The reaffirmed capabilities for Aβ peptides to promote tau seeding and aggregation, and the cross-talk between the two basic lesions that define AD suggest a specific and plausible mechanism by which extracellular Aβ peptides initiate the neuro-destructive pathological cascade that is unique to AD and its unique classification as a ‘double prion disorder’ [12,26,27,28,29]. Here, MAPT is linked to Alzheimer disease.