BDNF and major depressive disorder: A review examined the association between DNA methylation of seven candidate genes and depression, and found that brain-derived neurotropic factor (BDNF) and nuclear receptor subfamily 3 group C member 1 (NR3C1) gene methylation levels may be related to depression, whereas the relationship between serotonin transporter gene (SLC6A4; synonyms: 5-HTT and SERT) and depression was inconsistent11.