Further, BDNF serum levels are increased in preclinical stages of AD (Angelucci et al., 2010; Laske et al., 2011), when compensatory mechanisms are initiated in the attempt to prevent neuronal degeneration (Merlo et al., 2019), and in PBMCs derived from MCI patients, when exposed ex vivo to Aβ include CD4+ cells with higher levels of BDNF in comparison to PBMCs derived from AD patients (Baglio et al., 2013). This evidence concerns the gene BDNF and Alzheimer disease.