What You Need to Know about DNA Test Kits
If you're curious about whether your genes put you at elevated risk for cancer, hypertension, Alzheimer's disease, heart disease, diabetes, or a wide range of rarer "inheritable diseases," you may be tempted by ads for the many at-home (also called direct-to-consumer) DNA tests. Some genetic tests claim to provide personal nutrition advice based on your genetic profile.
Costing several hundred to a thousand dollars or so, DNA tests are now sold on the Internet, and there are plans to sell them in drugstores. Usually all you have to do is rub a swab inside your cheek and mail it to the company, which will scan your DNA, looking for mutations and variations that suggest increased risk, and then send you your DNA test results.
Sounds clear-cut, but DNA testing—especially when done at home—raises many practical and ethical questions and problems.
Too much genetic information? Or too little?
Home DNA tests fall into a regulatory gray area. They have not been reviewed by the FDA or any other agency, unlike most physician-ordered genetic tests or other kinds of at-home medical tests. There's little or no evidence that the great majority of the DNA tests are accurate, reliable, or "clinically meaningful" (in other words, useful or practical).
According to the FDA, genetic tests are medical devices—that is, they are intended to diagnose, prevent or treat diseases—and thus companies should submit data and get FDA clearance in order to continue marketing them. The companies, meanwhile, say that they're just supplying information rather than diagnosing or treating diseases, and that people have a right to know what's going on in their DNA. As of April 2011, the FDA has not barred the sale of the tests.
One problem is the overblown claims about home DNA testing made in much of the marketing material. In most cases, there's no research showing that the results of the home genetic tests can help people prevent disease or lead to better treatment or longer lives. Let's say a healthy young man takes a genetic test at home and finds out he's at high risk for eventually developing prostate cancer. What should he do? Get frequent PSA tests, a biopsy, ultrasound? It's not certain that any step would add even a day to his life.
And that's assuming the DNA test results are accurate to begin with—which is questionable. Last year the Government Accountability Office (GAO) published results from its investigation of home genetic tests, showing that companies produced inconsistent or even contradictory results from the same DNA sample. The GAO also cited many examples of deceptive marketing, bogus claims and erroneous advice, including companies using the results to sell "customized" supplements that supposedly help cure disease or repair DNA damage.
Unknowns about DNA testing
Before doing any genetic testing, discuss the risks and benefits thoroughly with your doctor or a genetic counselor. You may well decide not to be tested. Who will know the results of the test? What will your options be? Will your health insurance be affected? How accurate is the test?
Moreover, the results of DNA testing are often ambiguous. Relatively few diseases are controlled by a single abnormal dominant gene (such as Huntington's disease) or a pair of abnormal recessive genes (such as Tay-Sachs disease or sickle cell anemia). Most are multi-factorial—influenced by several genes, the passage of time and the social and physical environment. That is, a gene or genes that may put you at risk for, say, type 2 diabetes might not come into play if you maintain a healthy weight, eat sensibly and exercise as you age.
With those more complex diseases, testing may saddle you with unanswerable questions. If an abnormal gene or mutation turns up, you may feel doomed and see yourself as a sick person—even though it doesn't guarantee you’ll get the disease, or tell you when you'll get it (at age 50? or 90?). On the other hand, a good test result is no guarantee you won't get the disease, especially since most tests look only at a small portion of the more than 20,000 genes in the body.
Bottom line: The science of genetic risk prediction holds great promise, but is still in its infancy. For now, be wary about DNA testing, especially do-it-at-home genetic tests—unless you have a special family history, have consulted with a qualified professional, and have thought long and hard about the pros and cons.
Source: Adapted from The University of California, Berkeley Wellness Letter (February 2011)