A new era of PET began with the discovery that the amyloid-β (Aβ) ligand 2-(1-(6-[(2-[18F]fluoroethyl) (methyl)amino]-2-naphthyl)ethylidene)malononitrile ([18F]FDDNP (Figure 1a)) presented off-target binding to tau aggregates in the brains of patients with AD [20]. This evidence concerns the gene MAPT and Alzheimer disease.