Researchers at the University of Washington have assembled the first
comprehensive genetic map of an unborn child — a development that could
help usher in a new era of prenatal testing.
By analyzing fetal DNA circulating in the mother's blood, the
scientists were able to sequence the baby's genome 18 weeks into the
pregnancy. The technique also worked at eight weeks, with slightly lower
Because the approach requires only a blood sample from the mother and
saliva from the father, it poses none of the miscarriage risk
associated with invasive tests such as amniocentesis. And while most
existing prenatal tests are designed to check for single disorders,
including Down syndrome, a full-gene scan has the power to reveal a wide
range of potential problems before birth, said lead author Jacob
Kitzman, a doctoral student in genetics.
"It's much more comprehensive."
The procedure is still several years away from commercialization, project leader Jay Shendure said.
But the UW study, published in the June 6 issue of Science
Translational Medicine, marks a significant step forward in technology
that's been developing over the past several years — and which worries
some people, said Marcy Darnovsky of the Center for Genetics and Society
in Berkeley, Calif.
"I think it's a game-changer," she said. Cheap, safe genome
sequencing could give parents the power to practice a kind of eugenics,
preselecting children based on desirable traits.
"It could become a routine part of prenatal testing...which raises
questions about what people will do with the information," Darnovsky
Shendure cautioned against expecting too much — at least in the near
future. Scientists may be able to sequence the 3 billion DNA units that
make up each person's genetic heritage, but they still don't understand
the genetic basis of most common diseases.
"The capacity of genomics to generate data is outstripping our ability to interpret it in useful ways," he said.
Some genes can raise the odds that a person will develop conditions
such as diabetes or certain types of cancer. But most diseases arise
from a complex tangle of multiple genes and environmental factors.
What should prospective parents do, Darnovsky asked, if they're
presented with a report that predicts their unborn child has a 30
percent higher chance of developing breast cancer at age 50?
"The meaning of this data is going to be unclear for a very long time," she said.
That's why the UW scientists predict genome sequencing in the womb
will initially be most valuable for diagnosing the more than 3,000
diseases, including cystic fibrosis and sickle cell anemia, known to be
caused by a glitch in a single gene. Though individually rare, these
single-gene diseases strike about 1 percent of newborns and can account
for up to 40 percent of the pediatric care in some hospitals.
If a test for those diseases is available when he becomes a father, Kitzman would probably opt for it.
"On balance, I would prefer to know if my child was at risk for a
serious disorder so that I could begin to explore the options for
therapy and care," he said in an email.
UW obstetrics & gynecology professor Dr. Edith Cheng, who was not
involved in the study, said that more than a third of prospective
parents don't take advantage of existing genetic tests and that few of
her patients have been clamoring for more.
Prenatal sequencing will definitely be useful for families,
particularly as the cost drops, Cheng said. But she predicted it also
will be a powerful tool to study the way humans develop in the womb by
tracking genes that switch on and off throughout gestation.
The scientists found no troubling genetic signatures in the baby
whose genome was sequenced, nor could they have alerted his parents if
they had. The couple were anonymous.
The UW study built on the work of researchers in Hong Kong, who
discovered that DNA from the fetus appears in the mother's blood in
varying concentrations throughout pregnancy. A prenatal blood test for
Down syndrome that recently went on the market also targets that fetal
DNA, and a few companies claim they can use it to predict a baby's sex.
But to sequences the fetus' entire genome, the researchers had to
launch a needle-in-a-haystack search to differentiate the tiny fraction
of fetal DNA in the mother's blood from her own. They did it by mapping
both the mother's and father's genes, and using statistical analysis to
identify sequences that differed — and therefore must have come from the
To test their results, the researchers sequenced DNA in cord blood
collected after the healthy boy's birth. The sequence from the prenatal
test was more than 98 percent accurate. Sequencing of another fetus
eight weeks into the pregnancy, when the level of DNA in the mother's
blood is lower, was about 95 percent accurate.
The researchers filed for patents on their method, which could mean royalties for the UW if it proves marketable.
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