Abbreviations: DAs = dopamine agonists, DSM = Diagnostic and Statistical Manual of Mental Disorders, GD = gambling disorder, HAMD-17 = 17-item Hamilton Depression Rating Scale, ICD = International Classification of Diseases, MAO-B = monoamine oxidase type B, PD = Parkinson disease, PG = pathological gambling, UPDRS = Unified Parkinson Disease Rating Scale. This evidence concerns the gene MAOB and depressive disorder.