Alzheimer’s, << AWLTS hy muhrz, >> disease, often abbreviated as AD, is the most common cause of dementia late in life. Dementia is characterized by loss of the ability to think clearly. AD attacks few people younger than age 60, but it becomes increasingly common with age.
Scientists know that changes in the brain occur up to 10 years before symptoms of Alzheimer’s disease become apparent. Later, people with AD may forget names, conversations, or recent events. As the disease progresses, memory loss increases, and patients begin to lose other mental functions. Patients can become confused or disoriented, easily getting lost even in familiar locations. In later stages, patients lose the ability to remember or talk meaningfully. Eventually, they cannot care for themselves and become bedridden, requiring constant care. In their weakened condition, patients are vulnerable to pneumonia and other infectious diseases. Most patients die from such infections 10 to 12 years after developing AD.
In the past, elderly adults suffering from severe memory loss were often labeled senile, but they were probably suffering from what doctors now recognize as AD. Today, AD affects about half of all people over age 85.
The disease is named for Alois Alzheimer, a German psychiatrist and neurologist. Alzheimer first described the disease at a medical meeting in Europe in 1907.
Diagnosis.
There is no single test used to identify people with AD. Patients, or their family members, may first notice increasing forgetfulness, often accompanied by reduced interest in, or awareness of, ongoing activities. Physicians suspect AD if no other disease or disorder is found to explain the symptoms.
An autopsy performed after the patient dies can confirm the diagnosis of AD. In patients with AD, the nerve cells of the parts of the brain responsible for thinking, remembering, and reasoning appear distorted. Examination of brain tissue with a microscope reveals many deposits of a protein called amyloid. These abnormal deposits, called plaques, are surrounded by damaged and dead nerve cells. Clumps of abnormal, wiry protein, called neurofibrillary tangles, are also seen inside the nerve cells. Affected areas of the brain become severely shrunken.
In 2004, scientists developed a method of using positron emission tomography (PET) to detect amyloid plaques in the brain before a person shows symptoms of AD. PET produces images of the chemical activity of the brain. The technique uses a radioactive dye that finds and sticks to amyloid deposits and is visible in PET scans. Scientists believe the technique can eventually be used to detect AD and to measure the effectiveness of drugs used to treat it.
Causes.
The amyloid plaques and neurofibrillary tangles that characterize AD are rarely found in the brains of healthy people. Thus, researchers believe that AD results from the development of these abnormal structures. Scientific studies have provided evidence that genetic and environmental factors linked to the formation of amyloid plaques constitute the primary causes of AD.
The plaques found in AD patients are almost entirely made up of peptides (protein fragments) called amyloid-beta peptides (Aβ). In 1986, biologists discovered that Aβ is produced from the breakdown of a larger, normally occurring, protein called amyloid precursor protein (APP). The production of this protein in the body is controlled by a specific gene. Geneticists discovered that mutations in the APP gene could lead to the formation of abnormal Aβ protein. Cell biologists found that when mutant APP breaks down, it produces Aβ peptides that are especially sticky and prone to forming plaques.
Scientists have also discovered another protein, called presenilin, that controls the breakdown of APP in the brain. They found that mutations in the presenilin gene can also lead to AD. Mutated forms of presenilin also enhance the accumulation of amyloid plaques in the brain.
An additional gene associated with the development of AD controls production of a protein called apolipoprotein E (apoE). A person inherits two genes for apoE production. There are three variants of the gene: apoE epsilon-2, apoE epsilon-3, and apoE epsilon-4. People who have one or two apoE epsilon-4 genes have a higher risk of developing AD after the age of 60 than people who do not have that variant. However, scientists do not think the apoE epsilon-4 gene alone can cause AD. Some people with two copies of the apoE epsilon-4 gene do not develop AD, while others who do not have the gene at all go on to develop AD.
The neurofibrillary tangles characteristic of AD are composed of an abnormal nerve cell structural protein called tau. Scientists have observed a type of dementia caused by mutations in the tau gene. This dementia, called Pick’s disease, or fronto-temporal dementia, is similar to AD. The mutations lead to the development of neurofibrillary tangles, but amyloid plaques characteristic of AD are absent.
Not all instances of AD in people can be linked to genetic causes. Scientists have been successful in discovering some specific environmental factors that are connected to the development of AD, such as head injuries.
Treatment.
There is no cure for Alzheimer’s disease. Drugs called cholinesterase inhibitors (ChEI’s) can temporarily relieve symptoms of AD. These drugs block the action of the enzyme cholinesterase, which breaks down acetylcholine in the brain. Acetylcholine, a chemical that transmits nerve impulses, is reduced in AD patients as brain cells die. However, ChEI’s provide only modest and temporary improvement of symptoms, because they do nothing to stop the death of nerve cells. The drugs do not alter the course of the disease.
Monoclonal antibodies to treat AD became available in the early 2020’s. These drugs do not stop or reverse the disease, but they delay the appearance of severe symptoms. They work by helping the body’s immune system remove amyloid plaques from the brain.
Scientists are also working to develop a vaccine against AD. The vaccine would spur the immune system to attack and destroy Aβ protein, preventing the accumulation of amyloid plaques.
Proper nutrition, good hygiene, and reassurance can help preserve the comfort and dignity of AD patients. Several organizations, including the Alzheimer’s Association in the United States, the Alzheimer Society of Canada, and Alzheimer’s Australia, offer support and information to patients and their families.
