Functional single nucleotide polymorphisms in dopaminergic receptors D2 predict clinical response to Cariprazine

Cariprazine (CAR) is an antipsychotic drug for the treatment of schizophrenia (SCZ) and bipolar disorder (BD), and it acts as a partial agonist on the dopamine receptors (DR), D2, and D3. Although many single nucleotide polymorphisms (SNPs) in genes coding for these receptors are known to influence response to antipsychotics, to date, no study on CAR pharmacogenetics exists. In this pilot study, we investigated the relationship between SNPs in DRD2 (rs1800497 and rs6277) and DRD3 (rs6280), and response to CAR treatment, evaluated by the psychometric Brief Psychiatric Rating Scale (BPRS), in a cohort of Caucasian patients. We found a significant association between DRD2 rs1800497 and rs6277 and response to CAR treatment. When genotypes were combined into an arbitrary score, the receiver operating characteristic curve analysis showed that using a cut-off value of -2.5 the response to CAR treatment could be predicted with a positive likelihood ratio of 8.0. Our study report, for the first time, a correlation between SNPs in DRD2 and response to CAR treatment. After confirmation in a larger cohort of patients, our results could open the way for the identification of new tools for the provision of response to CAR treatment.

DRD3 Ser9Gly polymorphism and treatment response to antipsychotics in schizophrenia: A meta-analysis

The association between dopamine D3 receptor (DRD3) Ser9Gly polymorphism and treatment response to antipsychotic drugs (APDs) in schizophrenia (SCZ) has been widely reported with inconsistent results, thus we performed an updated meta-analysis to derive a more precise estimation of the relationship. PubMed, Cochrane Library, Medline, Embase, CNKI, Weipu and Wanfang databases were searched for eligible studies published until March 2022. Odds ratios (ORs) with 95 % confidence intervals (CIs) were used to assess the strength of the associations in four genetic models. A total of 13 studies with 1769 patients were included in this meta-analysis. Our findings suggested that Ser9Gly polymorphism was significantly associated with treatment response to APDs in SCZ in allele model (Ser vs Gly, OR = 0.72, 95 % CI = 0.58-0.89, P = 0.002), recessive model (Ser/Ser vs Ser/Gly + Gly/Gly, OR = 0.55, 95 % CI = 0.36-0.86, P = 0.008) and co-dominant model (Ser/Ser vs Gly/Gly, OR = 0.57, 95 % CI = 0.33-0.99, P = 0.045) in Caucasians, but not in Asians. meta-regression revealed that the associations were not confounded by mean age, male ratio and treatment duration (P > 0.05). In summary, our results indicated the DRD3 Ser9Gly may influence the efficacy of APDs in specific genetic models, of which Ser allele and Ser/Ser genotype contributed to poor treatment response in Caucasians.

Frequency of the Dopamine Receptor D3 (rs6280) vs. Opioid Receptor µ1 (rs1799971) Polymorphic Risk Alleles in Patients with Opioid Use Disorder: A Preponderance of Dopaminergic Mechanisms?

While opioids are a powerful class of drugs that inhibit transmission of pain signals, their use is tarnished by the current epidemic of opioid use disorder (OUD) and overdose deaths. Notwithstanding published reports, there remain gaps in our knowledge of opioid receptor mechanisms and their role in opioid seeking behavior. Thus, novel insights into molecular, neurogenetic and neuropharmacological bases of OUD are needed. We propose that an addictive endophenotype may not be entirely specific to the drug of choice but rather may be generalizable to altered brain reward circuits impacting net mesocorticolimbic dopamine release. We suggest that genetic or epigenetic alterations across dopaminergic reward systems lead to uncontrollable self-administration of opioids and other drugs. For instance, diminished availability via knockout of dopamine D3 receptor (DRD3) increases vulnerability to opioids. Building upon this concept via the use of a sophisticated polymorphic risk analysis in a human cohort of chronic opioid users, we found evidence for a higher frequency of polymorphic DRD3 risk allele (rs6280) than opioid receptor µ1 (rs1799971). In conclusion, while opioidergic mechanisms are involved in OUD, dopamine-related receptors may have primary influence on opioid-seeking behavior in African Americans. These findings suggest OUD-targeted novel and improved neuropharmacological therapies may require focus on DRD3-mediated regulation of dopaminergic homeostasis.

COMT by DRD3 Epistatic Interaction in Modulating Behaviors in Children with ADHD: A Pharmaco-Dynamic Behavioral Approach

OBJECTIVE

Examining the joint effect of two functional variants in two dopamine-related genes (DRD3 and COMT) on ADHD-relevant behaviors under three experimental conditions (EC).

