Alzheimer's Disease
Medical Author: Howard Crystal, MD
Medical Editors: William C. Shiel Jr., MD, FACP, FACR and Jay W. Marks, MD
Previous Contributing Medical Author: Yuri Bronstein, M.D. and Medical Editor: Stefan M. Pulst, M.D.
Alzheimer's Disease Doctor to Patient
Dementia Prevention: Brain Exercise
Medical Author: William C. Shiel, Jr., FACP, FACR
Medical Editor: Leslie J.
Schoenfield, M.D., PhD
Dementia is significant loss of intellectual abilities such
as memory capacity,
severe enough to interfere with social or occupational functioning. Dementia
is reported in as many as 1% of adults 60 years of age. Moreover, it has been
estimated that the frequency of dementia doubles every five years after 60 years
of age. So, dementia is clearly related to aging.
Alzheimer's disease is the most common form of dementia. Among other causes
are medical conditions (thyroid disease, drug toxicity, thiamine deficiency with
alcoholism, and others),
brain
injury, strokes, multiple sclerosis, infection of
the brain (such as meningitis and
syphilis),
HIV infection, hydrocephalus,
Pick's disease, and
brain tumors.
Read more about dementia prevention »
What is dementia?
Dementia is a syndrome characterized by:
- impairment in memory,
- impairment in another area of thinking such as the ability to organize thoughts and reason, the ability to use language, or the ability to see accurately the visual world (not because of eye disease), and
- these impairments are severe
enough to cause a decline in the patient's usual level of functioning.
Although
some kinds of memory loss are normal parts of aging, the changes due to aging
are not severe enough to interfere with the level of function. Many different
diseases can cause dementia, but Alzheimer's disease is by far the most common
cause for dementia in the United States and in most countries in the world.
What is Alzheimer's disease?
Alzheimer's disease (AD) is a slowly progressive disease of the brain that is
characterized by impairment of memory and eventually by disturbances in
reasoning, planning, language, and perception. Many scientists believe that
Alzheimer's disease
results from an increase in the production or accumulation of a specific protein
(beta-amyloid protein) in the brain that leads to nerve cell death.
The likelihood of having Alzheimer's disease increases substantially after the age of 70 and
may affect around 50% of persons over the age of 85. Nonetheless, Alzheimer's
disease is not a normal part of aging and is not something that inevitably
happens in later life. For example, many people live to over 100 years of age
and never develop Alzheimer's disease.
Who develops Alzheimer's disease?
The main risk factor for Alzheimer's disease is increased age. As a population ages, the
frequency of Alzheimer's disease continues to increase. Ten percent of people over 65
years of age and 50% of those over 85 years of age have Alzheimer's disease. Unless new treatments are developed to decrease
the likelihood of developing Alzheimer's disease, the number of individuals with
Alzheimer's disease in the United
States is expected to be 14 million by the year 2050.
There are also genetic risk factors for Alzheimer's disease. Most patients develop
Alzheimer's disease after
age 70. However, 2%-5% of patients develop the disease in the fourth or fifth decade of
life (40s or 50s). At least half
of these early onset patients have inherited gene mutations associated with
their Alzheimer's disease. Moreover, the children of a patient with early onset
Alzheimer's disease who has one of
these gene mutations has a 50% risk of developing Alzheimer's disease.
There is also a genetic risk for late onset cases. A relatively common form
of a gene located on chromosome 19 is associated with late onset Alzheimer's
disease. In the
majority of Alzheimer's disease cases, however, no specific genetic risks have yet been
identified.
Other risk factors for Alzheimer's disease include
high blood pressure
(hypertension), coronary artery disease, diabetes, and possibly elevated blood
cholesterol. Individuals who have completed less than eight years of education
also have an increased risk for Alzheimer's disease. These factors increase the
risk of Alzheimer's disease, but by no means do they mean that Alzheimer's
disease is inevitable in persons with
these factors.
All patients with Down syndrome will develop the brain changes of Alzheimer's
disease by 40 years of age. This fact was also a clue to the "amyloid hypothesis of Alzheimer's disease" (see
section later in this article).
Next: What are the symptoms of Alzheimer's disease? »
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