Perhaps your grandmother had Alzheimer’s disease; maybe your mom or dad is currently living with the disease. You may be concerned that you are seeing signs of the disease in yourself or a loved one. Whatever the situation, if your family has been touched by Alzheimer’s, it is natural to be curious if a genetic test is valuable in predicting the likelihood of developing the disease. Although the cause of Alzheimer’s is still unknown, scientists have identified a number of genes that impact your risk of developing the disease.
On Thursday, April 6, the U.S. Food and Drug Administration (FDA) announced that they have approved at-home genetic testing through the 23andMe Personal Genome Service Genetic Health Risk (GHR) test, which tests for genes associated with risk of 10 diseases or conditions, including late-onset Alzheimer's. People will be able to send 23andMe a saliva sample and receive their genetic data back through the mail.
We spoke with Keith Fargo, Ph.D., Director of Scientific Programs and Outreach at the Alzheimer’s Association, about what you need to know about this type of testing – and what the results tell (and don’t tell) you.
Two categories of genes influence whether a person develops a disease: risk genes and deterministic genes. Alzheimer's genes have been found in both categories. Can you explain the difference between these types of genes?
Risk genes increase the likelihood of developing a disease, but do not guarantee it will happen. Deterministic genes directly cause a disease; they guarantee that anyone who inherits one will develop the disorder.
23andMe says their genetic test evaluates more than 500,000 genes and gene variants. Regarding Alzheimer’s, it evaluates whether you have the APOE-e4 Alzheimer’s risk gene. It was the first Alzheimer’s risk gene identified and remains the one with strongest impact. Having one copy of the APOE-e4 gene increases your risk – having two copies increases it more – but it is hard to say exactly how much for any individual.
There are two other variations of APOE, known as e2 and e3. The e3 variation is relatively neutral and the e2 variation may provide some protection against Alzheimer’s dementia. The newly approved test does not evaluate for these variants. Plus, there are nearly 30 other genes that have been identified to also affect risk of late-onset Alzheimer’s, but (a) those genes don’t impact risk as much as APOE-e4, and (b) this test does not evaluate for them.
There are three more genes that have misspelling in their DNA or mutations where, if you have one, it’s a virtual certainty that you will develop Alzheimer’s dementia. These are the deterministic genes. The 23andMe test does not look for these gene mutations, either.
Part of the challenge with understanding the value of the newly approved test is that many people who have APOE-e4 never experience Alzheimer’s dementia symptoms, and many who do develop the disease do not have any copies of APOE-e4.
For this reason, and because of the current lack of proven preventive strategies, the Alzheimer’s Association does not recommend genetic testing for Alzheimer’s disease for the general population. If you are concerned about Alzheimer’s disease or memory changes in yourself or a loved one, the Association encourages you to have a frank conversation about your risk with your healthcare provider.
If someone’s parent or sibling had or has Alzheimer’s, is he or she at a higher risk of developing the disease?
The fact is this: everyone is already at risk. Of people 85 and older, one third of them have Alzheimer’s dementia. And having a family history of Alzheimer’s is not necessary for someone to develop the disease.
That being said, people who have a parent, brother or sister with Alzheimer’s are more likely to develop the disease, and those who have more than one first-degree relative with the disease are at even higher risk. But, again, it is hard to say exactly how much an individual’s risk may be.
If someone is interested in having genetic testing done, what are the first steps he or she should take?
The Alzheimer’s Association suggests that you talk to a genetic counselor before deciding to take the test and, if you decide to get genetic testing for Alzheimer’s, again after you receive the results. The National Society of Genetic Counselors website provides a searchable directory to locate a counselor by location and specialty.
What are the benefits of speaking with a genetic counselor?
A genetic counselor can help you understand what the test does and does not do. He or she can help you work through making a decision that is best for you in terms of ordering the genetic testing kit. Once you get the results back, he or she can help you determine what the results really mean.
Some people think that this is a diagnostic test for Alzheimer’s, but it’s not. It is a test for the presence of one or two copies of the APOE-e4 Alzheimer’s risk gene. It’s not going to answer the question most people have, which is: “Will I get Alzheimer’s disease?” You can have two copies of APOE-e4 and never develop Alzheimer’s disease. Conversely, you can have no copies of the gene and still develop the disease.
Do you believe that taking a genetic test is a proactive step in controlling one’s health?
For some people, yes. It may give them the motivation they need to make lifestyle changes that can reduce their risk of cognitive decline as they age, and possibly even reduce their risk of dementia. In fact, there are behaviors that we should all be doing to keep our brain healthy as we age. As a starting point, the Alzheimer’s Association has research-based brain health tips that we call 10 Ways to Love Your Brain. You can find them at www.alz.org.
That said, at the Alzheimer’s Association, we are concerned that people who receive results that confirm they don’t carry APOE-e4 will assume that means they won’t develop Alzheimer’s. The truth is that these people are still at risk.
With an unsupervised at-home test, there is a real possibility of people misunderstanding their results, which could result in making misinformed decisions about their health. A genetic counselor can be helpful in making informed decisions. If you choose to take a genetic test, discuss it with a genetic counselor before and after so that you are educated about the process, the test and what the results mean. And if you are already experiencing symptoms of cognitive decline, see a healthcare professional for a full evaluation.