Because growing evidence has also demonstrated that the Val66Met variation in human BDNF, where a valine (Val) amino acid is replaced with a methionine (Met) amino acid at position 66 of the BDNF protein, is associated with susceptibility to mental disorders, including depression [51], differences in the neuronal function due to the Val66Met variation are very interesting. This evidence concerns the gene BDNF and depressive symptom measurement.