Human dopamine transporter gene (DAT1) maps to chromosome 5p15.3 and displays a VNTR

Polymorphism of the COMT, MAO, DAT, NET and 5-HTT Genes, and Biogenic Amines in Parkinson's Disease

Epinephrine (E) and sympathetic nerve stimulation were described by Thomas Renton Elliott in 1905 for the first time. Dopamine (DA), norepinephrine (NE), E, and serotonin (5-HT) belong to the classic biogenic amines (or monoamines). Parkinson's disease (PD) is among the diseases in which it has been established that catecholamines may account for the neurodegeneration of central and peripheral catecholamine neural systems. PD is a chronic and progressive neurological disorder characterized by resting tremor, rigidity, and bradykinesia, affecting 2% of individuals above the age of 65 years. This disorder is a result of degeneration of DA-producing neurons of the substantia nigra and a significant loss of noradrenergic neurons in the locus coeruleus. In PD and other related neurodegerative diseases, catecholamines play the role of endogenous neurotoxins. Catechol-O-methyltransferase (COMT) and/or monoamine oxidase (MAO) catalyze the metabolism of monoamines. However, the monoamine transporters for DA, NE, and 5-HT namely DAT, NET, and SERT, respectively regulate the monoamine concentration. The metabolism of catecholamines and 5-HT involves common factors. Monoamine transporters represent targets for many pharmacological agents that affect brain function, including psychostimulators and antidepressants. In PD, polymorphisms of the COMT, MAO, DAT, NET, and 5- HTT genes may change the levels of biogenic amines and their metabolic products. The currently available therapies for PD improve the symptoms but do not halt the progression of the disease. The most effective treatment for PD patients is therapy with L-dopa. Combined therapy for PD involves a DA agonist and decarboxylase, MAOs and COMT inhibitors, and is the current optimal form of PD treatment maintaining monoamine balance.

Enhanced prepulse inhibition and low sensitivity to a dopamine agonist in HESR1 knockout mice

Transcription factor Hesr family genes are important in neuronal development. We demonstrated previously that HESR1 and HESR2 modified expression of the dopamine transporter (DAT) reporter gene. HESR-family genes have been investigated in development, but their functions, especially in relation to behaviors regulated by dopamine, in adult animals remain unclear. In the present study, we investigated the effects of Hesr1 and Hesr2 on behavior. A behavioral test battery to examine spontaneous activity, anxiety-like behavior, aggressive behavior, pain sensitivity, and sensorimotor gating was conducted in Hesr1 and Hesr2 knockout (KO) mice. Enhanced prepulse inhibition (PPI), which is a form of sensorimotor gating, was observed in only Hesr1 KO mice; other behavioral traits were mostly comparable to wild-type animals in both the Hesr1 and the Hesr2 KO lines. Next, we used a dopamine agonist, apomorphine, to confirm the involvement of the dopaminergic system. Injection of apomorphine reduced the enhanced PPI in Hesr1 KO mice. Additionally, dose-dependent sensitivity to the agonist was lower in the Hesr1 KO mice than in wild-type mice, suggesting that the enhanced PPI resulted from this alteration in dopamine sensitivity. Furthermore, DAT mRNA was downregulated in Hesr1 KO mice, whereas the dopamine D1 and D2 receptors were comparable. These findings suggest Hesr1 to be a novel factor that affects dopamine sensitivity and the sensorimotor gating system.

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.

Genetic modulation of borderline personality disorder: systematic review and meta-analysis

Borderline personality disorder (BPD) is a highly prevalent psychiatric disorder with high morbidity and mortality. Early theories ascribed an environmental etiology of BPD, but growing evidence supports a genetic vulnerability as well. The primary aim of this study was to systematically review genetic association studies focused on BPD. PubMed, ISI Web of Knowledge and PsycINFO databases were searched for studies published until December 2012. Meta-analyses were also performed when three or more studies reported genetic data on the same polymorphism. Data were analyzed with Cochrane Collaboration Review Manager Software (RevMan, version 5.0). Quality and publication bias were assessed. The systematic review of association studies examining genetic polymorphisms and BPD produced conflicting results. Meta-analyses were performed for three serotonergic polymorphisms: two common polymorphisms of the serotonin transporter gene (SLC6A4), the promoter insertion/deletion (5-HTTLPR) and the intron 2 VNTR (STin2 VNTR), and the rs1800532 (A218C) polymorphism of the tryptophan hydroxylase 1 gene (TPH1), all showing no association. No direct role of genetic polymorphisms was found in BPD. However, a few studies only are present in literature to draw definite conclusions. Further studies focusing on gene × gene and gene × environment interactions are needed to more deeply dissect the genetic role in the modulation of BPD.

