The dopamine receptor 2 (DRD2), the ankyrin repeat and kinase domain containing 1 (ANKK1), and tetratricopeptide repeat domain 12 (TTC12) gene-cluster on chromosome 11q23 has been linked to nicotine(13, 18–20), alcohol(21), and opiate(22) dependencies indicating that genetic variation within this region might contribute to the shared liability between different types of addictions. DRD2 has a central role in modulating the dopamine reward system that mediates the reinforcing effect of all known addictive substances(23). In addition, polymorphisms within this region might influence personality characteristics such as novelty seeking(24) that are associated with increased vulnerability to different types of addictions(25). For DRD2, the majority of studies have focused on a polymorphism known as Taq1A (rs1800497), which has been eventually shown to map in the neighbouring ANKK1. Studies testing association between Taq1A and smoking have reported positive(26, 27) as well as negative results(28, 29).
