Molecular genetic studies point to potential risk loci of psychotic depression shared with schizoaffective disorder (1q42, 22q11, 19p13), depression, bipolar disorder, and schizophrenia (6p, 8p22, 10p13-12, 10p14, 13q13-14, 13q32, 18p, 22q11-13) and several vulnerability genes possibly contributing to an increased risk of psychotic symptoms in depression (eg, BDNF, DBH, DTNBP1, DRD2, DRD4, GSK-3beta, MAO-A).
We firstly examined the SNPs in functional genomic regions, such as mRNA splicing, protein coding and the promoter regions in DRD2, DRD3 and DRD4, respectively, for association in 289 Han Chinese cases with schizophrenia and 367 healthy controls and then further analyzed the significantly associated single nucleotide polymorphisms (SNPs) with this disorder in an additional Han Chinese sample consisted of 1351 cases and 1640 control subjects.
No obvious interactions among the potential polymorphisms were found, which suggests that IL-10 and DRD4 confer vulnerability to schizophrenia independently.
This will include the (1) DRD4 gene associated with attentiondeficit/ hyperactivity disorder, located in a locus that underwent a positive selection; the (2) GABRB2 gene, a gene associated with schizophrenia and recently reported as the target of a positive selection; (3) MARK1, a candidate gene for autism that was reported as displaying a signature of adaptative evolution in the human lineage, and (4) the ADH and ALDH2 genes which are associated with alcoholism, and for which evidence of positive selection was identified in the human lineage since the divergence between humans and chimpanzees.
These observations strongly suggest that the -120-bp duplication polymorphism of DRD4 is associated with schizophrenia and that the -521 C/T polymorphism is associated with heroin addiction.
The long form variants of the uVNTR polymorphism in DRD4 were associated with schizophrenia, in a manner that was independent of the TP53 codon 72 polymorphism.
This study investigated whether single-nucleotide polymorphisms in the genes of dopamine receptors DRD1, DRD2, DRD3 and DRD4 are associated with antipsychotics-induced RLS in schizophrenia.
In this study, we investigated whether polymorphisms of the dopamine D4 receptor (DRD4) gene were associated with psychotic symptomatology rather than with a unique diagnosis such as schizophrenia.
To investigate the relationship between 48 bp variant number tandem repeat polymorphism in dopamine D4 receptor gene and response to clozapine in schizophrenic patients, the authors included 81 inpatients with a DSM-IV diagnosis of schizophrenia and patients meeting criteria for refractory to treatment were excluded.
In our sample of 814 patients comprising 114 with schizophrenia, 416 with bipolar affective disorder and 284 with unipolar affective disorder, we studied interactions between the tryptophan hydroxylase (TPH), the serotonin transporter (5-HTTLPR), and the dopamine receptor (DRD4) genes in relation to five major psychiatric symptomatology scores.
Meta-analyses of pooled ORs support association of schizophrenia to the Ser311Cys polymorphism in DRD2 and the T102C polymorphism in HTR2A, and of attention deficit hyperactivity disorder to the 48-bp repeat in DRD4.
Season of birth variations in tryptophan hydroxylase (TPH), the serotonin transporter (5-HTTLPR) and the dopamine D4 receptor (DRD4) gene polymorphisms are different for affective disorders and schizophrenia.
These data suggest that polymorphisms (-C616G, -C521T, and 48 bp repeat) at the DRD4 gene do not have a minor effect in the susceptibility to schizophrenia in our sample.
To address this issue, we studied the association of schizophrenia and polymorphisms including -616C>G, -603T>del, -602G>del, 600G>C, -521C>T, -376C>T and a 120 bp tandem duplication polymorphism (120 bp repeat) in 1.2 kb upstream from the initiation codon in the promoter region of the DRD4 gene with 210 schizophrenic cases and 206 healthy controls.
Studies in larger groups of adolescent schizophrenia patients are warranted to clarify the possible association between DRD4 exon III repeat alleles and the response to risperidone.
In addition, there was a significant association between the long form of DRD4 gene and schizophrenia in Caucasians, especially those with familial schizophrenia.