Examination of new and reported data of the DRD3/MscI polymorphism: no support for the proposed association with schizophrenia

The dopamine D3 (DRD3) receptor gene has been implicated in the aetiology of schizophrenia as a candidate gene since it combines both the dopamine receptor and limbic hypotheses of the disease. Previous association studies of a DRD3/MscI polymorphism suggested an increased frequency of homozygosity at the DRD3 receptor gene in schizophrenia. Homozygosity appeared to be particularly frequent in male patients, individuals with family history of the disease and in good responders to neuroleptic treatment. Many studies have since examined this polymorphism and have altered or extended the original homozygosity hypothesis. In this study, we have investigated the distribution of the DRD3/MscI polymorphism in 198 Irish schizophrenic patients and 235 ethnically matched controls. Patients and controls showed similar allele and genotype frequencies. Furthermore, linkage analysis using two microsatellite markers flanking the DRD3 gene was performed on 265 Irish schizophrenic families, with substantially negative results. Our findings, in combination with a review of previous studies do not support a role for the DRD3/MscI polymorphism in the pathogenesis of schizophrenia.