MAPT and Alzheimer disease: Over the years, in vitro and in vivo studies have identified novel functions of tau in both normal physiology and disease, with reported roles in axonal transport, protein trafficking, cognitive function (Wang and Mandelkow, 2016) and interactions with proteins such as α-synuclein (the main component of Lewy Bodies (LBs) in PD; Lei et al., 2010) and amyloid-ß (Aß; the primary constituent of plaques found in AD; Bloom, 2014).