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Objective: Schizophrenia is a one of multifactorial and complex disorders that arise from a combination of genetic and environmental factors. It has been well known that cannabis use is one of the environmental factors that increase the risk of psychotic disorder in individuals whom predisposed. Cathecol-O-Methyltransferase (COMT) enzyme plays an important role in dopamine metabolism. The functional polymorphism that causes a substation of Val by Met at codon 158 of the COMT protein has been shown in many studies to predispose the schizophrenia. In this study our aim was to investigate whether there is an interaction between premorbid cannabis use and COMT Val158Met polymorphism in the etiology of schizophrenia.
Method: Male schizophrenic patients with history of premorbid cannabis use (n=36) and non users (n=38) who had been followed in our service were recruited for the study. Clinical diagnoses were determined by SCID-I (The Structured Clinical Interview for DSM-IV-I). Patients were evaluated by sociodemographic form, PANSS (Positive and Negative Syndrome Scale), Calgary (The Calgary Depression Scale for Schizophrenia) and COMT enzyme Val158Met polymorphisms were defined from the isolated DNA of the patients by Polymerase Chain Reaction (PCR) and restriction Fragment Length Polymorphism (RFLP) analyses, as defined in literature.
Results: The main finding of the study was the statistically significant interaction with the carriers of COMT Val158Met Val/Val genotype (%88.9) and premorbid cannabis use in the etiology of schizophrenia. Val/Met+Met/Met carriers were less likely to develop schizophrenia with premorbid cannabis use. Schizophrenic patients with Val/Val genotype had statistically significant higher PANSS total scores than patients with Val/Met+Met/Met genotype and with Calgary as well.
Conclusion: The findings from this study confirm the association between COMT Val158 Met polymorphism and premorbid cannabis use in the cause of schizophrenia. Gene-environment interaction in terms of COMT Val158Met polymorphism and premorbid cannabis use plays an important role in schizophrenia and genetic polymorphism inşuences some clinical features as well.