MAPT and Alzheimer disease: Tau is one of the microtubule-associated proteins that regulate the stability of tubulin assemblies.27 Pathological hyperphosphorylation of tau is observed in AD brains, causing the accumulation of phosphorylated tau inside neuronal cells in the form of neurofibrillary tangles that eventually cause neuronal death.27–29 Hyperphosphorylated tau is cytotoxic.