MAPT and Alzheimer disease: Increased cerebral spinal fluid (CSF) and plasma levels of tau phospho-isoforms, such as p-tau181, p-tau217, and p-tau231, accurately predict amyloid-positivity by positron emission tomography (PET) and are robust biomarkers of AD status and severity [19, 45, 60, 65, 107], further supporting a link between Aβ and tau.