MAPT and Alzheimer disease: Multiple biomarkers (such as Aβ42, tau, etc.)have been explored or used for clinical diagnosis of AD, and of these, S100β is a promising biomarker for BBB damage whose increase in serum indicates potential leakage of BBB (Marchi et al., 2003; Blennow and Zetterberg, 2018; Kadry et al., 2020).