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Alzheimer's Disease

Causes of Alzheimer's Disease

There are two types of Alzheimer's disease , early-onset and late-onset. Early onset occurs before the age of 60-65 and is thought to be linked to genes on certain chromosomes. Mutations in these genes affect a protein called beta-amyloid , which causes damage in the brain when it builds up. Only a small percentage of Alzheimer's disease is early onset and because it is linked to genes, it can run in families. As a result, early onset is often referred to as familial Alzheimer's disease.

Early onset of Alzheimer's disease is also common in people with Down's syndrome. Down's syndrome is a result of having three copies of chromosome 21 instead of the regular two. It has been found that chromosome 21 can cause an excess of beta-amyloid to be produced. Having an extra chromosome 21 therefore produces even more beta-amyloid plaques.

The more common form of Alzheimer's disease is known as late onset . This type affects those over the age of 65 and appears to be related to a mutation on a gene known as ApoE . The ApoE gene occurs in several forms, but the three most common are ApoE 2, ApoE 3 and ApoE 4. The ApoE 4 form of the gene is a risk factor for late onset Alzheimer's disease.

Another risk factor, thought to be involved in both early and late onset Alzheimer's disease, is lower levels of an important neurotransmitter , acetyl choline , in the brain. Decreased levels of this neurotransmitter lead to problems sending messages between different brain structures.

Other risk factors include: gender (with Alzheimer's disease being twice as common in females), cardiovascular disease, diabetes, mild cognitive impairment , head injury, and low levels of formal education.

See Also:
About Dementia > Alzheimer's Disease > APOE
About Dementia > Alzheimer's Disease > Amyloid Hypothesis
About Dementia > Types of Dementia > Genetic Mutations
About Dementia > Alzheimer's Disease > Cholinergic Theory
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Last updated December 11, 2014
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