Original articleModeration of the Effect of Adolescent-Onset Cannabis Use on Adult Psychosis by a Functional Polymorphism in the Catechol-O-Methyltransferase Gene: Longitudinal Evidence of a Gene X Environment Interaction
Section snippets
Participants
Participants were members of the Dunedin Multidisciplinary Health and Development Study. The birth cohort of 1,037 children (52% male children) was established at age 3 when the investigators enrolled 91% of consecutive births between April 1972 and March 1973 in Dunedin, New Zealand. Cohort families represent the full range of socioeconomic status in the general population of New Zealand’s South Island. Follow-ups have been carried out at ages 3, 5, 7, 9, 11, 13, 15, 18, 21, and most recently
Results
Figure 1A shows the percentage of individuals meeting diagnostic criteria for schizophreniform disorder at age 26, as a function of COMT genotype and adolescent-onset cannabis use. In a hierarchical logistic regression model, the main effect of genotype was not significant, b = .05, SE = .27, z = .17, p = .87, the main effect of adolescent cannabis exposure was significant, b = 1.13, SE = .38, z = 2.96, p = .003, and the interaction between genotype and adolescent cannabis exposure was
Discussion
This study provides evidence that a functional polymorphism in the COMT gene interacted with adolescent-onset cannabis use to predict the emergence of adult psychosis. An alternative causal hypothesis must be considered. It is possible that preexisting early behavior or cognitive problems lead psychosis-prone carriers of the Val allele to take up cannabis use as teenagers. There was no main-effect risk for developing psychosis among carriers of the Val allele, however, and Val allele carriers
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