the chromosomes.

One might think there could be no down side to move toward a single blood test, since amniocentesis and chorionic villus sampling are invasive and carry a small but finite risk of miscarriage. But even here, Bianchi writes, the experience of future parents and the decisions they ultimately make can be affected. The multi-step process allows future parents several time points at which they can reflect on what they would do if the test reveals their fetus has Down’s. That is not the case if you just have one test and then need to make a decision.

The issues become even messier when one moves beyond that simple example.  Figuring out the sex of a fetus is important if the mother is a carrier for a disease that will affect only males. But that has also made gender selection possible.

Whole-genome tests will reveal traits that only raise the risk of a condition, not carve it in stone –  which “raises parental anxiety, as well as the possibility of termination of a clinically unaffected fetus,” Bianchi writes.  

And some detected abnormalities may have no known consequence except to cause worry.  (And yes, Bianchi notes, there’s also the issue of detecting nonpaternity and incest.)

She says that clinicians who care for pregnant women are going to have to be trained in how to deal with the information that pours from such tests. And the information-overload is only going to intensify as researchers probe not just the structure of fetal genes but also what those genes are doing -- when they’re active, when they’re not active. This could one day help reveal developmental abnormalities, but right now, it's probably enough to make scientists and clinicians go Aaaagh! since they don’t know too much about normal patterns of gene activity in a fetus, let alone abnormal ones.

If you want to learn more about the science of noninvasive prenatal genetic tests, check out a symposium held in May at Stanford University. Scientists explain the technology. Healthcare workers discuss how one puts it into practice. Industry reps offer their POV. There's talk about the politics of it all -- how it plays into the abortion debate. And how people with Down syndrome feel about their lives. And more.

The symposium organizer, Stanford law professor Hank Greely, takes a look at where we could  be 20 to 40 years from now.  If we get to the point where it is easy to create eggs in lab dishes from prospective mothers’ body cells so they don't have to have them extracted from their bodies  -- and researchers are on the way to doing that -- Greely foresees a day when prospective parents could be given a selection of embryos to choose from. (He’s writing a book about it all.)

“Do we know enough to use this wisely? The answer to that is certainly no,” he says. “But then it shouldn’t be asked that way. Do we know enough to use this wisely compared to how we make babies right now?”

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