Alzheimer's disease is an illness that causes the brain's neurons to deteriorate. This causes the sufferer to lose memory, loss of language skills, and changes in behavior. As the disease progresses to different areas of the brain, it affects different skills and abilities. Alzheimer's is a degenerative illness, meaning that it progresses and gets worse as the person gets older.

Alzheimer's disease is different from other types of senility, but it is the most common cause of dementia among senior citizens aged 65 and older. Not everyone gets Alzheimer's, and it is a disease and not a form of aging. Currently, there is no cure for Alzheimer's disease, nor is there any way to halt or reverse its progress through the brain.

Causes of Late-Onset Alzheimer's Disease

Is Alzheimers Hereditary?Most cases of Alzheimer's disease are late-onset, meaning that they affect people aged 65 and older. As of the time of this writing, scientists do not know for sure what factors cause late-onset Alzheimer's disease. The greatest risk factor for late-onset Alzheimer's disease is advanced age. The older a person gets, the more at risk they become for late-onset Alzheimer's disease.

Those with a family history of Alzheimer's are more likely to develop late-onset Alzheimer's disease, which suggests that there may be a hereditary link. However, many people develop late-onset Alzheimer's disease who do not have a family history of the disease. Scientists believe that one gene, Apolipoprotein E, or ApoE, is linked to late-onset Alzheimer's disease. People with this gene are more likely to develop late-onset Alzheimer's disease. This gene comes in three forms: ApoE2, ApoE3, and ApoE4. Approximately 25 percent of Americans have the ApoE4 gene. This gene puts people more at risk for developing late-onset Alzheimer's disease. In fact, some researchers estimate that the ApoE4 gene may be linked to 20 to 25 percent of cases of Alzheimer's disease. In contrast, approximately 5 percent of Americans have the ApoE2 gene. The presence of this gene seems to protect against developing late-onset Alzheimer's disease.

However, the presence of these genes does not guarantee that the carrier will develop or not develop the illness. For this reason, the ApoE genes are known as "risk" genes. This means that those with the genes may have a greater chance or a lesser chance of developing the illness.


Causes of Early-Onset Alzheimer's Disease

In contrast, early-onset Alzheimer's disease, or Alzheimer's disease that begins before the age of 65, is strongly linked to certain genes. Because of the strong genetic link, this illness is known as "familial Alzheimer's disease." Familial Alzheimer's disease is rare. It affects only approximately 10 percent of all Alzheimer's patients. However, the genetic link is so strong that if one parent has early-onset, or familial, Alzheimer's disease, all of the offspring have a 50 percent chance of developing the illness.

Genes Linked to Early-Onset Alzheimer's Disease include the genes that influence the coding of certain proteins. These proteins include: amyloid precursor protein (APP), presenilin-1 (PS-1) and presenilin-2 (PS-2). The presenilin-1 (PS-1) gene is the gene most often linked to early-onset Alzheimer's disease. Having any of these genes virtually guarantee that the person with genes will develop Alzheimer's. For this reason, these genes are known as "deterministic genes."

Will I get Alzheimer's Disease?

Even if you have deterministic genes for Alzheimer's disease, you may not contract the illness. Aside from identifying the genes, there is no way to know for sure whether an individual will develop Alzheimer's disease. Similarly, at the time of this writing, there is no known way to prevent or cure Alzheimer's disease.