It is important to note that if you take a genetic test and the results indicate you have APOE4, the genetic variant associated with late-onset Alzheimer’s disease, you are not destined to develop Alzheimer’s. “It’s not a diagnosis,” said Ramos, “And it’s just one factor. Your chance of getting late-onset Alzheimer’s is a mix of your environment, family history and DNA. That can be a complicated message to tease out.”
Even if you have one copy of the APOE4 variant, you are still unlikely to develop Alzheimer’s. For example, a woman with a single copy of APOE4 has a five to seven percent chance of getting Alzheimer’s by the age of 75. The rate increases to between 27 and 30 percent by age 85. (However, for women with two copies of the variant the risk increases to 60 percent by age 85.)
In addition, there are a number of potential genetic variants besides APOE4 associated with late-onset Alzheimer’s that are not captured by the 23andMe test. Nor does the test screen for the rare early onset version of Alzheimer’s. Finally, some people develop Alzheimer’s without possessing any copies of APOE4 genes whatsoever.
Still, genetic counselors warn you should think long and hard about how you would react to knowing you have a predisposition for Alzheimer’s or other diseases. “What I’m hoping is that the people who can handle this information are the people who seek it out,” said Leila Jamal, a genetic counselor and bioethicist at the Berman Institute at Johns Hopkins University. “The people who can’t aren’t going to be running to pay $200 to have this done.”