Polymorphisms of DRD2 and DRD3 genes and Parkinson's disease: A meta-analysis

Antinociceptive role of the thalamic dopamine D3 receptor in descending modulation of intramuscular formalin-induced muscle nociception in a rat model of Parkinson's disease

Pain in Parkinson's disease (PD) has been validated as one of the major non-motor dysfunctions affecting the quality of life and subsequent rehabilitation. In the present study, we investigated the role of the dopamine D3 receptor in the thalamic mediodorsal (MD) and ventromedial (VM) nuclei mediated descending control of nociception and intramuscular (i.m.) 2.5% formalin-induced persistent muscle nociception. Paw withdrawal reflexes were measured in naive rats and rats subjected to PD induced by unilateral microinjection of 6 μg 6-OHDA into the rat striatum. Formalin-induced muscle nociception in phase 1, inter-phase, and phase 2 was significantly greater in PD rats compared to naive and vehicle-treated rats (P < 0.001). PD rats exhibited bilaterally mechanical hyperalgesia and heat hypoalgesia in formalin-induced muscle nociception. Microinjection of SK609, a dopamine D3 receptor agonist, at various doses (2.5-7.5 nmol/0.5 μl) into the thalamic VM nucleus dose-dependently prolonged heat-evoked paw withdrawal latencies in both naive and PD rats. Administration of SK609 to either the MD or VM nuclei had no effect on noxious mechanically evoked paw withdrawal reflexes. Pre-treatment of the thalamic MD nucleus with SK609 significantly attenuated formalin-induced nociception, and reversed mechanical hyperalgesia, but not heat hypoalgesia. Pre-treatment of the thalamic VM nucleus with SK609 inhibited formalin-induced nociception in the late phase of phase 2 (30-75 min) and heat hypoalgesia, but not mechanical hyperalgesia (P < 0.05). It is suggested that the dopamine D3 receptors in the thalamus play an antinociceptive role in the descending modulation of nociception. Activation of D3 receptors within the thalamic MD and VM nuclei attenuates descending facilitation and enhances descending inhibition in rats during PD.

Application of novel hybrid machine learning systems and radiomics features for non-motor outcome prediction in Parkinson's disease

Objectives.Parkinson's disease (PD) is a complex neurodegenerative disorder, affecting 2%-3% of the elderly population. Montreal Cognitive Assessment (MoCA), a rapid nonmotor screening test, assesses different cognitive dysfunctionality aspects. Early MoCA prediction may facilitate better temporal therapy and disease control. Radiomics features (RF), in addition to clinical features (CF), are indicated to increase clinical diagnoses, etc, bridging between medical imaging procedures and personalized medicine. We investigate the effect of RFs, CFs, and conventional imaging features (CIF) to enhance prediction performance using hybrid machine learning systems (HMLS).Methods.We selected 210 patients with 981 features (CFs, CIFs, and RFs) from the Parkinson's Progression-Markers-Initiative database. We generated 4 datasets, namely using (i), (ii) year-0 (D1) or year-1 (D2) features, (iii) longitudinal data (D3, putting datasets in years 0 and 1 longitudinally next to each other), and (iv) timeless data (D4, effectively doubling dataset size by listing both datasets from years 0 and 1 separately). First, we directly applied 23 predictor algorithms (PA) to the datasets to predict year-4 MoCA, which PD patients this year have a higher dementia risk. Subsequently, HMLSs, including 14 attribute extraction and 10 feature selection algorithms followed by PAs were employed to enhance prediction performances. 80% of all datapoints were utilized to select the best model based on minimum mean absolute error (MAE) resulting from 5-fold cross-validation. Subsequently, the remaining 20% was used for hold-out testing of the selected models.Results.When applying PAs without ASAs/FEAs to datasets (MoCA outcome range: [11,30]), Adaboost achieved an MAE of 1.74 ± 0.29 on D4 with a hold-out testing performance of 1.71. When employing HMLSs, D4 + Minimum_Redundancy_Maximum_Relevance (MRMR)+K_Nearest_Neighbor Regressor achieved the highest performance of 1.05 ± 0.25 with a hold-out testing performance of 0.57.Conclusion.Our study shows the importance of using larger datasets (timeless), and utilizing optimized HMLSs, for significantly improved prediction of MoCA in PD patients.

