MAPT and Alzheimer disease: However, the role of tau protein in AD pathogenesis should be better understood with future research including investigation of the mechanisms/pathways regulating the degradation of tau as determined by its posttranslational state, studies on soluble, nonaggregated forms of tau as a primary AD agent, exploring the role of tau as an enhancer of Aβ-induced degeneration, and clarifying the mechanisms by which pathological forms of tau may negatively impact mitochondrial biology.