Alzheimer's disease

Alzheimer's disease is a progressive disorder of the brain that damages nerve cells and their connections. It is the most common cause of dementia, a term for cognitive impairment serious enough to interfere with daily life; dementia itself has other causes as well. The World Health Organization estimates that Alzheimer's contributes to roughly 60–70% of dementia cases worldwide. Unlike minor forgetfulness that may accompany ageing, Alzheimer's is a disease, and it is not an inevitable consequence of getting older.

The disease is associated with abnormal accumulations of amyloid beta and tau proteins, which form plaques and tangles, alongside the loss of neurons and the connections between them. These changes may begin years before noticeable symptoms, and scientists continue to investigate how they interact with other processes in the brain. Symptoms vary, but difficulties recalling recent events are common early on; changes in language, judgement, problem-solving or spatial skills may also appear. As the condition advances, cognitive changes can make conversation and independent daily activities increasingly difficult.

The biological causes are not fully known. For most people, risk likely reflects a combination of age-related changes in the brain and genetic, environmental and lifestyle influences; increasing age is a major risk factor, but younger-onset cases also occur. Rare inherited gene changes can cause Alzheimer's at younger ages, while most cases do not arise from one single gene. There is no single symptom or test that establishes the diagnosis on its own: clinicians assess medical history and changes in thinking, use cognitive tests, and may order laboratory tests or brain imaging to assess other explanations and support a diagnosis.

There is no cure, but care can address symptoms and support daily functioning. Some medicines may temporarily improve or stabilize memory and thinking for some people; newer treatments target amyloid and can slow decline in selected patients with early-stage disease. For example, the U.S. Food and Drug Administration granted traditional approval to lecanemab in 2023 for adults with Alzheimer's disease, based on a confirmatory trial. It is intended for people at the mild cognitive impairment or mild dementia stage studied in trials; treatment also carries risks, including amyloid-related imaging abnormalities and bleeding. Treatment decisions therefore require individualized clinical assessment. Practical support, planning and assistance for caregivers are also important as needs change.