MAPT and Alzheimer disease: The accumulation of toxic proteins may include existence of extracellular amyloid-β (Aβ) plaques and intraneuronal neurofibrillary tau tangles in AD [113-115], aggregation of alpha-synuclein (α-syn) in nigrostriatal neurons in Parkinson's disease (PD) [116, 117], and accumulation of huntingtin protein in Huntington's disease (HD) [118, 119].