While a direct-to-consumer genetic test can estimate your risk, it cannot tell you for certain whether you will or will not develop Alzheimer's disease. Variations in multiple genes, together with lifestyle factors such as diet and exercise, all play a role in determining a person’s risk.

The U.S. Food and Drug Administration (FDA) has allowed at least one direct-to-consumer genetic testing company, 23andMe, to offer a test for Alzheimer's disease risk. The test analyzes a gene called APOE. Certain variations in this gene are associated with the likelihood of developing late-onset Alzheimer's disease (the most common form of the condition, which begins after age 65). Specifically, the test allows you to find out how many copies (zero, one, or two) you have of a version of the gene called the e4 allele. People who have zero copies of the e4 allele have the same risk of late-onset Alzheimer's disease as the general population. The risk increases with the number of copies of the e4 allele, so people with one copy have an increased chance of developing the disease, and people with two copies have an even greater risk. However, many people who have one or two copies of the e4 allele never develop Alzheimer's disease, and many people with no copies of this allele ultimately get the disease.

Variations in the APOE gene are among many factors that influence a person’s overall risk of developing Alzheimer's disease. Variations in many other genes, which are not reported in the FDA-approved direct-to-consumer genetic test, also contribute to disease risk. Additionally, there are risk factors for Alzheimer's disease that have yet to be discovered. Therefore the APOE e4 allele represents only one piece of your overall Alzheimer's disease risk.

Currently, there are no effective approaches for preventing Alzheimer's disease, and while the disease can be treated, it has no cure. For these reasons, the National Institute on Aging and patient advocacy groups strongly recommend that people considering genetic testing for Alzheimer's disease, including direct-to-consumer genetic testing, talk with a doctor or genetic counselor about the reasons they want to undergo testing and how they would cope with the results.