The association study of polymorphisms in DAT, DRD2, and COMT genes and acute extrapyramidal adverse effects in male schizophrenic patients treated with haloperidol

Extrapyramidal symptoms (EPSs) are common adverse effects of antipsychotics. The development of acute EPSs could depend on the activity of dopaminergic system and its gene variants. The aim of this study was to determine the association between dopaminergic type 2 receptor (DRD2) dopamine transporter (SLC6A3) and catechol-O-methyltransferase (COMT) gene polymorphisms and acute EPSs in 240 male schizophrenic patients treated with haloperidol (15-mg/d) over a period of 2 weeks. Acute EPSs were assessed with Simpson-Angus Scale. Three dopaminergic gene polymorphisms, the DRD2 Taq1A, the SLC6A3 VNTR, and the COMT Val158Met, were determined. Extrapyramidal symptoms occurred in 116 (48.3%) of patients. Statistically significant associations were found for SLC6A3 VNTR and COMT Val158Met polymorphisms and EPS susceptibility. Patients with SLC6A3 9/10 genotype had almost twice the odds to develop EPSs compared with those with all other SLC6A3 genotypes (odds ratio, 1.9; 95% confidence interval, 1.13-3.30), and patients with COMT Val/Met genotype had 1.7 times greater odds to develop EPSs than those with all other COMT genotypes (odds ratio, 1.7; 95% confidence interval, 1.01-2.88). There was no statistically significant association between genotype and allele frequencies of DRD2, SLC6A3, or COMT polymorphisms and the development of particular EPSs.In conclusion, the results of the present study showed for the first time the association between acute haloperidol-induced EPSs and SLC6A3 VNTR and COMT Val158Met polymorphisms. Although the precise biological mechanisms underlying these findings are not yet understood, the results suggest that the dopaminergic gene variations could predict the vulnerability to the development of the acute EPSs in haloperidol-treated schizophrenic patients.

Increases in CSF dopamine in HIV patients are due to the dopamine transporter 10/10-repeat allele which is more frequent in HIV-infected individuals

Dysfunction of dopaminergic neurotransmission has been implicated in HIV infection. We showed previously increased dopamine (DA) levels in CSF of therapy-naïve HIV patients and an inverse correlation between CSF DA and CD4 counts in the periphery, suggesting adverse effects of high levels of DA on HIV infection. In the current study including a total of 167 HIV-positive and negative donors from Germany and South Africa (SA), we investigated the mechanistic background for the increase of CSF DA in HIV individuals. Interestingly, we found that the DAT 10/10-repeat allele is present more frequently within HIV individuals than in uninfected subjects. Logistic regression analysis adjusted for gender and ethnicity showed an odds ratio for HIV infection in DAT 10/10 allele carriers of 3.93 (95% CI 1.72-8.96; p = 0.001, Fishers exact test). 42.6% HIV-infected patients harbored the DAT 10/10 allele compared to only 10.5% uninfected DAT 10/10 carriers in SA (odds ratio 6.31), whereas 68.1 versus 40.9%, respectively, in Germany (odds ratio 3.08). Subjects homozygous for the 10-repeat allele had higher amounts of CSF DA and reduced DAT mRNA expression but similar disease severity compared with those carrying other DAT genotypes. These intriguing and novel findings show the mutual interaction between DA and HIV, suggesting caution in the interpretation of CNS DA alterations in HIV infection solely as a secondary phenomenon to the virus and open the door for larger studies investigating consequences of the DAT functional polymorphism on HIV epidemiology and progression of disease.

Rats classified as low or high cocaine locomotor responders: a unique model involving striatal dopamine transporters that predicts cocaine addiction-like behaviors

Individual differences are a hallmark of drug addiction. Here, we describe a rat model based on differential initial responsiveness to low dose cocaine. Despite similar brain cocaine levels, individual outbred Sprague-Dawley rats exhibit markedly different magnitudes of acute cocaine-induced locomotor activity and, thereby, can be classified as low or high cocaine responders (LCRs or HCRs). LCRs and HCRs differ in drug-induced, but not novelty-associated, hyperactivity. LCRs have higher basal numbers of striatal dopamine transporters (DATs) than HCRs and exhibit marginal cocaine inhibition of in vivo DAT activity and cocaine-induced increases in extracellular DA. Importantly, lower initial cocaine response predicts greater locomotor sensitization, conditioned place preference and greater motivation to self-administer cocaine following low dose acquisition. Further, outbred Long-Evans rats classified as LCRs, versus HCRs, are more sensitive to cocaine's discriminative stimulus effects. Overall, results to date with the LCR/HCR model underscore the contribution of striatal DATs to individual differences in initial cocaine responsiveness and the value of assessing the influence of initial drug response on subsequent expression of addiction-like behaviors.

Interaction between effects of genes coding for dopamine and glutamate transmission on striatal and parahippocampal function

The genes for the dopamine transporter (DAT) and the D-Amino acid oxidase activator (DAOA or G72) have been independently implicated in the risk for schizophrenia and in bipolar disorder and/or their related intermediate phenotypes. DAT and G72 respectively modulate central dopamine and glutamate transmission, the two systems most robustly implicated in these disorders. Contemporary studies have demonstrated that elevated dopamine function is associated with glutamatergic dysfunction in psychotic disorders. Using functional magnetic resonance imaging we examined whether there was an interaction between the effects of genes that influence dopamine and glutamate transmission (DAT and G72) on regional brain activation during verbal fluency, which is known to be abnormal in psychosis, in 80 healthy volunteers. Significant interactions between the effects of G72 and DAT polymorphisms on activation were evident in the striatum, parahippocampal gyrus, and supramarginal/angular gyri bilaterally, the right insula, in the right pre-/postcentral and the left posterior cingulate/retrosplenial gyri (P < 0.05, FDR-corrected across the whole brain). This provides evidence that interactions between the dopamine and the glutamate system, thought to be altered in psychosis, have an impact in executive processing which can be modulated by common genetic variation.

