Amyloid beta:

Watch this 2-Minute Neuroscience video to learn more about the role of amyloid beta in Alzheimer’s disease.

abnormally-folded protein that is normally present in the brain, and thus is thought to have some normal function (although what that might be is not yet understood), but which also displays a tendency to aggregate into insoluble clusters called amyloid plaques that are a characteristic of Alzheimer's disease.