MAOA and major depressive disorder: At present, there are several types of antidepressants used in clinical practice, including tricyclic antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), selective reversible inhibitors of monoamine oxidase A (RIMAs), and specific serotonin–norepinephrine reuptake inhibitors (SNRIs)[5], however, these drugs can produce many side-effects, therefore, considerable efforts are being invested in the discovery of better drugs for the treatment of depression[6].