Alzheimer’s disease is an irreversible, progressive brain disease that slowly destroys memory and thinking skills, and eventually even the ability to carry out the simplest tasks. In most people with Alzheimer’s disease, symptoms first appear after age 60.

Alzheimer’s disease is the most common cause of dementia among older people. Dementia is the loss of cognitive functioning—thinking, remembering, and reasoning—to such an extent that it interferes with a person’s daily life and activities. According to recent estimates, as many as 2.4 to 4.5 million Americans are living with Alzheimer’s disease.

Alzheimer’s disease is named after Dr. Alois Alzheimer. In 1906, Dr. Alzheimer noticed changes in the brain tissue of a woman who had died of an unusual mental illness. Her symptoms included memory loss, language problems, and unpredictable behavior. After she died, he examined her brain and found many abnormal clumps (now called amyloid plaques) and tangled bundles of fibers (now called neurofibrillary tangles). Plaques and tangles in the brain are two of the main features of Alzheimer’s disease. The third is the loss of connections between nerve cells (neurons) in the brain.

Brain Changes in Alzheimer’s disease
Although we still don’t know what starts the Alzheimer’s disease process, we do know that damage to the brain begins as many as 10 to 20 years before any problems are evident. Tangles begin to develop deep in the brain, in an area called the entorhinal cortex, and plaques form in other areas. As more and more plaques and tangles form in particular brain areas, healthy neurons begin to work less efficiently. Then, they lose their ability to function and communicate with each other, and eventually they die. This damaging process spreads to a nearby structure, called the hippocampus, which is essential in forming memories. As the death of neurons increases, affected brain regions begin to shrink. By the final stage of Alzheimer’s disease, damage is widespread and brain tissue has shrunk significantly.

Very Early Signs and Symptoms
Memory problems are one of the first signs of Alzheimer’s disease. Some people with memory problems have a condition called amnestic mild cognitive impairment (MCI). People with this condition have more memory problems than normal for people their age, but their symptoms are not as severe as those with Alzheimer’s disease. More people with MCI, compared with those without MCI, go on to develop Alzheimer’s disease.

Other changes may also signal the very early stages of Alzheimer’s disease. For example, recent research has found links between some movement difficulties and MCI. Researchers also have seen links between some problems with the sense of smell and cognitive problems. Brain imaging and biomarker studies of people with MCI and those with a family history of Alzheimer’s disease are beginning to detect early changes in the brain like those seen in Alzheimer’s disease. These findings will need to be confirmed by other studies but appear promising. Such findings offer hope that someday, we may have tools that could help detect Alzheimer’s disease early, track the course of the disease, and monitor response to treatments.

Mild Alzheimer’s Disease
As Alzheimer’s disease progresses, memory loss continues and changes in other cognitive abilities appear. Problems can include getting lost, trouble handling money and paying bills, repeating questions, taking longer to complete normal daily tasks, poor judgment, and mood and personality changes. People often are first diagnosed in this stage.

Moderate Alzheimer’s Disease
In this stage, damage occurs in areas of the brain that control language, reasoning, sensory processing, and conscious thought. Memory loss and confusion increase, and people begin to have problems recognizing family and friends. They may be unable to learn new things, carry out tasks that involve multiple steps (such as getting dressed), or cope with new situations. They may have hallucinations, delusions, and paranoia, and may behave impulsively.

Severe Alzheimer’s Disease
By the final stage, plaques and tangles have spread throughout the brain and brain tissue has shrunk significantly. People with severe Alzheimer’s disease cannot communicate and are completely dependent on others for their care. Near the end, the person may be in bed most or all of the time as the body shuts down.

What Causes Alzheimer’s Disease
Scientists don’t yet fully understand what causes Alzheimer’s disease, but it is clear that it develops because of a complex series of events that take place in the brain over a long period of time. It is likely that the causes include genetic, environmental, and lifestyle factors. Because people differ in their genetic make-up and lifestyle, the importance of these factors for preventing or delaying Alzheimer’s disease differs from person to person.

The Basics of Alzheimer’s Disease
Scientists are conducting studies to learn more about plaques, tangles, and other features of Alzheimer’s disease. They can now visualize plaques by imaging the brains of living individuals. They are also exploring the very earliest steps in the disease process. Findings from these studies will help them understand the causes of Alzheimer’s disease.

One of the great mysteries of Alzheimer’s disease is why it largely strikes older adults. Research on how the brain changes normally with age is shedding light on this question. For example, scientists are learning how age-related changes in the brain may harm neurons and contribute to Alzheimer’s disease damage. These age-related changes include inflammation and the production of unstable molecules called free radicals.

Genetics
In a very few families, people develop Alzheimer’s disease in their 30s, 40s, and 50s. These people have a mutation, or permanent change, in one of three genes that they inherited from a parent. We know that these gene mutations cause Alzheimer’s disease in these “early-onset” familial cases.

However, most people with Alzheimer’s disease have “late-onset” Alzheimer’s disease, which usually develops after age 60. Many studies have linked a gene called APOE to late-onset Alzheimer’s disease. This gene has several forms. One of them, APOE ε4, increases a person’s risk of getting the disease. About 40 percent of all people who develop late-onset Alzheimer’s disease carry this gene. However, carrying the APOE ε4 form of the gene does not necessarily mean that a person will develop Alzheimer’s disease, and people carrying no APOE ε4 forms can also develop Alzheimer’s disease.

Lifestyle Factors
A nutritious diet, exercise, social engagement, and mentally stimulating pursuits can all help people stay healthy. New research suggests the possibility that these factors also might help to reduce the risk of cognitive decline and Alzheimer’s disease. Scientists are investigating associations between cognitive decline and heart disease, high blood pressure, diabetes, and obesity. Understanding these relationships and testing them in clinical trials will help us understand whether reducing risk factors for these diseases may help with Alzheimer’s disease as well.

How Alzheimer’s Disease is Diagnosed

These tests may be repeated to give doctors information about how the person’s memory is changing over time.

Early diagnosis is beneficial for several reasons. Having an early diagnosis and starting treatment in the early stages of the disease can help preserve function for months to years, even though the underlying Alzheimer’s disease process cannot be changed. Having an early diagnosis also helps families plan for the future, make living arrangements, take care of financial and legal matters, and develop support networks.
References:
1. National Institute on Aging
2. Video by www.AboutAlz.org