Alzheimer's disease (AD), one form of dementia, is a progressive, degenerative brain disease. It affects memory, thinking, and behavior.

The rate of progression is different for each person. If AD develops rapidly, it is likely to continue to progress rapidly. If it has been slow to progress, it will likely continue on a slow course.

More than 4 million Americans currently have AD. The older you get, the greater your risk of developing AD, although it is not a part of normal aging. Family history is another common risk factor.

In addition to age and family history, risk factors for AD may include:

• Longstanding high blood pressure
• History of head trauma
• High levels of homocysteine (a body chemical that contributes to chronic illnesses such as heart disease, depression, and possibly AD)
• Female gender -- because women usually live longer than men, they are more likely to develop AD
  

References

http://www.nlm.nih.gov/medlineplus/ency/article/000760.htm