Neural markers of errors as endophenotypes in neuropsychiatric disorders

Learning from errors is fundamental to adaptive human behavior. It requires detecting errors, evaluating what went wrong, and adjusting behavior accordingly. These dynamic adjustments are at the heart of behavioral flexibility and accumulating evidence suggests that deficient error processing contributes to maladaptively rigid and repetitive behavior in a range of neuropsychiatric disorders. Neuroimaging and electrophysiological studies reveal highly reliable neural markers of error processing. In this review, we evaluate the evidence that abnormalities in these neural markers can serve as sensitive endophenotypes of neuropsychiatric disorders. We describe the behavioral and neural hallmarks of error processing, their mediation by common genetic polymorphisms, and impairments in schizophrenia, obsessive-compulsive disorder, and autism spectrum disorders. We conclude that neural markers of errors meet several important criteria as endophenotypes including heritability, established neuroanatomical and neurochemical substrates, association with neuropsychiatric disorders, presence in syndromally-unaffected family members, and evidence of genetic mediation. Understanding the mechanisms of error processing deficits in neuropsychiatric disorders may provide novel neural and behavioral targets for treatment and sensitive surrogate markers of treatment response. Treating error processing deficits may improve functional outcome since error signals provide crucial information for flexible adaptation to changing environments. Given the dearth of effective interventions for cognitive deficits in neuropsychiatric disorders, this represents a potentially promising approach.

Genetic influences on adolescent sexual behavior: Why genes matter for environmentally oriented researchers

There are dramatic individual differences among adolescents in how and when they become sexually active adults, and early sexual activity is frequently cited as a cause of concern for scientists, policymakers, and the general public. Understanding the causes and developmental impact of adolescent sexual activity can be furthered by considering genes as a source of individual differences. Quantitative behavioral genetics (i.e., twin and family studies) and candidate gene association studies now provide clear evidence for the genetic underpinnings of individual differences in adolescent sexual behavior and related phenotypes. Genetic influences on sexual behavior may operate through a variety of direct and indirect mechanisms, including pubertal development, testosterone levels, and dopaminergic systems. Genetic differences may be systematically associated with exposure to environments that are commonly treated as causes of sexual behavior (gene-environment correlation). Possible gene-environment correlations pose a serious challenge for interpreting the results of much behavioral research. Multivariate, genetically informed research on adolescent sexual behavior compares twins and family members as a form of quasi experiment: How do twins who differ in their sexual experiences differ in their later development? The small but growing body of genetically informed research has already challenged dominant assumptions regarding the etiology and sequelae of adolescent sexual behavior, with some studies indicating possible positive effects of teenage sexuality. Studies of Gene × Environment interaction may further elucidate the mechanisms by which genes and environments combine to shape the development of sexual behavior and its psychosocial consequences. Overall, the existence of heritable variation in adolescent sexual behavior has profound implications for environmentally oriented theory and research.

DAT1 polymorphism determines L-DOPA effects on learning about others' prosociality

Despite that a wealth of evidence links striatal dopamine to individualś reward learning performance in non-social environments, the neurochemical underpinnings of such learning during social interaction are unknown. Here, we show that the administration of 300 mg of the dopamine precursor L-DOPA to 200 healthy male subjects influences learning about a partners' prosocial preferences in a novel social interaction task, which is akin to a repeated trust game. We found learning to be modulated by a well-established genetic marker of striatal dopamine levels, the 40-bp variable number tandem repeats polymorphism of the dopamine transporter (DAT1 polymorphism). In particular, we found that L-DOPA improves learning in 10/10R genoype subjects, who are assumed to have lower endogenous striatal dopamine levels and impairs learning in 9/10R genotype subjects, who are assumed to have higher endogenous dopamine levels. These findings provide first evidence for a critical role of dopamine in learning whether an interaction partner has a prosocial or a selfish personality. The applied pharmacogenetic approach may open doors to new ways of studying psychiatric disorders such as psychosis, which is characterized by distorted perceptions of others' prosocial attitudes.

Multivariate analysis of dopaminergic gene variants as risk factors of heroin dependence

BACKGROUND

Heroin dependence is a debilitating psychiatric disorder with complex inheritance. Since the dopaminergic system has a key role in rewarding mechanism of the brain, which is directly or indirectly targeted by most drugs of abuse, we focus on the effects and interactions among dopaminergic gene variants.

OBJECTIVE

To study the potential association between allelic variants of dopamine D2 receptor (DRD2), ANKK1 (ankyrin repeat and kinase domain containing 1), dopamine D4 receptor (DRD4), catechol-O-methyl transferase (COMT) and dopamine transporter (SLC6A3) genes and heroin dependence in Hungarian patients.

METHODS

303 heroin dependent subjects and 555 healthy controls were genotyped for 7 single nucleotide polymorphisms (SNPs) rs4680 of the COMT gene; rs1079597 and rs1800498 of the DRD2 gene; rs1800497 of the ANKK1 gene; rs1800955, rs936462 and rs747302 of the DRD4 gene. Four variable number of tandem repeats (VNTRs) were also genotyped: 120 bp duplication and 48 bp VNTR in exon 3 of DRD4 and 40 bp VNTR and intron 8 VNTR of SLC6A3. We also perform a multivariate analysis of associations using Bayesian networks in Bayesian multilevel analysis (BN-BMLA).

FINDINGS AND CONCLUSIONS

In single marker analysis the TaqIA (rs1800497) and TaqIB (rs1079597) variants were associated with heroin dependence. Moreover, -521 C/T SNP (rs1800955) of the DRD4 gene showed nominal association with a possible protective effect of the C allele. After applying the Bonferroni correction TaqIB was still significant suggesting that the minor (A) allele of the TaqIB SNP is a risk component in the genetic background of heroin dependence. The findings of the additional multiple marker analysis are consistent with the results of the single marker analysis, but this method was able to reveal an indirect effect of a promoter polymorphism (rs936462) of the DRD4 gene and this effect is mediated through the -521 C/T (rs1800955) polymorphism in the promoter.

