Photo credit: Systems Bio
By Carl Zimmer
Loose pieces of DNA course through our veins. As cells in our body die, they cast off fragments of genes, some of which end up in the bloodstream, saliva and urine.
Cell-free DNA is like a message in a bottle, delivering secrets about what’s happening inside our bodies. Pregnant women, for example, carry cell-free DNA from their fetuses. A test that analyzes fetal DNA has proved to be more accurate in screening for Down syndrome than standard blood tests.
In 2012, Jay Shendure, a geneticist at the University of Washington, and his colleagues were able to reconstruct the entire genome of a fetus from cell-free DNA in a pregnant woman’s saliva. A team of Stanford University researchers collected DNA fragments from the blood of patients who had received heart transplants and managed to find DNA from their donated hearts. (Tellingly, levels were highest in patients who were rejecting their hearts.)
These days, scientists are especially excited by the prospect of using cell-free DNA to test for cancer. Instead of relying on invasive biopsies, they hope to find blood-borne fragments that carry distinctive cancer mutations.
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