METHOD

362 children with ADHD were assessed by parents and teachers during a week of baseline evaluation, followed by 1 week of MPH and placebo, administered in a double-blind crossover design.

RESULTS

Statistically significant 3-way (DRD3-by-COMT-by-EC; p = .004) and 2-way interactions (COMT by EC; p = .002) were observed on Conners'-Teachers scores. Children with the COMT Met/Met genotype had lower scores at baseline and on placebo compared to the other genotype groups. Furthermore, stratifying the children according to their COMT genotypes helped to detect statistically significant and biologically meaningful effects of DRD3 genotype.

CONCLUSIONS

These findings suggest that COMT and DRD3 genetic variants may together play a role in ADHD symptomatology and response to treatment through gene-gene interaction.

Evidence for Protein-Protein Interaction between Dopamine Receptors and the G Protein-Coupled Receptor 143

Protein-protein interactions between G protein-coupled receptors (GPCRs) can augment their functionality and increase the repertoire of signaling pathways they regulate. New therapeutics designed to modulate such interactions may allow for targeting of a specific GPCR activity, thus reducing potential for side effects. Dopamine receptor (DR) heteromers are promising candidates for targeted therapy of neurological conditions such as Parkinson's disease since current treatments can have severe side effects. To facilitate development of such therapies, it is necessary to identify the various DR binding partners. We report here a new interaction partner for DRD₂ and DRD₃, the orphan receptor G protein-coupled receptor 143 (GPR143), an atypical GPCR that plays multiple roles in pigment cells and is expressed in several regions of the brain. We previously demonstrated that the DRD₂/ DRD₃ antagonist pimozide also modulates GPR143 activity. Using confocal microscopy and two FRET methods, we observed that the DRs and GPR143 colocalize and interact at intracellular membranes. Furthermore, co-expression of wildtype GPR143 resulted in a 57% and 67% decrease in DRD₂ and DRD₃ activity, respectively, as determined by β-Arrestin recruitment assay. GPR143-DR dimerization may negatively modulate DR activity by changing affinity for dopamine or delaying delivery of the DRs to the plasma membrane.

Candidate Genes Encoding Dopamine Receptors as Predictors of the Risk of Antipsychotic-Induced Parkinsonism and Tardive Dyskinesia in Schizophrenic Patients

(1) Introduction: Extrapyramidal disorders form the so-called extrapyramidal syndrome (EPS), which is characterized by the occurrence of motor disorders as a result of damage to the basal ganglia and the subcortical-thalamic connections. Often, this syndrome develops while taking medications, in particular antipsychotics (APs). (2) Purpose: To review studies of candidate genes encoding dopamine receptors as genetic predictors of development of AP-induced parkinsonism (AIP) and AP-induced tardive dyskinesia (AITD) in patients with schizophrenia. (3) Materials and Methods: A search was carried out for publications of PubMed, Web of Science, Springer, and e-Library databases by keywords and their combinations over the last 10 years. In addition, the review includes earlier publications of historical interest. Despite extensive searches of these commonly used databases and search terms, it cannot be ruled out that some publications were possibly missed. (4) Results: The review considers candidate genes encoding dopamine receptors involved in pharmacodynamics, including genes DRD1, DRD2, DRD3, and DRD4. We analyzed 18 genome-wide studies examining 37 genetic variations, including single nucleotide variants (SNVs)/polymorphisms of four candidate genes involved in the development of AIP and AITD in patients with schizophrenia. Among such a set of obtained results, only 14 positive associations were revealed: rs1799732 (141CIns/Del), rs1800497 (C/T), rs6275 (C/T), rs6275 (C/T) DRD2; rs167771 (G/A) DRD3 with AIP and rs4532 (A/G) DRD1, rs6277 (C/T), rs6275 (C/T), rs1800497 (C/T), rs1079597 (A/G), rs1799732 (141CIns/Del), rs1045280 (C/G) DRD2, rs6280 (C/T), rs905568 (C/G) DRD3 with AITD. However, at present, it should be recognized that there is no final or unique decision on the leading role of any particular SNVs/polymorphisms in the development of AIP and AITD. (5) Conclusion: Disclosure of genetic predictors of the development of AIP and AITD, as the most common neurological adverse drug reactions (ADRs) in the treatment of patients with psychiatric disorders, may provide a key to the development of a strategy for personalized prevention and treatment of the considered complication of AP therapy for schizophrenia in real clinical practice.

