Forensic Study Shows Some People Are "Shedders" Who Leave Behind More DNA

"We have shown that it is possible to determine the shedder status of an individual."

In the 1997 film Gattaca, Vincent (Ethan Hawke) painstakingly brushes his hair, trims his nails, exfoliates his skin, and shaves his face — all to avoid shedding parts of his body carrying his DNA, which could betray his secret identity. When he’s done, he burns everything in an incinerator. This might seem like an excessive amount of precaution to take, even in a sci-fi universe, but as researchers show in a recent forensics study, some people called “shedders” leave much more of themselves behind than others.

And depending on the kind of person you are, it could get you into a lot of trouble.

We all drop skin flakes and body hair throughout the day, but it turns out some people drop more. In a paper published in the September issue of the journal Forensic Science International: Genetics, a team of researchers at Flinders University in Adelaide, Australia, outlined a new test for determining whether a person is a “shedder.” This profile, it seems, is as indelible as our eye color or fingerprints. Knowing whether a person is a light or heavy shedder can help forensic investigators perform a more well-informed search for DNA evidence at crime scenes, and with a test developed by the study’s authors, this determination can be made in just a few minutes.

Scientists use a swab to remove skin cells whose DNA is stained with a glowing dye.

Kanokwongnuwut et al

To perform the study, the researchers had 11 volunteers press their thumbs onto a glass slide immediately after washing their hands or 15, 60, or 180 minutes after. After performing several rounds of this experiment, the researchers applied a staining dye to highlight any DNA-containing skin cells the volunteers had left behind — revealing whether an individual was a light, medium, or heavy shedder. Generally, individuals left more of a DNA signature as more time passed after washing their hands, an effect that continued until about the one-hour mark, when it leveled out.

The most important observation the tests revealed is that a person’s status as a light, medium, or heavy shedder doesn’t change.

“We have shown that it is possible to determine the shedder status of an individual,” wrote the study’s authors, led by Piyamas Kanokwongnuwut, a forensic biology Ph.D. student at Flinders University. The main purpose of the study was to demonstrate that a person has a reproducible shedder status, one that neither hand-washing, skin scraping, nor any other care technique can erase. That’s not all they found, though.

“As a by-product, it is possible to rapidly determine the shedder status of a specific person of interest as this may be relevant in determining the likelihood of whether a major contributor in a mixed DNA profile was the last person to make contact with an item,” the authors write.

In other words, the team didn’t just show that individuals have a unique shedder profile; they also showed that having such a profile — and thereby knowing how much DNA they might shed after a given time — can help forensic investigators determine a timeline at a crime scene.

Fortunately for us, the world of Gattaca, in which our DNA profiles determine the jobs we can get, has not come yet. But this research suggests that a different kind of world has arrived, one in which the biological traces we leave behind can tell more about us than we ever imagined.

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