Szczepankiewicz and colleagues investigated the possible relationship between polymorphisms in the four dopamine receptor genes (−48 A/G in DRD1, −141 C ins/del in DRD2, 9 Ser/Gly in DRD3, and −521 C/T in DRD4) and the comorbidity of alcohol abuse in bipolar patients. This evidence concerns the gene DRD4 and alcohol abuse.