Associations of Genetic Polymorphisms and Neuroimmune Markers With Some Parameters of Frontal Lobe Dysfunction in Schizophrenia

We investigated the associations of DRD3 rs6280, HTR1A rs6295, BDNF rs6265, SCL6A4 rs16965628, and 5HT2A rs7322347 with schizophrenia in a case-control study, and associations of these genetic variants with several clinical features. We also investigated markers of inflammatory response (C-reactive protein, IL-2, IL-6, IL-10), the activity of leukocytic elastase (LE) and α1-proteinase inhibitor (a1-PI), antibodies to S100B and myelin basic protein (MBP) in schizophrenia. Clinical symptoms were assessed on three scales: Positive and Negative Syndrome Scale, The Bush - Francis Catatonia Rating Scale and Frontal Assessment Battery. All SNPs were typed using predesigned TaqMan SNP genotyping assays. The biomarkers related to the immune system were routinely tested using ELISA kits. The association with schizophrenia was found for DRD3 rs6280 (p = 0.05) and HTR2A rs7322347 (p = 0.0013). We found differences between groups by parameters of LE and a1-PI and LE/a1-PI (p < 0.001). And IL-6 was evaluated in the schizophrenia group (p < 0.001). We showed that patients with the TT allele (BDNF rs6265) had more severe impairments in frontal lobe function. a1-PI can serve as a marker for assessing the severity of frontal lobe damage in patients with frontal dementia. We found some biological parameters reflecting the severity of frontal dysfunction in schizophrenia.

Dopamine receptor D3 agonist (Pramipexole) reduces morphine-induced cardiac fibrosis

Morphine is routinely used for pain management in heart failure patients. However, extended morphine exposure associates with major adverse cardiovascular events. Reports link the dopamine receptor D2-family with morphine-induced nociception modulation. This study first assessed whether morphine induces cardiac remodeling in healthy mice, then whether DRD3 agonist (DRD3ag, D2-family member) adjunct therapy prevents morphine-induced cardiac remodeling. Mice received morphine (2 mg/kg/day i. p.) for 7 days (D7) and were either euthanized at D7 or kept 7 more days without morphine (i.e. withdrawal period, D8-D14): G1, morphine; G2, morphine/DRD3ag; G3, morphine + withdrawal; G4, morphine/DRD3ag + withdrawal; G5, morphine + withdrawal/DRD3ag. A separate cohort of animals were used as naïve tissues. We evaluated functional and molecular parameters of cardiac remodeling. Although we did not observe significant differences in systolic function, morphine induced both interstitial fibrosis and cardiomyocyte hypertrophy. Interestingly, DRD3ag abolished these effects. Compared to naïve tissues, collagen 1 increased after withdrawal in G3 and G4 and collagen 3 increased in G1-G4 but at higher levels in G1 and G2. Only G5 did not show collagen differences compared to naïve, suggesting DRD3ag treatment during withdrawal may be beneficial and prevent morphine-induced fibrosis. Smad2/3 phosphorylation increased during withdrawal, indicating a likely upstream pathway for the observed morphine-induced fibrosis. Overall, our data suggest that DRD3ag adjunct therapy decreases morphine-induced adverse cardiac remodeling.

Association of Mental Health-Related Proteins DAXX, DRD3, and DISC1 With the Progression and Prognosis of Chondrosarcoma

Chondrosarcoma is the second most common malignant bone tumor. Current therapies remain ineffective, resulting in poor prognoses. Biomarkers for chondrosarcoma and predictors of its prognosis have not been established. Mental health-related proteins have been associated with the pathogenesis, progression, and prognosis of many cancers, but their association with chondrosarcoma has not been reported. In this study, the expression and clinicopathological significance of the mental health-related proteins DAXX, DRD3, and DISC1 in chondrosarcoma tissue samples were examined, over an 84-months follow-up period. In immunohistochemical analysis, the rates of positive DAXX, DRD3, and DISC1 expression were significantly higher in chondrosarcoma than in osteochondroma tissue (P < 0.01). The percentages of positive DAXX, DRD3, and DISC1 expression were significantly lower in tissues with good differentiation (P < 0.01), AJCC stage I/ II (P < 0.01), Enneking stage I (P < 0.01), and non-metastasis (P < 0.05), respectively. In Kaplan-Meier survival analysis, significantly shorter mean survival times were associated with moderate and poor differentiation (P = 0.000), AJCC stage III/IV (P = 0.000), Enneking stage II/III (P = 0.000), metastasis (P = 0.019), invasion (P = 0.013), and positive DAXX (P = 0.012), and/or DRD3 (P = 0.018) expression. In Cox regression analysis, moderate and poor differentiation (P = 0.006), AJCC stage III/IV (P = 0.013), Enneking stage II/III (P = 0.016), metastasis (P = 0.033), invasion (P = 0.011), and positive DAXX (P = 0.033), and/or DRD3 (P = 0.025) staining correlated negatively with the postoperative survival rate and positively with mortality. In competing-risks regression analysis, differentiation (P = 0.005), metastasis (P = 0.014), invasion (P = 0.028), AJCC stage (P = 0.003), Enneking stage (P = 0.036), and DAXX (P = 0.039), and DRD3(P = 0.019) expression were independent predictors of death from chondrosarcoma. The areas under receiver operating characteristic curves for DAXX, DRD3, and DISC1 expression were 0.673 (95% CI, 0.557-0.788; P = 0.010), 0.670 (95% CI, 0.556-0.784; P = 0.011), and 0.688 (95% CI, 0.573-0.802; P = 0.005), respectively. These results suggest that DAXX, DRD3, and DISC1 could serve as biomarkers of chondrosarcoma progression and predictors of its prognosis.

