The relationship between cannabis and schizophrenia: a genetically informed perspective

Area of Science:

• Psychiatry
• Genetics
• Epidemiology

Background:

• Epidemiological studies suggest a link between heavy cannabis use and psychosis.
• Genetic models propose reverse causality from schizophrenia to cannabis use.
• Understanding the genetic relationship between cannabis use disorder (CUD) and schizophrenia (SCZ) is crucial.

Purpose of the Study:

• To estimate the genetic relationship between CUD and SCZ.
• To test for a causal association between CUD liability and SCZ liability.
• To adjust for the influence of tobacco smoking in this relationship.

Main Methods:

• Utilized summary statistics from large genome-wide association studies (GWAS).
• Employed genomic structural equation modeling and latent causal variable analysis.
• Conducted multivariable Mendelian randomization analyses.

Main Results:

• Genetic liability for CUD showed a significant association with SCZ (β=0.29, P=0.001).
• This association remained significant after adjusting for cannabis ever-use, tobacco smoking, and nicotine dependence.
• Mixed evidence for causality was observed, with latent causal variable analysis showing no causality but Mendelian randomization suggesting a risk-increasing effect (β=0.10, P=0.02).

Conclusions:

• Genetic liability for CUD is robustly associated with SCZ.
• The association is independent of tobacco smoking and cannabis ever-use.
• Evidence for a causal relationship between CUD and SCZ is mixed but warrants further investigation.