MAPT and Alzheimer disease: AD is a complex age-related neurodegenerative disorder that is characterized by aberrant accumulation of the amyloid β (Aβ) protein and its precipitation in the senile plaques, formation of neurofibrillary tangles (composed of aggregates of microtubule-associated protein tau), cognitive disability, dementia, olfactory dysfunction, and the progressive loss of neuronal structure and function.