MAPT and Alzheimer disease: Accumulation of neurofibrillary tangles because of hyperphosphorylated tau is a key pathological process in AD as well as in some other diseases of the nervous system such as frontotemporal degeneration and is referred to as “tauopathy.” Several studies have established that tau is a target of the UPP, and deficits in this pathway might play a role in the etiology of AD.