Although the etiology of schizophrenia seems to involve interactions between many genes, some of which code for proteins that regulate synaptic plasticity, notably the MMP-9 gene that has been widely studied in psychiatric disorders related to schizophrenia [42, 45], it should be acknowledged that polymorphism of complex interplay of the MMP-9 gene with the other genes and environmental risk factors could mediate cerebral toxoplasmosis, which contributes to a better explanation of the occurrence of schizophrenia. This evidence concerns the gene MMP9 and schizophrenia.