Alcohol dependence is caused by environmental and genetic factors. Alcohol acts indirectly on the brain's reward center, mainly via the μ-opioid receptor, which is encoded by the OPRM1 gene. Our study aimed to investigate the cause-effect relationship between alcohol dependence and the expression of co-occurring psychiatric disorders, and the genotype distribution of polymorphisms in the OPRM1 gene in groups of acutely dependent subjects, abstinent subjects, and healthy controls. We were interested in whether subjects differed statistically between groups and in the expression of co-occurring disorders with regard to the distribution of genotypes in the rs1799971 and rs677830 polymorphisms. Since gene expression is precisely regulated through the miRNA molecule system, two polymorphisms of the miRNA molecule genes regulating OPRM1 gene expression were also included in the study. These are the rs1011784 polymorphism in the MIR23B gene and the rs2296616 polymorphism in the MIR107 gene. The corresponding questionnaires were used to assess the expression of co-occurring disorders. DNA samples were analyzed by KASP, followed by statistical analysis. We found that the T allele of rs677830 polymorphism increased the risk of alcohol dependence when partnership, age, education, and smoking were also taken into account. For the other polymorphisms, we did not observe any effect on the occurrence of alcohol dependence, but we did observe an effect on the expression of comorbid symptomatology. The G allele of the rs1799971 polymorphism was associated with a lower expression of hostility in the group of healthy controls. Heterozygotes for this polymorphism in the abstinent group had a higher expression of social anxiety. In the abstinent group, carriers of at least one T allele of the rs677830 polymorphism had a lower expression of social anxiety. The reference G allele of the rs1011784 polymorphism was associated with a higher expression of compulsive and anxious symptoms in acutely dependent patients. The polymorphism rs2296616 had the greatest impact on the expression of comorbid symptomatology, with carriers of at least one polymorphic A allele in the healthy control group having a higher expression of depressive and anxiety symptoms. In the abstinent group, anxiety was expressed more in those homozygous for the reference G allele. In the healthy controls group, carriers of at least one polymorphic A allele were more likely to consume alcoholic beverages, but the differences were statistically significant only in heterozygotes. These results could help us assess the risk of co-occurring disorders, which would increase the success rate of addiction treatment.
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