Relating dopaminergic and cholinergic polymorphisms to spatial attention in infancy

Early selective attention skills are a crucial building block for cognitive development, as attention orienting serves as a primary means by which infants interact with and learn from the environment. Although several studies have examined infants' attention orienting using the spatial cueing task, relatively few studies have examined neurodevelopmental factors associated with attention orienting during infancy. The present study examined the relationship between normative genetic polymorphisms affecting dopamine and acetylcholine signaling and attention orienting in 7-month-old infants during a spatial cueing task. We focused on 3 genes, including the CHRNA4 C¹⁵⁴⁵T SNP (rs10344946), DAT1 3'UTR VNTR, and COMT Val¹⁵⁸Met SNP (rs4680), as previous adult research has linked spatial attention skills to these polymorphisms. Behavioral measures included both facilitation of orienting at the cued location as well as inhibition of return (IOR), in which attention orienting is suppressed at the cued location. Results indicated that COMT Val carriers showed robust IOR relative to infants with the Met/Met genotype. However, COMT was unrelated to infants' facilitation responses, and there were no effects of CHRNA4 or DAT1 on either facilitation or IOR. Overall, this study suggests that variations in dopamine signaling, likely in prefrontal cortex, contribute to individual differences in orienting during early development.

Dopamine transporter genotype dependent effects of apomorphine on cold pain tolerance in healthy volunteers

The aims of this study were to assess the effects of the dopamine agonist apomorphine on experimental pain models in healthy subjects and to explore the possible association between these effects and a common polymorphism within the dopamine transporter gene. Healthy volunteers (n = 105) participated in this randomized double-blind, placebo-controlled, cross-over trial. Heat pain threshold and intensity, cold pain threshold, and the response to tonic cold pain (latency, intensity, and tolerance) were evaluated before and for up to 120 min after the administration of 1.5 mg apomorphine/placebo. A polymorphism (3′-UTR 40-bp VNTR) within the dopamine transporter gene (SLC6A3) was investigated. Apomorphine had an effect only on tolerance to cold pain, which consisted of an initial decrease and a subsequent increase in tolerance. An association was found between the enhancing effect of apomorphine on pain tolerance (120 min after its administration) and the DAT-1 polymorphism. Subjects with two copies of the 10-allele demonstrated significantly greater tolerance prolongation than the 9-allele homozygote carriers and the heterozygote carriers (p = 0.007 and p = 0.003 in comparison to the placebo, respectively). In conclusion, apomorphine administration produced a decrease followed by a genetically associated increase in cold pain tolerance.

Are dopamine-related genotypes risk factors for excessive gestational weight gain?

Background

Excessive gestational weight gain is associated with postpartum weight retention and downstream child obesity. Dopamine plays a critical role in the regulation of energy intake and body weight. The purpose of this study was to examine the relationship between excessive gestational weight gain and dopamine pathway-related polymorphisms, namely the variable nucleotide tandem repeat in the 3′untranslated region (UTR) region of the SLC6A3 (DAT-1) dopamine transporter gene and the 30-base pair variable nucleotide tandem repeat polymorphism of the 5′UTR of the monoamine oxidase-A (MAO-A) gene.

Methods

Ninety-three women of mean age 31.7 ± 4.2 years were recruited from the Ottawa and Kingston birth cohort and assessed at 12–20 weeks’ gestation. Mean body mass index was 22.7 ± 2.5 kg/m². Excessive gestational weight gain was defined according to the 2009 Institute of Medicine guidelines based on body mass index. Genotype analyses were performed using polymerase chain reaction and agarose gel electrophoresis.

Results

There was no relationship between the prevalence or magnitude of excessive gestational weight gain among women with the 3′ UTR single nucleotide polymorphism of the DAT-1 gene. However, 70% (19 of 27) of women carrying the MAO-A 4/4 (high activity) allele exceeded recommendations for gestational weight gain compared with 48% (32 of 60) of those with the pooled 3/3, 3/4, and 3/3.5 (low activity) alleles (P < 0.05). Similarly, those with the MAO-A 4/4 allele had significantly greater gestational weight gain than those with the 3/3, 3/4, or 3/3.5 pooled genotypes (19.3 ± 4.1 versus 17.0 ± 5.0 kg, P = 0.03).

Conclusion

Carriers of the 4/4 variants of the MAO-A gene may be at increased risk for excessive gestational weight gain.

Candidate glutamatergic and dopaminergic pathway gene variants do not influence Huntington's disease motor onset

Huntington’s disease (HD) is a neurodegenerative disorder characterized by motor, cognitive, and behavioral disturbances. It is caused by the expansion of the HTT CAG repeat, which is the major determinant of age at onset (AO) of motor symptoms. Aberrant function of N-methyl-D-aspartate receptors and/or overexposure to dopamine has been suggested to cause significant neurotoxicity, contributing to HD pathogenesis. We used genetic association analysis in 1,628 HD patients to evaluate candidate polymorphisms in N-methyl-D-aspartate receptor subtype genes (GRIN2A rs4998386 and rs2650427, and GRIN2B rs1806201) and functional polymorphisms in genes in the dopamine pathway (DAT1 3′ UTR 40-bp variable number tandem repeat (VNTR), DRD4 exon 3 48-bp VNTR, DRD2 rs1800497, and COMT rs4608) as potential modifiers of the disease process. None of the seven polymorphisms tested was found to be associated with significant modification of motor AO, either in a dominant or additive model, after adjusting for ancestry. The results of this candidate-genetic study therefore do not provide strong evidence to support a modulatory role for these variations within glutamatergic and dopaminergic genes in the AO of HD motor manifestations.

