Alzheimer’s Disease – An Overview

Posted on August 13, 2018

Alzheimer’s is a progressive brain disease that causes worsening dementia and eventually leads to death. Alzheimer’s is different from mild forgetfulness that can be part of the normal aging process. Alzheimer’s disease is the leading cause of dementia, accounting for 60 to 80 percent of cases. Alzheimer’s disease cannot be cured, but treatments can decrease symptoms and improve the quality of life.

What is Alzheimer’s?

In Alzheimer’s disease, changes to the brain cause dysfunction that results in dementia. An abnormal protein called beta-amyloid builds up to form plaques between brain cells. Another type of fibrous protein called tau accumulates within brain cells, forming tangles. Beta-amyloid plaques and tangles of tau protein (called neurofibrillary tangles) begin in areas responsible for memory and spread through the brain, destroying nerve cells, shrinking brain tissue, and causing worsening symptoms.

What causes Alzheimer’s?

Fewer than 5 percent of people with Alzheimer’s directly inherit genes that make it extremely likely they will develop the condition. For most people, Alzheimer’s is most likely caused by a combination of inherited predisposition, lifestyle choices, and environmental risk factors. Read more about causes of Alzheimer’s.

The history of Alzheimer’s

Our understanding of Alzheimer’s disease has come a long way in the 100 years it has been studied. In 1906, German physician Alois Alzheimer observed a patient, Auguste D., who had unexplained worsening memory loss and language problems. After Auguste D.’s death, Alzheimer performed an autopsy and found what are now known as the main physical manifestations of Alzheimer’s disease in her brain tissue: shrinkage, plaques (now called beta-amyloid plaques), and tangled fibers (now called neurofibrillary or tau tangles). Several years later, Alzheimer was the first person to document different stages of Alzheimer’s disease when he studied a patient named Josef F., whose brain tissue upon death contained plaques but no tangled fibers.

Alzheimer’s disease was first published in the eighth edition of the Textbook of Psychiatry in 1910 and classified as a subtype of senile dementia. Study of the brain became more common after the electron microscope was invented in 1931, allowing scientists to study brain tissue in greater detail.

In the 1970s, Alzheimer’s disease began to receive greater attention and resources for research. The National Institute on Aging (NIA) was established in 1974. The NIA funds research and currently has a database of hundreds of open Alzheimer’s disease clinical trials. In 1976, neurologist Robert Katzman published a piece in the Archives of Neurology recognizing Alzheimer's as the most common form of dementia and a major public health challenge.

In the 1980s, the automation of DNA sequencing led to the discovery of genes involved in Alzheimer’s disease. The first gene associated with Alzheimer's disease was identified in 1987. Study of genes associated with Alzheimer’s continued to discover more genetic variants that lead to a higher risk of developing the disease in some people.

In 1984, University of California San Diego researchers George Glenner and Cai'ne Wong identified beta-amyloid, a cerebrovascular protein thought to trigger nerve cell damage in the brain. Two years later researchers identified tau protein, the main component of neurofibrillary tangles and the cause of nerve cell degeneration in the brains of people with Alzheimer’s disease. Based on these findings, drug researchers targeted ways to disrupt the creation and multiplication of these proteins in the 1990s.

The first Alzheimer’s drug, Cognex (Tacrine), was approved in the United States in 1993. This drug is now rarely prescribed due to the serious side effect of liver damage. The medications currently approved to treat dementia symptoms of Alzheimer’s disease – Aricept (Donepezil), Exelon (Rivastigmine), Namenda (Memantine), Galantamine (sold under the brand name Razadyne), and Namzaric (Donepezil/Memantine) – were introduced between 1996 and 2014.

In 2012, the first major clinical trial for the prevention of Alzheimer’s disease launched. The ongoing trial, sponsored by the Dominantly Inherited Alzheimer Network, is testing a drug therapy in people who inherited a genetic mutation that puts them at high risk for the disease.

Though the study of Alzheimer’s disease is only 100 years old, it is robust. The Alzheimer’s Association estimates that 90 percent of what we know about Alzheimer's disease has been discovered in the last 20 years. The past two decades have seen research expand to study links between Alzheimer’s disease and heart disease, traumatic brain injury (TBI), and glucose levels in the brain.

How common is Alzheimer’s?

Approximately 5.4 million people in the United States have Alzheimer’s disease. It is estimated that one-tenth of people age 65 or older and one-third of people age 85 or older have Alzheimer’s. Read more about types of Alzheimer’s.

How does Alzheimer’s progress?

Everyone diagnosed with Alzheimer’s disease experiences disease progression. Some individuals progress more quickly than others. People with Alzheimer’s can experience different symptoms at different intensities, and earlier or later in the course of the disease. There are three stages of Alzheimer’s that describe the most typical pattern of progression from mild symptoms that gradually worsen to cause increasing levels of disability. Read more about the stages of Alzheimer’s.

What is the prognosis for Alzheimer’s?

Alzheimer’s is a fatal disease in all cases. On average, people die between four and eight years after receiving a diagnosis of Alzheimer’s. Some people with Alzheimer’s live as long as 20 years after diagnosis. In 2014, Alzheimer’s disease was the sixth most common cause of death among all adults and the fifth most common cause of death for adults age 65 or older in the United States.

How does Alzheimer’s cause death?

In people with late-stage Alzheimer’s, the brain loses the ability to regulate the body, and systems deteriorate. If a person loses the ability to swallow, they may need to receive sustenance from a tube. Bowel and bladder function become impaired, and a urinary catheter may be necessary. Breathing becomes irregular, and mucus builds up in the lungs. All of these changes predispose the person to contract infections – especially pneumonia – which are often responsible for ending the life of someone with Alzheimer’s. Some researchers believe that deaths from Alzheimer’s are underreported because infection as listed as the cause on the death certificate rather than the underlying Alzheimer’s disease.

Resources

External resources

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FAQs

How is Alzheimer’s diagnosed?

There is not one conclusive test for Alzheimer’s. Neurologists diagnose likely cases of Alzheimer’s with a combination of detailed patient history and physical and neurological exam. Doctors sometimes order blood tests or brain imaging studies to rule out other possible causes of symptoms. Learn more about how Alzheimer’s is diagnosed.

What are the symptoms of Alzheimer’s?

Alzheimer’s causes dementia, a collection of symptoms related to a severe decline in cognitive (thinking and memory) problems. The most common Alzheimer’s symptoms are progressive loss of function related to memory, reasoning, communication, attention, and vision. Learn more about Alzheimer’s symptoms.

How is Alzheimer’s treated?

Alzheimer’s cannot be cured, and its progress cannot be slowed. However, there are medications that can temporarily improve dementia symptoms. Other medications may be prescribed to improve sleep or reduce anxiety or depression. Exercise and nutrition help those with Alzheimer’s stay in their best condition. Some people participate in clinical trials. Learn more about Alzheimer’s treatments.

Is Alzheimer’s contagious?

There is no evidence that Alzheimer’s is contagious between people. There are theories that Alzheimer’s may be spread via blood transfusions, other biological products, or when surgical instruments are imperfectly sterilized after brain surgery on infected humans. Studies are ongoing, but there is no evidence that one person can catch Alzheimer’s from another. The cause of Alzheimer’s remains unknown, and researchers continue to search for clues about how it originates. Read more about potential causes and risk factors for Alzheimer’s.

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