MAPT and Alzheimer disease: In summary, the previous two sections illustrate (1) that cohorts of cognitively normal individuals can show Aβ and tau pathologies, implying amyloid deposition is not necessarily causal; (2) that other cohorts diagnosed as ‘non-AD’ dementias can exhibit amyloid plaques and tau tangles, implying these lesions are not unique to AD, and (3) Aβ-negative cohorts diagnosed clinically as AD dementia can instead exhibit other pathologies, indicating pathogenic pathways to AD dementia unrelated to amyloid.