With this in mind, the aim of this study was to investigate if polymorphisms in the HTR2A (rs9316233), HTR3A (rs1062613), HTR3B (rs1176744), SERT (5-HTTLPR) and COMT (rs4680) genes contribute to pain perception in TMD myalgia and if pain and psychosocial factors such as stress, anxiety and depression correlate. The gene discussed is COMT; the disease is major depressive disorder.