DRD2 and mental disorder: Novel loci for IBS include interesting genes previously associated with depression and other mental disorders, such as RERE, that regulates retinoic acid signaling during development [44–46], PCLO, involved in synaptic vesicle trafficking, TMEM161B [47], a brain-expressed transmembrane protein [48], RBFOX1, a splicing regulator mainly expressed in neurons, that is one of the most pleiotropic genes among psychiatric disorders [49] or DRD2, encoding the dopamine receptor D2R and one of the strongest candidates for psychiatric disorders and traits [50].