Association between schizophrenia and homozygosity at the dopamine D3 receptor gene

Ventral striatal islands of Calleja neurons bidirectionally mediate depression-like behaviors in mice

The ventral striatum is a reward center implicated in the pathophysiology of depression. It contains islands of Calleja, clusters of dopamine D3 receptor-expressing granule cells, predominantly in the olfactory tubercle (OT). These OT D3 neurons regulate self-grooming, a repetitive behavior manifested in affective disorders. Here we show that chronic restraint stress (CRS) induces robust depression-like behaviors in mice and decreases excitability of OT D3 neurons. Ablation or inhibition of these neurons leads to depression-like behaviors, whereas their activation ameliorates CRS-induced depression-like behaviors. Moreover, activation of OT D3 neurons has a rewarding effect, which diminishes when grooming is blocked. Finally, we propose a model that explains how OT D3 neurons may influence dopamine release via synaptic connections with OT spiny projection neurons (SPNs) that project to midbrain dopamine neurons. Our study reveals a crucial role of OT D3 neurons in bidirectionally mediating depression-like behaviors, suggesting a potential therapeutic target.

A single nucleotide polymorphism-based formula to predict the risk of propofol TCI concentration being over 4 µg mL-1 at the time of loss of consciousness

We aim to develop a formula based on single nucleotide polymorphisms (SNPs) to predict whether the propofol target-controlled infusion (TCI) concentration would be over 4 μg mL^-1 at the time of loss of consciousness (LOC). We recruited 184 patients undergoing thyroid or breast surgeries with propofol anaesthesia. A total of 48 SNPs of CYP2B6, CYP2C9, UGT1A9, HNF4A, ABCB1, ABCC4, ABCG2, GABRA2, GABRA4, GABRB1, GABRB3, GABRG2, GABBR2, GAD1, SLC1A3, BDNF, and NRXN1, previously associated with propofol metabolic and pharmacology pathway, were genotyped. The formula was developed in the training cohort using the least absolute shrinkage and selection operator logistic regression model, and then validated in the testing cohort. The SNPs, GABBR2 rs1167768, GABBR2 rs1571927, NRXN1 rs601010, BDNF rs2049046, GABRA4 rs1512135, UGT1A9 rs11692021, GABBR2 rs2808536, HNF4A rs1884613, GABRB3 rs2017247, and CYP2B6 rs3181842 were selected to construct the SNP-based formula, which was used to calculate the risk score for over 4 μg mL^-1 TCI concentration of propofol at the time of LOC. Patients in the high-risk group were more likely to require a propofol concentration higher than 4 μg mL^-1 and presented a longer LOC latency. The SNP-based formula may significantly improve the safety and effectiveness of propofol-induced anaesthesia.

No association between the Ser9Gly polymorphism of the dopamine receptor D3 gene and schizophrenia: a meta-analysis of family-based association studies

BACKGROUND

Previous studies found that Ser9Gly (rs6280) might be involved in the occurrence of schizophrenia. However, no consist conclusion has yet been achieved. Compared to the case-control study, the family-based study took into account stratification bias. Thus, we conducted a meta-analysis of family-based studies to measure a pooled effect size of the association between Ser9Gly and the risk of schizophrenia.

METHODS

The relevant family-based studies were screened using the electronic databases by the inclusion criteria. Odds ratios (ORs) and 95% confidence intervals (CIs) were used to measure the correction between Ser9Gly polymorphism and schizophrenia susceptibility. Subgroup analysis was performed by stratification of ethnicity (i.e., East Asian, Caucasian, and other populations). Additionally, publication bias was evaluated by the funnel plot.

RESULTS

After literature searching, a total of 13 family-based association studies were included, which contained 11 transmission disequilibrium test (TDT) studies with 1219 informative meiosis and 5 haplotype-based haplotype relative risk (HRR) studies. No statistical significance of the heterogeneity was detected in TDT and HRR studies. Thus, the pooled effect size was calculated under the fixed effect model. The results found that the association was significantly protective in East Asian in TDT studies (204 informative meiosis, OR = 0.744, 95% CI = 0.564-0.980, Z-value = - 2.104, p = 0.035).

CONCLUSIONS

The meta-analysis based on the family study found a protective association of Ser9Gly in East Asian. In future, large sample molecular epidemiology studies are needed to validate our findings.

Primrose syndrome: a phenotypic comparison of patients with a ZBTB20 missense variant versus a 3q13.31 microdeletion including ZBTB20

Primrose syndrome is characterized by variable intellectual deficiency, behavior disorders, facial features with macrocephaly, and a progressive phenotype with hearing loss and ectopic calcifications, distal muscle wasting, and contractures. In 2014, ZBTB20 variants were identified as responsible for this syndrome. Indeed, ZBTB20 plays an important role in cognition, memory, learning processes, and has a transcription repressive effect on numerous genes. A more severe phenotype was discussed in patients with missense single nucleotide variants than in those with large deletions. Here, we report on the clinical and molecular results of 14 patients: 6 carrying ZBTB20 missense SNVs, 1 carrying an early truncating indel, and 7 carrying 3q13.31 deletions, recruited through the AnDDI-Rares network. We compared their phenotypes and reviewed the data of the literature, in order to establish more powerful phenotype-genotype correlations. All 57 patients presented mild-to-severe ID and/or a psychomotor delay. Facial features were similar with macrocephaly, prominent forehead, downslanting palpebral fissures, ptosis, and large ears. Hearing loss was far more frequent in patients with missense SNVs (p = 0.002), ectopic calcification, progressive muscular wasting, and contractures were observed only in patients with missense SNVs (p nonsignificant). Corpus callosum dysgenesis (p = 0.00004), hypothyroidism (p = 0.047), and diabetes were also more frequent in this group. However, the median age was 9.4 years in patients with deletions and truncating variant compared with 15.1 years in those with missense SNVs. Longer follow-up will be necessary to determine whether the phenotype of patients with deletions is also progressive.

