Stanford Center for Memory Disorders

Alzheimer's Disease

Alzheimer's disease is the most common cause of dementia in people aged 65 and older. Experts believe that up to 4 million people in the United States are currently living with the disease: one in ten people over the age of 65 and nearly half of those over 85 have Alzheimer's disease. At least 360,000 Americans are diagnosed with Alzheimer's disease each year and about 50,000 are reported to die from it.

In most people, symptoms of Alzheimer's disease appear after age 60. However, there are some early-onset forms of the disease, usually linked to a specific gene defect, which may appear as early as age 30. Alzheimer's disease usually causes a gradual decline in cognitive abilities, usually during a span of 7 to 10 years. Nearly all brain functions, including memory, movement, language, judgment, behavior, and abstract thinking, are eventually affected.

Alzheimer's disease is characterized by two abnormalities in the brain: amyloid plaques and neurofibrillary tangles. Amyloid plaques, which are found in the tissue between the nerve cells, are unusual clumps of a protein called beta amyloid along with degenerating bits of neurons and other cells.

Neurofibrillary tangles are bundles of twisted filaments found within neurons. These tangles are largely made up of a protein called tau. In healthy neurons, the tau protein helps the functioning of microtubules, which are part of the cell's structural support and deliver substances throughout the nerve cell. However, in Alzheimer's disease, tau is changed in a way that causes it to twist into pairs of helical filaments that collect into tangles. When this happens, the microtubules cannot function correctly and they disintegrate. This collapse of the neuron's transport system may impair communication between nerve cells and cause them to die.

Researchers do not know if amyloid plaques and neurofibrillary tangles are harmful or if they are merely side effects of the disease process that damages neurons and leads to the symptoms of Alzheimer's disease. They do know that plaques and tangles usually increase in the brain as Alzheimer's disease progresses.

In the early stages of Alzheimer's disease, patients may experience memory impairment, lapses of judgment, and subtle changes in personality. As the disorder progresses, memory and language problems worsen and patients begin to have difficulty performing activities of daily living, such as balancing a checkbook or remembering to take medications. They also may have visuospatial problems, such as difficulty navigating an unfamiliar route. They may become disoriented about places and times, may suffer delusions (such as the idea that someone is stealing from them or that their spouse is being unfaithful), and may become short-tempered and hostile. During the late stages of the disease, patients begin to lose the ability to control motor functions. They may have difficulty swallowing and lose bowel and bladder control. They eventually lose the ability to recognize family members and to speak. As Alzheimer's disease progresses, it begins to affect the person's emotions and behavior. Most people with Alzheimer's disease eventually develop symptoms such as aggression, agitation, depression, sleeplessness, or delusions.

On average, patients with Alzheimer's disease live for 8 to 10 years after they are diagnosed. However, some people live as long as 20 years. Patients with Alzheimer's disease often die of aspiration pneumonia because they lose the ability to swallow late in the course of the disease.

Projected changes between 2000 and 2025 in Alzheimer’s Disease prevalence by state.

Source: Alzheimer's Association. 2012 Alzheimer's disease facts and figures. Alzheimer's and Dementia: The Journal of the Alzheimer's Association. March 2012; 8:131–168.

Projected numbers of people aged ≥65 years in the U.S. population with Alzheimer’s Disease using the U.S. Census Bureau estimates of population growth.

Source: Alzheimer's Association. 2012 Alzheimer's disease facts and figures. Alzheimer's and Dementia: The Journal of the Alzheimer's Association. March 2012; 8:131–168.

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