Pharmacogenetic Profile and the Occurrence of Visual Hallucinations in Patients With Sporadic Parkinson's Disease

Visual hallucinations are significant nonmotor symptoms in the course of treatment of Parkinson's disease. Previous studies have shown that the interindividual variability and pharmacogenetic profile of Parkinson's disease patients seem to influence the occurrence of visual hallucinations. In our study, we investigated a possible relationship of sequence variants in DRD1, DRD2, DRD3, DAT1, and COMT genes with the presence of visual hallucinations in Parkinson's disease patients. A total of 224 Brazilian patients from the Pro-Parkinson service at the Clinical Hospital of the University of Pernambuco, diagnosed with sporadic Parkinson's disease, were enrolled. Parkinson's disease patients were divided into 2 groups based on the presence or absence of visual hallucinations. The sequence variants for DRD1, DRD2, DRD3, DAT1, and COMT were determined through the polymerase chain reaction-restriction fragment length polymorphism technique. Multiple Poisson regression analyses showed that individuals carrying the DRD3 Ser/Ser and Ser/Gly genotypes presented increased prevalence ratios of visual hallucinations (9.7-fold and 4.4-fold, respectively; P < .001). Regarding DAT1 rs28363170, there was a 9.82-fold increase in the prevalence ratio in patients with the 10/11 genotype, 8.78-fold for the 10/8 genotype, and 2.44-fold for the 9/8 genotypes (P < .001, for all). In addition, visual hallucinations were also associated with use of transdermal patches with rotigotine (PR, 3.7; 95%CI, 1.2-10.9; P = .017) and rasagiline (PR, 2.8; 95%CI, 1.3-6.0; P = .006). Our results suggest that the genetic variants DRD3 and DAT1, along with other therapeutic confounders, may influence the prevalence ratio of visual hallucinations.

DRD3 Gene and ADHD: A Pharmaco-Behavioural Genetic Study

Results of candidate gene investigations in ADHD have been difficult to replicate. The complexity of the phenotypes and their underlying determinants, and the relatively small effect sizes of genetic variants may, in part, be contributing to these inconsistencies. The objective of this study is to conduct an exploratory analysis using a comprehensive approach to investigate the role of candidate genes. This approach combines a dimensional behavioural approach akin to Research Domain Criteria (RDoC), a pharmaco-dynamic evaluation of behaviours relevant to ADHD, together with association and linkage testing in a large sample of children with ADHD. Parents, teachers, and research staff evaluated children with ADHD under three experimental conditions (EC): 1 week of baseline observation, followed by 1 week of methylphenidate (MPH) and 1 week of placebo, administered in a double-blind crossover order. Several quantitative behavioural and cognitive dimensions relevant for ADHD were also assessed. We combined family-based (FBAT) and quantitative trait genetic analyses (n = 575 probands with members of their nuclear families) to investigate the role of DRD3 (Ser-9-Gly) in ADHD and its relevant behavioural dimensions. Comparing the behaviours of children with different genotypes under the three EC showed a nominal association between the T allele and poorer behavioural scores during the MPH week (as assessed by teachers), particularly in boys. With the family-based analysis, the T allele showed a nominal association with increased risk for ADHD, response to placebo and MPH as assessed by research staff, and the modulation of other behavioural and cognitive dimensions. These results provide convergent, albeit preliminary evidence for the implication of the DRD3 (Ser-9-Gly) polymorphism in the aetiology of ADHD and the modulation of its various behavioural dimensions, including RDoC cognitive constructs and response to pharmacological probes. This illustrative example suggests that this research paradigm might help to reliably uncover the role of other candidate genes in ADHD.