Association of rs4680 COMT, rs6280 DRD3, and rs7322347 5HT2A With Clinical Features of Youth-Onset Schizophrenia

We investigated the associations of rs4680 COMT, rs6280 DRD3, and rs7322347 5HT2A with youth-onset schizophrenia in the Russian population in a case-control study, and the role of the genotype in the severity of clinical features. The association between rs7322347 and schizophrenia (p = 0.0001) is described for the first time. Furthermore, we found a link with rs6280 and rs4680 in females (p = 0.001 and p = 0.02 respectively) and with rs7322347 in males (p = 0.002). Clinical symptoms were assessed on three scales: the Clinician-Rated Dimensions of Psychosis Symptom Severity scale, Positive and Negative Syndrome Scale, and Frontal Assessment Battery. Gender differences in clinical features are of particular interest. In our study we found gender differences in the severity of clinical features-higher scores for delusions (Positive and Negative Syndrome Scale and Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition) in males and higher scores for depression, delusions, somatic concern, motor retardation, poor attention were found in females.

Familial risks and genetic counselling for common psychiatric disorders

The main aim of genetic counselling is to inform about disorders that may have a genetic basis. The following definition is a helpful starting point:

No association between dopamine D3 receptor gene Ser9Gly polymorphism (rs6280) and risk of schizophrenia: an updated meta-analysis

OBJECTIVE

Ser9Gly (rs6280) is a functional single-nucleotide polymorphism (SNP) in the dopamine receptor D3 (DRD3) gene that may be associated with schizophrenia. We performed a meta-analysis to determine whether Ser9Gly influences the risk of schizophrenia and examined the relationship between the Ser9Gly SNP and the etiology of schizophrenia.

METHODS

Case-control studies were retrieved from literature databases in accordance with established inclusion criteria. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to evaluate the strength of the association between Ser9Gly and schizophrenia. Subgroup analysis and sensitivity analysis were also performed.

RESULTS

Seventy-three studies comprising 10,634 patients with schizophrenia (cases) and 11,258 controls were included in this meta-analysis. Summary results indicated no association between Ser9Gly and risk of schizophrenia. In the dominant genetic model, the pooled OR using a random effects model was 0.950 (95% CI, 0.847-1.064; P=0.374).

CONCLUSION

Results of this meta-analysis suggest that the Ser9Gly SNP is not associated with schizophrenia. These data provide possible avenues for future case-control studies related to schizophrenia.

History of the Concept of Disconnectivity in Schizophrenia

Nearly 60 years ago Seymour Kety proposed that research on genetics and brain pathology, but not on neurochemistry, would ultimately lead to an understanding of the pathophysiology of schizophrenia. This article will demonstrate the prescience of Kety's proposal; advances in our knowledge of brain structure and genetics have shaped our current understanding of the pathophysiology of schizophrenia. Brain-imaging techniques have shown that schizophrenia is associated with cortical atrophy and ventricular enlargement, which progresses for at least a decade after the onset of psychotic symptoms. Cortical atrophy correlates with negative symptoms and cognitive impairment, but not with psychotic symptoms, in schizophrenia. Studies with the Golgi-staining technique that illuminates the entire neuron indicate that cortical atrophy is due to reduced synaptic connectivity on the pyramidal neurons and not due to actual loss of neurons. Results of recent genetic studies indicate that several risk genes for schizophrenia are within two degrees of separation from the N-methy-D-aspartate receptor (NMDAR), a subtype of glutamate receptor that is critical to synapse formation and synaptic plasticity. Inactivation of one of these risk genes that encodes serine racemase, which synthesizes D-serine, an NMDAR co-agonist, reproduces the synaptic pathology of schizophrenia. Thus, widespread loss of cortical synaptic connectivity appears to be the primary pathology in schizophrenia that is driven by multiple risk genes that adversely affect synaptogenesis and synapse maintenance, as hypothesized by Kety.

Dopamine D3 receptor Ser9Gly and catechol-o-methyltransferase Val158Met polymorphisms and acute pain in sickle cell disease

BACKGROUND

Pain in sickle cell disease (SCD) is characterized by episodes of acute pain, primarily responsible for acute health care utilization, and persistent chronic pain. Pain severity and frequency vary significantly among patients with SCD. In this study, we investigated the possible contribution of monoamine gene polymorphisms to pain variation.

METHODS

Adult subjects with SCD completed PAINReportIt, a computerized McGill Pain Questionnaire, from which we calculated the Composite Pain Index. Utilization data were obtained from the medical record and biweekly telephone calls for 12 months. Utilization is defined as admissions to the emergency department and/or the acute care center resulting from a sickle cell pain crisis. We performed genotyping for catechol-O-methyltransferase (COMT) Val158Met (rs4680) and dopamine D3 receptor (DRD3) Ser9Gly (rs6280) polymorphisms, which were analyzed for associations with pain phenotypes.

RESULTS

Binary logistic models revealed that DRD3 Ser9Gly heterozygote patients were more likely not to have an acute pain crisis (odds ratio [OR] [95% confidence interval {CI}], 4.37 [1.39-22.89]; P = 0.020), which remained so when demographic variables were considered (OR [95% CI], 4.53 [1.41-28.58]; P = 0.016). COMT Val158Met Met allele showed lower probability for zero utilization (OR [95% CI], 0.32 [0.12-0.83]; P = 0.020) than the Val allele. In the negative binomial regression analysis, subjects with COMT Met/Met genotype had utilization incident rate ratio (95% CI) of 2.20 (1.21-3.99) over those with Val/Val (P = 0.010).

CONCLUSIONS

These exploratory findings suggest that DRD3 Ser9Gly and COMT Val158Met may contribute to pain heterogeneity in SCD, as suggested by the different rates of acute pain crisis. Specifically, SCD patients with the DRD3 homozygote genotypes, COMT 158 Met allele or Met/Met genotype, are more likely to have acute care utilization, an indicator of acute pain. These results, however, will need to be further examined in future large prospective studies.

