MAPT and Alzheimer disease: Iron exists in two oxidation states: ferrous (Fe2+) (redox active) and (Fe3+) (redox-inert state); Fe3+ is associated with NFTs in AD and PSP (Smith et al., 1997; Pérez et al., 1998; Yamamoto et al., 2002) and can induce the aggregation of hyperphosphorylated tau.