Genetic polymorphisms of the dopamine and serotonin systems modulate the neurophysiological response to feedback and risk taking in healthy humans

Genetic differences in the dopamine and serotonin systems have been suggested as potential factors underlying interindividual variability in risk taking and in brain activation during the processing of feedback. Here, we studied the effects of dopaminergic (dopamine transporter [DAT1], catecholamine-O-methyltransferase val158met [COMT]) and serotonergic (serotonin transporter [5HTTLPR]) polymorphisms on risk taking and brain responses following feedback in 60 healthy female subjects. The subjects completed a well-established experimental gambling paradigm while an electroencephalogram was recorded. During the task, risk-taking behavior and prefrontal brain responses (feedback-related negativity [FRN]) following monetary gains and losses were assessed. FRN amplitudes were enhanced for nine-repeat-allele carriers of the DAT1 and short-allele carriers of 5HTTLPR, which are both presumably linked to less transporter activity and higher neurotransmitter levels. Moreover, nine-repeat DAT1 carriers displayed a trend toward increased risk taking in general, whereas 5HTTLPR short-allele carriers showed decreased risk taking following gains. COMT val158met genotype was unrelated to FRN amplitude and average risk taking. However, COMT met/met carriers showed a pronounced feedback P3 amplitude independent of valence, and a gradual increase in risk taking during the gambling task. In sum, the present findings underline the importance of genetic variability in the dopamine and serotonin systems regarding the neurophysiology of feedback processing.

A trio of human molecular genetics PCR assays

This laboratory exercise demonstrates three different analytical forms of the polymerase chain reaction (PCR) that allow students to genotype themselves at four different loci. Here, we present protocols to allow students to a) genotype a non-coding polymorphic Variable Number of Tandem Repeat (VNTR) locus on human chromosome 5 using conventional PCR, b) perform PCR - Restriction Fragment Polymorphism (PCR-RFLP) analysis to genotype a Single Nucleotide Polymorphism (SNP) of the TAS2R38 gene on human chromosome 7 and c) perform duplex Allele Specific Primer-PCR (ASP-PCR) to genotype SNPs of two enzyme-encoding genes in a single biochemical pathway on human chromosomes 4 and 12. All PCR reactions have been optimized to use a single easily purified sample of the students' own DNA and run under a single thermal cycler program using inexpensive reagents to produce robust and clearly interpretable results on a single agarose gel. As presented here, the lab occupies two lab periods of 2 h, 40 min each: DNA purification followed by PCR reactions set-up on Day 1 and enzyme digestion of the PCR-RFLP and agarose gel analysis on Day 2.

Toward developmental models of psychiatric disorders in zebrafish

Psychiatric disorders are a diverse set of diseases that affect all aspects of mental function including social interaction, thinking, feeling, and mood. Although psychiatric disorders place a large economic burden on society, the drugs available to treat them are often palliative with variable efficacy and intolerable side-effects. The development of novel drugs has been hindered by a lack of knowledge about the etiology of these diseases. It is thus necessary to further investigate psychiatric disorders using a combination of human molecular genetics, gene-by-environment studies, in vitro pharmacological and biochemistry experiments, animal models, and investigation of the non-biological basis of these diseases, such as environmental effects. Many psychiatric disorders, including autism spectrum disorder, attention-deficit/hyperactivity disorder, mental retardation, and schizophrenia can be triggered by alterations to neural development. The zebrafish is a popular model for developmental biology that is increasingly used to study human disease. Recent work has extended this approach to examine psychiatric disorders as well. However, since psychiatric disorders affect complex mental functions that might be human specific, it is not possible to fully model them in fish. In this review, I will propose that the suitability of zebrafish for developmental studies, and the genetic tools available to manipulate them, provide a powerful model to study the roles of genes that are linked to psychiatric disorders during neural development. The relative speed and ease of conducting experiments in zebrafish can be used to address two areas of future research: the contribution of environmental factors to disease onset, and screening for novel therapeutic compounds.

Auditory event-related potentials (P3a, P3b) and genetic variants within the dopamine and serotonin system in healthy females

The late positive components of the human event-related brain potential comprise electrocortical reflections of stimulus-driven attentional capture (the anteriorly distributed P3a) and top-down control detection of relevant events (the posteriorly distributed P3b). As of yet, the neuropharmacologic and neurogenetic origin of the P3a and P3b is not fully understood. In this study, we address the contribution of dopaminergic and serotoninergic mechanisms. Sixty healthy females completed an active auditory novelty oddball paradigm while EEG was recorded. In all subjects, genetic polymorphisms within the dopamine system (dopamine transporter [DAT1], catecholamine-O-methyltransferase val158met [COMT val158met]) and the serotonin system (serotonin transporter [5HTTLPR]) were assessed. Across genotypes, novels (relative to standards) elicited a fronto-centrally distributed P3a, and targets (relative to standards) a parieto-centrally distributed P3b. Genotypes effects were observed for both P3a (COMT, 5HTTPLR) and P3b (DAT1, COMT, 5HTTLPR) only at prefrontal electrode location (Fz). Specifically, the frontal P3a was enhanced in COMT met/met homozygotes, but not in DAT1 9R. The target-related P3b was enhanced in COMT met/met and DAT1 9R relative to its genetic counterparts, but only at frontal electrodes. This 'anteriorized' enhancement may reflect either an additional frontal component in the target-related P3 dependent on dopamine, or a more subtle shift in the neural ensemble that generates the target-related P3. Results for 5HTTLPR short allele homozygotes mimicked those in COMT met/met homozygotes. In all, the present findings suggest involvement of frontal-cortical dopaminergic and serotoninergic mechanisms in bottom-up attentional capture (COMT val158met, 5HTTLPR), with an additional top-down component sensitive to striatal signals (DAT1).