Evaluating historical candidate genes for schizophrenia

Prior to the genome-wide association era, candidate gene studies were a major approach in schizophrenia genetics. In this invited review, we consider the current status of 25 historical candidate genes for schizophrenia (for example, COMT, DISC1, DTNBP1 and NRG1). The initial study for 24 of these genes explicitly evaluated common variant hypotheses about schizophrenia. Our evaluation included a meta-analysis of the candidate gene literature, incorporation of the results of the largest genomic study yet published for schizophrenia, ratings from informed researchers who have published on these genes, and ratings from 24 schizophrenia geneticists. On the basis of current empirical evidence and mostly consensual assessments of informed opinion, it appears that the historical candidate gene literature did not yield clear insights into the genetic basis of schizophrenia. A likely reason why historical candidate gene studies did not achieve their primary aims is inadequate statistical power. However, the considerable efforts embodied in these early studies unquestionably set the stage for current successes in genomic approaches to schizophrenia.

DRD3 gene rs6280 polymorphism may be associated with alcohol dependence overall and with Lesch type I alcohol dependence in Koreans

BACKGROUND

Several polymorphisms of the dopamine D3 receptor (DRD3) gene are reported to be involved in the susceptibility to alcoholism. Although the DRD3 rs6280 (Ser9Gly) polymorphism plays an important role in various psychiatric disorders, findings regarding the association between this single-nucleotide polymorphism (SNP) and alcohol dependence (AD) have been inconsistent. Therefore, the present study investigated the association between the DRD3 gene rs6280 polymorphism with AD and Lesch type I AD in Korean subjects.

METHODS

The DRD3 rs6280 SNP was genotyped in a case-control sample comprising 245 AD patients and 130 healthy controls (HCs). Alcohol Use Disorders Identification Test (AUDIT) scores were also compared relative to genotype in all of the participants.

RESULTS

This SNP was significantly associated with both AD overall (χ(2) = 10.09 and p = 0.001, and χ(2) = 10.60 and p = 0.005, for the recessive and additive models, respectively) and with Lesch type I AD (χ(2) = 11.70 and p = 0.001, and χ(2) = 11.70 and p = 0.003, for the recessive and additive models, respectively). The allele frequency differed significantly (χ(2) = 8.45, p = 0.004) between Lesch type I AD and HC subjects. The AUDIT total (F = 6.56, p = 0.011), hazardous alcohol use (F = 7.12, p = 0.008), dependence symptoms (F = 5.10, p = 0.025), and harmful alcohol use (F = 4.83, p = 0.029) scores were significantly higher in those who did not possess the S allele (genotype GG) than in those who did (genotypes SS ± SG).

CONCLUSIONS

The findings of this study suggest that the DRD3 rs6280 polymorphism is associated with the development of both AD overall and Lesch type I AD in Koreans.

The dopamine D3 receptor gene and posttraumatic stress disorder

The dopamine D3 receptor (DRD3) gene has been implicated in schizophrenia, autism, and substance use-disorders and is related to emotion reactivity, executive functioning, and stress-responding, processes impaired in posttraumatic stress disorder (PTSD). The aim of this candidate gene study was to evaluate DRD3 polymorphisms for association with PTSD. The discovery sample was trauma-exposed White, non-Hispanic U.S. veterans and their trauma-exposed intimate partners (N = 491); 60.3% met criteria for lifetime PTSD. The replication sample was 601 trauma-exposed African American participants living in Detroit, Michigan; 23.6% met criteria for lifetime PTSD. Genotyping was based on high-density bead chips. In the discovery sample, 4 single nucleotide polymorphisms (SNPs), rs2134655, rs201252087, rs4646996, and rs9868039, showed evidence of association with PTSD and withstood correction for multiple testing. The minor alleles were associated with reduced risk for PTSD (OR range = 0.59 to 0.69). In the replication sample, rs2251177, located 149 base pairs away from the most significant SNP in the discovery sample, was nominally associated with PTSD in men (OR = 0.32). Although the precise role of the D3 receptor in PTSD is not yet known, its role in executive functioning and emotional reactivity, and the sensitivity of the dopamine system to environmental stressors could potentially explain this association.

Recent developments in the genetics of schizophrenia

Objectives:To examine the evidence concerning the recent developments in the genetics of schizophrenia.

Methods:An extensive literature search was performed and relevant papers were examined and analysed.

Findings:There is overwhelming evidence that schizophrenia shows familial aggregation. Recent molecular genetic studies support the presence of susceptibility genes on chromosomes 6 and 22. In addition, an association between schizophrenia, the dopamine D3 receptor gene and the 5-HT2areceptor gene has also been demonstrated.

Conclusions:Recent advances in DNA technology have paved the way for the detection of genes of major and minor effects in the aetiology of schizophrenia. If the presence of the recently identified susceptibility genes is confirmed, it is likely that these genes will be recognised in the near future.

Functional proteomics, human genetics and cancer biology of GIPC family members

GIPC1, GIPC2 and GIPC3 consist of GIPC homology 1 (GH1) domain, PDZ domain and GH2 domain. The regions around the GH1 and GH2 domains of GIPC1 are involved in dimerization and interaction with myosin VI (MYO6), respectively. The PDZ domain of GIPC1 is involved in interactions with transmembrane proteins [IGF1R, NTRK1, ADRB1, DRD2, TGFβR3 (transforming growth factorβ receptor type III), SDC4, SEMA4C, LRP1, NRP1, GLUT1, integrin α5 and VANGL2], cytosolic signaling regulators (APPL1 and RGS19) and viral proteins (HBc and HPV-18 E6). GIPC1 is an adaptor protein with dimerizing ability that loads PDZ ligands as cargoes for MYO6-dependent endosomal trafficking. GIPC1 is required for cell-surface expression of IGF1R and TGFβR3. GIPC1 is also required for integrin recycling during cell migration, angiogenesis and cytokinesis. On early endosomes, GIPC1 assembles receptor tyrosine kinases (RTKs) and APPL1 for activation of PI3K-AKT signaling, and G protein-coupled receptors (GPCRs) and RGS19 for attenuation of inhibitory Gα signaling. GIPC1 upregulation in breast, ovarian and pancreatic cancers promotes tumor proliferation and invasion, whereas GIPC1 downregulation in cervical cancer with human papillomavirus type 18 infection leads to resistance to cytostatic transforming growth factorβ signaling. GIPC2 is downregulated in acute lymphocytic leukemia owing to epigenetic silencing, while Gipc2 is upregulated in estrogen-induced mammary tumors. Somatic mutations of GIPC2 occur in malignant melanoma, and colorectal and ovarian cancers. Germ-line mutations of the GIPC3 or MYO6 gene cause nonsyndromic hearing loss. As GIPC proteins are involved in trafficking, signaling and recycling of RTKs, GPCRs, integrins and other transmembrane proteins, dysregulation of GIPCs results in human pathologies, such as cancer and hereditary deafness.

