Genetics of OUD
Genetic Contributions to Opioid Use Disorder
Opioid use disorder (OUD) has devastated communities across the United States, yet we still know remarkably little about why certain individuals are biologically predisposed to developing it. Human studies suggest that roughly half of OUD risk is inherited, but the specific genes involved remain largely unknown. Identifying them would open new avenues for predicting who is at risk and developing more targeted treatments.Ìý
In partnership with colleagues at the Institute for Behavioral Genetics and the University of Colorado Anschutz Medical Campus, we use a systems genetics approach to better understand the role of genetics in OUD. Unlike traditional single-strain research, our lab conducts longitudinal phenotyping across both sexes of across many genetically diverse inbred strains from the Hybrid Rat Divergence Panel (HRDP). Because rats within an inbred strain are genetically identical while rats across strains are unique, this panel provides a powerful, controlled model of genomic variation to track fine-grained behavioral and molecular trajectories.
Opioid Project & Core Discoveries
Our longitudinal phenotyping tracks multiple facets of the opioid use trajectory, including baseline pain sensitivity, oxycodone analgesia, analgesic tolerance, voluntary self-administration, and withdrawal phenotypes.Ìý
Our data demonstrates that genetic background and sex together account for a substantial proportion of variation in pain responses (Duffy et al., Genes, Brain and Behavior, 2024) and voluntary drug intake, yielding heritability estimates of 26–54% that mirror human clinical data (Duffy et al., Frontiers in Psychiatry, 2025). A key translational discovery is that rats experiencing the strongest initial pain relief from oxycodone are significantly more likely to escalate their drug use over time. This "analgesia-to-addiction" trajectory closely models observations in chronic pain patients, indicating that an individual's early analgesic response could serve as a critical predictive biomarker for OUD risk.Ìý
Through detailed behavioral profiling, we have mapped distinct oxycodone consumption patterns across different stages of the drug-taking trajectory. This mapping has allowed us to identify specific inbred rat strains that are highly vulnerable or uniquely resistant to oxycodone intake escalation. Several strains exhibit highly stable, controlled consumption patterns, offering a unique opportunity to uncover the cellular mechanisms driving OUD resistance. Conversely, other lines display severely dysregulated, compulsive intake patterns. These findings point to distinct, underlying genetic control mechanisms that govern drug intake behaviors across different phases of exposure.
To translate our behavioral profiling into targeted interventions, our research maps gene transcription across brain regions central to OUD pathology, including the nucleus accumbens, amygdala, and prefrontal cortex. By profiling which genes are turned "on" or "off" in vulnerable versus resistant brains, we generate extensive molecular datasets that isolate precise biological signatures of risk. We will leverage these transcriptional signatures to identify pharmacological compounds that reset the adverse molecular changes seen in vulnerable brains.
Our phenotype data revealed a striking divergence between sexes within specific genetic lines. This finding holds high translational value, as human epidemiological data indicate prominent differences between men and women that correspond with increased prevalence of OUD and overdose risk. In collaboration with colleagues at the BioFrontiers Institute, we are tracking how oxycodone exposure alters transcriptional activity within the nucleus accumbens. We suspect that distinct sex-specific patterns of transcriptional regulation directly drive differences in consumption behavior and escalation susceptibility.
We have recently extended our systems genetics program into the gut microbiome, examining the community of microorganisms in the digestive tract that influence central nervous system function. Our work shows that background genetics dictate substantial variation in baseline gut microbiome composition, with more than 50 bacterial groups differing significantly across rat strains. Furthermore, voluntary oxycodone self-administration produces distinct microbial shifts, altering 15 specific bacterial groups compared to control animals (Duffy et al. Scientific Reports, 2026).Ìý
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