Chris Hemsworth, Alzheimer’s and what to know about genetic testing
Actor Chris Hemsworth, Marvel’s Thor, generated a lot of interest in Alzheimer’s disease earlier this month when he revealed genetic testing showed he had two copies of the APOE-e4 gene, one of the known risk factors for developing the disease.
Hemsworth subsequently announced he would be stepping away from acting to spend more time with his family and reassess his priorities.
As of 2020, approximately 6 million Americans 65 years and older are living with Alzheimers; that number is expected to grow to 14 million by 2060.
Alzheimer’s remains elusive
At the cellular level, Alzheimer’s destroys neurons and connections between neurons in parts of the brain responsible for memory, language, reasoning and social behavior. In the later stages the disease, a person with Alzheimer’s loses their ability to live independently, and the disease is ultimately fatal.
The actual mechanism for how Alzheimer’s causes neural damage remains elusive. In the brains of those with Alzheimer’s, high levels of the toxic beat-amyloid protein 42 have been found clumped together in plaques that disrupt neuron communication. Research also found neurofibrillary tangles of the tau protein within neurons that also hamper synaptic communication between neurons. Chronic inflammation and vascular disease – problems that affect blood flow – also likely play a major role.
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Understanding Alzheimer’s risk factors
Alzheimer’s can affect anyone but it’s important to be aware of the major risk factors – and their caveats. Risk factors include:
Old age, meaning over 65: This is the most well known risk factor. But it’s important to remember that age does not cause Alzheimer’s. At a population level, the number of people diagnosed with Alzheimer’s doubles every five years after age 65. In fact, 1 in 3 people over 85 likely have some form of Alzheimer’s.
Genetics: Scientists believe genetics likely play a role in increased risk of Alzheimer’s. But how much of a role is uncertain. It’s important to remember your genes are not your destiny.
When thinking about genes, remember that there are two categories of genes that influence whether a person develops a disease: risk genes and deterministic genes.
- Risk genes: Hemsworth was found to have two copies of the APOE-e4 gene; one from each parent. Only 2% of the U.S. population has both copies. Having one or two copies of this gene increases the risk of developing Alzheimer’s but does not guarantee it will happen. Nonetheless, 40-65% of people diagnosed with Alzheimer’s were found to have the APOE-e4 gene.
- Deterministic genes: These genes directly cause a disease but fortunately are rare – and only contribute to 1% or less of Alzheimer’s cases. They’ve only been found in a few hundred extended families worldwide and cause early onset disease in those affected when they are in their 40s or mid-50s.
Family history: Those with a parent or sibling with Alzheimer’s are more likely to develop the disease than those who do not have a first-degree relative with Alzheimer’s.
This is an important reminder also of what does not cause Alzheimer’s: aluminum. In a previous article, I debunked the widely held concern that aluminum in every day products including antiperspirants could cause Alzheimer’s.
Read more here:Myths about aluminum and deodorant, explained
Who should be screened for Alzheimer’s?
Hemsworth’s reveal certainly has a lot of people asking themselves if they should do similar genetic testing.
There are existing genetic tests for both the APOE-e4 and the deterministic genes. But with all genetic testing, its important that it’s done after in-depth counseling with a physician or genetics counselor. Genetic testing results that reveal the presence of risk factors for Alzheimer’s or any life-changing disease can have a lot of consequences and must be taken in context.
Remember, when it comes to the APOE-e4 gene, in those diagnosed with Alzheimer’s, 40-65% had the gene present. This does not mean that if you have APOE-e4, you have a 40-65% chance of getting Alzheimer’s. This is a case of correlation of two things, not necessarily causation.
As such, routine genetic testing for Alzheimer’s is not currently recommended. However, those with first-degree relatives with Alzheimer’s or with relatives with early-onset Alzheimer’s dementia should speak with their physician regarding genetic testing.
Instead, I would recommend that most people focus on being up-to-date with their physician on other important screening tests recommended by the U.S. Preventative Services Task Force, including for lung, colorectal and breast cancer. I previously wrote about how we fell behind on these metrics during the pandemic.
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What you can do to mitigate your risk of Alzheimer’s?
It is important for all of us to be aware of what we can do to reduce our risk of Alzheimer’s since it is the leading cause of dementia. A CDC study published earlier this year identified eight modifiable risk factors for Alzheimer’s and related dementias. These included:
- High blood pressure
- Physical inactivity
- Obesity
- Diabetes
- Depression
- Smoking
- Hearing loss
- Binge drinking
The wide-ranging study across 31 states found that adults 45 and older with subjective cognitive decline were more likely to report four or more of the aforementioned risk factors than those without decline. The good news is that because these risk factors are modifiable (compared to inherited genes or family members with dementia), we have control over them.
So what’s the bottom line? Most people do not need genetic testing for Alzheimer’s. It’s more important be up-to-date on other screening tests. But if you have a first-degree relative with Alzheimer’s, talk to your doctor or a genetic counselor before testing.
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Michael Daignault, MD, is a board-certified ER doctor in Los Angeles. He studied Global Health at Georgetown University and has a Medical Degree from Ben-Gurion University. He completed his residency training in emergency medicine at Lincoln Medical Center in the South Bronx. He is also a former United States Peace Corps Volunteer. Find him on Instagram @dr.daignault and Twitter @MichaelDaignau3
