Is Dementia Hereditary?

Posted: 6/22/2018 1:04 PM by Interim HealthCare

Contributed by Kathleen Doheny, a Los Angeles-based journalist who specializes in health, behavior and fitness reporting. 


The greatest risk factor isn’t genes. It’s age.

When a loved one is diagnosed with dementia, getting good care for them is your first concern. But at some point down the line, it’s only natural to wonder: Does this mean I’ll get it, too? 
 
The answer is not necessarily. In fact, most cases of Alzheimer’s disease, the most common cause of dementia, are not hereditary. And even if you inherited genes that increase your risk of the disease, that doesn’t mean you’ll develop it.
 
''Alzheimer's and dementia is complex," says James Hendrix, PhD, director of global science initiatives for the Alzheimer's Association. Genes play a role, he notes, but they’re not the whole story for most people. In fact, the greatest risk factor isn’t genes but age. The older a person gets, the greater their likelihood of developing Alzheimer’s disease. One in 10 people over 65 has it, as do a third of people 85 and older.

Genes that increase risk

Researchers have identified variants of several genes that increase the risk of Alzheimer’s. The one with the strongest impact is called APOE-e4. It increases the risk of late-onset Alzheimer's, which begins at age 65 or older.
 
If you inherit one copy of APOE-e4, your risk for developing Alzheimer’s disease is thought to be about two to three times the average risk. If you inherit two copies (one from each parent), your risk is thought to be about 12 times higher than average, though the Alzheimer’s Association notes that “it is hard to say exactly how much” the variant increases the risk for any individual.
 
Those numbers sound scary, but experts estimate that APOE-e4 may be a factor in only about 25 percent of Alzheimer's cases. So again, age, not genes, is the most important influence on risk.
 
A tiny percentage of people inherit one or more genes that cause Alzheimer’s disease directly (versus increasing the risk). These genes are amyloid precursor protein (APP), presenilin-1 (PS-1) and presenilin-2 (PS-2). They are rare, accounting for only about 1 percent of all Alzheimer’s cases. Typically, this form of Alzheimer’s disease begins early, in the 40s or 50s. People who are in families that carry these genes usually know it.
 
Vascular dementia (often caused by a stroke) is not considered hereditary, though in rare cases it can be caused by an inherited genetic disorder. Lewy body dementia is also not generally considered a genetic disease, although a small percentage of families have a gene variation linked with the condition. Currently, no genetic test can assess the risk of developing it.

To test or not to test?

You can buy tests that check for the APOE-e4 gene variation linked with late-onset Alzheimer’s disease. (There is no direct-to-consumer test for the genetic variations that increase the risk of early-onset Alzheimer's disease). But should you?
 
It’s a personal decision.
 
According to the Alzheimer's Association, which does not recommend testing for the general population, the results of testing ''have no practical impact on medical treatment decisions" since there are no treatments currently available to prevent, stop or slow down the condition.
 
Hendrix cautions that the test results won't affect just you; they could have an impact on your close relatives. "You don't do it in a vacuum," he says. (In case you were wondering, having one or more copies of APOE-e4 does not necessarily mean that your siblings do, too.)
 
Hendrix's mother had late-onset Alzheimer's, and he says he will not get tested. His reasoning: "If I get my APOE-e4 tested and I turn out to have the mutation, what should I do with that information?" Either way, he says, his lifestyle would be the same, focusing on habits that are good for the brain.
 
For some people, however, genetic testing could give them extra motivation they need to make changes that can shrink their risk of cognitive decline.
 
The Alzheimer’s Association suggests getting genetic counseling before deciding to take the test, and then, if you do get tested, talking to your counselor again to understand what the results mean. You can find a counselor through the National Society of Genetic Counselors.
 
A note about privacy and insurance concerns
 
It is illegal to discriminate against people based on genetic mutations that increase the risk of or cause inherited disorders, based on state and federal laws. On the federal level, the law is called the Genetic Information Nondiscrimination Act (GINA). It prevents health insurance providers from using or requiring genetic information to make decisions about whether a person is eligible for health insurance or what coverage they get. It also makes it illegal for employers to use such information when deciding about hiring.
 
However, GINA is not all-encompassing. It does not apply, for instance, if the employer has fewer than 15 employees. Nor does it apply to U.S. military personnel or those who get health benefits through the Veterans Administration (VA) or Indian Health Service.
 
Another crucial point, says Hendrix: The law does not protect against genetic discrimination when it comes to other forms of insurance, including long-term care, life insurance and disability insurance. Your premiums might be higher for those if the insurer finds out about your risk; if you hide the information, your policy could be at risk when it is needed, he says.

Genes aren’t destiny

It’s important to remember that even if your genes or family history put you at increased risk for Alzheimer’s disease, you won’t necessarily develop it. And if you aren’t at increased risk, you could develop it anyway.
 
You can’t change your age or avoid aging, but you can take steps that may benefit your brain. According to the Alzheimer’s Association, there is growing evidence that getting regular physical activity, following a heart-healthy diet, challenging your mind and staying socially connected may reduce the risk of the disease.