MAPT and Alzheimer disease: Plasma pT217-tau in particular is revolutionizing the field, as it heralds future disease, and consistently discriminates AD from other neurodegenerative diseases, appears in the earliest presymptomatic stages of AD, and correlates strongly with premortem neuropathological tau burden (Barthelemy et al., 2020; Hansson et al., 2023; Janelidze et al., 2020; Mattsson-Carlgren et al., 2023; Olsson et al., 2016; Salvado et al., 2023).