Silent brain changes precede Alzheimer’s. Researchers have new clues about which come first

WASHINGTON (AP) — Alzheimer’s quietly ravages the brain long before symptoms appear and now scientists have new clues about the dominolike sequence of those changes — a potential window to one day intervene.

A large study in China tracked middle-aged and older adults for 20 years, using regular brain scans, spinal taps and other tests.

Compared to those who remained cognitively healthy, people who eventually developed the mind-robbing disease had higher levels of an Alzheimer’s-linked protein in their spinal fluid 18 years prior to diagnosis, researchers reported Wednesday. Then every few years afterward, the study detected another so-called biomarker of brewing trouble.

Scientists don’t know exactly how Alzheimer’s forms. One early hallmark is that sticky protein called beta-amyloid, which over time builds up into brain-clogging plaques. Amyloid alone isn’t enough to damage memory — plenty of healthy people’s brains harbor a lot of plaque. An abnormal tau protein that forms neuron-killing tangles is one of several co-conspirators.

The new research, published in the New England Journal of Medicine, offers a timeline for how those abnormalities pile up.

The study’s importance “cannot be overstated,” said Dr. Richard Mayeux, an Alzheimer’s specialist at Columbia University who wasn’t involved in the research.

“Knowledge of the timing of these physiological events is critical” for testing new ways of treating and maybe eventually even preventing Alzheimer’s, he wrote in an accompanying editorial.

The findings have no practical implications yet.

More than 6 million Americans, and millions more worldwide, have Alzheimer’s, the most common form of dementia. There’s no cure. But last year a drug named Leqembi became the first