Approach to the specificity and selectivity between D2 and D3 receptors by mutagenesis and binding experiments part I: Expression and characterization of D2 and D3 receptor mutants

D3/D2 sub-specificity is a complex problem to solve. Indeed, in the absence of easy structural biology of the G-protein coupled receptors, and despite key progresses in this area, the systematic knowledge of the ligand/receptor relationship is difficult to obtain. Due to these structural biology limitations concerning membrane proteins, we favored the use of directed mutagenesis to document a rational towards the discovery of markedly specific D3 ligands over D2 ligands together with basic binding experiments. Using our methodology of stable expression of receptors in HEK cells, we constructed the gene encoding for 24 mutants and 4 chimeras of either D2 or D3 receptors and expressed them stably. Those cell lines, expressing a single copy of one receptor mutant each, were stably constructed, selected, amplified and the membranes from them were prepared. Binding data at those receptors were obtained using standard binding conditions for D2 and D3 dopamine receptors. We generated 26 new molecules derived from D2 or D3 ligands. Using 8 reference compounds and those 26 molecules, we characterized their binding at those mutants and chimeras, exemplifying an approach to better understand the difference at the molecular level of the D2 and D3 receptors. Although all the individual results are presented and could be used for minute analyses, the present report does not discuss the differences between D2 and D3 data. It simply shows the feasibility of the approach and its potential.

Influence of COMT (rs4680) and DRD2 (rs1076560, rs1800497) Gene Polymorphisms on Safety and Efficacy of Methylphenidate Treatment in Children with Fetal Alcohol Spectrum Disorders

Fetal alcohol spectrum disorders (FASD) in a course of high prenatal alcohol exposure (hPAE) are among the most common causes of developmental disorders. The main reason for pharmacological treatment of FASD children is attention deficit hyperactivity disorder (ADHD), and methylphenidate (MPH) is the drug of choice. The aim of the study was to assess whether children born of hPAE with ADHD, with or without morphological FASD, differ in terms of catechol-O-methyltransferase (COMT) and dopamine receptor D2 (DRD2) gene polymorphisms, and if genetic predisposition affects response and safety of MPH treatment. The polymorphisms of COMT (rs4680) and DRD2 (rs1076560, rs1800497) were analyzed in DNA samples. A borderline significance was found for the correlation between MPH side effects and the G allele of COMT (rs4680) (p = 0.04994) in all ADHD children. No effect of COMT (rs4680) and DRD2 (rs1076560, rs1800497) polymorphisms and the treatment efficacy was observed. The analyzed DRD2 and COMT gene polymorphisms seem to play no role in MPH efficacy in ADHD children with hPAE, while low-activity COMT (Met158) variant carriers may be more intolerant to MPH. The MPH treatment is effective in ADHD independent of FASD, although the ADHD-FASD variant requires higher doses to be successful. These results may help in optimization and individualization in child psychiatry.

Longitudinal clustering analysis and prediction of Parkinson's disease progression using radiomics and hybrid machine learning

BACKGROUND

We employed machine learning approaches to (I) determine distinct progression trajectories in Parkinson's disease (PD) (unsupervised clustering task), and (II) predict progression trajectories (supervised prediction task), from early (years 0 and 1) data, making use of clinical and imaging features.

METHODS

We studied PD-subjects derived from longitudinal datasets (years 0, 1, 2 & 4; Parkinson's Progressive Marker Initiative). We extracted and analyzed 981 features, including motor, non-motor, and radiomics features extracted for each region-of-interest (ROIs: left/right caudate and putamen) using our standardized standardized environment for radiomics analysis (SERA) radiomics software. Segmentation of ROIs on dopamine transposer - single photon emission computed tomography (DAT SPECT) images were performed via magnetic resonance images (MRI). After performing cross-sectional clustering on 885 subjects (original dataset) to identify disease subtypes, we identified optimal longitudinal trajectories using hybrid machine learning systems (HMLS), including principal component analysis (PCA) + K-Means algorithms (KMA) followed by Bayesian information criterion (BIC), Calinski-Harabatz criterion (CHC), and elbow criterion (EC). Subsequently, prediction of the identified trajectories from early year data was performed using multiple HMLSs including 16 Dimension Reduction Algorithms (DRA) and 10 classification algorithms.

RESULTS

We identified 3 distinct progression trajectories. Hotelling's t squared test (HTST) showed that the identified trajectories were distinct. The trajectories included those with (I, II) disease escalation (2 trajectories, 27% and 38% of patients) and (III) stable disease (1 trajectory, 35% of patients). For trajectory prediction from early year data, HMLSs including the stochastic neighbor embedding algorithm (SNEA, as a DRA) as well as locally linear embedding algorithm (LLEA, as a DRA), linked with the new probabilistic neural network classifier (NPNNC, as a classifier), resulted in accuracies of 78.4% and 79.2% respectively, while other HMLSs such as SNEA + Lib_SVM (library for support vector machines) and t_SNE (t-distributed stochastic neighbor embedding) + NPNNC resulted in 76.5% and 76.1% respectively.

CONCLUSIONS

This study moves beyond cross-sectional PD subtyping to clustering of longitudinal disease trajectories. We conclude that combining medical information with SPECT-based radiomics features, and optimal utilization of HMLSs, can identify distinct disease trajectories in PD patients, and enable effective prediction of disease trajectories from early year data.

