Advancing substance use disorder biology by studying underlying gene x environment interactions

Substance use disorders (SUDs) are heritable, complex genetic disorders associated with a growing list of genetic variants that are common in the population at large. These variants occur in noncoding genomic regions and are presumed to confer risk by altering the expression of one or more target genes; yet, by definition, SUD cannot occur without repeated exposures to drugs, cannabis, or alcohol. Moreover, there seem to be critical neurodevelopmental windows, both in utero and adolescence, during which drug exposure impacts the brain most. Deciphering the molecular mechanisms by which genetic variants confer risk not only for drug use vs. dependency, but also for specific susceptibility toward a particular drug of abuse, will inform our understanding of disease prevention and treatment. Yet, clinical studies in humans are deeply confounded by the co-occurrence of developmental exposures to drugs with high genetic risk, making it particularly challenging to resolve the causal direction of associations drawn. Towards resolving this uncertainty, this review outlines key advances in animal models, human genetics and genomics, and the potential of human stem cell models, describing their applications and potential future applications in the field of SUD research.