The DRD2 gene in psychiatric and neurological disorders and its phenotypes

Dopamine promotes osteogenic differentiation of PDLSCs by activating DRD1 and DRD2 during orthodontic tooth movement via ERK1/2 signaling pathway

Introduction

Orthodontic tooth movement (OTM) involves complex interactions between mechanical forces and periodontal tissue adaptation, mainly mediated by periodontal ligament cells, including periodontal ligament stem cells (PDLSCs), osteoblasts, and osteoclasts. Dopamine (DA), a neurotransmitter known for its critical role in bone metabolism, is investigated in this study for its potential to enhance osteogenic differentiation in PDLSCs, which are pivotal in OTM. This study examined the potential of DA to facilitate OTM by binding to DA receptors (D1R and D2R) and activating the ERK1/2 signaling pathway. We propose that DA's interaction with these receptors on PDLSCs could enhance osteogenic differentiation, thereby accelerating bone remodeling and reducing the duration of orthodontic treatments, which offering a novel approach to improve clinical outcomes in orthodontic care.

Methods

This study utilized a rat OTM model, micro-CT, histological analyses, and in vitro assays to investigate dopamine's effect on osteogenesis. PDLSCs were cultured and treated with DA, and cytotoxicity, osteogenic differentiation, gene and protein expression assessed.

Results

Dopamine administration significantly increased trabecular bone density and osteogenic marker expression in an OTM rat model. In vitro, DA at 10 nM optimally promoted human PDLSCs osteogenesis without affecting proliferation. Blocking DA receptors or inhibiting the ERK1/2 pathway attenuated these effects, underscoring the importance of dopaminergic signaling in tension-induced osteogenesis during OTM.

Conclusion

Taken together, our study reveals that local dopamine administration at a concentration of 10 nM not only enhances tension-induced osteogenesis in vivo but also significantly promotes osteogenic differentiation of PDLSCs in vitro through D1 and D2 receptor-mediated ERK1/2 signaling pathway activation.

Genetic Aspects of Problematic and Risky Internet Use in Young Men-Analysis of ANKK1, DRD2 and NTRK3 Gene Polymorphism

BACKGROUND

Internet addiction disorder (IAD) is characterized by an excess of uncontrolled preoccupations, urges, or behaviors related to computer use and Internet access that culminate in negative outcomes or individual distress. PIU includes excessive online activities (such as video gaming, social media use, streaming, pornography viewing, and shopping). The aim of this study was to analyze the association of gene polymorphisms that may influence the severity of risky behaviors in young men with the frequency of Internet use. We speculate that there are individual differences in the mechanisms of Internet addiction and that gene-hormone associations may represent useful biomarkers for subgroups of individuals.

MATERIALS AND METHODS

The study was conducted in a sample of 407 adult males. Subjects were asked to complete the Problematic Internet Use Test (PIUT). Serum was analyzed to determine concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone (TT), sex hormone binding protein (SHBG), dehydroepiandrosterone sulfate (DHEA-S), estradiol (E2), prolactin (PRL), insulin (I), serotonin (5-HT), and dopamine (DA), as well as DRD2, ANKK1, and NTRK3 gene polymorphisms.

RESULTS

In the analysis of the ANKK1 gene, there was a specific association between ANKK1 polymorphisms and PRL and 5-HT blood concentrations. There was also an association between the ANKK1 polymorphisms and LH and DA concentrations. When analyzing the DRD2 gene polymorphism, we found that in the group with a moderate level of Internet dependence, there was an association between both the G/GG and GG/GG polymorphisms and FSH concentration.

CONCLUSIONS

Our study found that there may be an association between the NTRK3 gene polymorphism and PIU. The polymorphisms of ANKK1 and DRD2 genes may be factors that influence the concentrations of hormones (PRL, 5-HT, DA) that are associated with the results obtained in PIU.

Genetic Correlates as a Predictor of Bariatric Surgery Outcomes after 1 Year

This study analyzed genetic risk assessments in patients undergoing bariatric surgery to serve as a predictive factor for weight loss parameters 1 year after the operation. Thirty (30) patients were assessed for Genetic Addiction Risk Severity (GARS), which analyzes neurogenetic polymorphisms involved in addiction and reward deficiency. Genetic and psychosocial data collected before the operation were correlated with weight loss data, including changes in weight, body mass index (BMI), and percent of expected weight loss (%EWL). Results examined correlations between individual gene risk alleles, 1-year body weight data, and psychosocial trait scores. Spearman's correlations revealed that the OPRM1 (rs1799971) gene polymorphism had significant negative correlation with 1-year weight (rs = -0.4477, p < 0.01) and BMI (rs = -0.4477, p < 0.05). In addition, the DRD2 risk allele (rs1800497) was correlated negatively with BMI at 1 year (rs = -0.4927, p < 0.05), indicating that one risk allele copy was associated with lower BMI. However, this allele was positively correlated with both ∆Weight (rs = 0.4077, p < 0.05) and %EWL (rs = 0.5521, p < 0.05) at 1 year post-surgery. Moreover, the overall GARS score was correlated with %EWL (rs = 0.4236, p < 0.05), ∆Weight (rs = 0.3971, p < 0.05) and ∆BMI (rs = 0.3778, p < 0.05). Lastly, Food Cravings Questionnaire (FCQ) scores were negatively correlated with %EWL (rs = -0.4320, p < 0.05) and ∆Weight at 1 year post-surgery (rs = -0.4294, p < 0.05). This suggests that individuals with a higher genetic addiction risk are more responsive to weight loss treatment, especially in the case of the DRD2 polymorphism. These results should translate clinically to improve positivity and attitude related to weight management by those individuals born with the risk alleles (rs1800497; rs1799971).

Translational Genomic Research: The Association between Genetic Profiles and Cognitive Functioning or Cardiac Function Among Breast Cancer Survivors Completing Chemotherapy

Introduction: Emerging evidence suggests that Chemotherapy (CT) treated breast cancer survivors (BCS) who have "risk variants" in genes may be more susceptible to cognitive impairment (CI) and/or poor cardiac phenotypes. The objective of this preliminary study was to examine whether there is a relationship between genetic variants and objective/subjective cognitive or cardiac phenotypes. Methods and Analysis: BCS were recruited from Moffitt Cancer Center, Morsani College of Medicine, AdventHealth Tampa and Sarasota Memorial Hospital. Genomic DNA were collected at baseline for genotyping analysis. A total of 16 single nucleotide polymorphisms (SNPs) from 14 genes involved in cognitive or cardiac function were evaluated. Three genetic models (additive, dominant, and recessive) were used to test correlation coefficients between genetic variants and objective/subjective measures of cognitive functioning and cardiac outcomes (heart rate, diastolic blood pressure, systolic blood pressure, respiration rate, and oxygen saturation). Results: BCS (207 participants) with a mean age of 56 enrolled in this study. The majority were non-Hispanic white (73.7%), married (63.1%), and received both CT and radiation treatment (77.3%). Three SNPs in genes related to cognitive functioning (rs429358 in APOE, rs1800497 in ANKK1, rs10119 in TOMM40) emerged with the most consistent significant relationship with cognitive outcomes. Among five candidate SNPs related to cardiac functioning, rs8055236 in CDH13 and rs1801133 in MTHER emerged with potential significant relationships with cardiac phenotype. Conclusions: These preliminary results provide initial targets to further examine whether BCS with specific genetic profiles may preferentially benefit from interventions designed to improve cognitive and cardiac functioning following CT.

