MAPT and Alzheimer disease: We cross‐sectionally assessed combinations of cerebrospinal fluid measures (CSF p‐tau181 and t‐tau) and 18F‐PI‐2620 tau‐positron emission tomography (PET) in patients with AD (n = 64), clinically suspected 4RTs (progressive supranuclear palsy or corticobasal syndrome, n = 82) and healthy controls (n = 19).