Tau (neurofibrillary tangles)

Tau is a protein that normally stabilizes the internal skeleton of your nerve cells, by binding to microtubules. In Alzheimer's and related 'tauopathies', it goes wrong. It gets over-phosphorylated, falls off the microtubules, and clumps into paired helical filaments. Those form insoluble 'neurofibrillary tangles' (NFTs) inside neurons. The Braak staging system (stages I to VI) tracks how NFTs spread, from the entorhinal cortex through the hippocampus to the wider cortex. And this spread matches cognitive severity more tightly than amyloid plaque does. Tau buildup is thought to jam axon transport, hurt synapses, and eventually drive neurodegeneration. That makes tau the leading candidate for the actual neurotoxic agent in Alzheimer's. Current models put amyloid upstream and tau downstream. Tau biomarkers, especially phospho-tau 181 and 217 in spinal fluid and blood, have become key diagnostic targets in the AT(N) framework.

Last reviewed: June 22, 2026

This definition is educational and is not medical advice, a diagnosis, or treatment. Talk to a doctor about any health decisions. Read our full medical disclaimer