Genetic markers of dopaminergic transmission predict performance for older males but not females

Mobility and memory declines with aging can limit independence. Several single-nucleotide polymorphisms have been associated with cognitive performance, but studies investigating motor function are scant. We examined 4 single-nucleotide polymorphisms involved in dopaminergic metabolism: BDNF (Val66Met), DRD3 (Ser9Gly), DBH (C>T), and COMT (Val158Met) for their relationship to motor and cognitive function in healthy older adults (n = 4605 and n = 7331) who participated in the U.S. Health and Retirement Study. Individuals with genotypes associated with reduced dopamine metabolism exhibited poorer balance and memory. We found the most pronounced effects in the oldest participants (aged 85+ years), supporting the notion that age-related declines in dopamine availability contribute to magnified genotype effects with advancing age. Moreover, males demonstrated stronger associations than did females between a number of beneficial dopamine alleles and cognitive scores, suggesting that sex differences in dopaminergic transmission interact with genotype to influence performance. These findings point to common genetic variants related to dopaminergic metabolism that characterizes individual differences in motor and cognitive function in older adults.

Behavioral addictions in early-onset Parkinson disease are associated with DRD3 variants

BACKGROUND

Impulse control disorders (ICDs) comprise abnormal behaviors frequently found in patients with Parkinson's disease (PD) receiving antiparkinsonian medication. ICDs in PD would develop when dopaminergic treatment overstimulates the dopamine receptor D3 (DR3). Here we studied whether DR3 gene (DRD3) is associated to ICD in PD patients with early-onset (EOPD).

METHODS

We performed association analysis of the rs6280 DRD3 single nucleotide variation (SNV) (Ser9Gly) in a clinical sample of 126 non early-onset PD (NEOPD) and 73 EOPD (age at onset < 45). ICD was evaluated using the Questionnaire for Impulsive-Compulsive Disorders (QUIP) in PD.

RESULTS

In the total sample, we found that a younger onset of PD is linked to ICD traits with a potentially addictive reinforcement (ICDARs, behavioral addictions) (p = .017) and a trend for total ICDs (p = .078) while punding was not associated (p = .75). EOPD sample showed an increase of DRD3 C+ genotype for ICD (p = .022) and ICDARs (p = .043) but not for punding (p = .170). The post-hoc analyses including the time of evolution and Pramipexol or Ropinirole treatments, confirmed the independent effect of the DRD3 upon ICDs (p = .028) and ICDARs (p = .041) as well as the interaction between DRD3 and Pramipexol treatment upon ICDARs (OR = 4.60, 95% CI 1.20-17.632, p = .026). The NEOPD group showed no association between DRD3 and ICDs.

CONCLUSIONS

We found that behavioral addictions in PD are associated with an early onset of the disease, the rs6280 DRD3 SNV and the type of dopamine agonist. Further investigation in independent samples is warranted.

Methamphetamine-induced psychosis is associated with DNA hypomethylation and increased expression of AKT1 and key dopaminergic genes

Methamphetamine, one of the most frequently used illicit drugs worldwide, can induce psychosis in a large fraction of abusers and it is becoming a major problem for the health care institutions. There is some evidence that genetic and epigenetic factors may play roles in methamphetamine psychosis. In this study, we examined methamphetamine-induced epigenetic and expression changes of several key genes involved in psychosis. RNA and DNA extracted from the saliva samples of patients with methamphetamine dependency with and without psychosis as well as control subjects (each group 25) were analyzed for expression and promoter DNA methylation status of DRD1, DRD2, DRD3, DRD4, MB-COMT, GAD1, and AKT1 using qRT-PCR and q-MSP, respectively. We found statistically significant DNA hypomethylation of the promoter regions of DRD3 (P = 0.032), DRD4 (P = 0.05), MB-COMT (P = 0.009), and AKT1 (P = 0.0008) associated with increased expression of the corresponding genes in patients with methamphetamine psychosis (P = 0.022, P = 0.034, P = 0.035, P = 0.038, respectively), and to a lesser degree in some of the candidate genes in non-psychotic patients versus the control subjects. In general, methamphetamine dependency is associated with reduced DNA methylation and corresponding increase in expression of several key genes involved in the pathogenesis of psychotic disorders. While these epigenetic changes can be useful diagnostic biomarkers for psychosis in methamphetamine abusers, it is also consistent with the use of methyl rich diet for prevention or suppression of psychosis in these patients. However, this needs to be confirmed in future studies. © 2016 Wiley Periodicals, Inc.