The role of dopamine D(3) receptors in antipsychotic activity and cognitive functions

Dopamine D(3) receptors have a pre- and postsynaptic localization in brain stem nuclei, limbic parts of the striatum, and cortex. Their widespread influence on dopamine release, on dopaminergic function, and on several other neurotransmitters makes them attractive targets for therapeutic intervention. The signaling pathways of D(3) receptors are distinct from those of other members of the D(2)-like receptor family. There is increasing evidence that D(3) receptors can form heteromers with dopamine D(1), D(2), and probably other G-protein-coupled receptors. The functional consequences remain to be characterized in more detail but might open new interesting pharmacological insight and opportunities. In terms of behavioral function, D(3) receptors are involved in cognitive, social, and motor functions, as well as in filtering and sensitization processes. Although the role of D(3) receptor blockade for alleviating positive symptoms is still unsettled, selective D(3) receptor antagonism has therapeutic features for schizophrenia and beyond as demonstrated by several animal models: improved cognitive function, emotional processing, executive function, flexibility, and social behavior. D(3) receptor antagonism seems to contribute to atypicality of clinically used antipsychotics by reducing extrapyramidal motor symptoms; has no direct influence on prolactin release; and does not cause anhedonia, weight gain, or metabolic dysfunctions. Unfortunately, clinical data with new, selective D(3) antagonists are still incomplete; their cognitive effects have only been communicated in part. In vitro, virtually all clinically used antipsychotics are not D(2)-selective but also have affinity for D(3) receptors. The exact D(3) receptor occupancies achieved in patients, particularly in cortical areas, are largely unknown, mainly because only nonselective or agonist PET tracers are currently available. It is unlikely that a degree of D(3) receptor antagonism optimal for antipsychotic and cognitive function can be achieved with existing antipsychotics. Therefore, selective D(3) antagonism represents a promising mechanism still to be fully exploited for the treatment of schizophrenia, cognitive deficits in schizophrenia, and comorbid conditions such as substance abuse.

Association study between the rs165599 catechol-O-methyltransferase genetic polymorphism and schizophrenia in a Brazilian sample

Schizophrenia is a severe psychiatric disorder with frequent recurrent psychotic relapses and progressive functional impairment. It results from a poorly understood gene-environment interaction. The gene encoding catechol-O-methyltransferase (COMT) is a likely candidate for schizophrenia. Its rs165599 (A/G) polymorphism has been shown to be associated with alteration of COMT gene expression. Therefore, the present study aimed to investigate a possible association between schizophrenia and this polymorphism. The distribution of the alleles and genotypes of this polymorphism was investigated in a Brazilian sample of 245 patients and 834 controls. The genotypic frequencies were in Hardy-Weinberg equilibrium and no statistically significant differences were found between cases and controls when analyzed according to gender or schizophrenia subtypes. There was also no difference in homozygosis between cases and controls. Thus, in the sample studied, there was no evidence of any association between schizophrenia and rs165599 (A/G) polymorphism in the non-coding region 3' of the COMT gene.

Association study on pathological gambling and polymorphisms of dopamine D1, D2, D3, and D4 receptor genes in a Korean population

Several studies have reported that some dopaminergic receptor polymorphisms are associated with pathological gambling (PG). Considering that there are major race and ethnic group difference in dopaminergic polymorphisms, the result of genetic association studies should be confirmed in more homogeneous population to avoid problems of population stratification. The present study aimed to investigate whether selected polymorphisms in the dopamine receptors genes (DRD1, DRD2, DRD3, and DRD4) are associated with PG in Korean population which is consisted of only Korean ancestry. Subjects were 104 men with a diagnosis of PG and 114 unrelated age-matched normal control men. Genotyping was performed for the DRD1 gene -48 A/G, DRD2 gene TaqI A, DRD3 gene Ser9Gly, and DRD4 gene exon III variable number tandem repeat polymorphisms. The method of multifactor dimensionality reduction (MDR) was used to analyze gene-gene interactions. There were no differences in the frequencies of any studied polymorphisms between patients with PG and normal controls. MDR analysis did not show a significant effect of the 4 dopamine receptor gene polymorphisms on susceptibility to PG (P > 0.05). The present study suggests that the analyzed polymorphisms of the dopamine receptor genes might not be associated with PG in a Korean population.

Toward a modern search for schizophrenia genes

Genetic epidemiology has provided consistent evidence that schizophrenia has a genetic component It is now clear that this genetic component is complex and polygenic, with several genes interacting in epistasis. Although molecular studies have failed to identify any DNA variant that clearly contributes to vulnerability to schizophrenia, several regions have been implicated by linkage studies. To overcome the difficulties in the search for schizophrenia genes, it is necessary (i) to use methods of analysis that are appropriate for complex multifactorial disorders; (ii) to gather large enough clinical samples; and (iii) in the absence of genetic validity of the diagnostic classification currently used, to apply new strategies in order to better define the affected phenotypes. For this purpose, we describe here two strategies: (i) the candidate symptom approach, which concerns affected subjects and uses proband characteristics as the affected phenotype, such as age at onset, severity, and negative/positive symptoms; and (ii) the endophenotypic approach, which concerns unaffected relatives and has already provided positive findings with phenotypes, such as P50 inhibitory gating or eye-movement dysfunctions.

