MAPT and Alzheimer disease: It has been reported that exosomal amyloid peptides accumulate in the brain plaques of AD patients (Rajendran et al., 2006) and tau phosphorylated at Thr-181, an established biomarker for AD, is present at elevated levels in exosomes isolated from cerebrospinal fluid specimens of AD patients with mild symptoms (Saman et al., 2012).