Meta-analysis of the association between dopamine transporter genotype and response to methylphenidate treatment in ADHD

Attention-deficit/hyperactivity disorder (ADHD) is a prevalent childhood-onset neuropsychiatric disorder. Treatment with methylphenidate, which blocks dopamine and noradrenaline transporters, is clinically efficacious in reducing the symptoms of ADHD. However, a considerable proportion of patients show no or only insufficient response to methylphenidate. Following a pharmacogenetic approach, a number of studies have suggested that heterogeneity in treatment response across subjects might to some extent be due to genetic factors. In particular, a variable number tandem repeat (VNTR) polymorphism in the 3' untranslated region of the SLC6A3 gene, which codes for the dopamine transporter, has been considered as a predictor of treatment success. However, the literature has so far been inconsistent. Here we present results of a meta-analysis of studies investigating the moderating effect of the SLC6A3 VNTR on response to methylphenidate treatment in subjects with ADHD. Outcome measures from 16 studies including data from 1572 subjects were entered into a random-effects model. There was no significant summary effect for the SLC6A3 VNTR on the response to methylphenidate treatment (P>0.5) and no effect on specific symptom dimensions of hyperactivity/impulsivity and inattention (all P>0.2). However, in a subanalysis of naturalistic trials, we observed a significant effect of d=-0.36 (P=0.03), indicating that 10R homozygotes show less improvement in symptoms following treatment than the non-10/10 carriers. This meta-analysis indicates that SLC6A3 VNTR is not a reliable predictor of methylphenidate treatment success in ADHD. Our study leaves unanswered the question of whether other genetic polymorphisms or nongenetic factors may contribute to the observed heterogeneity in treatment response across ADHD subjects.

Two functional serotonin polymorphisms moderate the effect of food reinforcement on BMI

Food reinforcement, or the motivation to eat, has been associated with increased energy intake, greater body weight, and prospective weight gain. Much of the previous research on the reinforcing value of food has focused on the role of dopamine, but it may be worthwhile to examine genetic polymorphisms in the serotonin and opioid systems as these neurotransmitters have been shown to be related to reinforcement processes and to influence energy intake. We examined the relationship among 44 candidate genetic polymorphisms in the dopamine, serotonin, and opioid systems, as well as food reinforcement and body mass index (BMI) in a sample of 245 individuals. Polymorphisms in the monoamine oxidase A (MAOA-LPR) and serotonin receptor 2A genes (rs6314) moderated the effect of food reinforcement on BMI, accounting for an additional 5-10% variance and revealed a potential role of the single nucleotide polymorphism, rs6314, in the serotonin 2A receptor as a differential susceptibility factor for obesity. Differential susceptibility describes a factor that can confer either risk or protection depending on a second variable, such that rs6314 is predictive of both high and low BMI based on the level of food reinforcement, while the diathesis stress or dual-gain model only influences one end of the outcome measure. The interaction with MAOA-LPR better fits the diathesis stress model, with the 3.5R/4R allele conferring protection for individuals low in food reinforcement. These results provide new insight into genes theoretically involved in obesity, and support the hypothesis that genetics moderate the association between food reinforcement and BMI.

Dopaminergic Gene Polymorphisms Affect Long-term Forgetting in Old Age: Further Support for the Magnification Hypothesis

Emerging evidence from animal studies suggests that suboptimal dopamine (DA) modulation may be associated with increased forgetting of episodic information. Extending these observations, we investigated the influence of DA-relevant genes on forgetting in samples of younger (n = 433, 20–31 years) and older (n = 690, 59–71 years) adults. The effects of single nucleotide polymorphisms of the DA D2 (DRD2) and D3 (DRD3) receptor genes as well as the DA transporter gene (DAT1; SLC6A3) were examined. Over the course of one week, older adults carrying two or three genotypes associated with higher DA signaling (i.e., higher availability of DA and DA receptors) forgot less pictorial information than older individuals carrying only one or no beneficial genotype. No such genetic effects were found in younger adults. The results are consistent with the view that genetic effects on cognition are magnified in old age. To the best of our knowledge, this is the first report to relate genotypes associated with suboptimal DA modulation to more long-term forgetting in humans. Independent replication studies in other populations are needed to confirm the observed association.

