Prenatal DNA Sequencing

Earlier this year Illumina, the maker of the worlds most widely used DNA sequencing machines, agreed to pay nearly half a billion dollars for Verinata, a startup in Redwood City, California, that has hardly any revenues. What Verinata does have is technology that can do something as ethically fraught as it is inevitable: sequence the DNA of a human fetus before birth.

Verinata is one of four U.S. companies already involved in a rapidly expanding market for prenatal DNA testing using Illuminas sequencers. Their existing tests, all launched in the last 18 months, can detect Down syndrome from traces of fetal DNA found in a syringeful of the mothers blood. Until now, detecting Down syndrome has meant grabbing fetal cells from the placenta or the amniotic fluid, procedures that carry a small risk of miscarriage.

The noninvasive screen is so much safer and easier that its become one of the most quickly adopted tests ever and an important new medical application for Illuminas DNA sequencing instruments, which have so far been used mainly in research labs. In January, Illuminas CEO, Jay Flatley, told investors that he expects the tests will eventually be offered to as many as two million women a year in the United States, representing half of all pregnanciesup from around 250,000 mothers, mostly older, who now undergo the invasive tests. Its unprecedented in medical testing how fast this has gone from lab research to acceptance, says Diana Bianchi, executive director of the Mother Infant Research Institute at Tufts University and the chief clinical advisor to Verinata. Its a huge impact for any technology in its first year.

But this is likely to be just the start for prenatal DNA sequencing. The same labs and companies that launched the Down syndrome tests, like Verinata, have also figured out how they can get much more information from a mothers bloodstream, including the complete genome sequence of her fetus. Thats a technical breakthrough, and maybe a commercial one, too. Pregnancy, with its hopes, anxieties, and frequent doctors visits, could be where genome sequencing finally finds a major consumer application.

I think that we are going to sequence the genome of everyoneof every fetus in the first trimester, at least in part, says Arthur Beaudet, a pediatrician and head of human genetics at the Baylor College of Medicine, in Houston. Today some patients have their genomes sequenced to shed light on genetic diseases or illnesses like cancer, but one day people wont wait until theyre sick. We are already going to know the data at birth, he says.

That wont happen right away. For one thing, sorting out a fetuss exact DNA code via its mothers blood requires a huge amount of repeated sequencing, making it too expensive for routine use. (Illumina currently charges $9,500 to sequence the genome of an adult, and so far attempts to sequence fetal DNA have cost much more.) And there are still technical problems: the fetal genome results are still not accurate enough for making diagnoses. Ethically, too, the technology is a minefield. If we learn the genetic destiny of our children while they are still in the womb, what kinds of choices might we make?

Technically, all this is possible before weve figured out whether we should be doing it, says Jay Shendure, a genome scientist at the University of Washington. Youve got the whole genomethen what do you do with that? There are a lot of things that will have to get ironed out. Shendure works with Ariosa, one of Verinatas competitors. Last summer, his was one of two U.S. labs to demonstrate how the fetal genome might be revealed from a pregnant womans blood. He says the studies conducted so far on fetuses, including his own study, have been retrospectivethey studied blood samples stored by hospitals. But Shendure says he is now working with doctors at Stanford to implement the technology during an actual pregnancy. In other words, as early as this year the first human whose complete genetic code is known in advance could be born.

Full Genome

In 1997, a Hong Kong scientist named Dennis Lo showed that a pregnant womans blood contains trillions of bits of DNA from her baby. The DNA comes from cells in the placenta that have died and ruptured. By Los estimate, as much as 15 percent of the free-floating DNA in a mothers bloodstream is the fetuss. High-speed DNA sequencing can turn those fragments into a wealth of information.

Sequencing the DNA in the blood of a pregnant woman could reveal the full genetic code of a fetus.

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Prenatal DNA Sequencing