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
What is Alzheimer's Disease? Alzheimer's Disease 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.
Alzheimer's Disease 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 Alzheimer's Disease? Alzheimer's Disease Statistics
An estimated 5 million Americans are affected with Alzheimer's disease. Late-onset Alzheimer's disease is the most common form of dementia in older people.
Alzheimer's Disease Risk Factors & Causes
Risk Factors for late-onset Alzheimer's Disease include:
- Aging (the greatest known risk factor for Alzheimer's disease is increasing age)
- Female gender (women are more likely to develop Alzheimer's disease than men)
- Having a disease that damages the heart or blood vessels (such as stroke, high blood pressure, diabetes, heart disease or high cholesterol)
- A head injury
- Having a family history of Alzheimer's Disease (see below)
Alzheimer's Disease Inheritance & Family History
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.
|
Early-Onset
Familial Alzheimer's Disease Genetics
|
| Type |
Gene |
Location* |
| Type 1 |
APP |
21q21 |
| Type 3 |
PSEN1 |
14q24.3 |
| Type 4 |
PSEN2 |
1q31-q42 |
| *indicates chromosome number and gene location |
- 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 at chromosome location 19q13.2.
- 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.
Alzheimer's Disease Tests & Diagnosis
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.
Alzheimer's Disease Prevention & Related Issues
At this time, there is no known way to prevent late-onset Alzheimer's disease. However, it may be helpful to:
- Eat a healthy diet rich in fruits and vegetables
- Maintain a healthy weight
- Keep your brain active by engaging in social and intellectually stimulating activities
- Exercise regularly
- Protect your brain from injury
- Not smoke and avoid second-hand smoke
- Avoid excessive alcohol consumption
- Manage your blood pressure and cholesterol levels
Alzheimer's Disease Support & More Information
More information can be found at:
Support can be found at:
Alzheimer's Disease Sources