Last month, Chris Hemsworth introduced he was taking a break from acting after studying he has a gene variant that will increase his risk of developing Alzheimer’s disease. The revelation, which got here through a genetic test done for the docuseries Limitless, was not completely surprising, Hemsworth told Vanity Fair: His grandfather has Alzheimer’s, and the situation is extremely heritable.
The information got here as a shock, for sure. But it doesn’t imply Hemsworth’s future is foretold, in accordance to experts. In fact, his expertise is one reason experts say you might need to keep away from getting examined for this particular variant, even although the test is an option with some mail-in genetic tests.
For one thing, the tests can solely identify risk, not predict who will actually develop Alzheimer’s. Conversely, many individuals who develop the illness don’t have this genetic variant, or allele.
The gene, known as APOE-e4, is taken into account a risk issue however not a trigger of the disease.
“We know that individuals who've APOE-e4 [can] live a lengthy life with out developing Alzheimer’s,” said Dr. Richard Mayeux, chair of the neurology division on the Columbia University Vagelos College of Physicians and Surgeons.
Although lifestyle changes like train can help, there are few efficient methods to slow or delay Alzheimer’s.
"I don’t encourage genetic testing for Alzheimer’s, because if I discover that you have a mutation there’s nothing I can do to maintain you from getting this disease,” Mayeux said, although “that may change.”
What causes Alzheimer’s disease?
Alzheimer’s is the most common type of dementia, affecting some 6.5 million Americans, most of them sixty five and over. That quantity is probably going to double by 2050, in accordance to the Alzheimer’s Association. Experts are nonetheless teasing out the causes, however it’s clear that each genes and environmental factors play a role.
“It is a polygenic dysfunction meaning that there are many genes that may impact getting Alzheimer's disease,” said Dr. Douglas Scharre, director of the Division of Cognitive Neurology for the Ohio State University Wexner Medical Center. “Lifestyle factors could additionally be separate influencers of getting Alzheimer’s disease. Some conditions, like elevated cholesterol, have each genetic- and lifestyle-related dangers that may impact the risk of getting Alzheimer’s disease.”
There are different types of Alzheimer’s
There are two main types of Alzheimer’s disease, relying on when signs appear.
Late-onset Alzheimer’s impacts people sixty five or over, whereas signs of early-onset Alzheimer’s, which is a lot much less common, can begin as early as when somebody is of their 30s.
About 74% of late-onset Alzheimer’s is because of genetics (lifestyle and environment additionally have an effect on risk); APOE-e4 is the strongest known risk factor.
Early-onset Alzheimer’s signs have an effect on decrease than 10% of all individuals with the disease. Genes play an even bigger role here, Mayeux said, however not essentially APOE-e4. Three genes linked to early-onset Alzheimer’s are amyloid precursor protein (APP) on chromosome 21, presenilin 1 (PSEN1) on chromosome 14, and presenilin 2 (PSEN2) on chromosome 1.
Although Alzheimer’s does run in families, a parent with APOE-e4 won’t essentially pass on the gene to a child. Or they could have the gene and pass it on however not get the illness themselves, Mayeux said — it’s very unpredictable.
That’s one reason many experts don't recommend getting examined for APOE-e4, although they sometimes recommend testing for the genes concerned in early-onset Alzheimer’s.
APOE-e4 is additionally not the one gene implicated within the disease. “The newest analysis suggests there are near 50 different locations within the genome that might contain genes that increase your risk of Alzheimer’s,” Mayeux said.
There are three types of APOE
There are a quantity of different variations of the APOE gene, and also you inherit two copies of it — one from every parent.
APOE-e3, the most common, doesn’t appear to have an effect on Alzheimer’s risk one way or another. APOE-e2 may very well decrease the risk of Alzheimer’s, however it’s rare.
While APOE-e4 is the strongest genetic risk issue for late-onset Alzheimer’s, having the gene doesn’t imply you definitely will develop Alzheimer’s, in accordance to the National Institute on Aging.
If you reside to age 65, your chance of getting Alzheimer's illness at some level in your lifetime is about 15%, Scharre said. That’s if you don’t know your APOE-e4 status. If you do, issues change.
If each of the alleles you inherit are APOE-e2 or APOE-e3, your risk goes down to 9%, Scharre said.
If you have one APOE-e4 allele, your risk goes to 29%; if you have two APOE-e4 allele, your risk goes to 58%, he said, “but that additionally means that there's about a 40% chance you'll not get Alzheimer’s.”
Because Hemsworth has inherited two copies of APOE-e4, one from his mom and one from his father, his risk is nearer to 58%.
How common are the APOE variants?
About 75% of the inhabitants has APOE-e3, which confers no risk. About 25% have one or two copies of APOE-e4. Only 2% to 3% of individuals have two copies of APOE-e4.
Having one copy raises your lifetime risk of Alzheimer’s two- to threefold. Having two elevates your risk 5 to tenfold. But you continue to have to make it to your 60s or past to see that diagnosis happen, if it ever does, Mayeux said.
The APOE gene is concerned in ldl cholesterol transportation. According to analysis published in Science Translational Medicine, the APOE-e4 variant causes imbalances in lipids (fats) within the mind that contribute to dementia. APOE-e4 additionally raises your risk of cardiovascular disease.
Should I get tested?
As we said, many experts don’t recommend getting tested, because APOE-e4 isn’t a trigger of Alzheimer's; it’s a risk factor, and there's a lot of uncertainty that influences who does and doesn't get the condition.
Hemsworth learned his APOE-e4 status, which got here through a genetic test done for the docuseries Limitless, however most of us aren’t filming a docuseries about longevity. Does genetic testing have a role within the actual world?
While the tests are accurate, they arrive with a variety of caveats, Scharre said. “They’re not typically used within the clinic.”
It’s very different from testing for BRCA1 or 2 — genes that may raise your risk of breast and ovarian cancer. “That genetic evaluation can dictate therapy, and that’s an important step,” Mayeux said. “At this point, a lot of us don’t encourage genetic testing. If there’s any worth in genetic testing, it’s serving to you choose to get right into a clinical trial or to take preventive measures.”
If you do choose to get tested, you ought to confer with a genetic counselor earlier than and after, in accordance to the Alzheimer’s Association. Experts can assist contextualize a house test, and taking a test with out an authority can trigger a lot of pointless stress.
Alzheimer’s treatment and prevention
One of the explanations people don’t recommend testing for the variant is that there are no hugely efficient treatments for Alzheimer’s currently on the market.
In late November, researchers launched efficacy data on a model new monoclonal antibody, lecanemab, which can decelerate how quickly the illness progresses. The Food and Drug Administration is reviewing the drug for approval, and extra advances are expected. One IV drug, aducanumab, is already on the market under the model name Aduhelm.
There are three drugs generally prescribed for reminiscence signs — donepezil (Aricept), rivastigmine (Exelon), and galantamine (Razadyne) — although they can have side effects.
There are methods to decrease your risk of Alzheimer’s even when you have APOE-e4, Mayeux said. Many of the identical behaviors which have been proven to guard your coronary heart additionally protect your mind — namely train and wholesome eating, just like the Mediterranean diet.
“There’s fairly good research that support these observations,” Mayeux said.
In addition to exercise, avoiding smoking and extra alcohol, controlling hypertension and blood sugar, and stopping and managing listening to loss can additionally assist reduce your risk of Alzheimer’s disease.
For his part, Hemsworth told Vanity Fair that the outcomes of the genetic test may very well have been a blessing because he can work on making changes in his lifestyle that may assist fend off the disease. ●
