Since EVs can cross the blood–brain barrier and reach the blood, it was possible to identify several potential biomarkers in exosomes isolated from blood: increased levels of t-tau, p-tau, and Aβ42 in plasma/serum neurally derived blood exosomes were demonstrated to be an early marker for AD and cognitive decline progression (Fiandaca et al., 2015). This evidence concerns the gene MAPT and Alzheimer disease.