Cause+of+Alzheimer's+Disease,+JM

<A Tau Tangle

Causes of Alzheimer's Disease

No one is sure what exactly causes Alzheimer’s Disease, but there are three main theories :

i. ** Cholinergic Hypothesis:** Cholinergic Hypothesis is the oldest of the three hypotheses. It proposes that Alzheimer’s Disease it caused by the reduced production of a chemical called acetylcholine, which aides neurotransmission, that is, the ability of nerve cells to communicate with each other. As the brain loses acetylcholine, its nerve cells lose the ability to comunicate, which results in decreased brain functions. Cholinergic Hypothesis has not maintained widespread scientific support primarily because of the ineffectiveness of drugs meant to counteract the acetylcholine deficiency.

ii. ** Amyloid Hypothesis:** The Amyloid Hypothesis states that the primary cause of Alzheimer’s Disease is the build up Amyloid Beta in the brain. This theory is backed up by the fact that the protein responsible for Amyloid Beta synthesis is located in Chromosome 21, and people with Down Syndrome who have an extra copy of Chromosome 21 almost always develop Alzheimer’s Disease by age 40. It was also found that the gene APOE 4, the primary risk factor for Alzheimer’s Disease, leads to increased levels of Amyloid Beta. It has also been observed the GM mice with a mutant beta Amyloid production protein gene develop Amyloid build-up similar to those with Alzheimer’s disease. In many cases Amyloid Beta neuro deposits precede Alzheimer’s disease. An experimental vaccine has been used in early human trials to clear the Beta Amyloid plaques, but it did not have a significant impact on reducing dementia.

iii. ** Tau Hypothesis:** The Tau Hypothesis postulates that abnormal tau proteins in the brain cause Alzheimer’s disease. In this hypothesis a certain Tau Protein begin to pair with each other, creating long threads of Tau. These threads eventually form neurofibrilly tangles inside the nerve cells. Once this happens the connects between the nerve cells start to fail, inhibiting neuro-transmission. Tau tangles may also be responsible for the failing of biochemical communication between neurons and the latter neuron death. 

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How are the three theories similar? How are the three theories diferent? In which theory does neurofibrilly tangles develop?
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