BDNF and Alzheimer disease: Serum BDNF levels increased in the early stages of AD, reflecting the compensatory mechanism of early neurodegeneration, while in time, they will decrease, correlating with the severity of AD because of trophic support lacking and increasing Aβ plaque accumulation contributing to specific progressive degeneration in the affected brain region. BDNF in both groups is not detected in CSF because its level is below the detection limit. Further investigation is needed to define BDNF as an AD clinical diagnosis marker and for therapeutic monitoring.