MAPT and Alzheimer disease: CSF pathophysiological markers for AD include the beta-amyloid peptide 1–42 (Aβ42), which shows lower CSF levels the more the brain carries amyloid burden, total tau (t-tau), which directly reflects the intensity of neuronal degeneration, and phosphorylated tau (p-tau), which is believed to be a direct marker of tangle pathology (4).