Nardosinone Alleviates Parkinson's Disease Symptoms in Mice by Regulating Dopamine D2 Receptor

Nardostachyos Radix et Rhizoma (nardostachys) is the root and rhizome of Nardostachys jatamansi DC. Recent studies have shown that nardostachys may exert an anti-PD effect. In this study, the UHPLC-LTQ-Orbitrap-MS method was used to analyze the brain components of nardostachys in rats. Based on the results of UHPLC-LTQ-Orbitrap-MS analysis, nardosinone was identified to be the most effective anti-PD compound in nardostachys. To further verify this inference, a mouse PD model was established and the effect of nardosinone on PD mice was determined using classic behavioral tests. The results showed that nardosinone was indeed effective for relieving PD symptoms in mice. Moreover, network pharmacology analysis was used to elucidate the mechanism underlying the anti-PD effect of nardosinone. Dopamine receptor D2 (DRD2) was identified as the key target of nardosinone-PD interaction network, which was further verified by molecular docking and Western blotting. The results demonstrated that nardosinone and DRD2 could interact with each other. Furthermore, the expression level of DRD2 was decreased in the brain tissue of PD mice, and nardosinone could restore its expression to a certain extent. In conclusion, our findings suggest that nardosinone may reduce the motor and cognitive symptoms in the animal PD model by regulating DRD2 expression.

Regulatory rare variants of the dopaminergic gene ANKK1 as potential risk factors for Parkinson's disease

Parkinson’s disease (PD) is characterized by cerebral dopamine depletion that causes motor and cognitive deficits. The dopamine-related gene ANKK1 has been associated with neuropsychiatric disorders with a dopaminergic deficiency in the striatum. This study aims to define the contribution of ANKK1 rare variants in PD. We found in 10 out of 535 PD patients 6 ANKK1 heterozygous rare alleles located at the 5′UTR, the first exon, intron 1, and the nearby enhancer located 2.6 kb upstream. All 6 ANKK1 single nucleotide variants were located in conserved regulatory regions and showed significant allele-dependent effects on gene regulation in vitro. ANKK1 variant carriers did not show other PD-causing Mendelian mutations. Nevertheless, four patients were heterozygous carriers of rare variants of ATP7B gene, which is related to catecholamines. We also found an association between the polymorphic rs7107223 of the ANKK1 enhancer and PD in two independent clinical series (P = 0.007 and 0.021). rs7107223 functional analysis showed significant allele-dependent effects on both gene regulation and dopaminergic response. In conclusion, we have identified in PD patients functional variants at the ANKK1 locus highlighting the possible relevance of rare variants and non-coding regulatory regions in both the genetics of PD and the dopaminergic vulnerability of this disease.

Polymorphisms of Dopamine Receptor Genes and Parkinson's Disease: Clinical Relevance and Future Perspectives

Parkinson’s disease (PD) is a neurodegenerative disease caused by loss of dopaminergic neurons in the midbrain. PD is clinically characterized by a variety of motor and nonmotor symptoms, and treatment relies on dopaminergic replacement. Beyond a common pathological hallmark, PD patients may present differences in both clinical progression and response to drug therapy that are partly affected by genetic factors. Despite extensive knowledge on genetic variability of dopaminergic receptors (DR), few studies have addressed their relevance as possible influencers of clinical heterogeneity in PD patients. In this review, we summarized available evidence regarding the role of genetic polymorphisms in DR as possible determinants of PD development, progression and treatment response. Moreover, we examined the role of DR in the modulation of peripheral immunity, in light of the emerging role of the peripheral immune system in PD pathophysiology. A better understanding of all these aspects represents an important step towards the development of precise and personalized disease-modifying therapies for PD.

Differences in MTHFR and LRRK2 variant's association with sporadic Parkinson's disease in Mexican Mestizos correlated to Native American ancestry

Parkinson's disease (PD), a common neurodegenerative disorder, has a complex etiology where environmental and genetic factors intervene. While a number of genes and variants have been identified in recent decades as causative or protective agents of this condition, a limited number of studies have been conducted in mixed populations, such as Mexican Mestizos. The historical convergence of two founding groups and three ethnicities, and the increasing north-to-south gradient of Native American ancestry in Mexico resulted in a subpopulation structure with considerable genetic diversity. In this work, we investigate the influence of 21 known susceptibility variants for PD. Our case-control study, with a cohort of 311 Mexican Mestizo subjects, found a significant risk association for the variant rs1491942 in LRRK2. However, when stratification by ancestry was performed, a risk effect for MTHFR rs1801133 was observed only in the group with the highest percentage of European ancestry, and the PD risk effect for LRRK2 rs1491942 was significant in subjects with a higher ratio of Native American ancestry. Meta-analyses of these SNP revealed the effect of LRRK2 rs1491942 to be even more significant than previously described in populations of European descent. Although corroboration is necessary, our findings suggest that polymorphism rs1491942 may be useful as a risk marker of PD in Mexican Mestizos with greater Native American ancestry. The absence of associations with the remaining known risk factors is, in itself, a relevant finding and invites further research into the shared risk factors' role in the pathophysiological mechanisms of this neurodegenerative disorder.

