Should Mary Carmichael Get DTC Genetic Testing? My Full Post

Mary Carmichael at Newsweek is running an interesting week-long series of posts about deciding whether or not to buy DTC genetic testing for herself.  Carmichael series She asked me to contribute an “about 300 word” post on “How do I know if I can trust the results and should I be worried about what I might find out?” Monday, I sent her both a 389 word version and a 300 word version. Tuesday, she sent me back a 308 word version for posting, which I accepted. Today (Wednesday), the Newsweek site has posted a 230 word version.  Carmichael:  Day 3 It captures much of what I wanted to say, but not all. So here’s the original 389 word version.

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You can be confident you can’t trust the results.

SNP chips, though useful in research, aren’t good at providing health information. First, as the recent GAO report vividly showed, companies often interpret the same SNP results differently. The same DNA conferred an above-average risk of developing leukemia at one company, but a below-average risk for leukemia at another. You can’t trust any result unless there is a consensus on its interpretation.

You also can’t trust the reports as useful about your health. Personalized medicine isn’t just about genetics. If your test shows you have a genetically low risk of lung cancer but you smoke 4 packs a day, your actual risk is much higher than average.

Finally, even true SNP effects aren’t very big. 23andMe’s web page shows sample results. For breast cancer, its report shows that a woman with a 9.1% (genetic) chance of breast cancer, compared with an average for women of European ancestry of 12.5%. Will that 3.4 percentage point difference change your life – or be worth paying good money for? (Oh, and if you aren’t of European ancestry, good luck getting any meaning out of these tests – the research behind the results was almost always done with white people.)

You should not be very worried about what you find out – as long as you realize that it is almost always useless. But these companies do sell information on some powerful SNPs: APOE, linked to Alzheimer disease, and three mutations in BRCA 1 and BRCA 2 that powerfully raise a woman’s risk of ovarian and breast cancer.

You might worry about reactions to bad news about those genes. Two smart and knowledgeable people, James Watson and Steven Pinker, both excluded only APOE from their public whole genome sequences. Studies show negative psychological reactions are uncommon, but those studies included extensive genetic counseling – not required by these firms.

Without counseling, you could misinterpret results in dangerous ways. If you test negative for those BRCA 1 and 2 mutations, you might decide to avoid mammograms. That could be fatal. Not having those mutations lowers your genetic risk only from about 12.5% to about 12.4%.

Knowledge can be powerful, both when understood properly and – dangerously – when misunderstood. As a first step the FDA should require that every health-related genetic test be prescribed by, and be returned through, your doctor.