RZ performed extraction of DNA and was responsible for genotyping analyses and drafting of the manuscript. AK selected polymorphisms of studied genes, AA performed haplotype analysis. AB generated the main idea of the study. AG was responsible for selection and diagnosis of schizophrenia patients, and the organization of interviews with diseased and healthy subjects. AS designed the primers for selected polymorphisms. MP created study's laboratory design. Statistical analysis was performed by FM, who together with RZ and MP interpreted the data. AB, FM and MP finalized the manuscript. All authors read and approved the manuscript.