Association study of dopamine receptor genes polymorphisms with the risk of schizophrenia in the Han Chinese population

Schizophrenia is a highly heritable psychiatric disorder often associated with dopamine-related genetic variations. Thus, we performed a case-control study in 1504 Han Chinese population to evaluate the association of DRD1, DRD2 and DRD3 polymorphisms with schizophrenia. No statistically significant difference in allelic or genotypic frequency was found between schizophrenia and control subjects. Strong positive linkage disequilibrium was detected among the SNPs within DRD1 and DRD2. However, no positive haplotype distribution was found to be associated with schizophrenia. Our results indicated that DRD1, DRD2 and DRD3 may not be the susceptibility genes for schizophrenia in the Chinese Han population.

Gene-gene interactions between DRD3, MRP4 and CYP2B6 polymorphisms and its influence on the pharmacokinetic parameters of efavirenz in HIV infected patients

Genetic factors have a significant impact on the PK variability of EFV, much higher than other non-genetic factors, such as demography. In this work we have performed a comprehensive PG analysis of genes encoding the major metabolizing enzymes and transporters of EFV, establishing a clear relationship between the PK parameters and genetic factors, which explain 50% of the variability in EFV PK parameters. The most relevant associations for metabolizing enzymes were found in CYP2B6 (rs3745274), in agreement with previous studies. The influence of transporters on the kinetics of EFV was also proved with significant correlations between the PK parameters of EFV and MRP4 (rs1751034, rs2274407). Analysis of gene-gene interactions with CYP2B6 was particularly useful to reinforce the role of MRP4 and to reveal unknown associations, such as that of DRD3. However, the role of DRD3 cannot be a direct effect but an indirect one due to physical proximity of NAT and the DRD3 locus in the genome.

Dopamine D3 receptor Ser9Gly variant is associated with impulse control disorders in Parkinson's disease patients

INTRODUCTION

Impulse control disorders (ICD) are reported to occur at variable frequencies in different ethnic groups. Genetic vulnerability is suspected to underlie the individual risk for ICD. We investigated whether the allelic variants of dopamine (DRD3), glutamate (GRIN2B) and serotonin (HTR2A) receptors are linked to ICD in Indian Parkinson's disease (PD) patients.

METHODS

We conducted a prospective, case-control study which included PD patients (70 with ICD, 100 without ICD categorized after direct psychiatric interview of patient and caregiver) and 285 healthy controls. Single nucleotide polymorphism (SNP) variants of DRD3 p.S9G (rs6280), GRIN2B c.2664C>T (rs1806201) and HTR2A c.102T>C (rs6313) were genotyped.

RESULTS

Multivariate regression analysis revealed that DRD3 p.Ser9Gly (rs6280) heterozygous variant CT (OR = 2.22, 95% CI: 1.03-4.86, p = 0.041), higher daily Levodopa equivalent doses (LED) of drugs (for 100 mg LED, OR = 1.14, 95% CI: 1.01-1.29, p = 0.041), current dopamine agonist but not Levodopa use (OR = 2.16, 95% CI: 1.03-4.55, p = 0.042) and age of onset of motor symptoms under 50 years (OR 2.09, 95% CI: 1.05-4.18, p = 0.035) were independently associated with ICD.

CONCLUSION

DRD3 p.Ser9Gly (rs6280) CT genotype is associated with ICD in Indian PD patients and this association is novel. Enhanced D3 receptor affinity due to gain-of-function conferred by the glycine residues could impair reward-risk assessment in the mesolimbic system and contribute to development of impulsive behaviour, in carriers of this genotype.

The mRNA Expression Status of Dopamine Receptor D2, Dopamine Receptor D3 and DARPP-32 in T Lymphocytes of Patients with Early Psychosis

Peripheral blood lymphocytes are an attractive tool because there is accumulating evidence indicating that lymphocytes may be utilized as a biomarker in the field of psychiatric study as they could reveal the condition of cells distributed in the brain. Here, we measured the mRNA expression status of dopamine receptor D2 (DRD2), DRD3, and dopamine and cyclic adenosine 3',5'-monophosphate regulated phosphoprotein-32 (DARPP-32) in T lymphocytes of patients with early psychosis by quantitative real-time polymerase chain reaction (q-PCR) and explored the relationships between their mRNA levels and the psychopathological status of patients. The present study demonstrated that the mRNA expression levels of DRD3 in T lymphocytes were significantly different among controls, and in patients with psychotic disorder not otherwise specified (NOS) and schizophrenia/schizophreniform disorder. However, no significant differences in mRNA expression levels of DRD2 and DARPP-32 were found among the three groups. We found a significant positive correlation between the DRD2 mRNA level and the score of the excited factor of the Positive and Negative Syndrome Scale (PANSS) in patients with schizophrenia/schizophreniform disorder. These findings suggest that DRD3 mRNA levels may serve as a potential diagnostic biomarker differentiating patients with early psychosis from controls.

