Overview
Alzheimer’s ultimately causes brain cell death, since there is a loss of connection between neurons in the brain which causes the neurons to die. This creates an issue with the brain communicating with itself and other parts of the body.
The main features of Alzheimer’s are amyloid plaques– which are abnormal clumps- and neurofibrillary – which are tangled bundles of fibers. The plaques are densely clustered proteins scattered about. When there are too many, they can block the pathways in your brain, thus disabling brain cells from communicating with each other. The protein A-beta is in our brain, and when the protein clumps together, it can create amyloid plaque deposits (one of the key features of Alzheimer’s). Over time, these plaques can form in regions of the brain, especially the hippocampus. The neurofibrillary are brain proteins that get twisted, which interferes with necessary brain processes. This leads to brain cell death. Through research studies, scientists have named protein Tau as responsible for transporting nutrients and other molecules to other parts of the brain. They have found that in unhealthy brains, the Tau protein twists on itself after collapsing, which forms tangled fiber clumps. This prevents brain cells from getting nutrients, which also leads to brain cell death. The issue with mass brain cell death is that it actually results in shrinkage of certain areas of the brain. As Alzheimer’s disease progresses, other functions and areas are impaired, which leads to more severe symptoms, such as inability to swallow food correctly, falling, and fractures.
Changes in the brain, such as these build ups, can begin a decade or earlier before symptoms appear, which is what makes the disease so unmanageable and untreatable. Damage initially affects the hippocampus and the entorhinal cortex, which are parts of the brain where memory is formed, concluding why memory loss is the major symptom of any type of dementia.
As you can see by these diagrams, the brain shrinks considerably after Alzheimer’s progression. Amyloid plaques and tangles aren’t visible on CT or other brain scans.
The Alzheimer’s Gene
The apolipoprotein E gene, or APOE for short, is connected to increased risk of late-onset Alzheimer’s disease. You get one of each copy of the APOE gene from each parent, so it is a hereditary gene. One common form of the APOE gene is APOE e4 which escalates the chance of getting the disease, and a more severe form of the disease as well. Even one APOE e4 gene from one parent more than doubles the risk. Having two of the APOE e4 genes ups the risk eight-twelvefold.
There are 3 main genes known to be implicated in early onset Alzheimer’s. These genes are the APP, PSEN1, and PSEN2. These genes are ones that are hereditary, meaning passed down by parents. Though rare, any person who gets even one of these genes from either parent, let alone both, are anticipated to develop Alzheimer’s as early as age 30. The issue is that alterations in these genes cause excess production of amyloid-beta peptide proteins which leads to the formation of amyloid plaques, as discussed previously.
Despite the potential implications these genes have, they aren’t a decisive factor in actually getting the disease, and researchers are continuously doing more research to better understand the disease.