MAPT and Alzheimer disease: We investigated cognition, 18F‐fluorodeoxyglucose positron emission tomography (PET), and cerebrospinal fluid tau phosphorylated at threonine 181 (pTau181)/Aβ42 plus α‐synuclein seeding amplification assays (SAA) in controls, 217 SAA‐negative AD (ADSAA−), and 124 SAA‐positive AD (ADSAA+).