MAPT and Alzheimer disease: Studies have indicated that gene expression in saliva-derived exosomes can be used as a biomarker for the diagnosis of mCTE and also demonstrated the existence of a variety of AD-related genes in mCTE patients (Cheng et al., 2019), moreover, exosomes containing Tau are not only a circulating biomarker of AD, they also exist as a biomarker of chronic traumatic encephalopathy after CTE (Ling et al., 2017; Manek et al., 2018).