A study by Desai et al. [36] demonstrated that an increased level of cholecystokinin (CCK) in brain-gut peptides increased anxiety and depression-like behavior and that this anxiety and depression led also to the abnormal secretion of brain-gut peptides (which is also one of the possible mechanisms of the vicious circle between emotional disorders and physical symptoms in patients with NERD). The gene discussed is CCK; the disease is major depressive disorder.