Converging evidence implicates the dopamine D3 receptor gene in vulnerability to schizophrenia

The dopamine D3 receptor has been implicated in the pathophysiology of schizophrenia (SZ). A glycine-to-serine polymorphism at codon 9 of the dopamine D3 receptor gene (DRD3), rs6280, has been widely studied for its association with SZ, but with conflicting results. Altered levels of DRD3 mRNA have also been reported in SZ compared with normal controls. Moreover, it has been suggested that DRD3 is subject to recent positive selection in European populations. To explore the potential role of DRD3 in SZ from these various aspects, we conducted a threefold study. First, we tested the genetic association of rs6280 with SZ in 685 SZ patients and 768 normal controls. Second, we examined DRD3 mRNA levels in peripheral leukocytes in a subset of 37 patients and 37 controls. Finally, we investigated the possible recent positive selection on DRD3 in an East Asian population. Consequently, we observed that the genotypic distribution of rs6280 was nominally associated with SZ (P = 0.045), with the ancestral CC genotype being significantly over-represented in SZ patients. DRD3 mRNA levels were significantly lower in patients than in controls (P = 5.91E-5). The derived C-allele of rs6280 might have been subject to recent positive selection (P < 0.001) in the East Asian population. Taken together, our results suggest that DRD3, a gene possibly under natural selection, might be involved in vulnerability to SZ in the Han Chinese population. These findings may further add to the body of data implicating DRD3 as a schizophrenia risk gene.

Genetic Association Analysis of Dopamine DRD3 Ser9Gly Polymorphism and Schizophrenia in Malay Population

BACKGROUND

Molecular components of the dopamine receptor (DRD3) play an important role in the pathophysiology of schizophrenia (SCZ). Previous studies have demonstrated an association between the DRD3 Ser9Gly polymorphism and SCZ but the results have been inconclusive.

METHOD

In this study, we investigated this controversial association between the Ser9Gly (A/G) polymorphism and SCZ using Malay cases-control (261 cases/157 controls) samples. PCR-RFLP was performed to genotype the distribution of the DRD3 Ser9Gly polymorphism.

RESULTS

Both healthy control and SCHZ patient groups were in of Hardy-Weinberg equilibrium for the analyzed genetic variability. There was a significant association between the genotype distribution DRD3 polymorphisms and SCZ (χ(2)= 9.359; df = 2; P = 0.009).

CONCLUSION

We believe that further studies are required to examine the association between others dopamine-related genes and the behavioral phenotypes of SCZ.

Comorbid obsessive-compulsive personality disorder in obsessive-compulsive disorder (OCD): a marker of severity

INTRODUCTION

Comorbid obsessive-compulsive personality disorder (OCPD) is well-described in obsessive-compulsive disorder (OCD). It remains unclear, however, whether OCPD in OCD represents a distinct subtype of OCD or whether it is simply a marker of severity in OCD.

MATERIALS AND METHODS

The aim of this study was to compare a large sample of OCD subjects (n=403) with and without OCPD on a range of demographic, clinical and genetic characteristics to evaluate whether comorbid OCPD in OCD represents a distinct subtype of OCD, or is a marker of severity.

RESULTS

Our findings suggest that OCD with and without OCPD are similar in terms of gender distribution and age at onset of OC symptoms. Compared to OCD-OCPD (n=267, 66%), those with OCD+OCPD (n=136, 34%) are more likely to present with the OC symptom dimensions which reflect the diagnostic criteria for OCPD (e.g., hoarding), and have significantly greater OCD severity, comorbidity, functional impairment, and poorer insight. Furthermore there are no differences in distribution of gene variants, or response to treatment in the two groups.

CONCLUSION

The majority of our findings suggest that in OCD, patients with OCPD do not have a highly distinctive phenomenological or genetic profile, but rather that OCPD represents a marker of severity.

Association study of BDNF and DRD3 genes in schizophrenia diagnosis using matched case-control and family based study designs

Schizophrenia (SCZ) is a severe neuropsychiatric disorder with prominent genetic etiologic factors. The dopamine receptor DRD3 gene is a strong candidate in genetic studies of SCZ because of the dopamine hypothesis of SCZ and the selective expression of D(3) in areas of the limbic system implicated in the disease. We examined 15 single-nucleotide polymorphisms (SNPs) in DRD3 in our sample of European origin consisting of 95 small nuclear SCZ families and 167 case-control pairs. We also examined four BDNF SNPs in our samples because of evidence for BDNF regulation of DRD3 expression (Guillin et al., 2001). We found a nominally significant genotypic association with rs7633291 and allelic association with rs1025398 alleles. However, these observations did not survive correction for multiple testing. We did not find a statistically significant association with the other DRD3 and BDNF polymorphisms. Taken together, the results from the present study suggest that BDNF and DRD3 may not be involved in SCZ susceptibility.

Genetic polymorphisms in the dopamine-2 receptor (DRD2), dopamine-3 receptor (DRD3), and dopamine transporter (SLC6A3) genes in schizophrenia: Data from an association study

OBJECTIVE

To investigate the association between dopaminergic polymorphisms [DRD2 -141C Ins/Del, DRD3 Ser9Gly, and SLC6A3 VNTR] and schizophrenia.

METHODS

Two hundred and eighty-eight outpatients with schizophrenia (DSM-IV criteria) [mean age (SD)=36.4 (12.4), 60.1% males] and 421 unrelated healthy controls [mean age (SD)=40.6 (11.3), 51.3% males] from a homogeneous Spanish Caucasian population were genotyped using standard methods.

RESULTS

There was a significant difference in genotype distribution for the DRD2 -141C Ins/Del polymorphism [(chi(2) (2)=12.35, corrected p=0.012]. The -141C Del allele was more common in patients than in controls [0.19 vs. 0.13; chi(2) (1)=9.14, corrected p=0.018, OR (95% CI)=1.57 (1.17-2.10)]. Genotype and allele distributions for DRD3 Ser9Gly and SLC6A3 VNTR polymorphisms were similar in both groups. However, there was tentative evidence of an interaction effect between DRD3 Ser9Gly and SLC6A3 VNTR [Wald=9.56 (4), p=0.049]. Compared to the SLC6A3 10/10 genotype category, the risk of schizophrenia was halved among those with 9/10 [OR=0.51 (95% CI=0.30-0.89), p=0.017]. This protective effect was only present in combination with DRD3 Ser/Ser genotype because of the significant interaction between 9/10 and both Ser/Gly [OR=2.45 (95% CI=1.16-5.17), p=0.019] and Gly/Gly [OR=3.80 (95% CI=1.24-11.63), p=0.019].

