Alzheimer’s is a degenerative brain disease that causes worsening dementia and eventually leads to death. Alzheimer’s dementia is not the only form of dementia, but it is the most common. Alzheimer’s accounts for 60 percent to 80 percent of dementia cases.
Alzheimer’s is most commonly diagnosed in people aged 65 or older. Alzheimer’s and its effects are different from mild forgetfulness that can be part of the normal aging process in older adults.
Although Alzheimer’s disease currently cannot be cured, treatments can lessen symptoms and improve quality of life.
In Alzheimer’s disease, changes to the brain cause increasing cognitive dysfunction called dementia. Alzheimer’s is characterized by an abnormal buildup of two peptides, or protein molecules, in the brain: beta-amyloid and tau.
Beta-amyloid accumulates between brain cells (neurons) to form plaques. Collections of tau proteins within brain cells form neurofibrillary tangles.
Alzheimer’s shares some overlap with other forms of dementia and cognitive deficits. Amyloid plaques and neurofibrillary tangles are sometimes observed in people with other neurodegenerative diseases, such as Parkinson’s disease. People with Alzheimer’s are also sometimes diagnosed with other forms of dementia, including vascular dementia. People with Down syndrome are also at increased risk for developing Alzheimer’s disease.
Beta-amyloid plaques and neurofibrillary tangles often begin in areas of the brain that are responsible for memory and then spread through the brain. This is why memory problems are often among the earliest noticeable symptoms of Alzheimer’s.
As plaques and tangles spread, they destroy nerve cells, shrink brain tissue, and cause worsening symptoms. Eventually, they lead to an inability to function independently and death.
The cause of Alzheimer’s disease is not well understood. Most cases of Alzheimer’s are believed to be caused by a combination of family history, lifestyle, and environmental risk factors.
In some rare cases, risk of Alzheimer’s is determined by inherited genes that make it extremely likely for a person to develop the disease. This genetic risk accounts for less than 1 percent of cases and often leads to early onset Alzheimer’s disease that occurs in middle age.
Read more about causes of Alzheimer’s.
Everyone diagnosed with Alzheimer’s experiences disease progression. Some people progress more quickly than others. People with Alzheimer’s can experience different symptoms at different intensities and symptoms at earlier or later points in the course of disease progression.
Doctors use different staging systems to describe the progression of Alzheimer’s symptoms. These systems can have three, five, or seven stages. Read more about the stages of Alzheimer’s.
People in the early stages of Alzheimer’s often first experience mild cognitive impairment (MCI). MCI is a mild type of dementia that causes noticeable memory or language problems, but the cognitive decline seen in MCI isn’t enough to impact a person’s ability to perform daily tasks. Not everyone with MCI will go on to develop Alzheimer’s.
Alzheimer’s disease is believed to develop long before symptoms appear. Recent research has focused on identifying biomarkers to allow health care workers to diagnose Alzheimer’s as early as possible. Common tests for biomarkers include MRI imaging and tests of cerebrospinal fluid and blood. These tests look for early hallmarks of the disease.
Read more about how Alzheimer’s is diagnosed.
Alzheimer’s is a fatal disease. In most cases, people survive for four to eight years following a diagnosis of Alzheimer’s, although some people survive as long as 20 years.
Recent advancements in medications and other treatments can ease symptoms and may slow disease progression, particularly when treatment begins in the early stages of the disease.
Read more about treatments for Alzheimer’s.
In people with late-stage Alzheimer’s, brain atrophy leads to the loss of the ability to regulate basic bodily functions. If a person loses the ability to swallow, they may need to be fed with a tube. Bowel and bladder function may become impaired, and a urinary catheter may be necessary. Breathing becomes irregular, and mucus builds up in the lungs.
Degeneration of these bodily systems makes a person more likely to contract infections (especially pneumonia), which can often lead to death. Some researchers believe that deaths from Alzheimer’s are underreported because infections are listed as the cause of death rather than the underlying Alzheimer’s disease.
Our understanding of Alzheimer’s disease has come a long way in the 100 years since it was first identified. In the early 1900s, German psychiatrist and neuropathologist Alois Alzheimer observed a patient, Auguste D., who had unexplained worsening cognitive function including memory loss, paranoia, and confusion.
After Auguste D.’s death, Alzheimer performed an autopsy and identified what are now known as the main physical manifestations of Alzheimer’s disease: 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 Psychiatrie in 1910, where it was classified as a type of senile dementia. The invention of the electron microscope in 1931 allowed scientists to study brain tissue in greater detail and led to more studies of the brain.
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 Alzheimer’s 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. Since then, researchers have continued to discover genetic variants that increase risk for developing Alzheimer’s.
In 1984, University of California, San Diego researchers George Glenner and Cai’ne Wong identified beta-amyloid. Two years later, a team of researchers from New York identified tau protein — the main component of neurofibrillary tangles. 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 by the U.S. Food and Drug Administration (FDA) in 1993. This drug is now rarely prescribed due to its serious effects on the liver.
There are five medications currently approved by the FDA to treat dementia symptoms of Alzheimer’s disease. Three of these — Aricept (donepezil), Exelon (rivastigmine), and Razadyne (galantamine) — belong to a class of drugs called cholinesterase inhibitors. Cholinesterase inhibitors work by altering the function of a neurotransmitter called acetylcholine.
Another medication, Namenda (memantine), is a type of drug called an N-methyl-D-aspartate (NMDA) receptor antagonist. This medication works by altering the function of the neurotransmitter glutamate.
The final medication approved to treat dementia symptoms in people living with Alzheimer’s is Namzaric, a combination of donepezil and memantine. These drugs were introduced between 2000 and 2014.
In 2009, 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.
In 2021, the first medication designed to treat an underlying cause of Alzheimer’s disease was approved by the FDA. Aduhelm (aducanumab) removes beta-amyloid plaques and may slow disease progression in some cases.
Though the study of Alzheimer’s disease is only a century old, it is robust. The past two decades have seen research expand to study links between Alzheimer’s disease and heart disease, traumatic brain injury, and cholesterol levels in the brain.