Objective: To further investigate whether the functional polymorphisms of dopamine D2 receptor (DRD2) and dopamine D3 receptor (DRD3) genes associate with the development of tardive dyskinesia (TD) in schizophrenia, and whether the interactive effects of DRD2, DRD3, 5-hydroxytryptamine 2C receptor (HTR2C) and manganese superoxide dismutase (MnSOD) genes contribute to the severity of TD.
Methods: The patients with schizophrenia were assessed for TD by the Abnormal Involuntary Movement Scale (AIMS). Eventually, 42 schizophrenics with persistent TD were in the TD group, and 59 schizophrenics without TD were in the non-TD group. The polymorphism of each candidate gene was analyzed using a polymerase chain reaction-based restriction fragment length polymorphism analysis.
Results: The genotype distributions of the candidate genes in the groups were all consistent with the Hardy-Weinberg equilibrium. Allele frequencies for -759C/T and -697G/C polymorphisms in HTR2C gene showed a significant excess of -697 variant (P<0.05) in the patients with TD, compared against those in patients without TD. There were no differences in the distributions of the allelic frequencies and genotypes of Taq I. A polymorphism in DRD2 gene, of Ser/Gly polymorphism in DRD3 gene, and of Ala-9Val polymorphism in MnSOD gene between the TD group and non-TD group (P>0.05). Interestingly, as compared with the other joint allelic types, a significant excess of carrying both DRD3 variant allele (Gly) and MnSOD wild allele (Val) was found in the TD group (P<0.05). However, neither the allele and genotypes nor the clinical demographic characteristics contributed to the higher total AIMS scores in the patients of the TD group. There were no significant differences in any of the clinical demographic characteristics between the subgroups of any genotype in TD and non-TD groups.
Conclusion: The excess of -697 variant in the promoter regulation region of the HTR2C gene may be a risk factor for the susceptibility to the occurrence of TD in Chinese male patients with schizophrenia. A combination of DRD3 variant allele (Gly) and MnSOD wild allele (Val) may increase the susceptibility to the development of TD.