MAPT and Alzheimer disease: Fortunately, several AD biomarkers have been successfully translated into plasma-based assays, including Aβ peptide ratios and tau phosphorylated at various residues (including threonine181, threonine217, and threonine231).27,28,29 Of these, phosphorylated tau217 (p-tau217) may have the best diagnostic accuracy for AD and strongest correlation with Aβ and tau PET30,31,32 and therefore may be useful in identifying AD as a primary etiology in CBS.