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Causes of Alzheimer's Disease

Alzheimer's is a neurodegenerative disease, meaning that the symptoms are a result of a gradual and progressive deterioration of the brain. This can be visualized on CT or MRI scans of the brain as a loss of brain volume, and at the microscopic level by the presence of characteristic amyloid plaques and neurofibrillary tangles in the cerebral cortex.

The exact causes of Alzheimer's Disease remain unknown, but part may be due to the normal processes of aging, as rates of the disease reach close to 30% among individuals over age 90 [ref].

Genetic factors also play an important role, accounting for up to 80% of the risk of developing this disease [ref]. Early-onset Alzheimer's, in particular, is affected by genetic risk [ref]. The Apolipoprotein E4 (ApoE4) gene is thought to account for up to 50% of the risk of developing Alzheimer's Disease, with individuals who carry two copies of this gene having a higher risk and a tendency for earlier onset of the disease than individuals with only one copy, who in turn have a greater risk than people without any copies of this gene [ref]. (However, screening people for the presence of this gene is not likely to be helpful, as there are many people without it who still develop the illness [ref].)

Higher education levels seem to lower the risk of developing symptoms of Alzheimer's Disease [ref]. This is thought to be due to the fact that people with greater cognitive skills may have a larger reserve of brain functions such that it takes a greater amount of brain degeneration for the symptoms of the disease to become apparent.

Being overweight in middle-age, Type-2 Diabetes Mellitus, hypertension and hyperlipidemia all increase one's chances of developing Alzheimer's [ref, ref]. The reasons for these associations are not known. Dietary patterns may also play a role in the development of Alzheimer's Disease. For example, people who eat fish on a regular basis, especially ones that are high in omega-3 fatty acids, tend to have a lower risk of developing the disease. It is possible that these healthy diets prevent Alzheimer's in part by reducing obesity and diabetes. People who tend to be more physically active and excercise or walk regularly are at lower risk of developing Alzheimer's Disease [ref, ref].

Suffering from Depression during one's lifetime increases the risk of developing Alzheimer's Disease [ref]. This may be due to the high levels of cortisol that circulate in the body during states of depression, which can lead to the deterioration of certain brain centers like the hippocampus, which is involved in long-term memory. It is possible that suffering from other Mood or Anxiety Disorders may have similar effects.

 

Diagnosis

Course & Prevalence