MAPT and Alzheimer disease: Recently, efforts have been made to develop a biological definition of AD using a combination of biomarkers that include Aβ proteinopathy, assessed from cerebrospinal fluid or plasma Aβ assays or amyloid PET imaging, and phosphorylated and secreted AD tau, assessed from cerebrospinal fluid or plasma assays for p-tau217, p-tau181, and p-tau231 (84).