A success targeted nano delivery to lung cancer cells with multi-walled carbon nanotubes conjugated to bromocriptine

In this research, a new nano drug-based multi-walled carbon nanotubes (MWCNTs) was prepared and evaluated qualitatively. Bromocriptine (BRC) was conjugated to functionalized carbon nanotubes. Then, the CHNS, FT-IR, SEM, and RAMAN tests for characterization of the conjugated drug were done. The nanofluid-containing nano-drug was evaluated on lung cancer cells (A549 & QU-DB) and MRC5 by MTT and flow cytometry tests. Then, the gene expression studies of dopamine receptor genes were done before and after nano-drug treatment. After that, a western blotting test was carried out for further investigation of dopamine receptors protein production. Finally, Bax and Bcl-2 secretion were measured by the ELISA method in cells affected by MWCNTs-BRC Nf compared to untreated cells. The results showed that the nano-drug had a significant lethal effect on cancer cells, while it had no toxicity on MRC5. Also, the nano-drug could significantly induce apoptosis in lung cancer cells at a lower dose compared to the drug alone. In this study, a targeted nano-drug delivery system was designed, and its performance was evaluated based on neurotransmitter pathways, and the results showed that it may be useful in the treatment of lung cancer. However, additional studies on animal models are underway.

Hypothesizing Nutrigenomic-Based Precision Anti-Obesity Treatment and Prophylaxis: Should We Be Targeting Sarcopenia Induced Brain Dysfunction?

Background: The United States Centers for Disease Control and Prevention (CDC) estimates a total obesity rate of 30% for 12 states and a 20% obesity rate nationwide. The obesity epidemic continues to increase in spite of preventative measures undertaken worldwide. Pharmacological treatments promise to reduce total fat mass. However, medications may have significant side effects and can be potentially fatal. Data Retrieval: This brief review, based on a PUBMED search of the key terms "Obesity" and" Sarcopenia," will present evidence to corroborate the existence of Reward Deficiency Syndrome (RDS) in obesity and the involvement of catecholaminergic pathways in substance seeking behavior, particularly as it relates to carbohydrates cravings. Expert Opinion: The genetic basis and future genetic testing of children for risk of aberrant generalized craving behavior are considered a prevention method. Here we present evidence supporting the use of precursor amino acid therapy and modulation of enkephalinase, MOA, and COMT inhibition in key brain regions. Such treatments manifest in improved levels of dopamine/norepinephrine, GABA, serotonin, and enkephalins. We also present evidence substantiating insulin sensitivity enhancement via Chromium salts, which affect dopamine neuronal synthesis regulation. We believe our unique combination of natural ingredients will influence many pathways leading to the promotion of well-being and normal healthy metabolic functioning. Sarcopenia has been shown to reduce angiogenesis and possible cerebral blood flow. Exercise seems to provide a significant benefit to overcome this obesity-promoting loss of muscle density. Conclusion: Utilization of proposed nutrigenomic formulae based on coupling genetic obesity risk testing promotes generalized anti-craving of carbohydrates and can inhibit carbohydrate bingeing, inducing significant healthy fat loss and relapse prevention.

The Non-Anhydrous, Minimally Basic Synthesis of the Dopamine D2 Agonist [18F]MCL-524

The dopamine D2 agonist MCL-524 is selective for the D2 receptor in the high-affinity state (D2high), and, therefore, the PET analogue, [18F]MCL-524, may facilitate the elucidation of the role of D2high in disorders such as schizophrenia. However, the previously reported synthesis of [18F]MCL-524 proved difficult to replicate and was lacking experimental details. We therefore developed a new synthesis of [18F]MCL-524 using a "non-anhydrous, minimally basic" (NAMB) approach. In this method, [18F]F- is eluted from a small (10-12 mg) trap-and-release column with tetraethylammonium tosylate (2.37 mg) in 7:3 MeCN:H2O (0.1 mL), rather than the basic carbonate or bicarbonate solution that is most often used for [18F]F- recovery. The tosylated precursor (1 mg) in 0.9 mL anhydrous acetonitrile was added directly to the eluate, without azeotropic drying, and the solution was heated (150 °C/15 min). The catechol was then deprotected with the Lewis acid In(OTf)3 (10 equiv.; 150 °C/20 min). In contrast to deprotection with protic acids, Lewis-acid-based deprotection facilitated the efficient removal of byproducts by HPLC and eliminated the need for SPE extraction prior to HPLC purification. Using the NAMB approach, [18F]MCL-524 was obtained in 5-9% RCY (decay-corrected, n = 3), confirming the utility of this improved method for the multistep synthesis of [18F]MCL-524 and suggesting that it may applicable to the synthesis of other 18F-labeled radiotracers.

[Parkinson's disease and neuropsychology]

Liepelt-Scarfone et al. 1 legen einen sorgfältig erarbeiteten, informativen und (hoffentlich) handlungsleitenden Artikel zur neuropsychologischen Diagnostik bei Verdacht auf leichte kognitive Störungen bei M.Parkinson und Parkinson-Demenz vor. Besonders beeindruckt hat mich Tabelle 3, in der Effektstärken für die Unterscheidung von Parkinson-Patienten und „neurodegenerativ gesunden Personen“ für eine Vielzahl von neuropsychologischen Tests angegeben werden. Cohens d beschreibt für Werte zwischen 0,5 bis 0,8 einen mittleren, ab 0,8 einen starken Effekt. Es ist davon auszugehen, dass auch Parkinson-Patienten, die nicht die Kriterien der leichten kognitiven Störung oder der Demenz erfüllen, neuropsychologische Auffälligkeiten aufweisen.

Detecting local genetic correlations with scan statistics

Genetic correlation analysis has quickly gained popularity in the past few years and provided insights into the genetic etiology of numerous complex diseases. However, existing approaches oversimplify the shared genetic architecture between different phenotypes and cannot effectively identify precise genetic regions contributing to the genetic correlation. In this work, we introduce LOGODetect, a powerful and efficient statistical method to identify small genome segments harboring local genetic correlation signals. LOGODetect automatically identifies genetic regions showing consistent associations with multiple phenotypes through a scan statistic approach. It uses summary association statistics from genome-wide association studies (GWAS) as input and is robust to sample overlap between studies. Applied to seven phenotypically distinct but genetically correlated neuropsychiatric traits, we identify 227 non-overlapping genome regions associated with multiple traits, including multiple hub regions showing concordant effects on five or more traits. Our method addresses critical limitations in existing analytic strategies and may have wide applications in post-GWAS analysis.

DRD2 and ANKK1 genes associate with late-onset heroin dependence in men

Objectives: Dopamine plays an important role in reward system of heroin dependence (HD), and dopaminergic D2 receptor (DRD2) gene is a candidate for the aetiology of HD. Ankyrin repeat and kinase domain containing 1 (ANKK1) gene is proximal to DRD2 and may influence its expression. We explored whether DRD2 and ANKK1 associate with occurrence of HD, and whether the genetic variants influence personality traits in male patients with HD.Methods:DRD2/ANKK1 polymorphisms were analysed in 950 unrelated Han Chinese male participants (601 HD patients and 349 healthy controls). All participants were screened using the same assessment tools and all patients met the diagnostic criteria of HD. Personality traits were assessed in 274 patients and 142 controls using the Tridimensional Personality Questionnaire.Results: According to the allele, genotype and haplotype frequency analysis, we observed an association between HD and several DRD2/ANKK1 polymorphisms (rs1800497, rs1800498, rs1079597 and rs4648319); this was most notable in the late-onset HD subgroup. However, these DRD2/ANKK1 polymorphisms did not associate with specific personality traits in HD patients and controls.Conclusions:DRD2/ANKK1 may play an important role in occurrence of late-onset HD, but does not mediate the relationship between personality traits and HD in Han Chinese male population.

Modulation of orbitofrontal-striatal reward activity by dopaminergic functional polymorphisms contributes to a predisposition to alcohol misuse in early adolescence

BACKGROUND

Abnormalities in reward circuit function are considered a core feature of addiction. Yet, it is still largely unknown whether these abnormalities stem from chronic drug use, a genetic predisposition, or both.

