Wit
...increases a person’s chances of developing it. - There are three genes identified that cause rare, inherited forms of AD that tend to occur before age 65. There is also one gene identified that raises the risk of the more common form of AD that affects older people. - Women are more likely than men to develop AD mainly because they tend to live longer. - People with Down syndrome are at high risk for AD. They may develop signs around the age of 20, and by age 40, 95% of patients with Down syndrome will have evidence of AD based on autopsy findings. - Environmental toxins may play a role in AD, such as ingestion of heavy metals like lead. - Another risk factor relates to one's level of education and occupation. Two possible explanations have been put forth about the role of education and occupation. First, the more educated people perform better on tests of intellectual ability than others and are not easily identified as having symptoms of AD. Second, higher levels of education may increase brain reserve, delaying the onset of symptoms for many years. However, these theories have not yet been proven. - Anyone who suffers a severe blow to the head at any time in life is more prone to getting AD than those without such an experience. What are the affected areas of the brain? - AD affects the brain by destroying its basic component, which is the neuron. - Neuron loss occurs first in the hippocampus, which is the central switchboard of your memory system. That's why memory loss is often associated with the early stages of Alzheimer's. - From there, AD spreads to the amygdala and parts of the cerebral cortex. As neurons are damaged and destroyed in these areas of the brain, there's damage to other cognitive functions. Eventually, AD affects many parts of the brain. What are the characteristic changes in the brain? - There is a loss of brain cells and mass. - There are two abnormal structures in the brain associated with AD. - The first is a neuritic plaque (a.k.a. amyloid/senile plaque), which is a clump of degenerating axonal and dendritic nerve terminals that contain amyloid-beta protein and accumulate outside of neurons. - Another is a neurofibrillary tangle, which is a clump of altered tau protein in the cytoplasm of abnormal neurons in areas of the brain (hippocampus, cerebral cortex) most affected by AD. - These plaques and tangles represent the death of neurons throughout the brain. The brain shrinks in size, losing as much as 1/3 of its normal weight. Neuritic Plaque - On the screen, I’ve got a picture of a neuritic plaque. - The brain of the Alzheimer's patient will show buildup of a normal body-protein called amyloid-beta, which has been transformed into a form that’s toxic to the brain. - This transformed amyloid-beta is found between the neurons of the brain and becomes surrounded by the bits and pieces of the cells which it’s killed either directly or thru causing an inflammatory response and leading to neuron death. - Microglia, which are like immune cells, may view these plaques as foreign substances in the body and try to destroy them, triggering the inflammatory response. Or the microglia may be trying to remove damaged neurons. Neurofibrillary Tangle - The next image is a neurofibrillary tangle. - An important part of the neurofibrillary tangle is a protein called tau. - Tau proteins in the CNS provide internal support structure for neurons through their support of microtubules. - These proteins hold the microtubules together like how railroad ties would hold the railroad tracks together. - In AD, these tau proteins are altered, and as a result, the microtubules twist together. This ultimately forms the neurofibrillary tangles that you see on the screen. This may seriously damage neurons, causing them to die. Schematic Representation of the Plaque and Tangle What are the genes linked to AD? - There are two main types of AD. - One type is the more rare, early-onset AD. It usually affects people aged 30 to 60. Some cases of early-on...