Association of Multiple Dopamine D3 Receptor Gene 3'UTR Polymorphisms with Susceptibility to Parkinson's Disease and Clinical Efficacy of Piribedil Therapy

Objective: To investigate the correlation between the Dopamine D3 receptor (DRD3) 3'untranslated region (3'UTR) gene polymorphism and susceptibility to Parkinson's disease (PD) and the clinical effect of the DRD2 and DRD3 agonist piribedil treatment. Methods: Sanger sequencing was used to analyze the single nucleotide polymorphisms (SNPs) within the 3'UTR rs76126170, rs9868039, rs9817063, and rs3732790 loci of the DRD3 gene in 284 PD patients and 284 controls. PD patients were treated with piribedil sustained-release tablets (50 mg) combined with levodopa and benserazide hydrochloride tablets, three times daily (patients with first-diagnosed PD were only administrated with piribedil sustained-release tablets) for 3 months. The Unified Parkinson's Disease Rating Scale (UPDRS) and the Hoehn and Yahr disease stage were evaluated at baseline and after 3 months of treatment. Results: The T allele carriers of the DRD3 gene rs76126170 locus were more susceptible to PD than the C allele carriers (odds ratio [OR] = 3.44, 95% confidence interval [CI]: 2.46-4.80, p < 0.01). Carriers of the rs9868039 A allele had a decreased risk of PD compared to those with G allele (OR = 0.67, 95% CI: 0.53-0.86, p < 0.01). C allele carriers at rs9817063 were less likely to develop PD than those with T allele (OR = 0.74, 95% CI: 0.58-0.94, p = 0.02). No significant correlation was observed between the alleles or genotypes of the rs3732790 locus and PD susceptibility (p > 0.05). The various genotypes of the DRD3 gene loci rs76126170, rs9868039, and rs9817063 in PD patients were associated with significant differences with regard to reduction of UPDRS scores and Hoehn and Yahr stage after 3 months of treatment (p < 0.05). Conclusion: The alleles and genotypes of the DRD3 gene 3' UTR SNP loci rs76126170, rs9868039, and rs9817063 are associated with PD susceptibility and the clinical efficacy of piribedil treatment.

Influence of serum concentration in retinoic acid and phorbol ester induced differentiation of SH-SY5Y human neuroblastoma cell line

Numerous protocols to establish dopaminergic phenotype in SH-SY5Y cells have been reported. In most of these protocols there are variations in concentration of serum used. In this paper, we compared the effects of high (10%), low (3%) and descending (2.5%/1%) serum concentration in differentiation medium containing different proportion of retinoic acid (RA) and 12-O-Tetradecanoylphorbol-13-acetate (TPA) or RA-only on the undifferentiated SH-SY5Y cells with regards to cell morphology, biochemical and gene expression alterations. Cells differentiated in culture medium containing low and descending serum concentrations showed increased number of neurite projections and reduced proliferation rates when compared to undifferentiated cells. The SH-SY5Y cells differentiated in culture medium containing 3% RA and low serum or descending (2.5%/1% RA/TPA) were found to be more susceptible to 6-hydroxydopamine (6-OHDA) induced cytotoxicity. Cells differentiated with RA/TPA or RA differentiated showed increased production of the α-synuclein (SNCA) neuroprotein and dopamine neurotransmitter compared to undifferentiated cells, regardless serum concentrations used. There was no significant difference in the expression of tyrosine hydroxylase (TH) gene between undifferentiated and differentiated SH-SY5Y cells. However, the expression of dopamine receptor D2 (DRD2) gene was markedly increased (p<0.05) in differentiated cells with 3% serum and RA only when compared to undifferentiated cells. In conclusion, to terminally differentiate SH-SY5Y cells to be used as a cell-based model to study Parkinson's disease (PD) to investigate molecular mechanisms and drug discovery, the optimal differentiation medium should contain 3% serum in RA-only.

