MAOA and major depressive disorder: The mammalian monoamine oxidases (MAOs) are FAD-containingenzymescomprising two isoforms, MAO-A and MAO-B, responsible for the catalyticoxidative deamination of endogenous and exogenous amines in centraland peripheral nervous systems.8 Theseisoforms have a slightly different conformation of cavity-shapingloop 210-216, which is ultimately responsible for their selectivityand sensitivity.9 MAO-A catalyzes serotonin10 and norepinephrine;11 its antagonists are treatment strategies for depression.