MAPT and Alzheimer disease: First-generation tau tracers [18F]THK5351, [11C]PBB3 and [18F] flortaucipir all bind to the 3R + 4R combination of tau as in AD (Table 1; Chien et al., 2013; Maruyama et al., 2013; Okamura et al., 2013; Xia et al., 2013; Harada et al., 2016; Betthauser et al., 2017; Ono et al., 2017).