Dopaminergic foundations of schizotypy as measured by the German version of the Oxford-Liverpool Inventory of Feelings and Experiences (O-LIFE)-a suitable endophenotype of schizophrenia

The concept of schizotypy or “psychosis proneness” captures individual differences in perceptual, cognitive, and affective experiences that may relate to a range of psychotic disorders. The concept is an important way to assess the contribution of pre-existing psychological and genetically based biological features to the development of illnesses such as schizophrenia (so called endophenotypes). The Oxford-Liverpool Inventory of Feelings and Experiences (O-LIFE) is a widely used multi-dimensional measure of the construct and consists of four scales which mirror several groups of psychotic symptoms: Unusual Experiences (UnEx; positive symptoms), Cognitive Disorganization (CogDis; cognitive symptoms), Introvertive Anhedonia (IntAn; negative symptoms), and Impulsive Nonconformity (ImpNon; impulsive and antisocial symptoms). For the purpose of evaluating the suitability of schizotypy as an endophenotype of schizophrenia the current version of the O-LIFE was translated into German: its psychometric properties (including re-test reliability and construct validity) were examined in a large sample (n > 1200) and compared to those of the English original. The German version was both highly reliable and consistent with the original. The study aimed to show that schizotypy as measured by the O-LIFE can indeed be regarded as an endophenotype of schizophrenia in terms of genetic associations regarding relevant dopamine-related candidate polymorphisms of schizotypy [i.e., Val¹⁵⁸Met-polymorphism of the COMT gene, uVNTR of the MAOA gene, Taq1A-polymorphism of the DRD2 gene, VNTR of the SLC6A3 (DAT) gene]. We also wanted to compare the genetic associations of the O-LIFE to those published using other operationalizations of schizotypy. Our results show a large number of significant associations and borderline-significant trends between the O-LIFE sub-scales and a range of genes, thereby supporting using the O-LIFE in the search for endophenotypic markers.

Dopamine and training-related working-memory improvement

Converging evidence indicates that the neurotransmitter dopamine (DA) is implicated in working-memory (WM) functioning and that WM is trainable. We review recent work suggesting that DA is critically involved in the ability to benefit from WM interventions. Functional MRI studies reveal increased striatal BOLD activity following certain forms of WM interventions, such as updating training. Increased striatal BOLD activity has also been linked to transfer of learning to non-trained WM tasks, suggesting a neural signature of transfer. The striatal BOLD signal is partly determined by DA activity. Consistent with this assertion, PET research demonstrates increased striatal DA release during updating of information in WM after training. Genetic studies indicate larger increases in WM performance post training for those who carry advantageous alleles of DA-relevant genes. These patterns of results corroborate the role of DA in WM improvement. Future research avenues include: (a) neuromodulatory correlates of transfer; (b) the potential of WM training to enhance DA release in older adults; (c) comparisons among different WM processes (i.e., updating, switching, inhibition) regarding regional patterns of training-related DA release; and (d) gene-gene interactions in relation to training-related WM gains.

Genetic Analysis of Polymorphisms in Dopamine Receptor and Transporter Genes for Association with Smoking among Cancer Patients

BACKGROUND

Smoking among Russian cancer patients may be related to variations in the DRD2/ANKK1 (Taq1), DRD4 (exon III VNTR), and SLC6A3 genes.

METHODS

Seven hundred fifty patients provided smoking history and DNA.

RESULTS

Current smokers were more likely to be DRD2 A2 allele carriers versus nonsmokers (former/never smokers; 69 vs. 56%; OR = 1.69; 95% CI 1.13-2.53, p = 0.01) and former smokers (69 vs. 59%; OR = 1.54; 95% CI 0.97-2.46, p = 0.07). Ever smokers (current/former smokers) were more likely to be DRD2 A2 allele carriers versus never smokers (65 vs. 55%; OR = 1.50; 95% CI 1.00-2.27, p = 0.05). The risk of current smoking among DRD2 A2 allele carriers was present if the DRD4 short allele was also present (OR = 1.76; 95% CI 1.12-2.78, p = 0.02), and the risk of ever smoking among DRD2 A2 allele carriers was present if the DRD4 short allele was also present (OR = 1.62; 95% CI 1.02-2.55, p = 0.04). DRD2 A2 allele carriers had a shorter period of previous abstinence versus DRD2 A1 carriers (p = 0.02). Effects were not statistically significant when controlling for multiple comparisons.

CONCLUSIONS

The DRD2 A2 allele may increase the risk of smoking among cancer patients, convergent with studies using non-Western samples. However, additional replication is needed.

Neural coding of computational factors affecting decision making

We constantly need to make decisions that can result in rewards of different amounts with different probabilities and at different timing. To characterize the neural coding of such computational factors affecting value-based decision making, we have investigated how reward information processing is influenced by parameters such as reward magnitude, probability, delay, effort, and uncertainty using either fMRI in healthy humans or intracranial recordings in patients with epilepsy. We decomposed brain signals modulated by these computational factors, showing that prediction error (PE), salient PE, and uncertainty signals are computed in partially overlapping brain circuits and that both transient and sustained uncertainty signals coexist in the brain. When investigating the neural representation of primary and secondary rewards, we found both a common brain network, including the ventromedial prefrontal cortex and ventral striatum, and a functional organization of the orbitofrontal cortex according to reward type. Moreover, separate valuation systems were engaged for delay and effort costs when deciding between options. Finally, genetic variations in dopamine-related genes influenced the response of the reward system and may contribute to individual differences in reward-seeking behavior and in predisposition to neuropsychiatric disorders.

Genetics of impulse control disorders in Parkinson's disease

Impulse control disorders (ICD) have been recognised in Parkinson's disease (PD) as adverse effects of dopamine replacement therapy, particularly with dopamine agonists. Although virtually all PD patients are treated with dopaminergic drugs, only a minority will develop hyperdopaminergic states, suggesting predisposing and/or protecting factors. The age at onset, the sex and the dose or type of dopaminergic drugs have been identified as clinical predictive factors. Recent genetic studies have investigated associations between ICD and polymorphisms of genes involved in the dopamine metabolism pathway (COMT, DAT), dopamine receptors (DRD1, DRD2, DRD3, DRD4), serotonin receptors and its transporter (HTR2A, 5HTT), and glutamate receptors (GRIN2B). Although validation in larger and independent cohorts is needed, the results from these studies give us some insights into the pathophysiology of hyperdopaminergic states and may be useful, at term, in personalising antiparkinsonian treatment in clinical practice.

