Association of the OPRM1 A118G polymorphism and Pavlovian-to-instrumental transfer: Clinical relevance for alcohol dependence

Background: Pavlovian-to-instrumental transfer (PIT) quantifies the extent to which a stimulus that has been associated with reward or punishment alters operant behaviour. In alcohol dependence (AD), the PIT effect serves as a paradigmatic model of cue-induced relapse. Preclinical studies have suggested a critical role of the opioid system in modulating Pavlovian–instrumental interactions. The A118G polymorphism of the OPRM1 gene affects opioid receptor availability and function. Furthermore, this polymorphism interacts with cue-induced approach behaviour and is a potential biomarker for pharmacological treatment response in AD. In this study, we tested whether the OPRM1 polymorphism is associated with the PIT effect and relapse in AD. Methods: Using a PIT task, we examined three independent samples: young healthy subjects ( N = 161), detoxified alcohol-dependent patients ( N = 186) and age-matched healthy controls ( N = 105). We used data from a larger study designed to assess the role of learning mechanisms in the development and maintenance of AD. Subjects were genotyped for the A118G (rs1799971) polymorphism of the OPRM1 gene. Relapse was assessed after three months. Results: In all three samples, participants with the minor OPRM1 G-Allele (G+ carriers) showed increased expression of the PIT effect in the absence of learning differences. Relapse was not associated with the OPRM1 polymorphism. Instead, G+ carriers displaying increased PIT effects were particularly prone to relapse. Conclusion: These results support a role for the opioid system in incentive salience motivation. Furthermore, they inform a mechanistic model of aberrant salience processing and are in line with the pharmacological potential of opioid receptor targets in the treatment of AD.

High Frequency of the Opioid Receptor µ-1 (OPRM1) A118G Polymorphism, an Opioid Drug Therapy Related Gene, in the Indonesian Population

Background: The opioid receptor μ-1 (OPRM1) has become one of the most studied genes in pharmacogenetics, as this gene encodes the μ-opioid receptor (MOR), which plays a role in opioid drugs response, as well as in various disorders. One of its variants, A118G, which is found at a high frequency in the Asian population, has been associated with loss of sensitivity to and an increased requirement for analgesics in the treatment of pain, increased pain sensitivity, various types of substance dependencies, and the development of breast cancer. However, there are still limited reports about this gene polymorphism in the Indonesian population. Objective: The study aimed to determine the allele frequencies of the OPRM1 A118G polymorphism among the Indonesian population. Method: A cross-sectional study of 158 subjects, comprising 79 males and 79 females, was conducted among Indonesians, and genotype analysis was carried out by a modified allele-specific Polymerase Chain Reaction (PCR) method. Results: A frequency of 60.4% was found for the G allele among Indonesian samples, with a higher frequency being present in males (66.5%). The A allele was found at frequencies of 33.5% and 45.6% in males and females, respectively. A significant difference in allele frequency was found between males and females (p = 0.029, OR = 1.659, 95% CI [1.052–2.614]), while there was no significant difference in genotype frequencies between groups. Conclusion: A high prevalence of the OPRM1 A118G polymorphism was found in the Indonesian population, with the G allele frequency tending to be higher in males.