A vast majority of multi-cellular beings share a common feature: they have cells that eventually fail due to injuries, infection, or simply its age. When these cells die they release small amounts of DNA. This is an important feature found in tissues, (and for example,) in your blood scientists can find from which parts of the body these cells were made. What one research team has been doing lately is working upon linking the dead cells' DNA to their origins and seeing if their numbers can reflect normal or worsening conditions in patients before it becomes much more serious.
There are three teams being studied in the article. One group has used patients who have suffered brain injuries, and another looked into those with type 1 diabetes who have DNA circulating from damaged organ tissues like the brain and pancreas. It was noted in the Sciencemag article that since 2011 doctors have been able to trace the DNA of down-syndrome fetuses in pregnant women. The second team's research improves upon that approach, they use methylation signatures which help to zoom in on which parts of the body these cells are dying in. The signatures are sort of like a chemical id or fingerprint that makes it easier to identify their origins. What these scientists hope to do is be able to identify the problem areas before they become the actual disease. These tests when applied to patients can then be able detect early signs of cancer, tissue damage, and other health problems. One area of caution that was noted in the article is that cell death due to specific tissue damaging pathogens can skew the results because while the damaged cells are accumulating in that one area of the body it may not be the origin of the problem. This can be said to show how in a cancer patient who is showing signs of lung cancer may actually have an active cancer tumor further up in their system like the throat or mouth that spread to another area.
The final team mentioned didn't use methylation as the method of identifying the source but relied on the extraction of floating nucleosomes in the dying cells of patients with more advanced cancers. They used these DNA snippets to detect the locations of the originally targeted tissue. While there are skeptics out there about the reliability of these two approaches, the ability to increase the chances of detecting early cancers or diabetes and other diseases can make it so that they can be treated early or prevented altogether, leaving that person to avoid those harmful effects and lead a fuller and healthier life.