Alzheimer's disease is a complex and devastating condition. Genetic factors are only one piece of puzzle, as today's post will explain.
This guest blog post is written by Jamie Fong. Jamie is a board certified and licensed genetic counselor. She provides genetic counseling to people and families with or at risk for inherited neurodegenerative disease, including Alzheimer’s disease, frontotemporal dementia, prion disease, Huntington’s disease, amytrophic lateral sclerosis, and ataxia.
I'm grateful for Jamie taking the time to highlight the key points for my readers. The points she makes in #11 and #12 are especially helpful: you can participate and contribute to active research on Alzheimer's disease, and you can find a genetic counselor near you specializing in risk assessment for the condition.
In April, the direct to consumer test company 23andMe announced it received FDA approval to offer testing for 10 genetic risk factors. Each of the 10 genetic risk factors is associated with a particular health condition. Alzheimer’s disease is one of these conditions.
That a genetic risk factor associated with Alzheimer’s disease is among the tests included in 23andMe’s Genetic Health Risk Report is no surprise, as Alzheimer’s disease has considerable impact on our society. This is reflected by the large (and growing) number of people with the condition as well as by the skyrocketing number of caregiving hours devoted to and healthcare dollars spent on patients. Alzheimer’s disease appears to rank among the most popular conditions for which people seek direct to consumer genetic testing.
From 2011 to 2013, 23andMe previously offered genetic testing for Alzheimer’s disease. At the request of the FDA in 2013, the company stopped offering it, and the recent announcement heralds the test’s relaunch. You may have questions about 23andMe’s Alzheimer’s disease test or about what test results mean. The following are some points to consider.
1. Everyone has a chance to develop Alzheimer’s disease, a progressive brain disorder that affects memory and thinking. Age is the biggest risk factor for developing the condition. A person’s chance to develop Alzheimer’s disease increases with age.
2. 23andMe’s genetic test for Alzheimer’s disease determines the chance (or risk) of getting Alzheimer’s disease. The test cannot tell a person whether or not he will definitely develop the condition.
3. 23andMe’s genetic test for Alzheimer’s disease looks at a gene called APOE. ApoE occurs in 3 different versions. Another way to think about this is that ApoE comes in 3 different flavors. Each person carries 2 flavors, which can be the same 2 flavors or different 2 flavors. Only one flavor of ApoE is associated with increased chance to develop Alzheimer’s disease. This is known as the Alzheimer’s risk variant (or flavor), called “E4.” The other variants (or flavors) are not associated with increased chance to develop Alzheimer’s disease.
4. The effects of having an “E4” variant of ApoE depend on a person’s ethnic background. Among people of European ancestry, having one or 2 “E4” variants of ApoE is associated with increased chance to develop Alzheimer’s disease in his lifetime. However, it is not a certainty that a person with an “E4” variant will get sick.
5. The "E4" variant is common. About 20% of people with European ancestry have one “E4” variant of ApoE. About 3% of people with European ancestry have 2 “E4” variants.
6. People with African American ancestry are more likely than people with European ancestry to have an “E4” variant of ApoE. By comparison, people with Mexican American ancestry are less likely to have an “E4” variant. However, African Americans and Mexican Americans have a greater chance to develop Alzheimer’s disease than people of European ancestry, regardless of which ApoE version they have. Other genetic and socioeconomic factors likely play a role in these differences. This highlights our incomplete understanding of the genetics of Alzheimer’s disease among people with non-European ancestry.
7. A person who has no “E4” variants of ApoE may still be at risk to develop Alzheimer’s disease. In the absence of an “E4” variant, family history of Alzheimer’s disease may be the most helpful tool in determining a person’s chance to develop the condition.
8. The “E4” variant of ApoE is not the only genetic variant that contributes to Alzheimer’s disease risk. There are numerous other genetic variants involved in increasing a person’s chance to develop the condition. Some of these variants are known by researchers and clinicians, but many have not yet been discovered. 23andMe’s genetic test looks at none of the other Alzheimer’s disease risk variants.
9. Whether you have 0, 1, or 2 “E4” variants of ApoE, your doctor’s advice to you is constant. This means that your doctor’s recommendations do not depend on your 23andMe’s genetic test result. A heart healthy diet and regular cardiovascular exercise may reduce a person’s risk to develop Alzheimer’s disease. Be wary of claims of the benefits of dietary supplements and/or brain games. Nothing has been proven to prevent Alzheimer’s disease altogether.
10. 23andMe’s APOE test should not be used to confirm or rule out a diagnosis of Alzheimer’s disease. The condition is diagnosed by a multitude of other non-genetic tests. If you are concerned about symptoms, please consult your doctor.
11. There is hope for Alzheimer’s disease therapies in the near future. Consider participation in research. Check out www.endalznow.org.
12. If you have questions or want a tailored risk assessment, contact a genetic counselor or other genetics professional. Check out the “Find a Genetic Counselor” feature on www.nsgc.org.
Written by Jamie Fong, a board certified and licensed genetic counselor. She works with a multidisciplinary team of neurologists and neuropsychologists at the UCSF Memory and Aging Center, where she is involved in both the Center’s clinic and research programs. Jamie holds a Bachelor’s degree in Molecular and Cell Biology from UC Berkeley, and a Master’s degree in Genetic Counseling from Sarah Lawrence College.