METHODS

In the present study, we investigated this issue using a large sample of adolescent children by applying structural equation modeling to examine the effects of several dopaminergic polymorphisms of the D1 and D2 receptor type on the reward function of the ventral striatum (VS) and orbital frontal cortex (OFC), and whether this relationship predicted the propensity to engage in early alcohol misuse behaviors at 14 years of age and again at 16 years of age.

RESULTS

The results demonstrated a regional specificity with which the functional polymorphism rs686 of the D1 dopamine receptor (DRD1) gene and Taq1A of the ANKK1 gene influenced medial and lateral OFC activation during reward anticipation, respectively. Importantly, our path model revealed a significant indirect relationship between the rs686 of the DRD1 gene and early onset of alcohol misuse through a medial OFC × VS interaction.

CONCLUSIONS

These findings highlight the role of D1 and D2 in adjusting reward-related activations within the mesocorticolimbic circuitry, as well as in the susceptibility to early onset of alcohol misuse.

A review of the neurobiological underpinning of comorbid substance use and mood disorders

BACKGROUND

There is evidence that substance use disorders and other mental disorders may have shared biological mechanisms. However, the neurobiological basis of this comorbidity remains only partially explained. This review describes the historical evolution of the dual disorders concept and approach, and reviews the existing literature on neurobiological findings specifically regarding comorbid substance use and mood disorders.

METHODS

Searches were conducted using PubMed and Scopus in December 2017. A Boolean search was performed using combinations of "dual diagnosis" or "dual disorder" or "depression" or "bipolar" or "affective disorder" or "mood disorder" and "substance use" or "substance abuse" and "neurobiology" or "functional neuroimaging" or "genetics" or "neurotransmitters" or "neuroendocrinology" in the title or abstract, or as keywords, using no language restriction.

RESULTS

32 studies met the inclusion criteria. We found robust evidence for involvement of the neurotransmitters dopamine, GABA and glutamate and their receptors, as well as by the central corticotrophin-releasing hormone, hypothalamic-pituitary-adrenal axis activation, oxidative stress and inflammation. Recent studies focusing on neuroimaging and genetics have not shown consistent results.

LIMITATIONS

Only two search tools were used; most identified studies excluded the population of interest (comorbid mood and substance abuse disorders).

CONCLUSIONS

The neurobiological relevance for the occurrence of comorbid mood and substance abuse disorders has not been fully elucidated. Considering the high levels of individuals who experience comorbidity in these areas as well as the negative associated outcomes, this is clearly an area that requires further in-depth investigation. Furthermore, findings from this area can help to inform drug abuse prevention and intervention efforts, and especially how they relate to populations with psychiatric symptoms.

Repositioning Dopamine D2 Receptor Agonist Bromocriptine to Enhance Docetaxel Chemotherapy and Treat Bone Metastatic Prostate Cancer

Docetaxel resistance remains a major obstacle in the treatment of prostate cancer bone metastasis. In this study, we demonstrate that the dopamine D2 receptor (DRD2) agonist bromocriptine effectively enhances docetaxel efficacy and suppresses skeletal growth of prostate cancer in preclinical models. DRD2 is ubiquitously expressed in prostate cancer cell lines and significantly reduced in prostate cancer tissues with high Gleason score. Bromocriptine has weak to moderate cytotoxicity in prostate cancer cells, but effectively induces cell-cycle arrest. At the molecular level, bromocriptine inhibits the expression of c-Myc, E2F-1, and survivin and increases the expression of p53, p21, and p27. Intriguingly, bromocriptine markedly reduces androgen receptor levels, partially through Hsp90-mediated protein degradation. The combination of bromocriptine and docetaxel demonstrates enhanced in vitro cytotoxicity in prostate cancer cells and significantly retards the skeletal growth of C4-2-Luc tumors in mice. Collectively, these results provide the first experimental evidence for repurposing bromocriptine as an effective adjunct therapy to enhance docetaxel efficacy in prostate cancer. Mol Cancer Ther; 17(9); 1859-70. ©2018 AACR.

Effects of monoamines on the intrinsic excitability of lateral orbitofrontal cortex neurons in alcohol-dependent and non-dependent female mice

Changes in brain reward and control systems of frontal cortical areas including the orbitofrontal cortex (OFC) are associated with alcohol use disorders (AUD). The OFC is extensively innervated by monoamines, and drugs that target monoamine receptors have been used to treat a number of neuropsychiatric diseases, including AUDs. Recent findings from this laboratory demonstrate that D2, α2-adrenergic and 5HT_1A receptors all decrease the intrinsic excitability of lateral OFC (lOFC) neurons in naïve male mice and that this effect is lost in mice exposed to repeated cycles of chronic intermittent ethanol (CIE) vapor. As biological sex differences may influence an individual's response to alcohol and contribute to the propensity to engage in addictive behaviors, we examined whether monoamines have similar effects on lOFC neurons in control and CIE exposed female mice. Dopamine, norepinephrine and serotonin all decreased spiking of lOFC neurons in naïve females via activation of G_iα-coupled D2, α2-adrenergic and 5HT_1A receptors, respectively. Firing was also inhibited by the direct GIRK channel activator ML297, while blocking these channels with barium eliminated the inhibitory actions of monoamines. Following CIE treatment, evoked spiking of lOFC neurons from female mice was significantly enhanced and monoamines and ML297 no longer inhibited firing. Unlike in male mice, the enhanced firing of neurons from CIE exposed female mice was not associated with changes in the after-hyperpolarization and the small-conductance potassium channel blocker apamin had no effect on current-evoked tail currents from either control or CIE exposed female mice. These results suggest that while CIE exposure alters monoamine regulation of OFC neuron firing similarly in males and female mice, there are sex-dependent differences in processes that regulate the intrinsic excitability of these neurons.

Ethanol Dependence Abolishes Monoamine and GIRK (Kir3) Channel Inhibition of Orbitofrontal Cortex Excitability

Alcohol abuse disorders are associated with dysfunction of frontal cortical areas including the orbitofrontal cortex (OFC). The OFC is extensively innervated by monoamines, and drugs that target monoamine receptors have been used to treat a number of neuropsychiatric diseases, including alcoholism. However, little is known regarding how monoamines affect OFC neuron excitability or whether this modulation is altered by chronic exposure to ethanol. In this study, we examined the effect of dopamine, norepinephrine, and serotonin on lOFC neuronal excitability in naive mice and in those exposed to chronic intermittent ethanol (CIE) treatment. All three monoamines decreased current-evoked spike firing of lOFC neurons and this action required G_iα-coupled D2, α2-adrenergic, and 5HT_1A receptors, respectively. Inhibition of firing by dopamine or the D2 agonist quinpirole, but not norepinephrine or serotonin, was prevented by the GABA_A receptor antagonist picrotoxin. GABA-mediated tonic current was enhanced by dopamine or the D1 agonist SKF81297 but not quinpirole, whereas the amplitude of spontaneous IPSCs was increased by quinpirole but not dopamine. Spiking was also inhibited by the direct GIRK channel activator ML297, whereas blocking these channels with barium increased firing and eliminated the inhibitory actions of monoamines. In the presence of ML297 or the G-protein blocker GDP-β-S, DA induced a further decrease in spike firing, suggesting the involvement of a non-GIRK channel mechanism. In neurons from CIE-treated mice, spike frequency was nearly doubled and inhibition of firing by monoamines or ML297 was lost. These effects occurred in the absence of significant changes in expression of G_i/o or GIRK channel proteins. Together, these findings show that monoamines are important modulators of lOFC excitability and suggest that disruption of this process could contribute to various deficits associated with alcohol dependence.

An association study of Taq1A ANKK1 and C957T and - 141C DRD2 polymorphisms in adults with internet gaming disorder: a pilot study

BACKGROUND

Though Internet gaming disorder (IGD) is considered to share similar genetic vulnerability with substance addictions, little has been explored about the role of the genetic variants on IGD. This pilot study was designed to investigate the association of the Taq1A polymorphism of the ankyrin repeat and kinase domain containing 1 (ANKK1) gene and C957T and - 141C of the dopamine D2 receptor (DRD2) with IGD and their role on the personality and temperament traits in IGD among adult population.

