Alzheimer's disease

Alzheimer's disease is the most common cause of dementia — a slow, progressive brain disease that gradually erodes memory, thinking, and the ability to handle everyday life. It usually begins quietly, often after age 65, with small lapses: forgetting a recent conversation, misplacing things, struggling to find words. Over years it deepens, until a person may no longer recognize loved ones or care for themselves. Imagine a vast library where, year by year, the newest books vanish first and the shelves themselves slowly crumble — that captures the heartbreaking arc of the disease, which is not a normal part of aging but a specific illness that physically damages the brain.

Under the microscope, two abnormal protein clumps mark the disease. Sticky fragments of a protein called amyloid-beta build up between neurons (the brain's signaling cells) into clusters known as plaques, like litter piling up in the gaps of a city. Inside the neurons, a protein called tau — which normally acts as scaffolding that keeps the cell's internal transport tracks straight — twists into tangled knots called neurofibrillary tangles, so the tracks collapse and the cell starves. As plaques and tangles spread, synapses (the tiny junctions where neurons talk) are lost, the brain's immune cells stir up damaging inflammation, and whole regions wither. The damage typically starts in and around the hippocampus, the brain's memory-forming hub, which is why losing recent memories is so often the first sign.

There is no cure yet, but understanding the plaque-and-tangle story has shaped how doctors diagnose and treat it. Most older medicines only ease symptoms for a time by boosting the brain's remaining signaling chemicals, while newer antibody drugs aim to clear amyloid and modestly slow the decline in early stages. Researchers still debate exactly how amyloid, tau, inflammation, and other factors combine to drive the illness, and the search for treatments that truly halt it is one of the great open challenges of neuroscience.