CONCLUSIONS

This study provides evidence that a genetic variant in the DRD2 gene and possible interaction between DRD3 and SLC6A3 genes are associated with schizophrenia. These findings warrant examination in replication studies.

Current perspectives on selective dopamine D(3) receptor antagonists as pharmacotherapeutics for addictions and related disorders

Repeated exposure to drugs of abuse produces long-term molecular and neurochemical changes that may explain the core features of addiction, such as the compulsive seeking and taking of the drug, as well as the risk of relapse. A growing number of new molecular and cellular targets of addictive drugs have been identified, and rapid advances are being made in relating those targets to specific behavioral phenotypes in animal models of addiction. In this context, the pattern of expression of the dopamine (DA) D(3) receptor in the rodent and human brain and changes in this pattern in response to drugs of abuse have contributed primarily to direct research efforts toward the development of selective DA D(3) receptor antagonists. Growing preclinical evidence indicates that these compounds may actually regulate the motivation to self-administer drugs and disrupt drug-associated cue-induced craving. This report will be divided into three parts. First, preclinical evidence in support of the efficacy of selective DA D(3) receptor antagonists in animal models of drug addiction will be reviewed. The effects of mixed DA D(2)/D(3) receptor antagonists will not be discussed here because most of these compounds have low selectivity at the D(3) versus D(2) receptor, and their efficacy profile is related primarily to functional antagonism at D(2) receptors and possibly interactions with other neurotransmitter systems. Second, major advances in medicinal chemistry for the identification and optimization of selective DA D(3) receptor antagonists and partial agonists will be analyzed. Third, translational research from preclinical efficacy studies to so-called proof-of-concept studies for drug addiction indications will be discussed.

The dopamine D3 receptor (DRD3) gene and risk of schizophrenia: case-control studies and an updated meta-analysis

The dopamine D3 receptor (DRD3) has been suggested to be involved in the pathophysiology of schizophrenia. DRD3 has been tested for an association with schizophrenia, but with conflicting results. A recent meta-analysis suggested that the haplotype T-T-T-G for the SNPs rs7631540-rs1486012-rs2134655-rs963468 may confer protection against schizophrenia. However, almost all previous studies of the association between DRD3 and schizophrenia have been performed using a relatively small sample size and a limited number of markers. To assess whether DRD3 is implicated in vulnerability to schizophrenia, we conducted case-control association studies and performed an updated meta-analysis. In the first population (595 patients and 598 controls), we examined 16 genotyped single nucleotide polymorphisms (SNPs), including tagging SNPs selected from the HapMap database and SNPs detected through resequencing, as well as 58 imputed SNPs that are not directly genotyped. To confirm the results obtained, we genotyped the SNPs rs7631540-rs1486012-rs2134655-rs963468 in a second, independent population (2126 patients and 2228 controls). We also performed an updated meta-analysis of the haplotype, combining the results obtained in five populations, with a total sample size of 7551. No supportive evidence was obtained for an association between DRD3 and schizophrenia in our Japanese subjects. Our updated meta-analysis also failed to confirm the existence of a protective haplotype. To draw a definitive conclusion, further studies using larger samples and sufficient markers should be carried out in various ethnic populations.

Neurobehavioral evidence for changes in dopamine system activity during adolescence

Human adolescence has been characterized by increases in risk-taking, emotional lability, and deficient patterns of behavioral regulation. These behaviors have often been attributed to changes in brain structure that occur during this developmental period, notably alterations in gray and white matter that impact synaptic architecture in frontal, limbic, and striatal regions. In this review, we provide a rationale for considering that these behaviors may be due to changes in dopamine system activity, particularly overactivity, during adolescence relative to either childhood or adulthood. This rationale relies on animal data due to limitations in assessing neurochemical activity more directly in juveniles. Accordingly, we also present a strategy that incorporates molecular genetic techniques to infer the status of the underlying tone of the dopamine system across developmental groups. Implications for the understanding of adolescent behavioral development are discussed.

Correlates of response to Olanzapine in a North Indian Schizophrenia sample

Olanzapine is widely used for the treatment of schizophrenia and is considered a first line medication in India. Along with other factors, the variation in response and side effects to this agent may be accounted for by genetic differences among patients. Olanzapine was administered for 6 weeks to Indian subjects with schizophrenia or schizoaffective disorder (DSM-IV, n=130), as part of an open label study. Intent-to-treat analysis was performed, and 10 polymorphic markers from seven genes (dopamine D1, D2, D3 and D4 receptors, serotonin 2A receptor and the drug-metabolizing enzymes (CYP1A2 and CYP2D6)), together with demographic and clinical variables, were analyzed as potential predictors of response. Olanzapine was efficacious, but significant weight gain was noted. Baseline weight and a 120 bp deletion polymorphism at the dopamine receptor D4 (DRD4) gene were associated with changes in symptom scores. Predictable covariates of treatment response were also noted. These results merit replicate studies.

A functional polymorphism, rs6280, in DRD3 is significantly associated with nicotine dependence in European-American smokers

Nicotine enhances reward functions in the mesocorticolimbic dopamine system in general and the nucleus accumbens in particular. The genes encoding dopamine receptors are thus plausible candidates for involvement in nicotine dependence (ND). We investigated 13 single nucleotide polymorphisms (SNPs) spanning a region of the dopamine D(3) receptor gene (DRD3) to determine whether DRD3 is associated with ND. We studied a set of 2,037 subjects in 602 nuclear families representing two distinct American populations using three ND measures, namely, smoking quantity (SQ), the Heaviness of Smoking Index (HSI), and the Fagerström Test for ND (FTND). In the family based association study, we found that SNP rs6280 showed a strong association with ND in European-Americans (EAs) and the pooled sample, whereas SNPs rs1486012 and rs963468 had weak associations with ND in African-Americans (AAs) and the pooled sample. Further haplotype analysis with all contiguous 3-SNP groups revealed relatively weak evidence for association of DRD3 with ND in the EA and pooled samples. The results indicate that DRD3 is significantly associated with ND in EAs, and that rs6280, a functional polymorphism causing an amino acid change of serine to glycine (Ser9Gly) in the N-terminal extracellular domain of the D(3) receptor, likely is causative of the association between DRD3 and ND.

