Alzheimer Disease

What is Alzheimer disease?

Alzheimer disease is a degenerative disease of the brain that causes gradual loss of memory, judgment, and ability to function. The disorder usually appears in people older than age 65, but there are also forms of early-onset disease, which are less common.

Genetic changes are related to the following types of Alzheimer disease.

* Alzheimer disease, type 1
* Alzheimer disease, type 2
* Alzheimer disease, type 3
* Alzheimer disease, type 4

Additional types of Alzheimer disease have been reported, but the responsible mutations have not been adequately described, or the cause is not genetic.

Memory loss is the most common sign of this disease. The loss of memory becomes more than the usual forgetfulness experienced by most older people. Even in familiar settings, a person with Alzheimer disease may get lost or become confused. Normal daily tasks, such as doing simple math and naming objects and people, become challenging. Preparing meals, doing laundry, and performing other household chores can also become difficult. Problems with dressing, eating, and personal care as well as agitation, restlessness, and inappropriate behaviour develop as the disease progresses. In addition, personality changes and an inability to interact in a socially appropriate manner are common. The patient's speech eventually becomes difficult to understand, and the individual usually requires total care during the advanced stages of the disease. The course of the disease is usually 8 to 10 years, but can range from 1 to 25 years.

How common is Alzheimer disease?

Alzheimer disease currently affects an estimated 4.5 million Americans. Because more people are living longer, this number is expected to triple in the next 50 years.

What genes are related to Alzheimer disease?

Mutations in the APP, PSEN1, and PSEN2 genes cause Alzheimer disease.

Variations of the APOE gene increase the risk of developing Alzheimer disease.

About 75 percent of Alzheimer disease cases are classified as sporadic, which means they occur in people with no history of the disorder in their family. The cause of these cases is not known, but genetics may play a part. Virtually all of these cases are late-onset, which indicates that symptoms begin after age 65. The risk of developing the condition increases as a person gets older.

The remaining 25 percent of Alzheimer disease cases are hereditary, which means they are caused by mutated genes that can be passed from parent to child. These cases can be divided into early-onset disease (symptoms begin before age 65) and late-onset disease (symptoms begin after age 65).

Researchers have identified three genes that cause early-onset Alzheimer disease. Mutations in the amyloid precursor protein (APP) gene, presenilin 1 (PSEN1) gene, and presenilin 2 (PSEN2) gene lead to Alzheimer disease types 1, 3, and 4, respectively. Mutations in any of these genes result in the production of large amounts of a toxic protein fragment called amyloid beta peptide (a substance found in the brain and other tissues). A buildup of amyloid beta peptide leads to the formation of protein clumps called amyloid plaques in the brain, the death of nerve cells, and the progressive signs and symptoms of Alzheimer disease.

The genetic causes of late-onset (type 2) Alzheimer disease are less clear. No gene that definitely causes the condition has been identified; however, a gene called APOE has been studied extensively as a risk factor for the disease. In particular, one form (or allele) of this gene seems to increase an individual's risk for developing type 2 Alzheimer disease. Other genetic changes can also increase the risk of developing late-onset Alzheimer disease, but these genes have not been identified.

How do people inherit Alzheimer disease?

The early-onset forms of Alzheimer disease (types 1, 3, and 4) are inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In most cases, an affected person has one affected parent.

Most cases of late-onset (type 2) Alzheimer disease occur in people with no history of the disorder in their family.

What other names do people use for Alzheimer disease?

* AD
* Alzheimer dementia (AD)
* Alzheimer sclerosis
* Alzheimer's Disease
* Alzheimer syndrome
* Alzheimer-type dementia (ATD)
* DAT - Dementia Alzheimer's type
* familial Alzheimer disease (FAD)
* Presenile and senile dementia
* Primary Senile Degenerative Dementia
* SDAT

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Page last modified: September 2006

Source: NIH