The relationship DRD3 Ser9Gly polymorphisms and cognitive functions in schizophrenia: A preliminary study

Abstract

Objective: Dopamine is a neurotransmitter that plays an important role in the etiopathogenesis of schizophrenia and cognitive functions. The aim of this study was to investigate the effects of the Ser9Gly polymorphisms of dopamine D3 receptor (DRD3) on clinical features and cognitive functions in schizophrenia. Methods: The subjects were comprised of 40 outpatients with schizophrenia fulfilling the DSM-IV criteria. Psychotic symptoms were assessed with Scale for the Assessment of Positive Symptoms (SAPS) and Scale for the Assessment of Negative Symptoms (SANS). The DRD3 Ser9Gly polymorphisms were genotyped as serine/serine (Ser/Ser), serine/glycine (Ser/Gly), glycine/glycine (Gly/Gly). Neuropsychological evaluation included Wisconsin Card Sorting Test (WCST), Stroop Test (ST), and Verbal Memory Processes Test (VMPT). Results: The mean age of patients was 37.84±12.68, mean education year was 10.33±3.42. It was determined that patients with DRD3 Ser/Ser genotype had higher SAPS scores than those withGly/Gly genotype. Thirty-eight patients completed the neuropsychological tests. The WCST conceptual response lev-els of patients with Ser/Ser genotype were lower than those of the patients with Ser/Gly genotype. The patients were grouped as Ser/Ser genotype carriers and glycine allele carriers. It was found that the patients with DRD3 Ser/Ser genotype had higher scores of SANS and SAPS (close to the level of statistical significance) in comparison to glycine allele carriers. Patients with Ser/Ser genotype had higher scores of errors and perseverative error, had lower scores of correct, number of completed categories, the percentage of conceptual level responses and number of conceptual level responses at WCST compared to those of the other group. There was no difference between groups regarding scores of ST and VMPT. Conclusion: The patients with DRD3 Ser/Ser genotype had more psychotic symptoms and executive dysfunctions than the glycine allele carriers. These results show that DRD3 Ser9Gly polymorphism may be related with psychotic symptom severity and executive functions.