Contribution of functional dopamine D2 and D3 receptor variants to motor and non-motor symptoms of early onset Parkinson's disease

In the present study, we focused on investigating the contribution of functional dopamine D2 and D3 receptor variants to motor and/or non-motor symptoms of early onset Parkinson's disease (EOPD). Three functional single nucleotide polymorphisms (SNPs), DRD3 rs6280, DRD2 rs2283265 and DRD2 rs1076560, were genotyped in 128 Turkish EOPD patients and then, statistical analysis was conducted for the potential impacts of SNPs on clinical parameters. All three SNPs were found to be statistically significant in terms of PD-related pain: DRD3 [rs6280; risk allele "T" for pain; p = 0.031; odds ratio (OR)=4.25], DRD2 [rs2283265; risk allele "A" for pain; p = 0.001; OR=8.47] and, DRD2 [rs1076560; risk allele "A" for pain; p = 0.022; OR=4.58]. Additionally, bilateral disease [p = 0.011; OR=5.10] and gender [risk group "female"; p = 0.003; OR=8.53] were also identified as significant univariate risk factors for PD-related pain. Based on logistic regression analysis conducted with the significant univariate risk factors, this the first report to clarify that a female patient with bilateral PD and DRD2 rs2283265 polymorphism has a significant risk for PD-related pain. Our findings might contribute to improve life quality by offering treatment options for pain in PD patients with these clinical and genetic features.

Dopamine D3 receptor: A neglected participant in Parkinson Disease pathogenesis and treatment?

Parkinson disease (PD) is a neurodegenerative disorder characterized by motor and non-motor symptoms which relentlessly and progressively lead to substantial disability and economic burden. Pathologically, these symptoms follow the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) associated with abnormal α-synuclein (α-Syn) deposition as cytoplasmic inclusions called Lewy bodies in pigmented brainstem nuclei, and in dystrophic neurons in striatal and cortical regions (Lewy neurites). Pharmacotherapy for PD focuses on improving quality of life and primarily targets dopaminergic pathways. Dopamine acts through two families of receptors, dopamine D1-like and dopamine D2-like; dopamine D3 receptors (D3R) belong to dopamine D2 receptor (D2R) family. Although D3R's precise role in the pathophysiology and treatment of PD has not been determined, we present evidence suggesting an important role for D3R in the early development and occurrence of PD. Agonist activation of D3R increases dopamine concentration, decreases α-Syn accumulation, enhances secretion of brain derived neurotrophic factors (BDNF), ameliorates neuroinflammation, alleviates oxidative stress, promotes neurogenesis in the nigrostriatal pathway, interacts with D1R to reduce PD associated motor symptoms and ameliorates side effects of levodopa (L-DOPA) treatment. Furthermore, D3R mutations can predict PD age of onset and prognosis of PD treatment. The role of D3R in PD merits further research. This review elucidates the potential role of D3R in PD pathogenesis and therapy.

Association between dopamine receptor D2 TaqIA polymorphism and Parkinson disease risk: a meta-analysis

Although many publications have evaluated the correlation between dopamine receptor D2 (DRD2) TaqIA polymorphism and Parkinson disease (PD), the results remain inconclusive. In order to further address the association between DRD2 TaqIA polymorphism and PD risk, we performed a meta-analysis of all eligible studies from more databases. Related studies were identified from six databases involving PubMed, Springer Link, Ovid, Chinese Wanfang Data Knowledge Service Platform, Chinese National Knowledge Infrastructure (CNKI), and Chinese Biology Medicine (CBM) through Octorber 2018. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were used to assess the strength of the associations. A total of 13 studies including 3558 PD patients and 10186 controls were involved in this meta-analysis. Overall, no significant association was found between DRD2 TaqIA polymorphism and PD risk in the total population. A further subgroup study by ethnicity showed a significant association between DRD2 TaqIA polymorphism and PD in Caucasians (for A1 vs. A2: P=0.02, OR=1.14, 95% CI: 1.02-1.27; for (A1A1 + A1A2) vs. A2A2: P=0.03, OR=1.16, 95% CI: 1.02-1.33). No significant results were observed in Asians. In conclusion, this meta-analysis provides evidence that DRD2 TaqIA polymorphism may contribute to the PD development in Caucasians, and large-scale well-designed studies are required in future to confirm this conclusion.

Association between the DRD2 TaqIA gene polymorphism and Parkinson disease risk: an updated meta-analysis

BACKGROUND

DRD2 TaqIA polymorphism may be associated with an increased risk of developing Parkinson disease (PD). However, the individual study's results are still inconsistent.

METHODS

A meta-analysis of 4232 cases and 4774 controls from 14 separate studies were performed to explore the possible relationship between the DRD2 TaqIA gene polymorphism and PD. Pooled odds ratios (ORs) for the association and the corresponding 95% confidence intervals (CIs) were evaluated by a fixed-effect model.

