Importantly, despite evidence of Aβ neurotoxicity in vitro and in vivo animal models, studies in humans indicated that Aβ plaques and phospho tau neurofibrillary tangles are not exclusive to AD, and up to 30% of individuals in the normal aging population exhibit a similar amount of Aβ plaques in their brains as observed in typical AD cases (Iqbal, Liu, and Gong 2014; Gong, Liu, and Iqbal 2018). This evidence concerns the gene MAPT and Alzheimer disease.