Reference
Glossary – Alzheimer’s terms: what do they really mean?
Reference D · October 7, 2026 ·
A simple glossary of the most common terms related to Alzheimer’s—from amyloid and tau to p-tau217 and ApoE4.
When you’re diagnosed with Alzheimer’s, you soon encounter a new language. Amyloid, tau, p-tau217, ApoE4 and ARIA come up in research articles and conversations with doctors. Here is a simple glossary.
Amyloid
A protein that can build up between nerve cells in the brain in Alzheimer’s, forming what are known as amyloid plaques. The new drugs lecanemab and donanemab are designed to reduce amyloid in the brain.
Tau
A protein that normally helps stabilise the internal transport system of nerve cells. In Alzheimer’s, tau changes and can form tangles inside nerve cells. These changes in tau are clearly linked to disease progression and nerve cell damage.
p-tau217
A particular form of phosphorylated tau that can be measured in the blood. p-tau217 has become a very important biomarker because elevated levels can strongly suggest the underlying disease process of Alzheimer’s. In some situations, this blood test can reduce the need for more complex tests.
Biomarker
A biological measurement that provides information about what is happening in the body. In Alzheimer’s, biomarkers can be measured in blood and cerebrospinal fluid, or assessed using PET scans, among other methods.
PET
A type of brain scan that uses special tracers to look for, among other things, amyloid or tau in the brain.