MAPT and Alzheimer disease: Total tau protein is not altered in saliva of AD individuals (Lau et al., 2015; Ashton et al., 2018; Tvarijonaviciute et al., 2020) but more promisingly, the ratios of specific phosphorylated tau residues to total tau are reported to be significantly higher in AD saliva (Shi et al., 2011; Pekeles et al., 2019).