MAPT and Alzheimer disease: Dementia in elderly individuals is typically due to combinations of ageing-related brain pathologies which often, but not necessarily, include Alzheimer’s disease.1–3 Alzheimer’s disease is defined by the presence of both β-amyloid plaques and tau neurofibrillary tangles,4 which can be ascertained in vivo by PET imaging or biofluid biomarkers.5