Alzheimer's disease

Alzheimer's disease is a degenerative brain disorder and the leading cause of dementia, a decline in memory and thinking severe enough to disrupt daily life. It usually begins after age 65 and worsens over years. Its hallmarks, first described by the German physician Alois Alzheimer in 1906, are amyloid plaques, deposits of a protein fragment called beta-amyloid between neurons, and neurofibrillary tangles, twisted threads of the protein tau inside them. Neurons lose their synapses and die, and the brain shrinks.

The damage typically starts in the hippocampus and nearby entorhinal cortex, so difficulty retaining new information is often the first sign. Language, reasoning, orientation, behavior and self-care decline later. Most cases reflect a mix of aging, genes and other factors: the APOE e4 allele raises risk, rare inherited variants in APP, PSEN1 or PSEN2 cause an early-onset form, and people with Down syndrome, who carry an extra copy of APP, are at higher risk.

Diagnosis rests on the history, cognitive testing and ruling out other causes, increasingly backed by brain scans and amyloid or tau biomarkers in spinal fluid or blood. There is no cure. Some drugs ease symptoms for a time, and newer antibody drugs that clear amyloid can modestly slow decline in early disease.