BDNF and mood disorder: In humans, the presence of a single nucleotide polymorphism (SNP) in the BDNF gene, leading to valine to methionine substitution at position 66 in the prodomain region of the BDNF protein (BDNF Val66Met) determines the reduction of cerebral BDNF levels [17], and it is related to mood disorders and neurodegenerative diseases [18].