Linkage studies identified chromosomal regions on seven chromosomes harboring cannabis disorder risk genes, while candidate gene studies focused on CNR1, CB2, FAAH, and dopamine/GABA/opioid system genes.
Read this if you're curious about whether there are genes that make some people more susceptible to cannabis use problems.
Chromosomes 1, 3, 4, 9, 14, 17, and 18 harbor potential cannabis disorder risk genes
What the researchers found
This review synthesized the genetic research on cannabis use disorders, covering both linkage studies (mapping chromosomal regions) and candidate gene association studies.
Four linkage studies identified regions on chromosomes 1, 3, 4, 9, 14, 17, and 18. Notable candidates within these regions included MGLL (monoglyceride lipase, on chromosome 3) and a novel gene ELTD1 on chromosome 1.
Candidate gene studies examined two categories: cannabis-specific genes (CNR1/CB1 receptor, CB2, FAAH, MGLL, TRPV1, GPR55) and general addiction genes from dopamine (DRD2), GABA (GABRA2), and opioid (OPRM1) systems.
The review highlighted four major challenges: understanding biological complexity including gene-gene and gene-environment interactions; choosing between diagnostic and quantitative phenotypes; distinguishing which stage of cannabis involvement (use, misuse, dependence) genes influence; and problems of sample composition.
Why it matters
Understanding the genetic basis of cannabis use disorders could lead to better prediction of who is at risk and potentially targeted prevention strategies. The review mapped the landscape of genetic knowledge and identified critical research gaps.
The numbers in context
Regions on chromosomes 1, 3, 4, 9, 14, 17, and 18 identified. Cannabis-specific candidate genes: CNR1, CB2, FAAH, MGLL, TRPV1, GPR55. Non-specific candidates: GABRA2, DRD2, OPRM1.
How the study worked
Review of peer-reviewed linkage and candidate gene association studies related to cannabis use disorders, organized by study type and gene system.
What this study cannot tell us
Most candidate gene studies had small samples prone to false positives. Linkage studies identify broad regions, not specific genes. The review predated GWAS era. Gene-environment interaction studies were largely absent.
How to read the evidence
This is a comprehensive review of the pre-GWAS genetic literature, providing moderate evidence for genetic contributions to cannabis use disorders with acknowledged limitations.
When this study was published
Published in 2009. GWAS studies since then have identified specific genetic variants associated with cannabis use, confirming some candidate genes and identifying new ones.
The bigger picture
This review was published just before genome-wide association studies (GWAS) began providing much larger-scale genetic data on substance use disorders. Many of the candidate genes reviewed here have since been examined in GWAS, with some findings replicated and others not.
Questions still open
- Do cannabis-specific genes (like CNR1, FAAH) confer risk specifically for cannabis disorders or for addiction generally? How do genetic and environmental risk factors interact?
Common questions
Is there a "cannabis addiction gene"?
Can genetic testing predict cannabis addiction risk?
Read the original research
Candidate genes for cannabis use disorders: findings, challenges and directions.
Addiction (Abingdon, England), 104(4), 518-32
Citation
Agrawal, Arpana; Lynskey, Michael T. (2009). Candidate genes for cannabis use disorders: findings, challenges and directions.. Addiction (Abingdon, England), 104(4), 518-32. https://doi.org/10.1111/j.1360-0443.2009.02504.x
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