MAPT and Alzheimer disease: In this regard, CSF total-tau, phosphor-tau, Ab (1–40 or 1–42 form), total-tau/Ab ratio and phosphor-tau/Ab ratio have been some of the most widely used biomarkers aiding the diagnosis of Alzheimer’s disease and dementia, and high specificity and sensitivity can be achieved by combining different biomarkers (e.g., phosphor-tau/Ab ratio plus total tau) [125, 126].