The test, which is not yet commercially available, focuses on a different form of the protein tau.

It wasn't that long ago that the only way to test for Alzheimer's disease was to perform an autopsy on someone who had been suffering from dementia to look for the telltale tangles of tau and amyloid proteins in the brain. While these tangles are not necessarily the cause of Alzheimer's disease, they are certainly its major hallmark; their sticky, clumping action in the brain is at least partly responsible for the cognitive decline that all Alzhimer's patients experience.