Toxoplasma gondii Seropositivity Interacts with Catechol- O -methyltransferase Val105/158Met Variation Increasing the Risk of Schizophrenia.

Schizophrenia is a heterogeneous and severe psychotic disorder. Epidemiological findings have suggested that the exposure to infectious agents such as Toxoplasma gondii ( T. gondii ) is associated with an increased risk for schizophrenia. On the other hand, there is evidence involving the catechol-O-methyltransferase ( COMT ) Val105/158Met polymorphism in the aetiology of schizophrenia since it alters the dopamine metabolism. A case-control study of 141 patients and 142 controls was conducted to analyse the polymorphism, the prevalence of anti- T. gondii IgG, and their interaction on the risk for schizophrenia. IgG were detected by ELISA, and genotyping was performed with TaqMan Real-Time PCR. Although no association was found between any COMT genotype and schizophrenia, we found a significant association between T. gondii seropositivity and the disorder (χ 2 = 11.71; p -value < 0.001). Furthermore, the risk for schizophrenia conferred by T. gondii was modified by the COMT genotype, with those who had been exposed to the infection showing a different risk compared to that of nonexposed ones depending on the COMT genotype (χ 2 for the interaction = 7.28, p -value = 0.007). This study provides evidence that the COMT genotype modifies the risk for schizophrenia conferred by T. gondii infection, with it being higher in those individuals with the Met/Met phenotype, intermediate in heterozygous, and lower in those with the Val/Val phenotype.