The influence on the schizophrenic symptoms by the DRD2Ser/Cys311 and −141C Ins/Del polymorphisms

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Abstract
The hyperactivity of dopaminergic systems is one of the major etiological hypotheses of schizophrenia. The major support for this hypothesis is that effective antipsychotic drugs bind to dopamine receptors and improve acute schizophrenic symptoms. For this reason, we investigated the allelic association between schizophrenia and polymorphisms of the DRD2 genes for the Ser/Cys311 and –141C Ins/Del. The subjects were 190 schizophrenics (120 males and 70 females) and 103 normal controls (53 males and 50 females). There were no significant differences between the patients and controls in the allele frequencies and the frequencies of the genotypes. We found no statistical association between schizophrenia and polymorphisms of the DRD2 genes for the Ser/Cys311 and –141C Ins/Del. These results indicate that the DRD2 gene may not develop schizophrenia. Next, we examined whether the genotypes influence the symptoms of schizophrenia the using Positive and Negative Symptom Scale scores. The Ser/Cys patients exhibited significantly lower positive and negative symptom scores than Ser/Ser patients. Patients with Del/Del, Ins/Del, or Ins/Ins showed higher positive symptom scores in descending order. This result suggested that the Del allele worsens the positive symptoms. We concluded that the DRD2 receptor gene may not influence the onset of schizophrenia, but there is a strong possibility that the Cys311 and –141C Del have a significant influence on the symptoms of schizophrenia.