Stanford University scientists have figured out a way to sequence an unborn baby's genome solely from its mother's blood, making it easier for parents to screen their children for metabolic and immune system diseases, according to a paper published in the journal Nature on Wednesday.
The work is related to work from University of Washington researchers published in the journal Science Translational Medicine in June, in which a fetal genome sequence was determined from a maternal blood sample plus DNA samples from both parents.
Cutting dad out of the picture is actually an advantage, according to senior author Stephen Quake.
"A surprising fraction of the time, the guy who thinks he's the father isn't really the father," Quake said in a phone interview.
A pregnant woman's blood contains a surprisingly high amount of fetal DNA -- somewhere between 3 to 7 percent at the end of the first trimester and more than 30 percent at the end of the third trimester, according to Quake.
Previous attempts to draw out the baby's genetic code by separating out fetal DNA from the mother's have failed, but this latest research sidesteps the problem altogether.
"We don't try and separate the mother's DNA from the baby's DNA - we analyze everything that's there," Quake said.
Instead, the researchers use a "molecular counting" technique to pinpoint where the baby's genome sequence differs from its mother's, allowing the researchers to infer the father's genetic contribution.
In their Nature paper, Quake and his colleagues describe how they were able to use their method to determine that a fetus had DiGeorge syndrome, a genetic disorder linked to neuromuscular, cognitive and heart problems.
Doctors have done prenatal screening for decades, but previous methods involved inserting a needle into the mother's uterus to sample tissue directly from the fetus. Those methods could only detect a limited number of genetic conditions, and led to miscarriage in about one in 200 pregnancies.
The new fetal genome sequencing method paves the way for prenatal detection of a wide range of conditions - not just DiGeorge syndrome, but phenylketonuria (PKU), where babies can't digest the amino acid phenylalanine and severe combined immunodeficiency (sometimes referred to colloquially as "bubble boy disease").
"This way, you can treat the baby right when they're born. You can feed them right foods or put them in the right environment," Quake says.
SOURCE: Fan et al. "Non-invasive prenatal measurement of the fetal genome." Nature published online 4 July 2012.
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