Decoding Dementia’s Genetic Connections

In 2022, fans of actor Chris Hemsworth, known for his work as Thor in the Marvel cinematic universe, were shocked when a National Geographic documentary Limitless uncovered that he had inherited two copies of the APOE4 gene, putting him at an eight to ten times increased risk for Alzheimer’s than the general public. This discovery sparked many conversations about dementia worldwide, and led many to wonder if they too were at risk due to dementia in their family history or other genetic risk factors that could be present without them even knowing.

Dementia affects millions of individuals globally. While age, not genetics, is the primary risk factor, there's growing evidence that genetics can indeed play a role in determining an individual's susceptibility to certain types of dementia.

Genetic risk factors for different types of dementia

While it’s good to be informed and take precautions, family members of loved ones with dementia should keep in mind that not all dementia cases have a genetic link. The relationship between genetics and dementia is in fact quite complex and not yet fully understood. Alzheimer's disease, the most common form of dementia, can have genetic components, but environmental and lifestyle factors can also play a role. Other types of dementia, such as vascular dementia and frontotemporal dementia, also show a genetic link, but to varying degrees. As said earlier, age is, across the board, the biggest risk factor of all. According to the Alzheimer’s Association, after the age of 65, the risk of Alzheimer’s doubles every five years.

Let’s break genetic links down by the different types of the dementia:

1. Alzheimer's:

Genetic Links: While the majority of Alzheimer's cases are unrelated to genetics, about 1 percent of cases are linked to specific genetic mutations, according to the Alzheimer’s Association. Mutations in genes such as APP, PSEN1, and PSEN2 increase the risk of developing Alzheimer's.

Testing: Genetic testing, like the kind Chris Hemsworth participated in, can identify these mutations, allowing individuals to understand their risk. However, it's important to note that not everyone with these mutations develops Alzheimer's, and not everyone with Alzheimer's has these mutations. Chris Hemsworth’s discovery, for example, was not a diagnosis, and it is not guaranteed that he will develop Alzheimer’s later in life.

2. Vascular Dementia:

Genetic Links: Vascular dementia is often associated with conditions that affect blood vessels, such as strokes. Genetic factors influencing cardiovascular health can contribute to the risk of developing vascular dementia.

Testing: Cardiovascular risk assessments and genetic tests that identify factors like high blood pressure and cholesterol levels can serve as important preventive measures against vascular dementia.

3. Frontotemporal Dementia:

Genetic Links: Frontotemporal dementia has the strongest genetic link compared to other types of dementia. Mutations in genes such as MAPT, GRN and C9orf72 are associated with forms of frontotemporal dementia that are inherited from family members.

Testing: Genetic testing can identify these mutations, especially in families with a history of frontotemporal dementia. Like with Alzheimer's, note that the presence of these mutations doesn't guarantee the development of the disease.

4. Lewy Body Dementia and Others:

Genetic Links: Some other rare forms of dementia, like Lewy body dementia, may have genetic components, but research is ongoing to understand these connections better.

Testing: As of now, specific genetic tests for these rarer forms are not widely available. 

The link between genetics and dementia is fascinating and informative, but is still an evolving field of study. While genetic testing can offer insights into potential risks, it's essential to approach it with a nuanced understanding and recognize that risk is not the same thing as a diagnosis.

Whether a person has a genetic risk for dementia or not, it’s important for us all to engage in risk reduction strategies as we age. Managing heart health, exercising, maintaining a healthy diet and engaging in mentally stimulating activities can help in lowering the risk of dementia, as well as improving overall health and wellness. 

As scientists and researchers decode more about genetics and dementia in the future, it will hopefully bring us closer to the goal of more targeted and effective dementia interventions and medications. In the meantime, we can all do our best to help people with dementia and their caregivers feel seen and supported, just as we would want to be in their shoes.