Alzheimer’s disease is the most common neurodegenerative disorder that affects thinking, reasoning and memory. Although the reason behind its occurrence is not clear, researchers are able to find the genetic basis to a certain extent. With no specific reason, mutation occurs in certain genes that leads to the formation of certain substances in the brain. This condition causes irreparable destruction to the brain cells and damages the normal functioning of the brain.
Research has shown that the presence of mutated apolipoprotein E (APOE) gene on chromosome 19 increases the chance of Alzheimer’s disease. Moreover, the other mutated genes amyloid precursor protein (APP) on chromosome 21, presenilin 1 (PSEN1) on chromosome 14 and presenilin 2 (PSEN2) on chromosome 1 are also known to cause Alzheimer’s disease.
The maximum cases of Alzheimer’s disease occur because of the mutation in APOE gene. The APOE3 and APOE4 genes cause the condition while APOE2 provides protection to a certain extent.
One of the important functions of the normal APP, PSEN1, PSEN2 and APOE genes in the human body is to produce amyloid protein. The amyloid protein is important for neural development. It maintains the synapse and repairs any damage throughout the circuit. The mutation in these genes induce the overproduction of beta-amyloid protein that forms plaque in the brain cells. This plaque inhibits the flow of signals and blood from body to the brain.
The formation of tau tangles is another reason for Alzheimer’s disease. The formation of excessive beta-amyloid plaque in the brain causes hyperphosphorylation of the tau protein. This condition produces bigger tau tangles that contain both long and short tau proteins. In normal conditions, tau protein is responsible for maintaining synapse. When tau protein is mutated, the tau tangles produce toxic neurons that build plaque around the brain cells.
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