Reappraisal of the role of the DRD3 gene in essential tremor

OBJECTIVES

Analyze the distribution of polymorphism in the dopamine receptor D3 (DRD3) gene, which was previously reported as a susceptibility risk for essential tremor (ET), in a large cohort of ET.

METHODS

The role of 312G>A DRD3 polymorphism was analyzed using linkage analysis, association study and transmission disequilibrium test in a group of 433 ET patients, and two unrelated control groups with 121 and 151 individuals.

RESULTS

Allelic frequencies of glycine and serine forms of the DRD3 gene did not differ between patients and both control groups, and were in Hardy-Weinberg equilibrium. Linkage analysis identified obligatory recombinants in every large pedigree, even in those with relatively high frequency of glycine allele, thus excluding the linkage to this locus. Both alleles were transmitted with an equal likelihood to affected offspring. We also failed to replicate the relationship between glycine homozygosity and an earlier age of onset or more severe tremor course.

CONCLUSIONS

Our comprehensive genetic analysis in a large ET cohort strongly argues against the role of the DRD3 gene in ET pathogenesis.

Dopamine receptor D3 genotype association with greater acute positive symptom remission with olanzapine therapy in predominately caucasian patients with chronic schizophrenia or schizoaffective disorder

OBJECTIVE

To test association of dopamine receptor D3 (DRD-3) gene polymorphisms with olanzapine response in genetic samples from a registration phase clinical trial.

METHODS

Eighty-eight acutely ill patients with schizophrenia or schizoaffective disorder were genotyped for ser-9-gly (rs6280) and 23 other polymorphisms within the DRD-3 gene. Allelic association of clinical response (mean baseline- to-endpoint reduction in Positive and Negative Syndrome Scale [PANSS] total and subscores) over 6 weeks of olanzapine treatment was assessed using repeated measures analysis of variance.

RESULTS

Ser-9-gly genotypes were associated with differences in PANSS total score improvement from baseline to 6 weeks (p = 0.021). This association was most notable for improvement in positive symptoms (p = 0.0001), with patients with gly/gly genotype significantly more responsive. More patients with the gly/gly genotype had greater positive symptom remission (endpoint rating of minimal or none on all PANSS positive items, 39.1%) compared with patients with gly/ser and ser/ser genotypes (13.8%; p = 0.033). DRD-3 polymorphisms in disequilibrium with ser-9-gly were also significantly associated with greater positive symptom improvement (p = 0.0009-0.021), and one not in complete linkage disequilibrium, with lesser improvement (p = 0.027).

CONCLUSIONS

Gly/gly DRD-3 genotype predicted statistically and clinically significantly better acute positive symptom reduction compared with other ser-9-gly genotypes in patients treated with olanzapine.

The Ser9Gly polymorphism of the dopamine D3 receptor gene and risk of schizophrenia: an association study and a large meta-analysis

Dopamine D3 receptor (DRD3) binds antipsychotic drugs and is abundant in the limbic system of the brain. It has been shown to play important roles in schizophrenia. A number of studies investigated the Ser9Gly polymorphism of the DRD3 gene to test its possible association with schizophrenia; however, the results were inconsistent. Our study aims to further evaluate the possible association between the Ser9Gly polymorphism and schizophrenia using a case-control association study within the Han Chinese population as well as a meta-analysis covering all previous studies. Our study, based on 329 schizophrenic patients and 288 controls, found no significant difference in the genotype or allele distributions of Ser9Gly polymorphism, the meta-analysis showed that the Ser9Gly polymorphism was not associated with Schizophrenia. Our study does not support the contention that the Ser9Gly polymorphism of the DRD3 gene plays a major role in schizophrenia in the Chinese population.

No association between the DRD3 Ser9Gly polymorphism and schizophrenia

OBJECTIVE

To investigate the association between a Ser9Gly polymorphism of the dopamine D3 receptor gene (DRD3) and schizophrenia.

METHODS

408 schizophrenic patients and 172 control subjects were compared with regard to their DRD3 Ser9Gly genotypic and allelic frequencies. In addition, we carried out a family-based association study including 183 pedigrees (472 subjects) using the transmission disequilibrium test (TDT).

RESULTS

No significant differences of genotype or homozygosity distribution were identified between patients and controls. When patients were stratified according to gender, response to treatment, age at onset, no significant differences were observed. Neither allele A (Ser), or G (Gly) were preferentially transmitted from parents to affected offspring.

CONCLUSION

The hypothesis that the DRD3 Ser9Gly polymorphism plays a predisposing role in schizophrenia is not supported by this study.

Could HTR2A T102C and DRD3 Ser9Gly predict clinical improvement in patients with acutely exacerbated schizophrenia? Results from treatment responses to risperidone in a naturalistic setting

OBJECTIVE

This study seeks to replicate previous results indicating that T102C in the serotonin 2A receptor (HTR2A) and Ser9Gly in the dopamine D3 receptor (DRD3) were associated with a risperidone response to acutely exacerbated schizophrenia, and to determine whether possession of these alleles predicts clinical improvement in a naturalistic setting.

METHODS

We consecutively recruited 100 schizophrenia patients and assessed clinical improvement after 4 weeks of risperidone treatment.

RESULTS

The patients with T/T in the HTR2A gene showed less clinical improvement than did those with T/C or C/C (p = 0.044). In the case of the DRD3 gene, we did not find statically significant association with clinical improvement (p = 0.061). When patients were categorized into responders and nonresponders, the C allele was more frequent in responders (OR = 2.28, 95%CI = 1.06-4.91, p = 0.039). When combinations of the two polymorphisms were considered, patients who had T/T in the HTR2A gene and encoded Ser/Ser or Ser/Gly from DRD3 gene had a higher propensity to non-responsiveness compared to other subjects (OR = 3.57, 95%CI = 1.10-11.62, p = 0.039).

CONCLUSIONS

Our findings suggest that the HTR2A T102C could be a potential indicator of clinical improvement after risperidone treatment.