METHODS

Sixty-three subjects with IGD and 87 control subjects who regularly played Internet games were recruited. Self-administered questionnaires on self-control, dysfunctional impulsivity, and temperament and character domains were done. The Taq1A ANKK1 and the C957T and - 141C ins/del from the DRD2 genes were genotyped using the specific TaqMan PCR assay.

RESULTS

The distributions of allele and genotype frequencies were not significantly different between the IGD and control groups in both genders. In male, excessive gaming and use of gaming to escape from a negative feeling were associated with the del- genotype of the - 141C. Among IGD, the del+ genotype was associated with higher novelty seeking. Logistic regression showed no predictive value of these polymorphisms for IGD when using age and gender as covariates.

CONCLUSIONS

Though no direct association of the Taq1A ANKK1 and C957T DRD2 variants with IGD were observed, the - 141C polymorphism may play a role in IGD via mediating symptoms or temperament traits.

The role of C957T, TaqI and Ser311Cys polymorphisms of the DRD2 gene in schizophrenia: systematic review and meta-analysis

Background

The association between the dopamine D2 receptor (DRD2) gene and schizophrenia has been studied though no conclusive outcomes have been attained. The aim of this study was to perform a systematic review and meta-analysis to explore the relation between three polymorphisms of the DRD2 gene (C957T, TaqI and Ser311Cys) and schizophrenia.

Methods

The search was made in PubMed and EBSCO databases (up to February 2016). The systematic review included 34 case–control association studies (34 for C957T, 16 for TaqI and 36 for Ser311Cys). The association analysis comprised the allelic, additive, dominant, and recessive genetic models. The meta-analysis was performed following the preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement.

Results

The meta-analysis showed that TaqI (additive model: OR 0.57, 95% CI 0.30–1.14) and C957T (additive model: OR 0.75, 95% OR 0.58–0.97, recessive model: OR 0.79, 95% CI 0.64–0.98) exert a protective effect against developing schizophrenia. However, the sub-analysis for the C957T variant showed that this polymorphism exhibits a risk factor effect on Chinese individuals (allelic model: OR 1.33, 95% CI 1.04–1.70).

Conclusion

Our meta-analysis suggests an association of the DRD2 gene and the risk for schizophrenia, given that TaqI and C957T polymorphisms presented a protective effect against schizophrenia, and in the sub-analyses the C957T variant increased the risk for this disorder in the Chinese population.

Electronic supplementary material

The online version of this article (doi:10.1186/s12993-016-0114-z) contains supplementary material, which is available to authorized users.

Associations between a locus downstream DRD1 gene and cerebrospinal fluid dopamine metabolite concentrations in psychosis

Dopamine activity, mediated by the catecholaminergic neurotransmitter dopamine, is prominent in the human brain and has been implicated in schizophrenia. Dopamine targets five different receptors and is then degraded to its major metabolite homovanillic acid (HVA). We hypothesized that genes encoding dopamine receptors may be associated with cerebrospinal fluid (CSF) HVA concentrations in patients with psychotic disorder. We searched for association between 67 single nucleotide polymorphisms (SNPs) in the five dopamine receptor genes i.e., DRD1, DRD2, DRD3, DRD4 and DRD5, and the CSF HVA concentrations in 74 patients with psychotic disorder. Nominally associated SNPs were also tested in 111 healthy controls. We identified a locus, located downstream DRD1 gene, where four SNPs, rs11747728, rs11742274, rs265974 and rs11747886, showed association with CSF HVA concentrations in psychotic patients. The associations between rs11747728, which is a regulatory region variant, and rs11742274 with HVA remained significant after correction for multiple testing. These associations were restricted to psychotic patients and were absent in healthy controls. The results suggest that the DRD1 gene is implicated in the pathophysiology of psychosis and support the dopamine hypothesis of schizophrenia.

The Association Between Genetic Variants in the Dopaminergic System and Posttraumatic Stress Disorder: A Meta-Analysis

Posttraumatic stress disorder (PTSD) is a complex mental disorder and can severely interfere with the normal life of the affected people. Previous studies have examined the association of PTSD with genetic variants in multiple dopaminergic genes with inconsistent results. To perform a systematic literature search and conduct meta-analysis to examine whether genetic variants in the dopaminergic system is associated with PTSD. Data Sources: PubMed, Cochrane Library, Embase, Google Scholar, and HuGE. Study eligibility criteria and participants: The studies included subjects who had been screened for the presence of PTSD; the studies provided data for genetic variants of genes involved in the dopaminergic system; the outcomes of interest included diagnosis status of PTSD; and the studies were case-control studies. Study appraisal and synthesis methods: Odds ratio was used as a measure of association. We used random-effects model in all the meta-analyses. Between-study heterogeneity was assessed using I², and publication bias was evaluated using Egger test. Findings from meta-analyses were confirmed using random-effects meta-analyses under the framework of generalized linear model (GLM). A total of 19 studies met the eligibility criteria and were included in our analyses. We found that rs1800497 in DRD2 was significantly associated with PTSD (OR = 1.96, 95% CI: 1.15-3.33; P = 0.014). The 3'-UTR variable number tandem repeat (VNTR) in SLC6A3 also showed significant association with PTSD (OR = 1.62, 95% CI: 1.12-2.35; P = 0.010), but there was no association of rs4680 in COMT with PTSD (P = 0.595). Sample size is limited for some studies; type and severity of traumatic events varied across studies; we could not control for potential confounding factors, such as age at traumatic events and gender; and we could not examine gene-environment interaction due to lack of data. We found that rs1800497 in DRD2 and the VNTR in SLC6A3 showed significant association with PTSD. Future studies controlling for confounding factors, with large sample sizes and more homogeneous traumatic exposure, are needed to validate the findings from this study.

Fischer 344 and Lewis Rat Strains as a Model of Genetic Vulnerability to Drug Addiction

Today it is well acknowledged that both nature and nurture play important roles in the genesis of psychopathologies, including drug addiction. Increasing evidence suggests that genetic factors contribute for at least 40–60% of the variation in liability to drug dependence. Human genetic studies suggest that multiple genes of small effect, rather than single genes, contribute to the genesis of behavioral psychopathologies. Therefore, the use of inbred rat strains might provide a valuable tool to identify differences, linked to genotype, important in liability to addiction and related disorders. In this regard, Lewis and Fischer 344 inbred rats have been proposed as a model of genetic vulnerability to drug addiction, given their innate differences in sensitivity to the reinforcing and rewarding effects of drugs of abuse, as well their different responsiveness to stressful stimuli. This review will provide evidence in support of this model for the study of the genetic influence on addiction vulnerability, with particular emphasis on differences in mesolimbic dopamine (DA) transmission, rewarding and emotional function. It will be highlighted that Lewis and Fischer 344 rats differ not only in several indices of DA transmission and adaptive changes following repeated drug exposure, but also in hypothalamic-pituitary-adrenal (HPA) axis responsiveness, influencing not only the ability of the individual to cope with stressful events, but also interfering with rewarding and motivational processes, given the influence of corticosteroids on dopamine neuron functionality. Further differences between the two strains, as impulsivity or anxiousness, might contribute to their different proneness to addiction, and likely these features might be linked to their different DA neurotransmission plasticity. Although differences in other neurotransmitter systems might deserve further investigation, results from the reviewed studies might open new vistas in understanding aberrant deviations in reward and motivational functions.

