Fetal genome mapped from mother's blood for first time

For the first time, a fetus has had its entire genome mapped from a sample of its mother's blood. This technical tour de force could open the door to new methods of prenatal genetic diagnosis.

In 1997, researchers led by Dennis Lo of the Chinese University of Hong Kong showed that "floating" fetal DNA can be detected in maternal blood plasma – it passes across the placenta from fetal cells that have broken down.

Lo's discovery sparked a lot of interest, because it raised the possibility of diagnosing genetic problems in a fetus without the need for invasive procedures such as chorionic villus sampling (CVS) or amniocentesis to extract fetal cells, both of which carry a small risk of inducing a miscarriage.

But it's hard to distinguish fetal sequences from the larger quantity of a woman's own DNA. This has so far largely limited practical applications of the technique to unambiguous situations in which particular fetal genes are not carried by the mother. For instance, fetal sex can be determined by detecting sequences from the male Y chromosome. It's also possible to identify fetuses at risk of rhesus disease, where the mother's immune system attacks a protein on her fetus's red blood cells, by looking for the gene for this rhesus protein in the blood of women who are rhesus negative.

Lo has previously worked on methods to detect fetuses with Down's syndrome from floating fetal DNA. Now, through a combination of brute-force DNA sequencing and sophisticated bioinformatics, his team has shown that it should be possible to detect any genetic disease from a sample of a pregnant woman's blood.


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