Objective: Etiopathogenesis of schizophrenia (SCZ) involves several risk genes that induce inflammation, environmental stress factors and changes in the innate immune system. Patients with SCZ have the highest rate of cigarette smoking and severe nicotine dependence. Myeloperoxidase (MPO), a member of subfamily of peroxidases, is most abundantly expressed in immune cells. The aim of this study was to investigate the relationship between the MPO rs2333227 variant and SCZ/smoking etiopathogenesis.  
Method: The study included 54 patients with SCZ, 94 smokers and 92 healthy controls. MPO rs2333227 variant was genotyped by polymerase chain reaction- restriction fragment length polymorphism (PCR-RFLP) method. Odds ratio (OR) and 95% confidence interval (95%CI) were calculated using the χ2 test.  
Results: G/G and G/A genotypes of MPO rs2333227 were detected in our study samples. The frequencies of the G/G and G/A genotypes were 53.7%, 46.3%; 56.3%; 43.7%; 68.9%, 31.1% in SCZ patients, smokers, and the control group, respectively. The allele frequencies were G: 76.9% (SCZ patients), 77.4% (smokers) 83.7% (controls); A: 23.1% (SCZpatients),22.6% (smokers), and 16.3% (controls). There was no significant difference between the SCZ patients, smokers and controls regarding MPO rs2333227 variant either in terms of allele frequency or genotype frequency. Then we genotyped the groups as women and men. MPO rs2333227 variant genotype distribution did not differ between men and women (p>0.05).  
Conclusion: This study does not support the role of MPO rs2333227 variant in increasing genetic risk for SCZ/smoking in Turkish population.