Beyond the bilingual advantage: The potential role of genes and environment on the development of cognitive control

In recent years there has been considerable debate about the presence or absence of a bilingual advantage in tasks that involve cognitive control. Our previous work has established evidence of differences in brain activity between monolinguals and bilinguals in both word learning and in the avoidance of interference during a picture selection task. Recent models of cognitive control have highlighted the importance of a set of neural structures that may show differential tuning due to exposure to two languages. There is also evidence that genetic factors play a role in the availability of dopamine in neural structures involved in cognitive control. Thus, it is important to investigate whether there are interactions effects generating variability in language acquisition when attributed to genetic (e.g., characteristics of dopamine turnover) and environmental (e.g., exposure to two languages) factors. Here preliminary results from genotyping of a sample of bilingual and monolingual individuals are reported. They reveal different distributions in allele frequencies of the DRD2/ANKK1 taq1A polymorphism. These results bring up the possibility that bilinguals may exhibit additional flexibility due to differences in genetic characteristics relative to monolinguals. Future studies should consider genotype as a possible contributing factor to the development of cognitive control across individuals with different language learning histories.

Moderating Effects of Genetic Polymorphisms on Improvements in Cognitive Impairment in Breast Cancer Survivors Participating in a 6-Week Mindfulness-Based Stress Reduction Program

Breast cancer (BC) survivors often report cognitive impairment, which may be influenced by single-nucleotide polymorphisms (SNPs). The purpose of this study was to test whether particular SNPs were associated with changes in cognitive function in BC survivors and whether these polymorphisms moderated cognitive improvement resulting from the Mindfulness-Based Stress Reduction for Breast Cancer (MBSR[BC]) program. BC survivors recruited from Moffitt Cancer Center and the University of South Florida's Breast Health Program, who had completed adjuvant radiation and/or chemotherapy treatment, were randomized to either the 6-week MBSR(BC) program (n = 37) or usual care (UC; n = 35) group. Measures of cognitive function and demographic and clinical history data were attained at baseline and at 6 and 12 weeks. A total of 10 SNPs from eight genes known to be related to cognitive function were analyzed using blood samples. Results showed that SNPs in four genes (ankyrin repeat and kinase domain containing 1 [ANKK1], apolipoprotein E [APOE], methylenetetrahydrofolate reductase [MTHFR], and solute carrier family 6 member 4 [SLC6A4]) were associated with cognitive impairment. Further, rs1800497 in ANKK1 was significantly associated with improvements in cognitive impairment in response to MBSR(BC). These results may help to identify individuals who would be better served by MBSR(BC) or other interventions.

Monoamine oxidase a promoter variable number of tandem repeats (MAOA-uVNTR) in alcoholics according to Lesch typology

Background: The aim of this study was to examine the association between the MAOA-uVNTR gene polymorphism in a homogeneous subgroups of patients with alcohol dependence categorized according to Lesch’s typology. Methods: DNA was provided from alcohol dependent (AD) patients (n = 370) and healthy control subjects (n = 168) all of Polish descent. The history of alcoholism was obtained using the Polish version of the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA). Samples were genotyped using PCR methods. Results: We found no association between alcohol dependence and MAOA gene polymorphism. Conclusions: Lesch typology is a clinical consequence of the disease and its phenotypic description is too complex for a simple genetic analysis.

Hypothesizing dopaminergic genetic antecedents in schizophrenia and substance seeking behavior

The dopamine system has been implicated in both substance use disorder (SUD) and schizophrenia. A recent meta-analysis suggests that A1 allele of the DRD2 gene imposes genetic risk for SUD, especially alcoholism and has been implicated in Reward Deficiency Syndrome (RDS). We hypothesize that dopamine D2 receptor (DRD2) gene Taq1 A2 allele is associated with a subtype of non-SUD schizophrenics and as such may act as a putative protective agent against the development of addiction to alcohol or other drugs of abuse. Schizophrenics with SUD may be carriers of the DRD2 Taq1 A1 allele, and/or other RDS reward polymorphisms and have hypodopaminergic reward function. One plausible mechanism for alcohol seeking in schizophrenics with SUD, based on previous research, may be a deficiency of gamma type endorphins that has been linked to schizophrenic type psychosis. We also propose that alcohol seeking behavior in schizophrenics, may serve as a physiological self-healing process linked to the increased function of the gamma endorphins, thereby reducing abnormal dopaminergic activity at the nucleus accumbens (NAc). These hypotheses warrant further investigation and cautious interpretation. We, therefore, encourage research involving neuroimaging, genome wide association studies (GWAS), and epigenetic investigation into the relationship between neurogenetics and systems biology to unravel the role of dopamine in psychiatric illness and SUD.

The role of attachment styles in regulating the effects of dopamine on the behavior of salespersons

Two classic strategic orientations have been found to pervade the behavior of modern salespersons: a sales orientation (SO) where salespersons use deception or guile to get customers to buy even if they do not need a product, and a customer orientation (CO) where salespersons first attempt to discover the customer's needs and adjust their product and selling approach to meet those needs. Study 1 replicates recent research and finds that the Taq A1 variant of the DRD2 gene is not related to either sales or CO, whereas the 7-repeat variant of the DRD4 gene is related to CO but not SO. Study 2 investigates gene × phenotype explanations of orientation of salespersons, drawing upon recent research in molecular genetics and biological/psychological attachment theory. The findings show that attachment style regulates the effects of DRD2 on CO, such that greater avoidant attachment styles lead to higher CO for persons with the A2/A2 variant but neither the A1/A2 nor A1/A1 variants. Likewise, attachment style regulates the effects of DRD4 on CO, such that greater avoidant attachment styles lead to higher CO for persons with the 7-repeat variant but not other variants. No effects were found on a SO, and secure and anxious attachment styles did not function as moderators.

Emerging roles for atypical antipsychotics in chronic post-traumatic stress disorder

Post-traumatic stress disorder is an anxiety disorder that may occur after the individual is exposed to severe psychologic trauma such as combat, sexual assault, or childhood physical or sexual abuse. Chronic post-traumatic stress disorder may result in considerable psychologic pain and suffering for the individual in addition to significant functional impairment. In addition to the heterogeneity of symptoms that occur in post-traumatic stress disorder, there may also be extensive comorbidity with other anxiety disorders, mood disorders, psychotic disorders, and other psychiatric disorders. This complicates the treatment picture. Currently, accepted treatments for post-traumatic stress disorder include psychotherapy, in particular cognitive behavioral-based approaches and antidepressant medication. However, many patients are refractory to these initial treatments or have only a partial response. In light of this, may clinicians combine additional classes of psychotropic agents and different psychotherapeutic approaches to enhance treatment response. This article reviews the literature on the use of atypical antipsychotics in the treatment of post-traumatic stress disorder. Most of the research to date has involved combat veterans partially responsive or refractory to treatment, namely with antidepressants. Studies have shown improvement across post-traumatic stress disorder symptom clusters, as well as improvement in comorbid psychotic symptoms or disorders. More research is needed to confirm these recent findings and further delineate the role of atypical antipsychotics in the treatment of post-traumatic stress disorder. Currently, possible indications for their use include treatment-resistant post-traumatic stress disorder and post-traumatic stress disorder with comorbid psychotic features.

Developmental imaging genetics: linking dopamine function to adolescent behavior

Adolescence is a period of development characterized by numerous neurobiological changes that significantly influence behavior and brain function. Adolescence is of particular interest due to the alarming statistics indicating that mortality rates increase two to three-fold during this time compared to childhood, due largely to a peak in risk-taking behaviors resulting from increased impulsivity and sensation seeking. Furthermore, there exists large unexplained variability in these behaviors that are in part mediated by biological factors. Recent advances in molecular genetics and functional neuroimaging have provided a unique and exciting opportunity to non-invasively study the influence of genetic factors on brain function in humans. While genes do not code for specific behaviors, they do determine the structure and function of proteins that are essential to the neuronal processes that underlie behavior. Therefore, studying the interaction of genotype with measures of brain function over development could shed light on critical time points when biologically mediated individual differences in complex behaviors emerge. Here we review animal and human literature examining the neurobiological basis of adolescent development related to dopamine neurotransmission. Dopamine is of critical importance because of (1) its role in cognitive and affective behaviors, (2) its role in the pathogenesis of major psychopathology, and (3) the protracted development of dopamine signaling pathways over adolescence. We will then focus on current research examining the role of dopamine-related genes on brain function. We propose the use of imaging genetics to examine the influence of genetically mediated dopamine variability on brain function during adolescence, keeping in mind the limitations of this approach.

