Addiction Risk: Genes Affecting Brain Reward Key, Not Just Substances
Most of the genetic risk for developing a substance use disorder stems not from genes directly influencing addiction, but from those governing impulse control, reward processing, and behavioral inhibition, according to a recent study led by Rutgers Health. The research, published in Nature Mental Health, analyzed genetic data from over 2.2 million individuals to map the complex interplay between genes and vulnerability to addiction.
Researchers, headed by Holly Poore, a faculty instructor of psychiatry at Rutgers Robert Wood Johnson Medical School, identified two primary genetic pathways contributing to substance use disorders: a broad “behavioral disinhibition” pathway and substance-specific pathways. The behavioral disinhibition pathway encompasses brain systems responsible for reward, self-control, and risk assessment. This pathway, researchers found, is not unique to addiction, but is likewise linked to conditions like attention-deficit/hyperactivity disorder (ADHD) and conduct problems.
“Most of the genetic predisposition to substance use disorders isn’t about how bodies respond to drugs; it’s about how brains are wired,” said Danielle Dick, director of the Rutgers Addiction Research Center and senior author of the study. “Those same genes show up across many outcomes – things like ADHD, conduct problems and other risky behaviors – and then layered on top of that are genes that are more specific to each substance.”
The study examined genetic links to alcohol, tobacco, cannabis, and opioid use disorders, alongside related traits like risk-taking and early substance initiation. By modeling these conditions together, the researchers were able to identify hundreds of genetic variants associated with broad externalizing behaviors, as well as genes more specific to individual substances. This approach, researchers say, allowed for a more comprehensive understanding of genetic influences than previous studies focusing on single disorders in isolation.
Traditionally, genetic research in this field has taken a siloed approach, with separate genome-wide association studies for each substance, according to Poore. “But substance use disorders almost never occur in isolation, and decades of twin and family studies have shown that they share a lot of their genetic roots with each other and with other externalizing conditions. By modeling that shared genetic architecture directly, we were able to discover more about both the broad and specific biological pathways that contribute to addiction.”
Researchers developed polygenic scores – combining thousands of genetic variants into a single measure of genetic liability – to assess risk. Broad externalizing polygenic scores proved effective in predicting vulnerability to multiple substance use disorders, while substance-specific scores offered more targeted insights into individual drug dependencies.
The genomic discoveries also prompted network and drug-target analyses, suggesting potential biological systems and existing medications that could be repurposed for treatment. The overlap between genes linked to the broad externalizing pathway and those implicated in other psychiatric disorders highlights a shared biological basis across conditions.
The study’s authors acknowledge limitations, noting that their analysis was primarily based on individuals of European ancestry. They emphasize the demand for more diverse genomic research to ensure findings are applicable and equitable across all populations.
“Addiction is incredibly complex, and this study shows just how important it is to look beyond any single substance or single gene,” Poore said. “By understanding the common genetic roots that link substance use disorders with other forms of behavioral disinhibition – as well as the pathways that are specific to alcohol, nicotine, cannabis or opioids – we can build a more complete picture of vulnerability and ultimately support better prevention, intervention and treatment strategies.”
The research involved an international collaboration with institutions including SUNY Downstate Health Sciences University, the University of California San Diego, Massachusetts General Hospital, and Vanderbilt University Medical Center.