Index
- Alzheimer's and heredity, what's that got to do with it?
- Alzheimer's disease, definition
- What is the cause of this disease?
- What is the part of heredity in this pathology?
- Genes linked to the inheritance of Alzheimer's disease
Alzheimer's and heredity, what's that got to do with it?
With age, various illnesses tend to occur. These are mainly neurodegenerative diseases that impact on the autonomy of seniors. Among the most common is Alzheimer's disease. This disease evolves over several years and mainly affects the part of the brain intended to control memory. Eventually, the patient becomes entirely dependent on his or her surroundings and requires continuous attention. If the destruction of certain neurons is at the origin of this disease, the question still persists as to the existence of a genetic predisposition. In the following paragraphs, we will discuss the relationship between the onset of Alzheimer's and heredity.
Alzheimer's disease, definition
Among the neurodegenerative diseases affecting seniors, Alzheimer's disease is the most common. Specifically, it is more common in people over 65 years of age. From this age, an incidence of 2 to 4% is recorded. Beyond the age of 80, the incidence rises to 15%. This pathology is known by the majority for its effects on memory and spatio-temporal orientation. In fact, this disease is characterized by a slow and progressive death of neurons. Two possible causes are pointed out in relation to this neuron degeneration: an accumulation outside the neurons of the beta-amyloid protein which forms senile plaques and neurofibrillary degeneration. In addition to this, the link between Alzheimer's and heredity is also to blame, according to the scientists. In common parlance, this disease is also characterized by the term "dementia".
What is the cause of this disease?
As mentioned above, there are two very distinct causes of Alzheimer's disease:
- The formation of amyloid plaques - also called senile plaques, these are formed as a result of the accumulation of beta-amyloid protein outside the neurons. Note that this protein is naturally present in the brain.
- Neurofibrillary degeneration - this lesion is caused by the modification of the Tau protein. Tau protein is naturally present in Their modification causes the breakdown of certain nerve cells and leads to the death of neurons.
What is the part of heredity in this pathology?
The neurological lesions that appear in Alzheimer's disease can also be explained by heredity. Indeed, scientists have never ruled out the link between Alzheimer's and heredity. A genetic predisposition to the disease would explain a tiny part of the pathology. And from a genetic point of view, all the mechanisms underlying this disease are as if there were two forms of Alzheimer's. As you can see, the genetic predispositions to these two forms of the disease are not the same.
As for the sporadic form of Alzheimer's, genetics has no role to play in its occurrence. In fact, only age is the main risk factor for this form of the disease.
But as far as the hereditary form is concerned, age does not matter. In fact, this pathology can even occur before the age of 50 in some people. This early form of Alzheimer's disease is strongly linked to heredity. The genes linked to this form were identified in the 1990s, and research on them continues to this day.
Genes linked to the inheritance of Alzheimer's disease
Even though the genetic form of this pathology is very rare, it is important to shed light on its genetic factor. In fact, when this form appears, scientists have noticed a mutation of genes in patients. In concrete terms, three mutations have been identified as being at the origin of the hereditary form of Alzheimer's disease. These mutations affect chromosome 21 in 25% of cases, chromosome 1 in 2.5% of cases, and chromosome 14 for the remaining 70%. Thus, each descendant of a patient has received a copy of all his or her chromosomes in his or her genes. The existence of this copy may be enough to develop the disease even if one of the parents does not have one of the genes on the three chromosomes mentioned. Such transmission of the disease is called "dominant transmission". It should also be noted that each person with Alzheimer's disease has a 50% chance of passing it on to his or her children.
In addition, other genes have also been identified as a risk factor for the disease. This is the case, for example, of the ApoE gene. This gene can exist in the form of : ApoE4, ApoE3, ApoE2. Carriers of these genes are more likely to develop Alzheimer's disease than the rest of the population. However, research into this neurodegenerative disease is still ongoing. And according to recent studies, abnormalities in about 20 genes may have a slight impact on the development of the sporadic form of Alzheimer's disease.
Finally, the existence of a genetic predisposition to this disease cannot be explained by the fact that he has had family members who have suffered from Alzheimer's. In fact, the existence of an hereditary form of the disease only arises when a patient under the age of 60 is found to have had a parent with Alzheimer's disease.
