Methylation and expression quantitative trait loci rs1799971 in the OPRM1 gene and rs4654327 in the OPRD1 gene are associated with opioid use disorder

Opioid use disorder (OUD) is a chronic and relapsing brain disease that results in significant mortality worldwide. Genetic factors are estimated to contribute to 40%-60% of the liability, with polymorphisms of opioid receptor genes implicated in this disorder. However, the mechanisms underlying these associations are not yet fully understood. In the present study, we first examined the methylation levels in the promoter region of the OPRM1, OPRD1, and OPRK1 genes in 111 healthy controls (HCs) and 120 patients with OUD, and genotyped three tag SNPs in these genes. Correlations between these SNPs and the methylation levels of the CpG sites and expression levels of the genes were analyzed. After identifying the mQTLs and eQTLs, we determined the associations between the mQTLs/eQTLs and susceptibility to and characteristics of OUD in 930 HCs and 801 patients with OUD. Our results demonstrated that SNPs rs1799971 in the OPRM1 gene and rs4654327 in the OPRD1 gene were both mQTLs and eQTLs. We observed unique correlations between mQTLs and methylation levels of several CpG sites in the OUD group compared to the HC group. Interestingly, both the two mQTLs and eQTLs were associated with the susceptibility to OUD. In conclusion, we suppose that mQTLs and eQTLs in genes may underlie the associations between certain risk genetic polymorphisms and OUD. These mQTLs and eQTLs could potentially serve as promising biomarkers for better management of opioid misuse.