DRD2/ANKK1 Taq1A polymorphism (rs1800497) has opposing effects on D2/3 receptor binding in healthy controls and patients with major depressive disorder

The A1 allele of the DRD2/ANKK1 Taq1A polymorphism (rs1800497) is associated with reduced striatal D(2/3) receptor binding in healthy individuals (Con) as well as depression and addiction. However, the effect of rs1800497 on D(2/3) receptor binding in depressed patients as well as the SNP's effect on D(2/3) binding during reward-associated dopamine release is unknown. Twelve unmedicated patients with major depressive disorder (MDD) and 24 Con completed PET scans with [(11)C]raclopride, once without receiving monetary rewards (baseline) and once while winning money. In Con, the A1 allele was associated with reduced baseline binding potential (BP(ND)) in the middle caudate and ventral striatum. However, in MDD patients the A1 allele was associated with increased baseline BP(ND) in these regions. There were no significant associations between rs1800497 and change in BP(ND) during reward-associated dopamine release. Conceivably, the A1 allele predisposes to depression and addiction via its effect on the post-synaptic D(2) receptor.

The association between DRD2/ANKK1 and genetically informed measures of alcohol use and problems

In 1990, Blum and colleagues first reported an association between DRD2 and alcoholism. While there have been subsequent replications of this genetic association, there have also been numerous studies that failed to detect an association between DRD2 and alcohol dependence. We propose that one aspect contributing to this inconsistency is the variation in alcohol phenotype used across studies. Within the population-based Finnish twin sample, FinnTwin16, we previously performed multivariate twin analyses to extract latent genetic factors, which account for the variation across seven measures of alcohol consumption (frequency of drinking, frequency × quantity, frequency of heavy drinking, frequency of intoxication and maximum drinks in a 24-hour period) and problems (the Rutgers Alcohol Problem Index-RAPI and the Mälmö-modified Michigan Alcohol Screen Test-MmMAST) in 3065 twins. In the present study, we examined the association between 31 DRD2/ANKK1 single-nucleotide polymorphisms (SNPs) and the genetic factor scores generated by twin analyses in a subset of FinnTwin16 (n = 602). We focus on two of the genetic factors: a general alcohol consumption and problems factor score, which represents shared genetic variance across alcohol measures, and a alcohol problems genetic factor score, which loads onto the two indices of problematic drinking (MAST and RAPI). After correction for multiple testing across SNPs and phenotypes, of the 31 SNPs genotyped across DRD2/ANKK1, one SNP (rs10891549) showed significant association with the general alcohol consumption and problems factor score (P = 0.004), and four SNPs (rs10891549, rs1554929, rs6275, rs6279), representing two independent signals after accounting for linkage disequilibrium, showed significant association with the alcohol problems genetic factor score (P = 0.005, P = 0.005, P = 0.003, P = 0.003). In this study, we provide additional positive evidence for the association between DRD2/ANKK1 and alcohol outcomes, including frequency of drinking and drinking problems. Additionally, post hoc analyses indicate stronger association signals using genetic factor scores than individual measures, which suggest that accounting for the genetic architecture of the alcohol measures reduces genetic heterogeneity in alcohol dependence outcomes in this sample and enhances the ability to detect association.

Genetic analysis of Parkinson's disease-linked leucine-rich repeat kinase 2

Mutations in LRRK2 (leucine-rich repeat kinase 2) are the most common genetic cause of PD (Parkinson's disease). To investigate how mutations in LRRK2 cause PD, we generated LRRK2 mutant mice either lacking its expression or expressing the R1441C mutant form. Homozygous R1441C knockin mice exhibit no dopaminergic neurodegeneration or alterations in steady-state levels of striatal dopamine, but they show impaired dopamine neurotransmission, as was evident from reductions in amphetamine-induced locomotor activity and stimulated catecholamine release in cultured chromaffin cells as well as impaired dopamine D2 receptor-mediated functions. Whereas LRRK2-/- brains are normal, LRRK2-/- kidneys at 20 months of age develop striking accumulation and aggregation of α-synuclein and ubiquitinated proteins, impairment of the autophagy-lysosomal pathway, and increases in apoptotic cell death, inflammatory responses and oxidative damage. Our further analysis of LRRK2-/- kidneys at multiple ages revealed unique age-dependent biphasic alterations of the autophagic activity, which is unchanged at 1 month of age, enhanced at 7 months, but reduced at 20 months. Levels of α-synuclein and protein carbonyls, a general oxidative damage marker, are also decreased in LRRK2-/- kidneys at 7 months of age. Interestingly, this biphasic alteration is associated with increased levels of lysosomal proteins and proteases as well as progressive accumulation of autolysosomes and lipofuscin granules. We conclude that pathogenic mutations in LRRK2 impair the nigrostriatal dopaminergic pathway, and LRRK2 plays an essential role in the dynamic regulation of autophagy function in vivo.

COMT and ANKK1-Taq-Ia genetic polymorphisms influence visual working memory

Complex cognitive tasks such as visual working memory (WM) involve networks of interacting brain regions. Several neurotransmitters, including an appropriate dopamine concentration, are important for WM performance. A number of gene polymorphisms are associated with individual differences in cognitive task performance. COMT, for example, encodes catechol-o-methyl transferase the enzyme primarily responsible for catabolizing dopamine in the prefrontal cortex. Striatal dopamine function, linked with cognitive tasks as well as habit learning, is influenced by the Taq-Ia polymorphism of the DRD2/ANKK1 gene complex; this gene influences the density of dopamine receptors in the striatum. Here, we investigated the effects of these polymorphisms on a WM task requiring the maintenance of 4 or 6 items over delay durations of 1 or 5 seconds. We explored main effects and interactions between the COMT and DRD2/ANKK1-Taq-Ia polymorphisms on WM performance. Participants were genotyped for COMT (Val(158)Met) and DRD2/ANKK1-Taq-Ia (A1+, A1-) polymorphisms. There was a significant main effect of both polymorphisms. Participants' WM reaction times slowed with increased Val loading such that the Val/Val homozygotes made the slowest responses and the Met/Met homozygotes were the fastest. Similarly, WM reaction times were slower and more variable for the DRD2/ANKK1-Taq-Ia A1+ group than the A1- group. The main effect of COMT was only apparent in the DRD2/ANKK1-Taq-Ia A1- group. These findings link WM performance with slower dopaminergic metabolism in the prefrontal cortex as well as a greater density of dopamine receptors in the striatum.

Reduction of bulimia nervosa symptoms after psychostimulant initiation in patients with comorbid ADHD: five case reports

Studies reveal a higher occurrence of bulimia nervosa (BN) in patients with attention deficit/hyperactivity disorder (ADHD) compared to controls. Due to this high degree of comorbidity, some clinicians have used psychostimulants in this population. The goal of this article is to describe five patients with comorbid BN and ADHD and their responses to a course of psychostimulants. After medication initiation, all five patients experienced a decrease in binge/purging and an improvement in ADHD symptoms. Overall, the medications were well tolerated. Possible mechanisms underlying the relationship between ADHD and BN, and words of caution are discussed. The need for clinical trials to further evaluate the efficacy of psychostimulants in this population is warranted.

Association between the dopamine D2 receptor (DRD2) polymorphism and the personality traits of healthy Japanese participants

BACKGROUND

Dopamine neurotransmitter systems have been associated with reward-related and novelty-seeking personality traits. We investigated the possible relationship between the personality traits measured by the Temperament and Character Inventory (TCI) and the TaqI A and -141C Ins/Del polymorphisms in the dopamine D2 receptor gene (DRD2).

