MAPT and Alzheimer disease: In cell assays, AD- and PD-associated protein aggregates show similarities to prions in terms of (i) binding to or uptake by cells of Aβ [96], tau [28, 63] or α-synuclein aggregates [63, 91], (ii) seeding in or on cells of Aβ [96], tau [63, 80] or α-synuclein aggregates [54, 63, 91], and (iii) intercellular spread of tau [28] and α-synuclein deposition [34].