Is Alzheimer's disease hereditary?

Age: The primary risk factor for Alzheimer's disease

Let's start by acknowledging that research into neurodegenerative diseases is ongoing, and not all questions have been definitively answered. However, age remains the primary risk factor for Alzheimer's disease. This holds even when multiple disease cases occur within the same family. Often, the initial symptoms of Alzheimer's appear between the ages of 70 and 75.

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When several family members live to be 80 or older, it is statistically likely to see an increase in cases of Alzheimer's disease. This likelihood is further compounded if factors such as smoking or sedentary lifestyles are present. Does this mean that genetics should be completely ruled out? No, genetics also play a role.

Is Alzheimer's disease hereditary?

In reality, genetic factors play a minor role in explaining the onset of Alzheimer's disease. Since the 1990s, researchers have identified abnormalities in about twenty genes that may predispose individuals to develop degenerative disease. The ApoE gene is one of these genes. Other genes include PSEN1, PSEN2, APP, SORL1, NOTCH3, and TYROBP. However, it is crucial to understand that being a carrier of a variant of one or more of these genes does not guarantee the development of the disease. Genetics plays a marginal role compared to the other risk factors mentioned earlier. In other words, genetic inheritance is neither necessary nor sufficient to trigger the initial symptoms of Alzheimer's disease. This is why scientists use the term "susceptibility genes" with caution.

This demonstrates how complex Alzheimer's disease is, with some of its causes remaining elusive. New research and studies continuously reshape our understanding of this disease. Nevertheless, it is not possible to assert today that Alzheimer's disease is hereditary. At least, it is not directly hereditary.

To delve further into the genetic factors associated with this degenerative disease, we must make a distinction:

Genetic risk factors: These refer to genetic variations that may increase the risk of developing the disease.

Rare genetic mutations: These are anomalies in the genetic code inherited from parents or family members. If one parent carries such a mutation, there is a 50% chance it will be passed on to their child. Being a carrier of such a genetic mutation significantly increases the risk of developing the disease compared to the previous scenario.

However, it can be confidently stated that Alzheimer's cases are generally not the result of rare genetic mutations. It is the interplay of environmental factors and genetics that increases the risk of developing the disease.

Genetic disease vs. hereditary disease: Are they the same?

Sometimes, due to simplification or lack of understanding, genetics and heredity are conflated. A reminder is necessary because a genetic disease is not necessarily hereditary, and vice versa. To put it simply, what is genetic is logically present in the genes, whereas what is hereditary is transmitted. Calling a disease hereditary means it is innate, determined by birth because it is inherited from parents. Hereditary diseases are passed from one generation to the next.

In contrast, a genetic disease can be acquired through the modification or mutation of certain cells in the body at some point in life. Many cancers fall into this category; they have genetic causes but are not hereditary because they are not transmitted or inherited. In the case of Alzheimer's disease, it is more often the genetic factor than the hereditary factor that may be implicated—among other factors. However, there is an extremely rare case where the disease has a dominant hereditary explanation. This occurs when the first symptoms appear early, sometimes before the age of 50 or even earlier.

Age, lifestyle, medical history, genetics... Thus, as things stand today, no single factor can adequately explain the onset of Alzheimer's disease. Researchers remain vigilant and continue their studies in the hope of one day gaining a better understanding of the causes of this degenerative disease, ultimately aiming for improved treatment and prevention.

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