MAPT and Alzheimer disease: In blood, N-p-tau181, N-p-tau217 and N-p-tau231 biomarkers (Fig. 1) are increased early in the Alzheimer’s disease continuum starting from the preclinical stage, and correlate well with CSF p-tau, t-tau, amyloid PET and tau PET.21,24–27 Similarly, a commercial Simoa t-tau assay (the most widely used blood t-tau biomarker) targeting N-terminal-to-mid-region epitopes is widely available.