OPRM1 and major depressive disorder: Other transcription factors that impact EGFR and OPRM1, such as specificity protein 1 (SP1), Yin Yang 1 (YY1), signal transducer and activator of transcription 1 (STAT1) and 3 (STAT3) and transcription factor proto-oncogene JUN (JUN), demonstrate the importance of neuronal plasticity and inflammation in the pathophysiology of MDD.