METHODS

The sample consisted of 1084 healthy Japanese medical students and medical staff (age=29.0±9.7 years), each of whom completed the TCI. Their genomic DNA was isolated from whole blood and genotyped using the TaqMan allele-specific assay method. The associations between gene polymorphisms and the scores for TCI were statistically analyzed by one-way analysis of covariance (ANCOVA) adjusting age. Males and females were analyzed separately. Epstatis was assesses using two-way ANCOVA between the DRD2 and ANKK1 genes.

RESULTS

Men with the Ins/Del genotype of the -141C Ins/Del polymorphism had significantly higher self-directedness scores than those with the Ins/Ins genotype (p=0.021). None of the TCI scores differed among women with regard to the three genotype groups of the -141C Ins/Del polymorphism. The DRD2/ANKK1 Taq1 A polymorphism did not affect any TCI factor for either men or women. An epistatic analysis did not reveal main effects of the two genes with regard to TCI scores, but an ANKK1×DRD2 interaction significantly predicted TCI scores.

CONCLUSION

These findings suggest the possibility that the -141C Ins/Del polymorphism and the DRD2/ANKK1 Taq1 A polymorphism are not strongly linked to personality traits directly, but influences them under the interaction between the DRD2 and ANKK1 genes.

Epigenetic changes in lymphocytes of solvent-exposed individuals

Aim: We investigated global DNA methylation alterations in lymphocytes of solvent workers and chronic toxic encephalopathy (CTE) patients and explored potential gene–environment interactions for GST. Population & methods: A cross-sectional study was set up in 41 referents, 128 solvent workers and 23 CTE patients. Results: We found a global DNA hypermethylation in the solvent-exposed population compared with the referents (p = 0.001, r = -0.544). Global DNA methylation was negatively associated with exposure. Furthermore, GSTP1 genotypic polymorphism was found to be significantly associated (p = 0.033) with global DNA hypomethylation, which indicates a potential role for gene–environment interaction in the etiology of solvent-induced neurobehavioral disorders. Conclusion: This study indicates that solvent-induced DNA methylation alterations have an impact on neurotoxicity and development of CTE.

Factors associated with attention deficit/hyperactivity disorder among US children: results from a national survey

Background

The purpose of this study was to investigate the association between Attention Deficit/Hyperactivity Disorder (ADHD) and various factors using a representative sample of US children in a comprehensive manner. This includes variables that have not been previously studied such as watching TV/playing video games, computer usage, family member’s smoking, and participation in sports.

Methods

This was a cross-sectional study of 68,634 children, 5–17 years old, from the National Survey of Children’s Health (NSCH, 2007–2008). We performed bivariate and multivariate logistic regression analyses with ADHD classification as the response variable and the following explanatory variables: sex, race, depression, anxiety, body mass index, healthcare coverage, family structure, socio-economic status, family members’ smoking status, education, computer usage, watching television (TV)/playing video games, participation in sports, and participation in clubs/organizations.

Results

Approximately 10% of the sample was classified as having ADHD. We found depression, anxiety, healthcare coverage, and male sex of child to have increased odds of being diagnosed with ADHD. One of the salient features of this study was observing a significant association between ADHD and variables such as TV usage, participation in sports, two-parent family structure, and family members’ smoking status. Obesity was not found to be significantly associated with ADHD, contrary to some previous studies.

Conclusions

The current study uncovered several factors associated with ADHD at the national level, including some that have not been studied earlier in such a setting. However, we caution that due to the cross-sectional and observational nature of the data, a cause and effect relationship between ADHD and the associated factors can not be deduced from this study. Future research on ADHD should take into consideration these factors, preferably through a longitudinal study design.

Krüppel-like factor 11 differentially couples to histone acetyltransferase and histone methyltransferase chromatin remodeling pathways to transcriptionally regulate dopamine D2 receptor in neuronal cells

The importance of Krüppel-like factor (KLF)-mediated transcriptional pathways in the biochemistry of neuronal differentiation has been recognized relatively recently. Elegant studies have revealed that KLF proteins are important regulators of two major molecular and cellular processes critical for neuronal cell differentiation: neurite formation and the expression of neurotransmitter-related genes. However, whether KLF proteins mediate these key processes in a separate or coordinated fashion remains unknown. Moreover, knowledge on the contribution of chromatin dynamics to the biochemical mechanisms utilized by these proteins to perform their function is absent. Here we report the characterization of two antagonistic, chromatin-mediated mechanisms by which KLF11, also known as TIEG2 (transforming growth factor-β-inducible early gene 2) and MODY VII (maturity onset diabetes of the young VII), regulates transcription of the fopamine D2 receptor (Drd2) gene. First, KLF11 activates transcription by binding to a distinct Sp-KLF site within the Drd2 promoter (-98 to -94) and recruiting the p300 histone acetyltransferase. Second, Drd2 transcriptional activation is partially antagonized by heterochromatin protein 1 (HP1), the code reader for histone H3 lysine 9 methylation. Interestingly, KLF11 regulates neurotransmitter receptor gene expression in differentiating neuronal cell populations without affecting neurite formation. Overall, these studies highlight histone methylation and acetylation as key biochemical mechanisms modulating KLF-mediated neurotransmitter gene transcription. These data extend our knowledge of chromatin-mediated biochemical events that maintain key phenotypic features of differentiated neuronal cells.

Generational association studies of dopaminergic genes in reward deficiency syndrome (RDS) subjects: selecting appropriate phenotypes for reward dependence behaviors

Abnormal behaviors involving dopaminergic gene polymorphisms often reflect an insufficiency of usual feelings of satisfaction, or Reward Deficiency Syndrome (RDS). RDS results from a dysfunction in the "brain reward cascade," a complex interaction among neurotransmitters (primarily dopaminergic and opioidergic). Individuals with a family history of alcoholism or other addictions may be born with a deficiency in the ability to produce or use these neurotransmitters. Exposure to prolonged periods of stress and alcohol or other substances also can lead to a corruption of the brain reward cascade function. We evaluated the potential association of four variants of dopaminergic candidate genes in RDS (dopamine D1 receptor gene [DRD1]; dopamine D2 receptor gene [DRD2]; dopamine transporter gene [DAT1]; dopamine beta-hydroxylase gene [DBH]).

METHODOLOGY

We genotyped an experimental group of 55 subjects derived from up to five generations of two independent multiple-affected families compared to rigorously screened control subjects (e.g., N = 30 super controls for DRD2 gene polymorphisms). Data related to RDS behaviors were collected on these subjects plus 13 deceased family members.

RESULTS

Among the genotyped family members, the DRD2 Taq1 and the DAT1 10/10 alleles were significantly (at least p < 0.015) more often found in the RDS families vs. controls. The TaqA1 allele occurred in 100% of Family A individuals (N = 32) and 47.8% of Family B subjects (11 of 23). No significant differences were found between the experimental and control positive rates for the other variants.

CONCLUSIONS

Although our sample size was limited, and linkage analysis is necessary, the results support the putative role of dopaminergic polymorphisms in RDS behaviors. This study shows the importance of a nonspecific RDS phenotype and informs an understanding of how evaluating single subset behaviors of RDS may lead to spurious results. Utilization of a nonspecific "reward" phenotype may be a paradigm shift in future association and linkage studies involving dopaminergic polymorphisms and other neurotransmitter gene candidates.