RESULTS

The pooled results revealed a significant association between DRD2 gene TaqIA polymorphism under recessive genetic model (OR: 0.91, 95% CI:0.83,0.99, P = .031) and additive genetic models (OR:0.93,95%CI:0.87,0.99, P = .032), but not associated with PD susceptibility under other genetic models in the whole population. Moreover, subgroups based on ethnicity and genotyping methods showed this association in the Caucasian subgroup under recessive genetic model (OR: 0.85, 95% CI:0.76,0.95, P = .003) and additive genetic models (OR:0.87,95%CI:0.79,0.96, P = .004) were existed. Besides, no significant association was detected under 6 genetic models in the Asian populations and PCR-RFLP subgroup.

CONCLUSIONS

The current meta-analysis suggested that a significant association between DRD2 TaqIA polymorphism and PD under the recessive genetic mode, and additive genetic models, especially in Caucasians.

Axonal degeneration in Parkinson's disease - Basal ganglia circuitry and D2 receptor availability

Basal ganglia (BG) circuitry plays a crucial role in the control of movement. Degeneration of its pathways and imbalance of dopaminergic signalling goes along with movement disorders such as Parkinson's disease. In this study, we explore the interaction of degeneration in two BG pathways (the nigro-striatal and dentato-pallidal pathway) with D2 receptor signalling to elucidate an association to motor impairment and medication response. Included in the study were 24 parkinsonian patients [male, 62 years (± 9.3 SD)] compared to 24 healthy controls [male, 63 years (± 10.2 SD)]; each participant passed through three phases of the study (i) acquisition of metadata/clinical testing, (ii) genotyping and (iii) anatomical/diffusion MRI. We report a decline in nigro-striatal (p < .003) and dentato-pallidal (p < .0001) connectivity in the patients compared to controls, which is associated with increasing motor impairment (relating to nigro-striatal, r = -0.48; p < .001 and dentato-pallidal connectivity, r = -0.36; p = .035). Given, that variations of the ANKK1 Taq1 (rs 1,800,497) allele alters dopamine D2-dependent responses, all participants were genotyped respectively. By grouping patients (and controls) according to their ANKK1 genotype, we demonstrate a link between D2 receptor signalling and decline in connectivity in both investigated pathways for the A1- variant (nigro-striatal pathway: r = -0.53; p = .012, dentato-pallidal pathway: r = -0.62; p = .0012). In patients with the A1+ variant, we only found increased brain connectivity in the dentato-pallidal pathway (r = 0.71; p = .001) correlating with increasing motor impairment, suggesting a potentially compensatory function of the cerebellum. Related to medication response carriers of the A1+ variant had a better drug effect associated with stronger brain connectivity in the nigro-striatal pathway (r = 0.54; p < .02); the A1- group had a good medication response although nigro-striatal connectivity was diminished (r = -0.38; p < .05); these results underscore differences in receptor availability between both groups in the nigro-striatal pathway. No effect onto medication response was found in the dentato-pallidal pathway (p > .05). Interplay between basal ganglia connectivity and D2 receptor availability influence the clinical presentation and medication response of parkinsonian patients. Furthermore, while current models of basal-ganglia function emphasize that balanced activity in the direct and indirect pathways is required for normal movement, our data highlight a role of the cerebellum in compensating for physiological imbalances in this respect.

Dopamine receptor D2 genetic variations is associated with the risk and clinicopathological variables of urothelial cell carcinoma in a Taiwanese population

Dopamine receptor D2 (DRD2) is overexpressed in several kinds of cancers and was correlated with the prognosis of these cancers. Polymorphisms within the DRD2 gene were shown to be associated with lung and colon cancers. The purpose of this study was to explore effects of DRD2 gene polymorphisms on the susceptibility to and clinicopathological characteristics of urothelial cell carcinoma (UCC). In total, 369 patients diagnosed with UCC and 738 healthy controls were enrolled to analyze DRD2 genotypes at four loci (rs1799732, -141C>del; rs1079597, TaqIB; rs6277, 957C>T; and rs1800497, TaqIA) using a TaqMan-based real-time polymerase chain reaction (PCR). We found a significantly lower risk for UCC in individuals with the DRD2 rs6277 CT genotype compared to those with the wild-type CC genotype (adjusted odds ratio (AOR)=0.405, 95% confidence interval (CI): 0.196~0.837, p=0.015). In 124 younger patients (aged < 65 years) of the recruited UCC cohort, patients who carried at least one T allele of DRD2 rs1800497 were at higher risk (AOR=2.270, 95% CI: 1.060~4.860, p=0.033) of developing an invasive stage (pT2~pT4). In 128 female patients of the recruited UCC cohort, patients who carried at least one deletion allele of DRD2 rs1799732 showed a higher incidence of having an invasive stage (AOR=2.585, 95% CI: 1.066~6.264, p=0.032) and a large tumor (AOR=2.778, 95% CI: 1.146~6.735, p=0.021). Further analyses of The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) datasets revealed correlations of the expression of DRD2 with an invasive tumor, tumor metastasis, and the lower survival rate in patients with UCC. Our findings suggest that DRD2 levels might affect the progression of UCC, and the polymorphisms rs6277, rs1800497, and rs1799732 of DRD2 are probably associated with the susceptibility and clinicopathologic development of UCC in a Taiwanese population.

