BDNF and major depressive disorder: The rs6265, also known as Val66Met or G196A polymorphism of BDNF, can lead to in a valine-to-methionine substitution at codon residue 66.[14,15] The Met allele is related to less BDNF activity[16] and lower serum levels.[17] It also appears to be associated with memory impairments,[16,18] reduced hippocampal activity.[19] In addition, lower plasma BDNF levels have been reported in depression patients.[20,21] A small amount of the BDNF protein was also found in the post-mortem amygdala, hippocampus, anterior cingulate cortex as well as prefrontal cortex in patients with depression.[22–24]