What you should know before you buy
If you’re like many Americans, your life or the life of someone you know has been touched by Alzheimer’s disease. And like many people, you may worry about whether you or a loved one is likely to develop this devastating condition. A new at-home genetic test can let you know if you’re at risk, but you need to be aware of its limitations before you buy it.
Two types of genetic tests
Last April, to the surprise of many experts, the U.S. Food and Drug Administration (FDA) reversed itself and allowed the company 23andMe to market at-home-also called direct-to-consumer, or DTC-genetic tests for 10 diseases, including late-onset Alzheimer’s disease. 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.
In 2013, the FDA stopped 23andMe (23 is the number of pairs of chromosomes in each human 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 disease, 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 these diseases) but which you can pass on to your children.
The newly approved tests are different, however-they evaluate your risk. The company’s lab scans the DNA in your saliva for genetic variants linked to more-complicated disorders, such as 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.
Interpreting the results
With late-onset Alzheimer’s and other multifactorial conditions, having one or more disease-associated gene variants doesn’t guarantee that you will develop the disease-it merely increases your risk. In the case of Alzheimer’s, the test looks for the presence of the APOE4 gene, which is the most common risk factor for the development of the disease.
If you have one copy of this abnormal gene, you face a two- to threefold elevated risk of developing late-onset 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 are not yet understood, come into play.
Further complicating the interpretation of results is the fact that many people who have the APOE4 gene will never develop Alzheimer’s. Conversely, many who do develop the disease don’t have the APOE4 variant. For example, if you are age 80 and have one copy of the APOE4 gene variant, your risk of having Alzheimer’s disease is about 35 percent. If you do not have the risk gene, your chances of having Alzheimer’s disease at age 80 are at 15 percent.
Little to gain, much to lose?
Currently, no treatment has been shown to help prevent Alzheimer’s or to lead to a longer life in people who develop the condition. Until better methods of treatment are available, the practical value of knowing your risk is limited.
Some people may feel that knowing they have the APOE4 gene will spur them on to initiate and stick with a risk-mitigation strategy; that is, exercise, eat right, and do brain games. But a 2016 study in the BMJ suggests that’s not likely.
The authors analyzed 18 studies on the impact of communicating DNA-based disease risk estimates on behaviors that would reduce the health risks. Their conclusion? Knowledge of genetic disease risk does little to motivate people to change their behavior. Another thing to keep in mind: Alzheimer’s experts say such lifestyle modifications are good advice for everyone-even if they don’t have the APOE4 gene.
On the downside, knowing your APOE4 status certainly can lead to worry and psychological distress if you have the gene and have trouble putting your risk in perspective. And negative results can provide false reassurance that you’ll never develop the condition.
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, who might deny future coverage if legislation to protect patients with preexisting conditions is eliminated.
A personal decision
The science of genetic risk prediction holds great promise. But for now, genetic testing for lateonset Alzheimer’s disease is not recommended. In fact, a panel of experts assembled by the National Institutes of Health in 2011-the National Institute on Aging and Alzheimer’s Association Working Group-recommended against testing for the APOE4 gene outside of a research setting. Their rationale for the recommendation, which still stands, is that no preventive treatment or cure is currently available, thus testing offers no benefit.
Nevertheless, if you still would like to know whether you have the APOE4 variant, understand the limitations and risks of at-home testing, and don’t mind paying for it (it is not covered by insurance), it’s your choice.
If you decide to go for it, the Alzheimer’s Association strongly recommends pre- and post-test genetic counseling. Before a test, a counselor can help you think through issues such as knowing how your status could affect your employment or ability to obtain health or long-term care insurance. Genetic counseling is recommended again when the results are available to explain the findings and help you put them in perspective.
Although you are not required to use a genetic counselor with home testing, 23andMe provides links to a directory of genetic counselors on its website. Be aware that your insurance is not likely to cover genetic counseling as it relates to late-onset Alzheimer’s disease testing for the same reason it doesn’t cover the actual test-it’s not currently recommended.