The pathological and clinical discoveries have led to propose several hypotheses of AD pathogenesis and thus, much effort has been devoted to design drugs painstakingly to target at etiological entities such as Aβ, tau proteins, neurotransmitter receptors, etc. In the meantime, some AD hypotheses have been realized to align in a pathological sequence to merge as a series of harmful cellular and neural events in a cascade and furthermore, to potentiate the pathological consequence in a vicious cycle by the presence of positive feedback loops. This evidence concerns the gene MAPT and Alzheimer disease.