Association of the DRD2 CAn-STR and DRD3 Ser9Gly polymorphisms with Parkinson's disease and response to dopamine agonists

Dopamine agonists (DAs) play important roles in the treatment of Parkinson's disease (PD). Currently, it is thought that genetic variations in the genes encoding dopamine receptors (DR) are important factors in determining inter-individual variability in drug responses. To investigate the association between Dopamine receptor D type 2 (DRD2) dinucleotide short tandem repeat (CA_n-STR) and Dopamine receptor D type 3 (DRD3) Ser9Gly polymorphisms and the risk of PD, as well as the possible reasons for PD patients using different doses of DAs, we recruited 168 idiopathic PD patients and 182 controls. There were no significant differences in DRD2 CA_n-STR and DRD3 Ser9Gly genotypes (p=0.184, p=0.196) or in allele frequencies (p=0.239, p=0.290) between PD patients and controls. There was no association between DRD2 CA_n-STR polymorphism and doses of DAs. Among three different DRD3 Ser9Gly genotypes (Ser/Ser, Ser/Gly, Gly/Gly), patients carrying Gly/Gly genotype used higher doses of DAs than patients with Ser/Gly and Ser/Ser genotypes (p=0.001). In pramipexole subgroup, the Gly/Gly group took more pramipexole than the other genotype groups (p<0.001), whereas the doses of piribedil were not significantly different among three genotypes (p=0.735). Our results suggest that genotype in DRD3 Ser9Gly was the main factor determining different doses of DAs and PD patients carrying Gly/Gly genotype require higher doses of pramipexole for effective treatment. This study may provide insights into understanding possible reasons for different responses to DAs in Chinese PD patients.

[The association of the DRD3 gene with Parkinson's disease]

OBJECTIVE

To investigate the association between dopamine receptor DRD3 gene tag single nucleotide polymorphisms (SNPs) and the risk of Parkinson's disease (PD).

MATERIAL AND METHODS

One hundred and forty-three patients with PD and 96 healthy individuals from the Russian population were examined. Ten tag SNPs (rs963468, rs2134655, rs9817063, rs324035, rs11721264, rs1800828, rs3773678, rs167770, rs167771, rs7633291) within DRD3 have been genotyped.

RESULTS AND CONCLUSION

Associations between 4 polymorphisms (rs11721264, rs3773678, rs167771, rs324035) and PD have been found. Our study confirms the involvement of polymorphic features of dopamine receptors genes in the pathophysiology in PD.

Advances in understanding genomic markers and pharmacogenetics of Parkinson's disease

INTRODUCTION

The inheritance pattern of Parkinson's disease (PD) is likely multifactorial (owing to the interplay of genetic predisposition and environmental factors). Many pharmacogenetic studies have tried to establish a possible role of candidate genes in PD risk. Several studies have focused on the influence of genes in the response to antiparkinsonian drugs and in the risk of developing side-effects of these drugs.

AREAS COVERED

This review presents an overview of current knowledge, with particular emphasis on the most recent advances, both in case-control association studies on the role of candidate genes in the risk for PD as well as pharmacogenetic studies on the role of genes in the development of side effects of antiparkinsonian drugs. The most reliable results should be derived from meta-analyses of case-control association studies on candidate genes involving large series of PD patients and controls, and from genome-wide association studies (GWAS).

EXPERT OPINION

Prospective studies of large samples involving several genes with a detailed history of exposure to environmental factors in the same cohort of subjects, should be useful to clarify the role of genes in the risk for PD. The results of studies on the role of genes in the development of side-effects of antiparkinsonian drugs should, at this stage, only be considered preliminary.

Efficient and biologically relevant consensus strategy for Parkinson's disease gene prioritization

BACKGROUND

The systemic information enclosed in microarray data encodes relevant clues to overcome the poorly understood combination of genetic and environmental factors in Parkinson's disease (PD), which represents the major obstacle to understand its pathogenesis and to develop disease-modifying therapeutics. While several gene prioritization approaches have been proposed, none dominate over the rest. Instead, hybrid approaches seem to outperform individual approaches.

METHODS

A consensus strategy is proposed for PD related gene prioritization from mRNA microarray data based on the combination of three independent prioritization approaches: Limma, machine learning, and weighted gene co-expression networks.

