S100A9 and Alzheimer disease: Recently, Gleerup et al. (2019) found that Aβ42 and tau protein could be candidates for salivary biomarkers of AD, and several proteins detectable in human saliva by proteomic approaches (Castagnola et al., 2012) have been investigated for their implication in AD, such as S100A7, S100A8, S100A9, and S100A12 (Cristóvão and Gomes, 2019) as well as cystatins C (Kaur and Levy, 2012) and B (Skerget et al., 2010).