5-HT is a representative monoamine neurotransmitter implicated in regulating several physiological activities and behaviors, including those related to emotion and anxiety, and low levels of 5-HT have turned out to be associated with depression (Pascucci et al., 2007; Taylor and Munafo, 2016; Wang et al., 2016). The gene discussed is HTR5A; the disease is depressive disorder.