Curious cases: Altered dose-response relationships in addiction genetics

Area of Science:

• Neuroscience
• Genetics
• Pharmacology

Background:

• Most addictive substances exhibit inverted U-shaped dose-response curves, producing both positive (reward, euphoria) and negative (aversion, dysphoria) effects.
• Current Diagnostic and Statistical Manual (DSM) diagnoses for substance dependence do not incorporate dose-response criteria or the balance of drug effects.
• Heritable factors significantly influence substance dependence, with genetic studies identifying modest effects at individual loci but stronger associations with gene clusters.

Purpose of the Study:

• To review recent findings on how altered dose-response relationships, influenced by genomic variation, contribute to addiction phenotypes.
• To highlight convergent evidence from human and mouse models supporting the role of dose-response dynamics in addiction.
• To emphasize the importance of considering individual differences in dose-response relationships for addiction nosology and treatment.

Main Methods:

• Review of human genetic studies (linkage and genome-wide association studies) identifying gene variants associated with substance dependence.
• Analysis of mouse models with altered gene expression or knockouts to investigate functional effects on drug responses.
• Integration of human and animal data to establish convergent evidence for specific gene-environment interactions in addiction.

Main Results:

• Convergent evidence from human and mouse models implicates altered dose-response relationships in mediating the effects of genomic variation on addiction.
• Specific genes, including those for α5 nicotinic acetylcholine receptor, cadherin 13, receptor type protein tyrosine phosphatase Δ, and neuronal cell adhesion molecule, show altered dose-response relationships in mouse models, supported by human data.
• These genetic variations influence both rewarding and aversive aspects of drug effects, contributing to addiction phenotypes.

Conclusions:

• Altered dose-response relationships are central to understanding the impact of genetic variation on addiction.
• Elucidating dose-response curves for both rewarding and aversive drug effects is crucial.
• Individual differences in dose-response relationships should be considered in addiction classification and therapeutic strategies.