Autism, DRD3 and repetitive and stereotyped behavior, an overview of the current knowledge

The SNP rs167771 of the dopamine-3-receptor gene (DRD3) has been associated with autism spectrum disorder (ASD) in samples from the United Kingdom, The Netherlands and Spain. The DRD3 polymorphisms of rs167771 are significantly associated with a specific type of repetitive and stereotyped behavior, called sameness. Repetitive and stereotyped behavior occurs in several neuropsychiatric disorders and the combined picture across these disorders strongly suggests the involvement of the basal ganglia - frontal lobe circuitry. In autism, abnormalities of the basal ganglia, in particular the caudate nucleus, are the best replicated findings in neuroimaging studies. Interestingly, the DRD3 gene is highly expressed in the basal ganglia, most notably the caudate nucleus. The rs167771 SNP was recently also found to be related to risperidone-induced extra-pyramidal side effects (EPS) in patients with autism, which is important since risperidone is approved for the treatment of aggression, irritability and rigid behavior in ASD. To conclude, striatum abnormalities in autism are associated with repetitive and stereotyped behavior in autism and may be related to DRD3 polymorphisms.

Buspirone anti-dyskinetic effect is correlated with temporal normalization of dysregulated striatal DRD1 signalling in L-DOPA-treated rats

Dopamine replacement with l-DOPA is the most effective therapy in Parkinson's disease. However, with chronic treatment, half of the patients develop an abnormal motor response including dyskinesias. The specific molecular mechanisms underlying dyskinesias are not fully understood. In this study, we used a well-characterized animal model to first establish the molecular differences between rats that did and did not develop dyskinesias. We then investigated the molecular substrates implicated in the anti-dyskinetic effect of buspirone, a 5HT1A partial agonist. Striatal protein expression profile of dyskinetic animals revealed increased levels of the dopamine receptor (DR)D3, ΔFosB and phospho (p)CREB, as well as an over-activation of the DRD1 signalling pathway, reflected by elevated ratios of phosphorylated DARPP32 and ERK2. Buspirone reduced the abnormal involuntary motor response in dyskinetic rats in a dose-dependent fashion. Buspirone (4 mg/kg) dramatically reduced the presence and severity of dyskinesias (by 83%) and normalized DARPP32 and ERK2 phosphorylation ratios, while the increases in DRD3, ΔFosB and pCREB observed in dyskinetic rats were not modified. Pharmacological experiments combining buspirone with 5HT1A and DRD3 antagonists confirmed that normalization of both pDARPP32 and pERK2 is required, but not sufficient, for blocking dyskinesias. The correlation between pDARPP32 ratio and dyskinesias was significant but not strong, pointing to the involvement of convergent factors and signalling pathways. Our results suggest that in dyskinetic rats DRD3 striatal over-expression could be instrumental in the activation of DRD1-downstream signalling and demonstrate that the anti-dyskinetic effect of buspirone in this model is correlated with DRD1 pathway normalization.

Molecular characterization and differential expression of multiple goose dopamine D2 receptors

Dopamine D2 receptor (DRD2) gene, a member of the dopamine receptors gene family, has been studied as a candidate gene for broodiness due to its special effects on avian prolactin secretion. Here, the genomic DNA and cDNA sequences of goose (Anser cygnoides) DRD2 gene were cloned and characterized for the first time. The goose DRD2 cDNA is 1353bp in length and encodes a protein of 450 amino acids. The length of goose DRD2 genomic DNA is 8350bp, including seven exons and six introns. We identified four goose DRD2 variants, which were generated due to alternative splicing. Bioinformatics analysis indicates that all the deduced DRD2 amino acid sequences contain seven putative transmembrane domains and four potential N-glycosylation sites. A phylogenetic tree based on amino acid sequences displays that the goose DRD2 protein is closely related to those of avian species. Semi-quantitative RT-PCR analysis demonstrates that the DRD2-1, DRD2-2 and DRD2-4 transcripts are differentially expressed in the pituitary, ovary, hypothalamus, as well as in the kidney, whereas the DRD2-3 transcript is widely expressed in all the examined tissues at different levels. Meanwhile, 54 single nucleotide polymorphisms (SNPs) and 4 insert-deletion (indel) variations were identified in the coding region and partial intron region of the goose DRD2 gene. Those findings will help us gain insight into the functions of the DRD2 gene in geese.

Genetic variants of the BDNF and DRD3 genes in bipolar disorder comorbid with anxiety disorder

BACKGROUND

The high comorbidity rate between bipolar disorder (BP) and anxiety disorder (AD) has been studied in depth. This comorbidity is not as high in Han Chinese in Taiwan. Therefore, we explored the genetic effects BP comorbid with AD.

