MAPT and Alzheimer disease: Tau can be phosphorylated at multiple sites, and several of these sites have been investigated as biomarkers for AD (Ishiguro et al, 1999; Kohnken et al, 2000; Hu et al, 2002; Buerger et al, 2002b; Hampel et al, 2004; Singer et al, 2009; Meredith et al, 2013; Russell et al, 2016; Janelidze et al, 2020b).