Last month we reported that the FDA had clamped down on 23andMe, a consumer genetic testing service whose results might be less than accurate. 23andMe isn’t the only such service hoping to make money off your DNA, and it’s human nature to want to know what you’re made of.
Kira Peikoff wanted to know, and her story in the New York Times, “I Had My DNA Picture Taken, With Varying Results,” perfectly illustrates the rocky informational terrain genetic testing can carve.
Peikoff, who is 28, has a family history of heart disease, rheumatoid arthritis, Alzheimer’s disease and breast cancer. In the interests of both her personal health profile and science, she tried three different testing services to see if they provided consistent results.
“The answers were eye-opening,” she writes, “and I received them just as one of the companies, 23andMe, received a stern warning from the Food and Drug Administration over concerns about the accuracy of its product. At a time when the future of such companies hangs in the balance, their ability to deliver standardized results remains dubious, with far-reaching implications for consumers.”
She paid $99 for 23andMe’s saliva test kit whose report included 240-plus health conditions and traits. Genetic Testing Laboratories (GTL) charged $285 for a report on 25 disease risks and required a professional to collect the blood sample, and Pathway Genomics (Pathway), $399, offered a report on 24 disease risks. Pathway requires a doctor to order a kit on a patient’s behalf.
About two months after sending in the samples, 23andMe said her most elevated risks were for psoriasis and rheumatoid arthritis, with her lifetime odds of getting the diseases at about 1 in 5 and 8 in 10, respectively. According to GTL, her lowest risks were for psoriasis (2 in 100) and rheumatoid arthritis (2.6 in 100).
For coronary heart disease, 23andMe and GTL agreed that her risk was about average, 26 to 29 in 100; Pathway reported her odds as “above average.”
The inconsistencies about Type 2 diabetes were more about language than numbers. GTL said her risk was “medium” at 10.3 in 100; 23andMe said it was “decreased” at 15.7 in 100. They both calculated her odds at about three-quarters of the average, but how they described it communicated different things: “In isolation,” she writes, “the first would have left me worried; the second, relieved.”
The whole concept of risk, though, is sketchy. Medical ethicists and other experts note that there’s a lack of industry standards for weighing risk factors and defining terminology. What qualifies as high, medium and low risk is hardly consistent within the medical community.
Peikoff offers some reasons for the discrepancies. The tests are based on reading segments of DNA called SNPs (“snips”), for single nucleotide polymorphisms. But such segments vary among people. So in seeking an “average” risk, you could be comparing apples to oranges.
Scientists have identified about 10 million SNPs within our 3 billion nucleotides. To sequence that entire genome would cost around $3,000; Peikoff’s tests analyzed fewer than 1 million SNPs.
The testing companies choose which SNPs to read. Peikoff’s tests for coronary heart disease used four to 15 markers, with almost no overlap, although two tests reached similar conclusions about her odds.
For rheumatoid arthritis, though, the tests examined the same five markers, plus a few others; still, they delivered contradictory interpretations.
The estimates of average risks also varied. 23andMe listed the typical odds of obesity at nearly 6 in 100, and GTL them at 3 in 10.
“But,” Peikoff reports, “the major issue, experts say, is that the causes of most common diseases remain unknown. Genes account for just 5 to 20 percent of the whole picture.”
So if you’re not examining environmental factors, such as exposure to certain chemicals, you’re getting only a part of the genetic pie, and not a very big one.
Only 23 diseases that start in adulthood that can be treated have highly predictive tests. All are rare, and hereditary breast cancer the most common. A small number of people who get tested will receive that helpful information, but most will get results that aren’t useful and might be misleading or confusing.
“To be sure,” Peikoff concludes, “my tests did provide some beneficial information. They all agreed that I lack markers associated with an increased risk of breast cancer and Alzheimer’s.
“That said, they were testing for only a small fraction of the genetic risks for these diseases, not for rare genetic variants that confer much of the risk. I could still develop those diseases, of course, but I don’t have reason to pursue aggressive screenings as I age.”
“Until and unless the predictive science improves,” she reports, “experts advise consumers to take most of their results with a grain of salt.”
If you take the tests, do so more for entertainment purposes than as a guidepost for your medical future.
For more information, see our newsletter, “Learning Your Own DNA Sequence: The Promise and Peril of Genetic Testing.”