In serum, many studies have reported a reduction of BDNF levels in AD patients as compared to healthy subjects.87, 89, 92, 94, 95 In addition, patients with mild cognitive impairment (MCI) may also be characterized by decreased BDNF levels as compared to controls.87, 93 Furthermore, decreased levels of BDNF in MCI and AD patients seem to be associated with hippocampal structural changes and decrease in cognitive performance.87, 93, 96 Despite these evidences, there is still a lack of consensus about BDNF profile in AD patients. This evidence concerns the gene BDNF and Alzheimer disease.