What Is Alzheimer’s Disease?
Alzheimer’s disease is a neurological* disorder in which structures called
plaques and tangles form in the cerebral (se-REE-bral) cortex (KOR-teks),
the outer surface of the brain, as well as in the brain matter just under the
cortex. The cortex has several functional areas, including those involved
with vision, hearing, speech, understanding, and bodily awareness.
Plaques and tangles interfere with the normal functioning of the neurons
(NOO-rahnz), or nerve cells, and the transmission of messages between
the brain and other parts of the body. Although these structures occur to
some extent with normal aging, they are much more prevalent in people.
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who have Alzheimer’s disease.
Alzheimer’s disease is the most common form of dementia*. Autopsies*
reveal the following abnormalities in the brains of people with Alzheimer’s:
■ Twisted nerve cell fibers, known a neurofibrillary tangles
■ A mutated or changed protein called tau found in these tangles
■ Outside the cells high concentrations of patches of plaque deposits
composed of a sticky substance called beta amyloid, especially in
the area of the cerebral cortex* and the hippocampus, the regions
most responsible for memory and cognition
■ Surrounding the plaques debris of dying neurons
■ Decreases in a brain chemical called acetylcholine, a neurotransmitter*
that helps signals move from one nerve cell to another
Alzheimer’s disease is not a normal part of aging.
What warning Causes Alzheimer’s Disease?
In the early 2000s, scientists did not fully understand what causes
Alzheimer’s disease, and they suspected several factors may play a role.
Age is the most important risk factor; the number of people with the
disease doubles every five years beyond age 65.
Family history is another risk factor. Genes* seem to play a role
in certain Alzheimer’s cases. Studies in the early 2000s suggested that
genes are associated with both the common form of Alzheimer’s disease,
which affects many people and generally begins at ages over 65, with
increasing frequency as people age, and with a rare early onset form of
the disease with onset between the ages of 30 and 60. At least five genes
might be implicated in early-onset form, which runs in families and is
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However, regarding the late onset form of the disease, researchers were
as of 2009 unable to trace a clear link to heredity or to other factors,
such as dietary habits, occupation, personality type, or environmental factors.
Several risk factors were suspected of interacting with other predisposing
factors. As of 2009, the only risk factor identified in late-onset
Alzheimer’s disease was a gene that makes one form of a protein called apolipoprotein
E (ApoE). There are three forms of ApoE: ApoE2, ApoE3, and
ApoE4. ApoE4 increases the risk but does not always cause Alzheimer’s
disease. Everyone has ApoE, which helps carry cholesterol in the blood, but only about 15 percent of people have the form that increases the risk
of Alzheimer’s disease. Possibly other genes may increase the risk of the
disease or protect against it, but in the early 2000s these had not been
Several other risk factors may predispose one to develop Alzheimer’s:
■ Heart disease
■ High blood pressure
■ Stroke, especially small strokes called transischemic attacks or TIAs
■ High cholesterol
■ Infection from a virus
■ Low levels of the vitamin folate
■ Blows to the head from accidents or from repeated blows as in boxing
or contact sports such as football
■ Certain disorders such as Down syndrome associated with Trisomy 21
■ Lifestyle factors, such as smoking, poor nutrition, drug use