Analysis of phosphorylated tau in blood has so far been focused on the development and validation of assays for p-T181 [182,246,250,251,252,253], demonstrating that increased plasma p-T181 (1) correlates with amyloid and tau PET measures [250,254,255], allowing the identification of individuals with Aβ pathology but tau PET-negative measurements [253], (2) goes in parallel with CSF p-T181 [182,255], and (3) can help in the differential diagnosis of non-AD types of dementias [253,254,255]. This evidence concerns the gene MAPT and Alzheimer disease.