Alzheimer’s disease (AD) 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 AD. The third is the loss of connections between nerve cells (neurons) in the brain.

Watch a short video: “Inside the Brain: Unraveling the Mystery of Alzheimer’s Disease

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 AD. In most people with AD symptoms first appear after age 60, and although it is still not known what starts the AD process, damage to the brain begins as many as 10 to 20 years before any problems are evident.

Causes and Risk Factors
While scientists know Alzheimer’s disease involves progressive brain cell failure, they have not yet identified any single reason why cells fail. However, they have identified certain risk factors that increase the likelihood of developing Alzheimer’s.
• Age – The greatest known risk factor for Alzheimer’s is increasing age. Most individuals with the disease are 65 or older. The likelihood of developing Alzheimer’s doubles about every five years after age 65. After age 85, the risk reaches nearly 50 percent. Strategies for overall healthy aging may help keep the brain healthy and may even offer some protection against developing Alzheimer’s or related diseases. Try to keep your weight within recommended guidelines, avoid tobacco and excess alcohol, stay socially connected, and exercise both your body and mind.

• Family history – Another risk factor is family history. Research has shown that those who have a parent, brother or sister, or child with Alzheimer’s are more likely to develop Alzheimer’s. The risk increases if more than one family member has the illness. When diseases tend to run in families, either heredity (genetics) or environmental factors or both may play a role.

• Genetics (heredity) – Scientists know genes are involved in Alzheimer’s. There are two categories of genes that can play a role in determining whether a person develops a disease. Alzheimer genes have been found in both categories: 
Risk genes increase the likelihood of developing a disease, but do not guarantee it will happen. Scientists have so far identified one Alzheimer risk gene called apolipoprotein E-e4 (APOE-e4). Everyone inherits a copy of some form of APOE from each parent. Those who inherit one copy of APOE-e4 have an increased risk of developing Alzheimer’s. Those who inherit two copies have an even higher risk, but not a certainty. Scientists do not yet know how APOE-e4 raises risk. In addition to raising risk, APOE-e4 may tend to make symptoms appear at a younger age than usual.
Deterministic genes directly cause a disease, guaranteeing that anyone who inherits them will develop the disorder. Scientists have found rare genes that directly cause Alzheimer’s in only a few hundred extended families worldwide. When Alzheimer’s disease is caused by deterministic genes it is “familial Alzheimer’s disease,” and many family members in multiple generations are affected. True familial Alzheimer’s accounts for less than 5 percent of cases. Genetic tests are available for both APOE-e4 and the rare genes that directly cause Alzheimer’s. However, health professionals do not currently recommend routine genetic testing for Alzheimer’s disease.

• Head injury: There appears to be a strong link between serious head injury and future risk of Alzheimer’s. Protect your head by buckling your seat belt, wearing your helmet when participating in sports, and “fall-proofing” your home.

• Heart-head connection: Some of the strongest evidence links brain health to heart health. Your brain is nourished by one of your body’s richest networks of blood vessels. Every heartbeat pumps about 20 to 25 percent of your blood to your head, where brain cells use at least 20 percent of the food and oxygen your blood carries. The risk of developing Alzheimer’s or vascular dementia appears to be increased by many conditions that damage the heart or blood vessels. These include high blood pressure, heart disease, stroke, diabetes and high cholesterol. Work with your doctor to monitor your heart health and treat any problems that arise.

Very Early Signs and Symptoms
Memory problems are one of the first signs of AD. 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 AD. More people with MCI, compared with those without MCI, go on to develop Alzheimer’s Disease.

Brain imaging and biomarker studies of people with MCI and those with a family history of AD are beginning to detect early changes in the brain like those seen in AD. These findings will need to be confirmed by other studies but appear promising. Such findings offer hope that some day scientists will have the tools that could help detect AD early, track the course of the disease, and monitor response to treatments.

Mild Alzheimer’s Disease
As AD 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 AD 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.

Other Forms of Dementia
Dementia is a general term for loss of memory and other mental abilities severe enough to interfere with daily life. It is caused by physical changes in the brain.

Alzheimer’s disease is the most common type of dementia, accounting for 60 to 80 percent of cases, but it is important to get an early and accurate diagnosis. Some of other other causes of dementia include Mild Cognitive Impairment, Vascular Dementia, Mixed Dementia, Dementia with Lewy Bodies, Parkinson’s Disease, Frontotemporal Dementia, Creutzfeldt-Jakob Disease (CJD), Normal Pressure Hydrocephalus, Huntington’s Disease, Wernicke-Korsakoff Syndrome.

For more information about these other forms of dementia, click here.