Dopamine genes and pathological gambling in discordant sib-pairs

Pathological gambling (PG) is an impulse control disorder that has been considered as a behavioral addiction. Recent studies have suggested the involvement of the dopaminergic system in addictions and impulse control disorders and associations of dopamine receptor genes (DRD1, DRD2, and DRD4) and PG have been reported. In the present study, 140 sib-pairs discordant for the diagnosis of PG (70 males and 70 females on each group) were recruited through the Gambling Outpatient Unit at the Institute of Psychiatry, University of Sao Paulo and were assessed by trained psychiatrists. A family-based association design was chosen to prevent population stratification. All subjects were genotyped for dopamine receptor genes (DRD1 -800 T/C, DRD2 TaqIA RFLP, DRD3 Ser9Gly, DRD4 48bp exon III VNTR, DRD5 (CA) repeat) and the dopamine transporter gene (SCL6A3 40 bp VNTR). Our results suggest the association of PG with DRD1 -800 T/C allele T (P = .03).

No association between the Ser9Gly polymorphism of the dopamine D3 receptor gene and schizophrenia in a Spanish sample

This study aims to further evaluate the controversial association between the Ser9Gly polymorphism in codon 9 of the D3 dopamine receptor gene (DRD3) and schizophrenia in psychiatric inpatients acutely hospitalized in two general hospitals in Madrid, Spain. The Ser9Gly polymorphism of the DRD3 was examined in 178 schizophrenic patients, 286 patients with other psychiatric diagnoses, and 132 controls recruited. Genotype frequencies were in Hardy-Weinberg equilibrium. No association was found between schizophrenia and the Ser9Gly polymorphism of the D3 dopamine receptor gene.

G protein-coupled receptors in major psychiatric disorders

Although the molecular mechanisms underlying psychiatric illnesses such as depression, bipolar disorder and schizophrenia remain incompletely understood, there is increasing clinical, pharmacologic, and genetic evidence that G protein-coupled receptors (GPCRs) play critical roles in these disorders and their treatments. This perspectives paper reviews and synthesizes the available data. Dysfunction of multiple neurotransmitter and neuropeptide GPCRs in frontal cortex and limbic-related regions, such as the hippocampus, hypothalamus and brainstem, likely underlies the complex clinical picture that includes cognitive, perceptual, affective and motoric symptoms. The future development of novel agents targeting GPCR signaling cascades remains an exciting prospect for patients refractory to existing therapeutics.

Association analysis between the C516T polymorphism in the 5-HT2A receptor gene and schizophrenia

Data from epidemiological studies have demonstrated that genetics is an important risk factor for schizophrenia. Disturbances of serotonergic brain pathways have been implicated in the pathophysiology of schizophrenia. Some studies have suggested that the efficacy of atypical antipsychotics on schizophrenia treatment may be related to the serotonin 2A receptor (5-HT2A), and that serotonergic drugs may induce psychotic symptoms. Thus, the aim of this study was to investigate the association between the C516T polymorphism and schizophrenia in a Brazilian population composed by 246 patients and 315 healthy matched controls in a case-control approach. No statistically differences were observed in allelic (chi2=1.77, 1d.f., p=0.18) or genotypic (chi2=1.69, 2d.f., p=0.42) distributions between cases and controls. The results suggest that the C516T polymorphism of the 5-HT2A receptor gene is not related to the susceptibility for schizophrenia in our Brazilian sample.

Serotonin and dopamine receptor gene polymorphisms and the risk of extrapyramidal side effects in perphenazine-treated schizophrenic patients

RATIONALE

Perphenazine, a classical antipsychotic drug, has the potential to induce extrapyramidal side effects (EPS). Dopaminergic and serotonergic pathways are involved in the therapeutic and adverse effects of the drug.

OBJECTIVES

To evaluate the impact of polymorphisms in the dopamine D(2) and D(3) and serotonin 2A and 2C receptor genes (DRD2, DRD3, HTR2A, and HTR2C) on short-term effects of perphenazine monotherapy in schizophrenic patients.

MATERIALS AND METHODS

Forty-seven Estonian inpatients were evaluated before and after 4-6 weeks of treatment by Simpson-Angus rating scale, Barnes scale, and Positive and Negative Symptom Scale. Genotyping was performed for common DRD2, DRD3, HTR2A, and HTR2C gene polymorphisms, previously reported to influence receptor expression and/or function.

RESULTS

Most of the patients (n = 37) responded to the treatment and no significant association was observed between the polymorphisms and antipsychotic response. The 102C allele of HTR2A and the -697C and 23Ser alleles of HTR2C were more frequent among patients with EPS (n = 25) compared to patients without EPS (n = 22) (p = 0.02, 0.01, and 0.02, respectively). The difference between patients with and without EPS in variant allele frequencies remained significant after multiple model analyses including age, gender, and duration of antipsychotic treatment as covariants. There was no significant association between EPS occurrence and polymorphisms in the DRD2 and DRD3 genes.

CONCLUSIONS

An association was observed between polymorphisms in HTR2A and HTR2C genes and occurrence of acute EPS in schizophrenic patients treated with perphenazine monotherapy. Larger study populations are needed to confirm our findings.

No allelic association or interaction of three known functional polymorphisms with bipolar disorder in a northern Swedish isolated population

Most genetic association studies in bipolar disorder have focussed on genes involved in major neurotransmitter systems or brain development. Functional polymorphisms in the serotonin transporter (5-HTTLPR), catechol-O-methyltransferase (Val158Met) and dopamine D3 receptor (Ser9Gly) genes have all been associated with bipolar disorder. We aimed at investigating whether these functional variants contribute to the genetic etiology of bipolar disorder in a northern Swedish isolated population. Moreover, we wanted to gain information about the synergistic contribution of these functional variants. Neither of these functional polymorphisms was associated with bipolar disorder in the northern Swedish patient-control sample nor did we find evidence of gene-gene interaction. Together, our data suggest that these functional variants are not involved in the etiology of bipolar disorder in the northern Swedish population nor did gene-gene interaction analysis support a central role of these variants in bipolar disorder.