Review of biological mechanisms and pharmacological treatments of comorbid PTSD and substance use disorder

Posttraumatic stress disorder (PTSD) and alcohol/substance use disorder (A/SUD) are frequently comorbid. Comorbidity is associated with poorer psychological, functional, and treatment outcomes than either disorder alone. This review outlines biological mechanisms that are potentially involved in the development and maintenance of comorbid PTSD and A/SUD including neurotransmitter and hypothalamic-pituitary-adrenal dysregulation, structural differences in the brain, and shared genetic risk factors. The literature regarding pharmacological treatments that have been investigated for comorbid PTSD and A/SUD is also reviewed. Empirical data for each proposed mechanism and pharmacological approach is reviewed with the goal of making recommendations for future research. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

Partial agonist therapy in schizophrenia: relevance to diminished criminal responsibility

Pathological gambling (PG), classified in the DSM-IV among impulse control disorders, is defined as inappropriate, persistent gaming for money with serious personal, family, and social consequences. Offenses are frequently committed to obtain money for gambling. Pathological gambling, a planned and structured behavioral disorder, has often been described as a complication of dopamine agonist treatment in patients with Parkinson's disease. It has never been described in patients with schizophrenia receiving dopamine agonists. We present two patients with schizophrenia, previously treated with antipsychotic drugs without any suggestion of PG, who a short time after starting aripiprazole, a dopamine partial agonist, developed PG and criminal behavior, which totally resolved when aripiprazole was discontinued. Based on recent advances in research on PG and adverse drug reactions to dopamine agonists in Parkinson's disease, we postulate a link between aripiprazole and PG in both our patients with schizophrenia and raise the question of criminal responsibility.

Pharmacogenomic implications of variants of monoaminergic-related genes in geriatric psychiatry

Response to psychiatric medications in later life is highly heterogeneous and complex. Monoaminergic-related polymorphisms may influence medication response and susceptibility to side effects in elderly individuals. Individuals with the lower function short (S) allele of the serotonin transporter gene (SLC6A4) insertion/deletion (indel) promoter polymorphism (5-HTTLPR) have both increased the likelihood of adverse drug events and increased the need for higher antidepressant concentrations to obtain maximum antidepressant response. By contrast, carriers of the higher expression homozygous long allele (L/L) genotype may respond at lower concentrations. The differential role of these polymorphisms appears at early stages of treatment rather than in the final antidepressant outcome. Research findings suggest that the rs25531 SNP may influence functional expression of the L allele. Similarly, a variable number of tandem repeats in the second intron of the serotonin transporter gene may influence the expression of SLC6A4 and the implications of these variants may be influenced by aging. Two polymorphisms, rs2242466 (-182T/C) and rs5569 (1287G/A), in the norepinephrine transporter gene (SLC6A2 or NET) have been associated with antidepressant response. Studies in dopamine-related polymorphisms have focused on associations with neuroleptic-induced movement disorders. The rs1800497 variant (Taq1A) of the dopamine receptor D2 (DRD2) gene located in a noncoding 3´ region may regulate expression of D2 receptors. The rs6280 variant (Ser9Gly) of the dopamine receptor 3 (DRD3) gene may influence the binding affinity of D3 receptors as a result of serine to glycine substitution of the receptor protein. A multicenter collaborative research effort would be an effective strategy to increase sample sizes to further investigate how gene variants impact the pharmacodynamics and pharmacokinetics of psychotropic drugs in elderly persons.

Population-based case-control study of DRD2 gene polymorphisms and alcoholism

Several independent lines of evidence for genetic contributions to vulnerability to alcoholism exist. Dopamine is thought to play a major role in the mechanism of reward and reinforcement in response to alcohol. D2 dopamine receptor (DRD2) gene has been among the stronger candidate genes implicated in alcoholism. In this study, alcohol use was assessed in 196 randomly selected Kota individuals of Nilgiri Hills, South India. Six DRD2 SNPs were assessed in 81 individuals with alcoholism and 151 controls to evaluate the association between single nucleotide polymorphisms (SNPs) and alcoholism. Of the three models (dominant, recessive, and additive) tested for association between alcoholism and DRD2 SNPs, only the additive model shows association for three loci (rs1116313, TaqID, and rs2734835). Of six studied polymorphisms, five are in strong linkage disequilibrium forming onesingle haplotype block. Though the global haplotype analysis with these five SNPs was not significant, haplotype analysis using all six SNPs yielded a global P value of .033, even after adjusting for age. These findings support the importance of dopamine receptor gene polymorphisms in alcoholism. Further studies to replicate these findings in different populations are needed to confirm these results.

Neural markers of genetic vulnerability to drug addiction

This chapter will summarize genetics findings derived from various strategies and highlight important neural markers (or correlates) in some specific and extensively studied genes. Most studies highlighted here focus on alcohol and nicotine dependence (AD and ND, respectively). AD and ND are among the most prevalent addictive disorders worldwide, are among the best studied, and are also associated globally with the largest socioeconomic impact.We describe different mechanisms through which genes can have an impact on the addictive behaviors, distinguishing between the genes that inscribe the proteins affecting the metabolism of the addictive substance (e.g., ADH/ALDH for alcohol or CYP2A6 for nicotine) and genes that code for the brain transmitter systems, such as genes involved in cerebral neurotransmission thought to be involved in addiction (e.g., brain reward system, mood regulation, opioid system). Strategies include linkage analyses, association studies, whole genome association studies as well as intermediate/endophenotype studies. Moreover, some important findings derived from animal studies and from neuroimaging studies are highlighted. In conclusion, we provide the reader with an overview of most important studies related to AD and ND and give an outlook how these findings may become useful and beneficial in the future.

Incorporating genetics into your studies: a guide for social scientists

There has been a surge of interest in recent years in incorporating genetic components into on-going longitudinal, developmental studies and related psychological studies. While this represents an exciting new direction in developmental science, much of the research on genetic topics in developmental science does not reflect the most current practice in genetics. This is likely due, in part, to the rapidly changing landscape of the field of genetics, and the difficulty this presents for developmental scientists who are trying to learn this new area. In this review, we present an overview of the paradigm shifts that have occurred in genetics and we introduce the reader to basic genetic methodologies. We present our view of the current stage of research ongoing at the intersection of genetics and social science, and we provide recommendations for how we could do better. We also address a number of issues that social scientists face as they integrate genetics into their projects, including choice of a study design (candidate gene versus genome-wide association versus sequencing), different methods of DNA collection, and special considerations involved in the analysis of genotypic data. Through this review, we hope to equip social scientists with a deeper understanding of the many considerations that go into genetics research, in an effort to foster more meaningful cross-disciplinary initiatives.

Gene-environment interaction in psychological traits and disorders

There has been an explosion of interest in studying gene-environment interactions (GxE) as they relate to the development of psychopathology. In this article, I review different methodologies to study gene-environment interaction, providing an overview of methods from animal and human studies and illustrations of gene-environment interactions detected using these various methodologies. Gene-environment interaction studies that examine genetic influences as modeled latently (e.g., from family, twin, and adoption studies) are covered, as well as studies of measured genotypes. Importantly, the explosion of interest in gene-environment interactions has raised a number of challenges, including difficulties with differentiating various types of interactions, power, and the scaling of environmental measures, which have profound implications for detecting gene-environment interactions. Taking research on gene-environment interactions to the next level will necessitate close collaborations between psychologists and geneticists so that each field can take advantage of the knowledge base of the other.

Frontostriatal involvement in task switching depends on genetic differences in d2 receptor density

Recent studies suggest an association of dopamine D2 receptor (DRD2) availability with flexibility in reward-based learning. We extend these results by demonstrating an association of genetically based differences in DRD2 density with the ability to intentionally switch between nonrewarded tasks: noncarriers of the A1 allele of the DRD2/ANKK1-TaqIa polymorphism, associated with higher DRD2 density, show increased task-switching costs, increased prefrontal switching activity in the inferior frontal junction area, and increased functional connectivity in dorsal frontostriatal circuits, relative to A1 allele carriers. A DRD2 haplotype analysis in the same sample confirmed these results, indicating an association between high D2 density and increased task-switching effort. Our results provide evidence that converges with that from association studies relating increased D2 density to deficits in cognitive flexibility in schizophrenia. We suggest that individual differences in striatal D2 signaling in healthy humans modulate goal-directed gating to prefrontal cortex, thus leading to individual differences in switching intentionally to newly relevant behaviors.