Consumer genetic tests may have a lot of false positives

Consumer genetic tests may bring up a lot of false positives, according to a new study that compared results from direct-to-consumer tests to results from clinical laboratories.

In this case, 40 percent of the results from the consumer tests were false positives. But it’s important to note that the findings, published online this week in the journal Genetics in Medicine, cover a very small sample size and don’t show that consumer tests always have a 40 percent false positive rate. The research was done by scientists at Ambry Genetics, a medical laboratory in California. By looking through their own database, they found that 49 people had been referred to them because of some worrying results from their consumer genetic tests. (The study didn’t name the companies, but popular consumer genetics companies include 23andMe and Ancestry.com.) That’s hardly a random sampling.

Still, scientists at Ambry were able to confirm only 60 percent of the results when they compared the raw data from consumer tests with more thorough genetic tests done by themselves and other clinical laboratories. So, 40 percent of variants in a variety of genes reported in DTC raw data were false positives, meaning that they said a genetic variant was there when it wasn’t. (Most of these turned out to be variants linked to cancer.) Additionally, the authors write, some variants classified as “increased risk” were not only classified as “benign” by clinical laboratories, but they were actually common variants.

Most consumer companies don’t immediately give you raw data from the test. (Plus, they’re usually not cleared by the US Food and Drug Administration to provide health diagnoses.) But you can often take the time to download the raw data and send it to third-party sites to interpret it. One recent study of these companies found that sometimes, they just match the raw data to risk results from publicly available databases — even though the databases themselves can be wrong. So there are plenty of places where you can get faulty information.

As consumer genetics grow more popular, so does the potential that people will misinterpret the results. Earlier this month, the FDA cleared 23andMe to sell genetic tests for cancer risk directly to consumers. Their kit tests test for three mutations known to predispose people to developing cancer, but there are hundreds more that it won’t take into account, and experts say that the test could create a “false illusion of safety.” This newest study is another warning to be wary of the results that you get from these tests. They might not be trustworthy, for better or for worse.

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