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

Memory impairment is a necessary feature for the diagnosis of this or
any type of dementia. Change in one of the following areas must also
be present: language, decision-making ability, judgment, attention,
and other areas of mental function and personality.

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.

Alternative Names:


Senile dementia/Alzheimer's type (SDAT)

Causes, incidence, and risk factors:


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
There are two types of AD -- early onset and late onset. In early
onset AD, symptoms first appear before age 60. Early onset AD is much
less common, accounting for only 5-10% of cases. However, it tends to
progress rapidly.

The cause of AD is not entirely known but is thought to include both
genetic and environmental factors. A diagnosis of AD is made based on
characteristic symptoms and by excluding other causes of dementia.

Prior theories regarding the accumulation of aluminum, lead, mercury,
and other substances in the brain leading to AD have been disproved.
The only way to know for certain that someone had AD is by
microscopic examination of a sample of brain tissue after death.

The brain tissue shows "neurofibrillary tangles" (twisted fragments
of protein within nerve cells that clog up the cell), "neuritic
plaques" (abnormal clusters of dead and dying nerve cells, other
brain cells, and protein), and "senile plaques" (areas where products
of dying nerve cells have accumulated around protein). Although these
changes occur to some extent in all brains with age, there are many
more of them in the brains of people with AD.

The destruction of nerve cells (neurons) leads to a decrease in
neurotransmitters (substances secreted by a neuron to send a message
to another neuron). The correct balance of neurotransmitters is
critical to the brain.

By causing both structural and chemical problems in the brain, AD
appears to disconnect areas of the brain that normally work together.

About 10 percent of all people over 70 have significant memory
problems and about half of those are due to AD. The number of people
with AD doubles each decade past age 70. Having a close blood
relative who developed AD increases your risk.

Early onset disease can run in families and involves autosomal
dominant, inherited mutations that may be the cause of the disease.
So far, three early onset genes have been identified.

Late onset AD, the most common form of the disease, develops in
people 60 and older and is thought to be less likely to occur in
families. Late onset AD may run in some families, but the role of
genes is less direct and definitive. These genes may not cause the
problem itself, but simply increase the likelihood of formation of
plaques and tangles or other AD-related pathologies in the brain