Marvel actor and Thor star Chris Hemsworth made headlines recently as he announced a break from acting due to the discovery that he is at higher risk of developing Alzheimer’s. Hemsworth carries two copies (one from each parent) of ApoE4, a gene closely linked to Alzheimer’s — which increases his risk of contracting the disease by eight to ten times.

Alzheimer’s (the most prevalent type of dementia, at about 60–80% of cases) can impair memory, cognition, and communication. It is not required for someone to have a family history of Alzheimer’s to get the disease. However, evidence indicates that those with first-degree relatives who have the disease — such a parent or sibling — are more likely to get it than people without such a relative.

A person is even more at risk if they have multiple first-degree relatives who have the disease. A combination of genetic and environmental factors are likely involved when it comes to dementias that run in families.

The Role Genetics Plays In Developing Alzheimer’s

Risk genes and deterministic genes are the two types that affect a person’s likelihood of getting a disease. In both of these groups, inherited Alzheimer’s genes have been discovered by researchers.

Risk Genes

These kinds of genes enhance the risk of contracting an illness but do not guarantee it. Numerous genes that raise the risk of Alzheimer’s have been discovered by researchers. The first risk gene discovered, APOE-e4, continues to have the greatest influence on risk. According to research, the APOE-e4 gene is present in 40–65% of individuals with an Alzheimer’s diagnosis.

What Is The APOE-4 Gene?

One of the three common APOE gene variants, along with APOE-e2 and APOE-e3, is APOE-e4. Every parent gives us a copy of an APOE allele in some form. Those who receive one copy of APOE-e4 from either their mother or father are more likely to get Alzheimer’s disease.

There is an even larger risk, but not a guarantee, for those who receive two copies from their mother and father. Along with increasing risk, APOE-e4 may tend to cause symptoms to appear earlier than what is considered normal.

Although inheriting APOE4 does not guarantee that a person will develop Alzheimer’s disease, it is the gene that carries the highest risk of the disease. 20–30% of people in the US are thought to have one or two copies of APOE-e4, and 2% of Americans are thought to have two copies.

It is unclear why APOE4 raises the risk of developing Alzheimer’s. The APOE protein aids in the transportation of lipids such as cholesterol throughout the body. According to recent research, lipid processing issues in the brain may be a major factor in the development of Alzheimer’s disease and other associated conditions.

How To Test For The APOE-4 Gene

Both APOE-e4 and the uncommon genes that cause Alzheimer’s disease directly can be tested genetically. The Alzheimer’s Association advises against routine genetic testing for the likelihood of developing Alzheimer’s disease until a person has received appropriate counseling and is equipped with the knowledge necessary to make an informed choice, including the social and financial implications of knowing this genetic information.

However, there may be some circumstances in which a person with Alzheimer’s disease should talk with their doctor about genetic testing because the results may have an impact on the course of treatment. For instance, if a person has the APOE-e4 gene, they may be more likely to experience significant side effects from anti-amyloid medications like aducanumab. A genetic counselor should be consulted both before and after a person decides to undertake testing.

Deterministic Genes

These genes immediately result in an illness, ensuring that everybody inheriting it will contract it. Only a small number of families worldwide carry one of the rare genes known to cause Alzheimer’s disease.

These genes, which are thought to be responsible for 1% or fewer occurrences of Alzheimer’s, can lead to familial early-onset variants of the disease, in which symptoms typically appear between the ages of 40 and 50. The majority of Alzheimer’s patients are 65 years of age or older when the disease first manifests.

Even though the hereditary genes that cause “familial Alzheimer’s” are uncommon, their identification has led to the discovery of significant hints that have advanced our understanding of the disease.

These genes are all involved in the generation or processing of beta-amyloid, the primary protein fragment in plaques. The primary suspect in the deterioration and death of brain cells is beta-amyloid.

Conclusion

Numerous genes are connected to Alzheimer’s disease by researchers. Some genes enhance your risk of contracting the illness (risk genes). Though uncommon, some genes (deterministic genes) ensure contracting the disease. However, there are other variables involved in developing Alzheimer’s disease beyond genetic risk factors, something researchers are still earnestly studying — including racial and socioeconomic backgrounds.

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