METHODS

We recruited 1316 participants: 286 with BP-I, 681 with BP-II, and 349 healthy Controls. Genotypes of the BDNF Val66Met and DRD3 Ser9Gly polymorphisms were determined using polymerase chain reactions plus restriction fragment length polymorphism analysis.

RESULTS

The DRD3 Ser9Gly polymorphism was associated with BP-II comorbid with AD (BPII(+AD)), and the BDNF Val66Met polymorphism was associated with BP-I comorbid with AD (BPI(+AD)). An interaction between the Val/Val genotype of the BDNF Val66Met and Gly/Gly polymorphism of the DRD3 Ser9Gly was found in BPII(+AD), but not in BP-II not comorbid with AD (BPI(-AD)) compared with healthy Controls.

LIMITATION

The low comorbidity rate of AD in both BP subtypes, especially BP-I, limit generalizing our findings.

CONCLUSION

The involvement of the dopaminergic pathway in AD was confirmed, particularly with BP-II rather than BP-I. Because the Val/Val genotype of the BDNF Val66Met polymorphism, rather than the other two polymorphisms, has been associated with anxiety, it seems to affect BP-I comorbid with AD without the involvement of the DRD3 Seg9Gly polymorphism, but may modify the involvement of DRD3 Gly/Gly in BP-II comorbid with AD.

Meta-analysis of the influence of DRD3 Ser9Gly variant on susceptibility for essential tremor

The dopamine D3 receptor (DRD3) Ser9Gly variant has attracted more attention since the variant was observed to be associated with risk of essential tremor (ET). A number of association studies concerning the DRD3 Ser9Gly variant and ET susceptibility have been conducted in various populations. However, some results were contradictory. To derive a more precise estimation of the relationship between the DRD3 Ser9Gly variant and the genetic risk of ET, we performed a comprehensive meta-analysis which included seven case-control studies. The meta-analysis was conducted in four genetic models: dominant, recessive, heterozygous, and homozygous. The odds ratio and 95% confidence intervals were used as the measure of association. The combined results of overall analysis showed a lack of association of the DRD3 Ser9Gly variant and ET, regardless of the genetic model of Ser9Gly. Publication bias and heterogeneity were absent in most analyses. In conclusion, the present meta-analysis does not support the notion that the DRD3 Ser9Gly variant is a genetic risk factor for ET.

Gene environment interaction studies in depression and suicidal behavior: An update

Increasing evidence supports the involvement of both heritable and environmental risk factors in major depression (MD) and suicidal behavior (SB). Studies investigating gene-environment interaction (G × E) may be useful for elucidating the role of biological mechanisms in the risk for mental disorders. In the present paper, we review the literature regarding the interaction between genes modulating brain functions and stressful life events in the etiology of MD and SB and discuss their potential added benefit compared to genetic studies only. Within the context of G × E investigation, thus far, only a few reliable results have been obtained, although some genes have consistently shown interactive effects with environmental risk in MD and, to a lesser extent, in SB. Further investigation is required to disentangle the direct and mediated effects that are common or specific to MD and SB. Since traditional G × E studies overall suffer from important methodological limitations, further effort is required to develop novel methodological strategies with an interdisciplinary approach.

Implications of genome wide association studies for addiction: are our a priori assumptions all wrong?

Substantial genetic contributions to addiction vulnerability are supported by data from twin studies, linkage studies, candidate gene association studies and, more recently, Genome Wide Association Studies (GWAS). Parallel to this work, animal studies have attempted to identify the genes that may contribute to responses to addictive drugs and addiction liability, initially focusing upon genes for the targets of the major drugs of abuse. These studies identified genes/proteins that affect responses to drugs of abuse; however, this does not necessarily mean that variation in these genes contributes to the genetic component of addiction liability. One of the major problems with initial linkage and candidate gene studies was an a priori focus on the genes thought to be involved in addiction based upon the known contributions of those proteins to drug actions, making the identification of novel genes unlikely. The GWAS approach is systematic and agnostic to such a priori assumptions. From the numerous GWAS now completed several conclusions may be drawn: (1) addiction is highly polygenic; each allelic variant contributing in a small, additive fashion to addiction vulnerability; (2) unexpected, compared to our a priori assumptions, classes of genes are most important in explaining addiction vulnerability; (3) although substantial genetic heterogeneity exists, there is substantial convergence of GWAS signals on particular genes. This review traces the history of this research; from initial transgenic mouse models based upon candidate gene and linkage studies, through the progression of GWAS for addiction and nicotine cessation, to the current human and transgenic mouse studies post-GWAS.