What is amyloid and tau?

Amyloid plaques are clumps of a protein called beta-amyloid that collect between nerve cells and disrupt how they work. The National Institute on Aging says beta-amyloid forms when a larger protein, the amyloid precursor, breaks down, and the beta-amyloid 42 form is thought to be especially toxic. Along with tau tangles inside cells, plaques are a hallmark of Alzheimer's disease.

Not on its own. Amyloid plaques are a hallmark of Alzheimer's, but the National Institute on Aging notes that people can have amyloid plaques and never develop Alzheimer's symptoms. That is why doctors weigh an amyloid scan alongside other tests. A scan showing few or no plaques usually means Alzheimer's is not the cause of a person's memory or thinking problems.

Scientists are still working it out. The National Institute on Aging says Alzheimer's brain changes may come from a complex interplay between abnormal tau, beta-amyloid and other factors. When brain cells called microglia fail to clear away waste, including plaques, Alzheimer's can develop. Once beta-amyloid reaches a tipping point, tau appears to spread rapidly through the brain. Blood vessel problems may add to the damage.

Yes, for early Alzheimer's. The National Institute on Aging says lecanemab and donanemab are FDA approved drugs that target beta-amyloid to reduce plaques, and in studies they slowed cognitive decline in some people with early Alzheimer's or mild cognitive impairment over 18 months. They can cause swelling or bleeding in the brain, called ARIA, so doctors monitor with MRI scans.

Yes. The National Institute on Aging describes three ways to look for it. An amyloid PET scan shows plaque deposits in the brain. A spinal tap measures beta-amyloid 42 and tau in the fluid around the brain. And some doctors can now order a blood test for beta-amyloid, depending on availability. Results are considered together with other tests, not alone.