Alzheimer's disease

Alzheimer's disease is a neurodegenerative condition and the leading cause of dementia, responsible for roughly 60 to 70 percent of cases. Its hallmark is a steady decline in cognitive abilities and daily functioning. Early signs often involve trouble recalling recent events, and as the illness progresses, symptoms may expand to include language difficulties, disorientation (such as getting lost easily), mood swings, loss of motivation, neglect of personal care, and behavioral changes. Over time, affected individuals tend to withdraw from family and social life. Eventually, bodily functions deteriorate, leading to death. After a dementia diagnosis, median survival ranges from three to twelve years. The presence of a movement disorder, called extrapyramidal signs, raises the risk of death by a factor of 1.6.

The underlying causes of Alzheimer's are still not well understood. A mix of environmental and genetic factors contributes to its development. The strongest known genetic risk factor is a variant of the apolipoprotein E gene, which codes for a protein involved in fat metabolism. Additional risk factors include a history of head injury, clinical depression, and high blood pressure. The disease's progression is largely marked by the buildup of abnormal protein deposits in the cerebral cortex—specifically, amyloid plaques and neurofibrillary tangles. These misfolded proteins disrupt normal cell function and, over time, cause irreversible damage to neurons and loss of synaptic connections in the brain. A probable diagnosis is made by reviewing the patient's history and conducting cognitive tests, along with medical imaging and blood tests to exclude other conditions. Early symptoms are often mistaken for typical aging. The only way to confirm Alzheimer's definitively is by examining brain tissue after death, but modern neuroimaging and fluid biomarkers now allow for a probable diagnosis while the person is still alive.

No treatments exist that can halt or reverse the disease's progression, though some may temporarily ease symptoms. A healthy diet, regular physical activity, and social engagement are generally beneficial in aging and may help lower the risk of cognitive decline and Alzheimer's. As the condition worsens, affected individuals become increasingly dependent on others, which often places a heavy burden on caregivers—socially, psychologically, physically, and financially. Exercise programs can improve daily living activities and potentially lead to better outcomes. For behavioral problems or psychosis linked to dementia, antipsychotic medications are sometimes used, but they carry an increased risk of early death.

As of 2020, about 50 million people worldwide had Alzheimer's disease. It most commonly begins after age 65, though up to 10 percent of cases are early-onset, affecting people in their 30s to mid-60s. Among those 65 and older, roughly 6 percent are affected, and women are more likely than men to develop it. The disease is named after German psychiatrist and pathologist Alois Alzheimer, who first described it in 1906. The financial toll on society is enormous, with global annual costs estimated at US$1 trillion. Alzheimer's and related dementias rank as the seventh leading cause of death worldwide.

Given the disease's widespread impact, many countries fund large-scale Alzheimer's research. For instance, the U.S. National Institutes of Health's National Plan to Address Alzheimer's Disease has a budget of US$3.98 billion for fiscal year 2026. In the European Union, the 2020 Horizon Europe research programme allocated over €570 million for dementia-related projects.

The course of Alzheimer's is typically described in three stages—early (mild), middle (moderate), and late (severe)—marked by a progressive pattern of cognitive and functional decline. The disease initially targets the hippocampus, a brain region linked to memory, which likely explains the earliest symptom of memory impairment. As the illness advances, memory loss worsens.

First symptoms are often mistaken for aging or stress. Detailed neuropsychological testing can detect mild cognitive difficulties up to eight years before a person meets the clinical criteria for an Alzheimer's diagnosis. These early signs can interfere with the most complex daily activities. The most noticeable problem is difficulty remembering recently learned facts and trouble absorbing new information. Subtle issues with executive functions—such as attention, planning, flexibility, and abstract thinking—or impairments in semantic memory (memory of meanings and concept relationships) may also appear early. Apathy and depression can occur at this stage, with apathy persisting as the most constant symptom throughout the disease. People who show objective cognitive impairment but not more severe symptoms may be diagnosed with mild cognitive impairment (MCI). When memory loss is the main feature of MCI, it is called amnestic MCI, which is often considered a prodromal or early phase of Alzheimer's. Amnestic MCI has a greater than 90 percent chance of being linked to Alzheimer's.

In the early stage of Alzheimer's, learning and memory problems become more pronounced. In a small number of cases, difficulties with language, executive functions, perception (agnosia), or movement execution (apraxia) are more prominent than memory issues. Not all types of memory are equally affected. Older personal memories (episodic memory), learned facts (semantic memory), and implicit memory—the body's knowledge of how to perform routine actions like using a fork or drinking from a glass—are less impaired.