BackgroundThe role of oxidative stress in schizophrenia has been demonstrated, particularly in subjects with treatment-resistant schizophrenia (TRS). In such patients, the decreased levels of antioxidants in conjunction with the increased generation of reactive oxygen species in the brain exposes the neurons to a higher risk of damage.Methods and findingsWe evaluated the association of deletion polymorphisms of two genes of the antioxidant Glutathione S-Transferase family, GSTT1 and GSTM1, with susceptibility to TRS. A total of 54 TRS patients (mean age 38.7 years) and 78 healthy control subjects (mean age 39.0 years) were enrolled in this study. The subjects were matched by sex, age, and smoking and alcohol consumption habits. In the case group, the frequencies of GSTT1-null and GSTM1-null genotypes were 24.1 and 51.9%, respectively, whereas for the control group, the frequencies were 12.8 and 46.2%, respectively. Analysis performed with respect to the risk of developing TRS associated with the GSTT1 and GSTM1 deletion polymorphisms, resulted in odds ratio (OR) values of 2.1 and 1.2, respectively. However, the association was not found to be significant (p = 0.1229 and p = 0.5916, respectively). The analysis performed with respect to the combined genotypes of GSTT1 and GSTM1 revealed that the double-null genotype confers a 4.6-fold increased risk of developing TRS (p = 0.0412).ConclusionThe results of the present study indicate that a combination of GST deficiencies may play a role in enhanced susceptibility to TRS, and the present genotype of one of these genes may buffer the deficiency caused by the lack (null genotype) of the other. The results suggest that combined deletion polymorphisms of GSTT1 and GSTM1 can have implications in the prediction of the clinical course of the disease.

Introduction: Clozapine (CLZ) is the gold standard drug for treatment-refractory schizophrenia (TRS). However, approximately 30% of patients partially respond to CLZ, defining this subset with super refractory schizophrenia (SRS). Alterations in enzyme activity may affect CLZ responses; the CYP3A4, CYP1A2 and CYP2C19 genes are primarily responsible for CLZ metabolism. Objective: The aim of this study was to assess if CYP2C19 variants were associated with TRS or SRS. Methods: CYP2C19*2 loss-of-function and CYP2C19*17 gain-of-function polymorphism genotype testing were performed in 108 individuals undergoing pharmacological treatment for TRS or SRS. DNA was extracted and polymorphisms were analyzed by polymerase chain reaction (PCR) and sequencing. Results: CYP2C19*17 had positive correlations with SRS and lower Brief Psychiatric Rating Scale (BPRS) scores for TRS. In addition, CYP2C19*2 was associated with lower CLZ dosages for TRS. Conclusion: These results show that CYP2C19*2 and CYP2C19*17 polymorphisms influence CLZ responses during schizophrenia treatment.

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Escitalopram (ESC), a selective serotonin reuptake inhibitor indicated for the treatment of depression and anxiety disorders, is primarily metabolized by cytochrome P450 (CYP) 2C19, which is a highly polymorphic enzyme known to cause inter-individual differences in pharmacokinetics. We hypothesized that CYP2C19 polymorphisms are associated with major depressive disorder (MDD) remission in patients treated with ESC in the long term. Thirty-one patients with MDD receiving chronic treatment with ESC monotherapy or combination therapy with other antidepressants (mirtazapine and bupropion), in naturalistic conditions, were included in the study. For comparison of genotype and phenotype frequencies, a group of 126 healthy subjects was also included. The CYP2C19*2, CYP2C19*3, and CYP2C19*17 polymorphisms were analyzed by RFLP-PCR genotyping. The CYP2C19 genotypes and phenotypes were similar in patient and healthy subject groups. Four phenotypes were found in the healthy subject group: ultra-rapid (UM; 28%), extensive (EM; 52%), intermediate (IM; 17%), and poor metabolizers (PM; 3%). The patient group showed the UM (22.5%), EM (55%), and IM (22.5%) phenotypes. The UM patients had significantly higher ESC doses than both EM and IM patients (20.7 AE 4.5, 15.7 AE 3.8, and 14.0 AE 3.3 mg/day, respectively; p ¼ 0.0041). Furthermore, all patients using ESC in combination with mirtazapine or bupropion antidepressants (ESC plus mirtazapine or bupropion) were UM metabolizers, suggesting that the *17 ultra-rapid allele seems to be the factor responsible for lower response to ESC, even at higher doses. The CYP2C19 UM phenotype is associated with higher ESC doses and antidepressant combinations for symptom remission in MDD patients.

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