MAPT and Alzheimer disease: Moreover, the permeability of the blood–brain barrier has been reported to be increased with age in the hippocampus of healthy individuals (Montagne et al., 2015) and in AD (Rosenberg, 2014; van de Haar et al., 2016), suggesting that aged individuals with compromised blood–brain barrier might be more susceptible to passage of plasma tau proteins in the brain and potential seeding of a tau pathology.