What is Alzheimer’s Disease and how is it caused from the chromosomes?
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Alzheimer's disease is irreversible progressive degeneration of neurons of the brain (especially Cerebral cortex and hippocampus). It is a brain disorder which starts with loss of memory and conditions worsen upto where a person is not able to perform simple tasks. The disease progresses in three broad stages, and the symptoms are visible in mid 60's.
- At first, the patient notices forget fullness. Symptoms of dimentia are evident.
- In the second phase, there is a severe loss of memory particularly for recent events. The victim also becomes disoriented as to time or space, losing his way even on familiar streets. Anxiety increases with sudden changes in mood.
- In the third phase, the patient becomes severely disoriented and may suffer from symptoms of psychosis like hallucinations (hearing voices or seeing faces when no one is there) and paranoid delusions (A fixed irrational idea not shared by others and not responding to reasoned arguments).
Alzheimer's disease is thought to be caused by the abnormal build-up of proteins in and around brain cells. One of the proteins involved is called amyloid, deposits of which form plaques around brain cells. The other protein is called tau, deposits of which form tangles within brain cells.
These Proteins are abnormal protein which are caused by the gene mutation which are present on the chromosome. Cases of early-onset Alzheimer disease which are caused by gene mutations can be passed from parent to child. This results in what is known as early-onset familial Alzheimer disease (FAD).
There are three single-genes on different chromosomes which are mutated to cause early age Alzheimer's disease. The three single-gene mutations associated with early-onset Alzheimer's disease are:
- Amyloid precursor protein (APP) on chromosome 21.
- Presenilin 1 (PSEN1) on chromosome 14.
- Presenilin 2 (PSEN2) on chromosome 1.
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