Alternative Names
AD; Alzheimer dementia (AD); Alzheimer sclerosis; Alzheimer Disease;
Alzheimer syndrome; Alzheimer-type dementia (ATD); DAT; Familial Alzheimer
disease (FAD); Presenile and senile dementia; Primary Senile Degenerative
Dementia; SDAT
Symptoms & Characteristics
Alzheimer's disease (AD) is a progressive disorder that affects the regions
of the brain that control thought, memory and language. Early symptoms may
include forgetfulness of the names of friends and family as well as short term
memory loss. As symptoms worsen, people with AD have problems talking, reading
or writing. They may forget how to do simple tasks, become anxious or
aggressive, and even wander away from home. Eventually, affected people require
around the clock care.
Alzheimer's disease typically affects people over 65 years old. This is
called late-onset Alzheimer's disease. When AD occurs in people under 65 years
old, it is called early-onset Alzheimer's disease. AD typically strikes at
random with no family history, called sporadic AD, but can also run in
families, called familial AD.
Management & Treatment
Treatment is supportive, as each symptom is managed on an individual basis and assisted living arrangements or care in a nursing home is typically necessary.
Medications that increase cholinergic activity by inhibiting acetylcholinesterase produce a modest but useful behavioral or cognitive benefit in a minority of affected people. Antidepressants are sometimes used to treat associated depression.
A variety of clinical trials evaluating the use and effectiveness of anti-inflammatory agents (NSAIDs), estrogens, nerve growth factors, ginkgo biloba, statins, BACE inhibitors, and antioxidants are under way or being reviewed.
How Common Is It?
About 5 million Americans are affected with Alzheimer's disease. Late-onset
Alzheimer's disease is the most common form of dementia in older people.
Genetics & Inheritance
About 75% of people with Alzheimer's disease have sporadic
Alzheimer's disease. Sporadic Alzheimer's disease is most likely a
multifactorial condition, which means that it involves a combination of
genetic, lifestyle and environmental factors.
- Many environmental factors have been proposed to contribute to
AD, but no clear associations have been made at this time.
About 25% of people with Alzheimer's disease have familial
Alzheimer's disease. Familial AD can be further subcatagorized as
early-onset or late-onset. There are currently four major identified types of
familial AD. Types 1, 3, and 4 are characterized as early-onset AD, while Type
2 is characterized as APOE-associated late-onset AD.
Early-onset familial Alzheimer's disease represents about 5% of familial
cases and can be caused by mutations in one of three genes: APP, PSEN1,and
PSEN2.
We all have two copies of the APP, PSEN1, and PSEN2 genes - one from each
parent. Having a single mutation in either one of the APP, PSEN1, or PSEN2
genes is sufficient enough to cause the disease, and a person with a
mutation has a very high chance to someday develop the disease (called
highly penetrant). This is called autosomal dominant inheritance. An affected person has a
50% chance with each pregnancy to have an affected child.
Late-onset familial Alzheimer's disease represents about 95% of familial cases.
The genetic causes of late-onset familial AD are less clear. Similar to
sporadic Alzheimer's disease, this disorder is probably related to variations
in one or more genes in combination with lifestyle and environmental factors.
- APOE-associated Alzheimer's disease is associated with a specific
variation (called e4) of the APOE gene. This variant increases a person's
risk (or susceptibility) to develop Alzheimer's disease. The APOE gene is
on chromosome 19 at the location q13.2.
- People with one copy of the e4 variant are at increased risk, while
people with two copies appear to be at an even greater risk to develop the
disease.
- People with at least one copy of the e4 variant also appear to be at
increased risk for heart disease.
- The APOE e4 variant may also play a significant role in cases that appear
to be sporadic with no family history.
In addition to the APOE e4 variant, researchers have proposed that certain
single nucleotide polymorphisms (SNPs), which are small variations in a single
"letter" of DNA that can be found throughout our entire genetic make-up, may
also cause susceptibility to Alzheimer's disease. Further research is needed to
replicate the study findings across different ethnic groups and clearly
establish associations.
Other yet to be identified or adequately classified genes are also likely to
contribute to both early-onset and late-onset familial AD.
There are other genetic conditions, such as Parkinson's disease, as well as non-genetic conditions,
which have symptoms that overlap with Alzheimer's disease. As such, a genetic consultation with a trained genetic professional may be beneficial for a complete evaluation and accurate diagnosis.
Genetic Testing
Clinical genetic testing for Alzheimer's disease can be
broken down into two categories: early-onset AD testing and
late-onset AD testing.
Early-onset AD: Testing for early-onset Alzheimer's disease in the
absence of physical symptoms is called presymptomatic (or predictive) testing. Testing often
involves specific clinical evaluations and protocols. Clinical genetic testing for early-onset Alzheimer's disease
may be available through genetic consultation for people who are considered at
risk.
Late-onset AD: Susceptibility testing for the APOE e4 variant that causes
susceptibility to late-onset Alzheimer's disease is available online (over the
internet) or through genetic consultation for people who are considered at risk.
Go to the Tests tab to link to providers, compare providers
and read provider reviews.
A trained genetic professional can discuss the benefits and limitations of genetic testing for both early-onset AD testing and late-onset AD, coordinate testing and interpret results in the context of personal and family medical history.
- A board-certified genetic counselor is available by telephone.
Informational genetic testing for susceptibility to
Alzheimer's disease is available online (over the internet). Informational genetic testing for susceptibility to
Alzheimer's disease is also available as part of a whole genome scan. Whole genome scanning involves analyzing thousands of SNPs
at once related to a number of different health conditions.
- At this point, many genetic professionals do not consider this testing
clinically useful or medically relevant, but for informational purposes
only. Go to the Tests tab to link to online providers, compare
providers and read provider reviews.
Support & More Information
More information can be found at:
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Sources
Last Reviewed February 2, 2010