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Last week Chris Hemsworthan Australian actor best known for his portrayal of Thor in the Marvel cinematic universe films, announced in ainterview to Vanity Fair want to take a break from acting. The reason would lie in the discovery of having a significantly increased risk of developing the disease Alzheimers. By undergoing a genetic test, in fact, it emerged that Chris Hemsworth would have it in his genome two copies of ApoE-e4genetic variant associated with a greater risk of developing this form of dementia: 2-3% of the population that shares this condition with the actor, in fact, has a up to 10 times more likely to develop disease compared to those without both copies of the gene, although, as experts point out, this may not necessarily happen. Be that as it may, Hemsworth has decided to take some time off to focus on stock for mitigate the risk of its occurrence.
Alzheimer’s disease is the most common form of dementia senilein which, through various mechanisms, the cognitive functions of patients are severely affected, damaging the abilities related to memoryto the languageto the thoughtto the judgement: this implies serious difficulties in carrying out normal daily activities and it can cause other problems as well, including states of confusion, mood changes, and disorientation. According to the Higher Institute of HealthAlzheimer’s disease affects approximately 5% of people over 60 years old: in Italy there are an estimated 500,000.
The different forms of ApoE and the risk of Alzheimer’s
The causes that lead to the onset of the disease have not yet been clarified uniquely, but it is thought that, as risk factors, they come into play both genetic and environmental factors. In particular, over the years researchers have identified a few genes associated with Alzheimer’s disease what increase the risk of occurrence (but they do not determine it in a certain way, as instead happens for some genetic diseases such as Huntington’s disease, or for a very rare form of Alzheimer’s – less than 1% of cases – called autosomal dominant with early onset). Among these, the most common is that of apolipoprotein E (ApoE), responsible for the production of a protein that helps carry cholesterol molecules in the bloodstream. Although its role in the onset of the disease has been known for several decades, the reason is not clear: among the hypotheses examined there is that it may be associated with damage to brain cells or a state of inflammation which then leads to dementia.
While encoding the same gene, ApoE it has different forms, called alleles: it can be present in a person’s genome ApoE-e2the least common form, associated with a less risk of onset of Alzheimer’s disease; ApoE-e3, the most common form, which appears to have no effect on the likelihood of developing Alzheimer’s; finally, there is ApoE-e4associated with a increased risk of Alzheimer’s onset and early disease onset. Since each gene is present in the human genome in duplicate, one inherited from the father and one inherited from the mother, about 15-25% of the general population has an ApoE-e4 allele in its genome, while the 2-3% of the population have both copies of the same allele. Therefore, having one or more copies of the ApoE-e4 gene increases the risk of developing Alzheimer’s disease: 2 to 3 times for those with only one copy and 8 to 12 times for those with two, like Hemsworth.
To test or not to test?
Actually, being a gene which affects the riskbut which does not directly determine the disease, not all people who have this genetic variant eventually develop Alzheimer’s and at the same time the disease can also arise in those who do not have the ApoE-e4 alleles. Basically, genetic testing is not a diagnosis. This is why, for some experts, it could even be counterproductive to undergo it.
“Typically, in my clinical practice, I dissuade people from getting tested “said al New York Times Gary Small, a psychiatrist at Hackensack University Medical Center. “If you have a family history of dementia, you should assume you are at increased risk; therefore, doing the genetic test will not tell much more“. Others, however, believe that a certain test result can lead to a positive attitude, in which the person will adopt the behaviors deemed most effective to mitigate the onset of the disease (as Hemsworth decided to do).
“The reason I believe in testing for ApoE-e4 is that some people really want to know more about themselves, and that really democratizes the ability to know these riskssaid Richard Isaacson, an associate professor of neurology at Weill Cornell Medical College.Not whether they will develop the disease, but what they can do about it.In general, however, experts recommend that always accompany the test with genetic counselingas the concepts related to the risk associated with a multifactorial disease such as Alzheimer’s are not immediate to understand.
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