Opioid and Dopamine Genes Interact to Predict Naltrexone Response in a Randomized Alcohol Use Disorder Clinical Trial

Background: While the opiate antagonist, naltrexone, is approved for Alcohol Use Disorder (AUD), not everyone benefits. This study evaluated whether the OPRM1 SNP rs1799971 interacts with the dopamine transporter gene DAT1/SLC6A3 VNTR rs28363170 or the catechol-o-methyltransferase (COMT) gene SNP rs4680 in predicting naltrexone response.

Methods: Individuals who met DSM-IV alcohol dependence were randomly assigned to naltrexone (50 mg/day) or placebo based on their OPRM1 genotype (75 G allele carriers and 77 A allele homozygotes) and also genotyped for DAT1 VNTR (9 vs 10 repeats) or COMT SNP (val/val vs. met carriers). Heavy drinking days (%HDD) were evaluated over 16 weeks and at the end of treatment. Effect sizes (d) for naltrexone response were calculated based on genotypes.

Results: Naltrexone, relative to placebo, significantly reduced %HDD among OPRM1 G carriers who also had DAT1 10/10 (p=0.021, d=0.72) or COMT val/val genotypes (p=0.05, d=0.80), and to a lesser degree in those OPRM1 A homozygotes who were also DAT1 9-repeat carriers (p=0.09, d=0.70) or COMT met carriers (p=0.03, d=0.63). All other genotype combinations showed no differential response to naltrexone. Diarrhea/abdominal pain was more prominent in OPRM1 A homozygotes who were also DAT 9 or COMT met carriers.

Conclusions: These results suggest that Individuals with AUD with a more opioid-responsive genotype (OPRM1 G carriers) respond better to naltrexone if they have genotypes indicating normal/less dopamine tone (DAT1 10,10 or COMT val,val), while those with a less responsive opioid-responsive genotype (OPRM1 A homozygotes) respond better to naltrexone if they have genotypes indicating greater dopamine tone (DAT1 9-repeat or COMT met carriers). These results could lead to more personalized AUD treatments.

Keywords: COMT; DAT1; OPRM1; Alcohol Treatment; Naltrexone; Pharmacogenetics.