[Genetic polymorphisms commonly influencing efficacy of diverse addictive substances]

Opioids, such as morphine and fentanyl, are widely used as effective analgesics for the treatment of acute and chronic pain. In addition, the opioid system has a key role in the rewarding effects of morphine, ethanol, cocaine and various other drugs. The authors have focused on G-protein-activated inwardly rectifying potassium (GIRK) channel subunits, GIRK2 and GIRK3, that are important molecules in opioid transmission, and found that the single-nucleotide polymorphisms (SNPs) within the GIRK2 and GIRK3 gene regions were significantly associated with postoperative requirements of analgesics including opioids in patients who underwent abdominal surgery and mRNA expression of these genes in postmortem specimens, one of which was also associated with vulnerability to methamphetamine (METH) dependence. Further, by conducting a multistage genome-wide association study (GWAS) in healthy subjects, the authors found that genetic polymorphisms within a linkage disequilibrium block that spans 2q33.3-2q34 were strongly associated with the requirements for postoperative opioid analgesics after painful cosmetic surgery. The C allele of the best candidate SNP, rs2952768, was associated with more analgesic requirements, and consistent results were obtained in patients who underwent abdominal surgery. In addition, carriers of the C allele in this SNP exhibited less vulnerability to severe drug dependence in patients with methamphetamine dependence, alcohol dependence, and eating disorders and a lower 'Reward Dependence score on a personality questionnaire in healthy subjects. Furthermore, the C/C genotype of this SNP was significantly associated with the elevated expression of a neighboring gene, CREB1. The results show that SNPs in this locus are the most potent genetic factors associated with human opioid sensitivity known to date, affecting both the efficacy of opioid analgesics and liability to severe substance dependence. These outcomes provide valuable information for the personalized treatment of pain and drug dependence.