Plasma concentrations of tau phosphorylated at threonine 181 (p-tau181) correlate highly with CSF measures of p-tau181 and with PET measures of Aβ and tau pathology11, -, 15 and have been shown to distinguish between AD and other neurodegenerative disorders with high diagnostic accuracy comparable to that of CSF and PET-based measures of tau pathology.11, -, 13,16. This evidence concerns the gene MAPT and Alzheimer disease.