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Home Genetic Tests: Are They for You?

by John Swartzberg, M.D.  

In April 2017, to the surprise of many experts, the FDA reversed an earlier decision and allowed the company 23andMe to market at-home—also called direct-to-consumer, or DTC—genetic tests for 10 diseases. You can buy the tests online and simply mail in a saliva sample. Until recently the only way to get such tests was through a doctor or genetic counselor. This is a big step into a brave new world about which I have mixed feelings.

In 2013 the FDA stopped 23andMe (23 is the number of pairs of chromosomes in each cell) from selling such DTC tests, requiring more data about the accuracy of the tests and the ability of the company to explain the results adequately to customers. The company reportedly satisfied these demands and made changes to the way it markets its tests. In 2015 the agency allowed 23andMe to sell DTC “carrier tests” for more than 36 genetic disorders, such as cystic fibrosis, sickle cell anemia, and Tay-Sachs disease. Such testing tells you if you carry a single copy of the genetic variant (or mutation) for one of these diseases, which would not affect you (it takes two copies to cause the disease) but which you can pass on to your children.

The newly approved tests are different—they evaluate your risk. The company’s lab scans the DNA in your saliva for genetic variants linked to more-complicated disorders, including Parkinson’s and late-onset Alzheimer’s disease, which involve the interaction of genes with lifestyle, environmental, and other factors. Other companies will un­­doubtedly follow 23andMe with a flood of similar tests.

With such multifactorial conditions, having one or more abnormal genes doesn’t doom you to the disease—it merely increases your risk. This may be hard for some people to grasp, which is why the company’s website offers links to genetic counselors who can explain these matters. For instance, if you have one copy of the abnormal gene ApoE4, you face a two- to three-fold elevated risk of developing Alzheimer’s; two copies, a 12-fold increased risk. But even if you have two copies, there’s a good chance you won’t develop the disease. Other genes as well as additional factors, most of which we don’t understand yet, come into play.

Home testing may sound appealing, but there has been little or no evidence that the tests are accurate or reliable or of any practical value, except for carrier tests for would-be parents. In 2010, for in­­stance, in­­vestigators from the Government Accountability Office sent the same DNA sample to different home-testing companies and got inconsistent—sometimes contradictory—results. Presumably the tests are more accurate now. But still, I’ve seen no research showing that the results of such tests, even if they are accurate, can help prevent disease or lead to better treatment or longer lives—they might, or they might not. They certainly can lead to worry and psychological distress for people who have trouble putting their risk in perspective. What’s more, there may be privacy concerns. If companies don’t safeguard test results, customers with abnormal results could have their information seen, and used, by others, including insurance companies.

The science of genetic risk prediction holds great promise. If you understand the limitations and risks of at-home testing, it’s your choice. But for now, if you want your genes tested, I’d still advise having it done through a health care professional trained in genetics.

Also see Family History 101.