MAPT and Alzheimer disease: AD neuropathological changes are detectable in the cerebrospinal fluid (CSF), where decreased levels of Aβ42 fragment (or the ratio Aβ42/40 [16]) reflecting amyloid pathology, increased levels of total-tau (t-tau) and phospho-tau (p-tau) protein, reflecting neuronal injury and tau pathology respectively, define an AD profile in living humans.