There's a Good Chance Your Relatives' DNA Is Online. That Means People Can Find You, Too.

There's a Good Chance Your Relatives' DNA Is Online. That Means People Can Find You, Too.

When the infamous "Golden State Killer", who was known for a series of rapes and murders in California in the 1970s and 1980s, was caught last April, he unleashed a collective sigh of relief. But the way the authorities tracked down the killer - with data from a genealogy website - left people with worrying feelings about the power of genetic testing.

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That's because the Golden State killer got caught by his DNA when police adapted the samples to his third cousin, who uploaded genetic data into a genealogy database. Since then, the debate on the ethics of using genealogical web pages to support forensic investigations has changed.

And now a new study shows how comprehensive these genealogy sites really are. The researchers found that around 60 percent of people in a database of more than 1.2 million people could be compared to at least one other person in the database who was a third cousin or an even closer relationship.

In fact, a genetic database only needs to cover 2 percent of a target population to find at least a third cousin match for just about every person, she wrote in the study, which was published yesterday (October 11) in the journal Science.

The group analyzed data from 1.28 million anonymous people on a genealogy website called My Heritage. (The main author of the study, Yaniv Erlich, is the lead scientific director of the website.) By comparing so-called identity segments (IBD) in human DNA, the server can also locate distant relatives, such as cousins, second or third degree. The greater the amount of IBD between two people, the closer their relationship is.

Researchers targeted common IBD segments that would correspond to second, third or fourth cousins. They found that 60 percent of their searches resulted in a match - most of them were a third cousin or closer. The researchers then did a similar but smaller search on GEDmatch (the database used to catch the Golden State killer) and found that 76 percent of their 30 random searches matched a third cousin or relative.

They also found that people of northern European descent were the easiest to associate. About 75 percent of the individuals in the database came from Northern Europe, and they were 30 percent more likely to be in agreement than those with a genetic background from sub-Saharan Africa.

The team found that the identity of the anonymous person could be easily determined by examining family lines and demographic information, such as the person's age or place of residence, once these relatives were found. They showed this by discovering the identity of an anonymous woman after they found their distant relatives.

In fact, between April and August of this year, at least 13 cold cases in the US (including the Golden State killer) were resolved by such searches, the study said. What makes them so powerful is that while forensic database searches - which are tightly regulated - can only be found close to first or second degree individuals, the search for genetic databases can find more distant ones.

"While policymakers and the general public favor such expanded forensic crime-solving skills, they rely on databases and services that are open to all," the authors write. "So the same technique could also be used for harmful purposes, such as re-identifying researchers from their genetic data."

The researchers suggest that guidelines for the protection of human genetic data should be introduced. They also recommend that gene databases begin to protect raw genetic data files with a secure digital signature to make accessing them more difficult.