Can a direct-to-consumer genetic test tell me whether I will develop Alzheimer disease?
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 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 disease risk. The test analyzes a gene called APOE. Certain variations in this gene are associated with the likelihood of developing late-onset Alzheimer 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 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 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 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 disease that have yet to be discovered. Therefore the APOE e4 allele represents only one piece of your overall Alzheimer disease risk.
Currently, there are no effective approaches for preventing Alzheimer disease, and while the disease can be treated, it has no cure. For these reasons, the National Institute on Aging recommends against genetic testing for Alzheimer disease except in a research setting (such as a clinical trial). Patient advocacy groups strongly recommend that people considering genetic testing for Alzheimer disease, including direct-to-consumer genetic testing, talk with a genetic counselor about the reasons they want to undergo testing and how they would cope with the results.
What does it mean to have Neanderthal or Denisovan DNA?
Several direct-to-consumer genetic testing companies report how much DNA a person has inherited from prehistoric humans, such as Neanderthals and Denisovans. This information is generally reported as a percentage that suggests how much DNA an individual has inherited from these ancestors. The percentage of Neanderthal DNA in modern humans is zero or close to zero in people from African populations, and is about 1 to 2 percent in people of European or Asian background.
The percentage of Denisovan DNA is highest in the Melanesian population (4 to 6 percent), lower in other Southeast Asian and Pacific Islander populations, and very low or undetectable elsewhere in the world.
Neanderthals were very early (archaic) humans who lived in Europe and Western Asia from about 400,000 years ago until they became extinct about 40,000 years ago. Denisovans are another population of early humans who lived in Asia and were distantly related to Neanderthals. (Much less is known about the Denisovans because scientists have uncovered fewer fossils of these ancient people.) The precise way that modern humans, Neanderthals, and Denisovans are related is still under study.
However, research has shown that modern humans overlapped with Neanderthal and Denisovan populations for a period, and that they had children together (interbred). As a result, many people living today have a small amount of genetic material from these distant ancestors.
Scientists have sequenced Neanderthal and Denisovan genomes from fossils discovered in Europe and Asia. This genetic information is helping researchers learn more about these early humans. Determining which areas of the genome are shared with archaic humans, and which areas are different, will also help researchers find out what differentiates modern humans from our closest extinct relatives.
In addition to the percentage of Neanderthal or Denisovan DNA, direct to-consumer testing reports may include information about a few genetic variants inherited from these ancestors that influence specific traits. Studies have suggested that certain genetic variations inherited from archaic humans may play roles in hair texture, height, sensitivity of the sense of smell, immune responses, adaptations to high altitude, and other characteristics in modern humans.
These variations may also influence the risk of developing certain diseases. However, the significance of Neanderthal or Denisovan genetic variants on disease risk is still an area of active study, and most direct-to-consumer test results currently do not include them.
While knowing how much DNA a person has in common with his or her Neanderthal or Denisovan ancestors may be interesting, these data do not provide practical information about a person’s current health or chances of developing particular diseases. Having more or less DNA in common with archaic humans says nothing about how “evolved” a person is, nor does it give any indication of strength or intelligence. For now, knowing which specific genetic variants a person inherited from Neanderthal or Denisovan ancestors provides only limited information about a few physical traits.
How do direct-to-consumer genetic testing companies protect their customers’ privacy?
A person’s genetic data represent personal, private health information. If you are considering direct-to-consumer genetic testing, it is important to know how the testing company will protect your information. In particular, you should know how the company will handle your sample (for example, saliva), how it plans to safeguard your data, and whether and how your data will be used for secondary purposes (such as research or advertising).
Questions that can help you assess a company’s privacy practices include:
- What does the company do with your sample once it has completed the analysis? Will the sample be stored, shared, sold, or destroyed?
- Once you take the test, who owns your genetic data?
- How does the company safeguard your genetic data and other personal information that you provide? Is it stored in a database that is protected from unauthorized access? What happens if the database is hacked or otherwise compromised?
- Can you delete your results from the company’s database if you wish?
- Does the company use your information for internal research, advertising, or other secondary purposes?
- Will the company share your genetic data or sell it to pharmaceutical or biotechnology companies, academic institutions, or nonprofit organizations? If so, will the shared data include other information that could identify you (such as your name or date of birth)? For what purposes will your data be used? Will you be informed when your data are shared or sold?
- If you do not want your genetic data shared, sold, or used for research, can you opt out? What happens if you agree to share your information but want to opt out later?
- Will you be notified in the future if the company changes its privacy policies?
- What would happen to your sample and your genetic information if the company is sold or goes out of business?
In some cases, even if a testing service promises not to share your genetic information with others, they may be required by law to disclose the information to authorities in response to a warrant, court order, or other legal requirement. Many companies now provide explicit information about whether and how your genetic data may be accessed by law enforcement officials.
If you upload your data to public databases, such as those administered by some third-party interpretation services, that information will be available to law enforcement. Be sure to read and understand how your data may be accessed by authorities before you submit your sample. Because everyone shares genetic similarities with their relatives, it may have implications not only for your own privacy but for that of people who are related to you.