RESULTS

The consensus strategy outperformed the individual approaches in terms of statistical significance, overall enrichment and early recognition ability. In addition to a significant biological relevance, the set of 50 genes prioritized exhibited an excellent early recognition ability (6 of the top 10 genes are directly associated with PD). 40 % of the prioritized genes were previously associated with PD including well-known PD related genes such as SLC18A2, TH or DRD2. Eight genes (CCNH, DLK1, PCDH8, SLIT1, DLD, PBX1, INSM1, and BMI1) were found to be significantly associated to biological process affected in PD, representing potentially novel PD biomarkers or therapeutic targets. Additionally, several metrics of standard use in chemoinformatics are proposed to evaluate the early recognition ability of gene prioritization tools.

CONCLUSIONS

The proposed consensus strategy represents an efficient and biologically relevant approach for gene prioritization tasks providing a valuable decision-making tool for the study of PD pathogenesis and the development of disease-modifying PD therapeutics.

Association of Parkinson disease age of onset with DRD2, DRD3 and GRIN2B polymorphisms

INTRODUCTION

Dopamine and glutamate are crucial neurotransmitters in Parkinson disease (PD). While recent large meta-analyses reported that genetic variation of dopamine (DRD2, DRD3) and glutamine (NMDA, GRIN2B) neurotransmitter receptors was not associated with PD risk, they could conceivably influence PD phenotype. We studied the association of these receptor polymorphisms relating to PD age of onset.

METHODS

There were 664 PD patients and 718 controls, all Caucasian, with stored DNA at Mayo Clinic, Jacksonville, Florida. Genotyping was performed for DRD2 (Taq 1A, rs1800497), DRD3 (rs6280), and NMDA (GRIN2B, rs7301328) polymorphisms with ABI Taqman assays. Single nucleotide polymorphism associations with age of onset were evaluated using dominant, recessive, and additive genotypic models.

RESULTS

DRD3 variant carriers had an approximate 4.4-year decrease in mean age of onset when both copies of the minor allele were present (P = 0.0034) and an approximate 1.5-year decrease in mean age at onset for every additional minor allele (P = 0.023) (recessive and additive models, respectively). There was no association with age of onset for DRD2 or GRIN2B under any statistical model (all P ≥ 0.22).

CONCLUSIONS

The DRD3 (rs6280) polymorphism, but not DRD2 (Taq1A) or GRIN2B, influences younger PD age of onset in the US Caucasian population. Validation of these findings in larger studies with other ethnic groups is indicated.

Association of BDNF and BCHE with Alzheimer's disease: Meta-analysis based on 56 genetic case-control studies of 12,563 cases and 12,622 controls

Alzheimer's disease (AD) is a common neurodegenerative disorder that can destroy the memory of sufferers and lead to distress for the individual and society. Brain-derived neurotrophic factor (BDNF) and butyrylcholinesterase (BCHE) are two genes associated with β-amyloid plaques and neurofibrillary tangles that are two key factors in the pathophysiology of AD. The aim of the current meta-analysis was to evaluate the association between BDNF Val66Met (rs6265), BDNF C270T (rs2030324) and BCHE-K (rs1803274) polymorphisms and AD. A comprehensive meta-analysis was performed using the online database PubMed without a time limitation. A total of 56 articles evaluating 12,563 cases and 12,622 controls were selected for the current meta-analysis. The results showed a moderate association of the BDNF C270T polymorphism with the risk of AD in Asians under a dominant model (P=0.03; odds ratio, 1.88; 95% confidence interval, 1.08-3.27). No other significant association was found during the meta-analysis for the other two polymorphisms (P>0.05). The current meta-analysis suggests that BDNF C270T is a risk factor for AD in Asians. This meta-analysis has been, to the best of our knowledge, the most comprehensive meta-analysis of BDNF Val66Met, BDNF C270T and BCHE-K to date.

Meta-analyses of seven GIGYF2 polymorphisms with Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder that affects ~2% of the global population aged ≥65 years. Grb10-interacting GYF protein-2 (GIGYF2) can influence the development of PD through the regulation of insulin-like growth factor-1. The aim of the present meta-analysis study was to establish the contribution of GIGYF2 polymorphisms to PD. The study was conducted based on nine eligible studies consisting of 7,246 PD patients and 7,544 healthy controls. The results indicated that the GIGYF2 C.3630A>G polymorphism increased the risk of PD by 37% [P=0.008; odds ratio (OR), 1.37; 95% confidence interval (CI), 1.08-1.73] and that the GIGYF2 C.167G>A polymorphism was significantly associated with PD (P=0.003; OR, 3.67; 95% CI, 1.56-8.68). The meta-analyses of the other five GIGYF2 polymorphisms (C.1378C>A, C.1554G>A, C.2940A>G, C.1370C>A and C.3651G>A) did not reveal any significant associations. The present meta-analyses of the GIGYF2 genetic polymorphisms may provide a comprehensive overview of this PD candidate gene for future studies.