DRD2 and schizophrenia: Given the central role of the dopaminergic neurotransmitter system in the antipsychotic response, related genes have been widely investigated in studies on treatment response/resistance in schizophrenia, focusing in particular on gene variations encoding the dopamine D2 (DRD2) and D3 (DRD3) receptors (Arranz et al., 2011; Reynolds, 2012a; Brandl et al., 2014).