SLC6A4 and major depressive disorder: Previous research indicates that genes like sirtuin1(SIRT1), 5-hydroxytryptamine (5-HT), Brain-derived neurotrophic factor (BDNF), Catechol-O-methyltransferase (COMT), oxytocin receptor(OXTR), nuclear receptor subfamily three group C member 2(NR3C2), solute Carrier Family 6 Member 4(SLC6A4), and FKBP Prolyl Isomerase 5(FKBP5) are associated with depression.