WASHINGTON (AP) 鈥� Alzheimer鈥檚 quietly ravages the brain long before symptoms appear and now scientists have new clues about the dominolike sequence of those changes 鈥� 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鈥檛 know exactly how Alzheimer鈥檚 forms. One early hallmark is that sticky protein called beta-amyloid, which over time builds up into brain-clogging plaques. Amyloid alone isn鈥檛 enough to damage memory 鈥� plenty of healthy people鈥檚 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鈥檚 importance 鈥渃annot be overstated,鈥� said Dr. Richard Mayeux, an Alzheimer鈥檚 specialist at Columbia University who wasn鈥檛 involved in the research.
鈥淜nowledge of the timing of these physiological events is critical鈥� for testing new ways of treating and maybe eventually even preventing Alzheimer鈥檚, he wrote in an accompanying editorial.
The findings have no practical implications yet.
More than 6 million Americans, and millions more worldwide, have Alzheimer鈥檚, the most common form of dementia. There鈥檚 no cure. But last year became the first approved with clear evidence that it could slow the worsening of early Alzheimer鈥檚 鈥� albeit for a few months.
It works by clearing away some of that gunky amyloid protein. The approach also is being tested to see if it's possible to delay Alzheimer's onset if high-risk people are treated before symptoms appear. Still other drugs are being developed to target tau.
Tracking silent brain changes is key for such research. Scientists already knew that in that strike younger people, a toxic form of amyloid starts accumulating about two decades ahead of symptoms and at some point later tau kicks in.
The new findings show the order in which such biomarker changes occurred with more common old-age Alzheimer鈥檚.
Researchers with Beijing鈥檚 Innovation Center for Neurological Disorders compared 648 people eventually diagnosed with Alzheimer鈥檚 and an equal number who remained healthy. The amyloid finding in future Alzheimer's patients was the first, 18 years or 14 years prior to diagnosis depending on the test used.
Differences in tau were detected next, followed by a marker of trouble in how neurons communicate. A few years after that, differences in brain shrinkage and cognitive test scores between the two groups became apparent, the study found.
鈥淭he more we know about viable Alzheimer鈥檚 treatment targets and when to address them, the better and faster we will be able to develop new therapies and preventions,鈥� said Claire Sexton, the Alzheimer's Association's senior director of scientific programs. She noted that blood tests are coming soon that promise to also help by making it easier to track amyloid and tau.
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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute鈥檚 Science and Educational Media Group. The AP is solely responsible for all content.
Lauran Neergaard, The Associated Press
