For example, patients with depression typically show increased expression levels of serotonin receptor subtype 1A (HTR1A), and treatment of depression most often involves the use of selective serotonin reuptake inhibitors (SSRIs) which block 5-HTT, thereby increasing the amount of available serotonin for neural signaling [1,3]. The gene discussed is SLC6A4; the disease is depressive symptom measurement.