By sampling the mother's blood and father's saliva, scientists can now accurately map a fetus' entire genome.

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enetic researchers at the University of Washington have managed to sequence nearly the entire genome of an 18-week-old fetus, a remarkable feat in itself. But the real stunner is that they did it using only a sample of the mother's blood and a swab of the father's saliva. "This is not science fiction anymore," geneticist Jay Shendure tells The New York Times. The research, published in the journal Science Translational Medicine, suggests a future in which parents can screen their in-utero offspring for more than 3,000 genetic mutations, plus other genetic traits such as athleticism. That, of course, raises some pretty big ethical questions, chief among them, says Marcy Darnovsky at the Center for Genetics and Society: "Who deserves to be born?" Here, a look at this groundbreaking research, and some of its more worrying implications:

How does this new test work?
Scientists discovered in the 1990s that about 13 percent of the DNA floating freely in a pregnant woman's blood, outside her cells, belonged to her fetus. The fetus gets half its DNA from mom and half from dad, so by using the father's saliva to sort out the fetus' DNA from the mother's in the blood sample, Shendure and his colleagues cobbled together the offspring's genome. Anything that didn't come from the mother and father was presumably a spontaneous genetic mutation. The scientists correctly identified 39 of the 44 mutations confirmed in testing after the child was born.

What kind of diseases can this test find?
There are already tests available to discover Down syndrome, paternity, and gender. But this new technology opens up prenatal diagnosis of more than 3,000 so-called Mendelian disorders, which stem from a single mutated gene. These maladies — Huntington's disease, cystic fibrosis, hemophilia, Tay-Sachs disease, sickle-cell anemia, and Marfan syndrome, for example — are rare, but collectively are found in about 1 percent of births.

How long before it hits the market?
"This paper is a tour de force," Johns Hopkins medical geneticist Ada Hamosh tells Discovery News, but "in no way is this ready for prime time." First there's the cost: Right now, sequencing the genome of one fetus costs $20,000 to $50,000. Then there's the technique's large number of false positives (3,800 in the test case). However, "the cost of DNA sequencing is falling at a blistering pace, and accuracy is improving as well," says Andrew Pollack in The New York Times. Shendure's teams predict a version of their test will be widely available in three to five years, though outside experts call that optimistic.

What about the ethical implications?
The researchers acknowledge that painlessly sequencing a fetus' genome "raises many ethical questions that must be considered carefully within the scientific community and on a societal level." All prenatal testing raises concerns among anti-abortion advocates, since parents are presumably more likely to opt for abortion if they discover big genetic disorders. And it's not outside the realm of possibility that if parents suddenly have access to the entire genome, says Pollack, they "may be tempted to terminate if the fetus lacked a favorable trait like athletic prowess." Indeed, "one always hopes, vainly, that in utero testing will be for the benefit of the unborn child," Josephine Quintavalle at Britain's ProLife Alliance tells The Telegraph. But "given our past track record, it is difficult to imagine that this new test will not lead to more abortions."

Sources: Discovery News, New York Times, Science, Telegraph