The National Longitudinal Study of Adolescent Health (Add Health) sibling pairs data

This article describes the design and phenotype and genotype data available for sibling pairs with varying genetic relatedness in the National Longitudinal Study of Adolescent Health (Add Health). Add Health is a nationally representative longitudinal study of over 20,000 adolescents in the United States in 1994-1995 who have been followed for 15 years into adulthood. The Add Health design included oversamples of more than 3,000 pairs of individuals with varying genetic resemblance, ranging from monozygotic twins, dizygotic twins, full siblings, half siblings, and unrelated siblings who were raised in the same household. Add Health sibling pairs are therefore nationally representative and followed longitudinally from early adolescence into adulthood with four in-home interviews during the period 1994-2009. Add Health has collected rich longitudinal social, behavioral, environmental, and biological data, as well as buccal cell DNA from all sample members, including sibling pairs. Add Health has an enlightened dissemination policy and to date has released phenotype and genotype data to more than 10,000 researchers in the scientific community.

Genetic biomarkers of depression

Depression is a term that has been used to describe a variety of ailments, ranging from minor to incapacitating. Clinically significant depression, termed as major depression, is a serious condition characterized not only by depressed mood but also by a cluster of somatic, cognitive, and motivational symptoms. Significant research efforts are aimed to understand the neurobiological as well as psychiatric disorders, and the evaluation of treatment of these disorders is still based solely on the assessment of symptoms. In order to identify the biological markers for depression, we have focused on gathering information on different factors responsible for depression including stress, genetic variations, neurotransmitters, and cytokines and chemokines previously suggested to be involved in the pathophysiology of depression. The present review illustrates the potential of biomarker profiling for psychiatric disorders, when conducted in large collections. The review highlighted the biomarker signatures for depression, warranting further investigation.

Epistatic interactions implicating dopaminergic genes in bulimia nervosa (BN): relationships to eating- and personality-related psychopathology

We explored the influence of interactions between polymorphisms acting upon postsynaptic receptors (DRD2 TaqA1 rs1800497 and DRD4 7R) and dopamine regulators (COMT rs4680 and DAT1) on the expression of eating symptoms and personality traits in women with bulimia-spectrum eating disorders. We had 269 bulimic women provide blood for genetic assays, and measured eating-disorder symptoms and psychopathological traits using structured interviews and self-report questionnaires. We observed two epistatic interactions on symptom indices: interactions (in predicted directions) of DRD2 by DAT were seen on Body Mass Index (p=.023), and of DRD4 by COMT on self-harming behaviors (p=.014)--with genetic effects that would correspond to reduced dopamine transmission coinciding with more-pathological scores. Our findings suggest that genes acting in the dopamine system interact to influence both eating-related and personality psychopathology, with the result that lower levels of dopamine neuro-transmission correspond to increased psychopathology and body mass in women with bulimia-spectrum disorders. We discuss the implications of our observations.

Association of genetic polymorphisms with personality profile in individuals without psychiatric disorders

OBJECTIVE

Population-based twin studies demonstrate that approximately 40-50% of the variability in personality dimensions results from genetic factors. This study assessed selected polymorphisms in the COMT Val158Met, MAOA 3'VNTR, 5HTTLPR, 102T/C 5-HT2A, DAT 3'VNTR and DRD2 exon 8 genes and evaluated their association with personality profiles, anxiety levels, and depressiveness in healthy subjects.

METHODS

This study included 406 unrelated (mean age 38.51 years), mentally and somatically healthy Caucasian subjects of Polish origin. The prevalence of the gene variants mentioned above and their association with personality profiles, anxiety levels, and depressiveness was assessed using the Temperament and Character Inventory, NEO Five-Factor Inventory, Spielberger's State-Trait Anxiety Inventory and Beck's Depression Inventory.

RESULTS

The effects of the 5HTTLPR gene on the s/s genotype and empathy (C2) were lowest in the entire group. The effects of gender, age and the HT2A gene for the T/T genotype and attachment (RD3) were highest in women. The effects of gender, age and the DAT gene on the 9/9 DAT genotype, compassion (C4) and cooperativeness (C) were lowest in women. The effects of gender, age and the COMT gene on the Met/Met genotype and neuroticism (NEU) NEO-FFI were also lowest in women.

CONCLUSIONS

Our results suggest considerable influence of individual genes on the formation of personality traits.

Custom genotyping for substance addiction susceptibility genes in Jordanians of Arab descent

Background

Both environmental and genetic factors contribute to individual susceptibility to initiation of substance use and vulnerability to addiction. Determining genetic risk factors can make an important contribution to understanding the processes leading to addiction. In order to identify gene(s) and mechanisms associated with substance addiction, a custom platform array search for a genetic association in a case/control of homogenous Jordanian Arab population was undertaken. Patients meeting the DSM-VI criteria for substance dependence (n = 220) and entering eight week treatment program at two Jordanian Drug Rehabilitation Centres were genotyped. In addition, 240 healthy controls were also genotyped. The sequenom MassARRAY system (iPLEX GOLD) was used to genotype 49 single nucleotide polymorphisms (SNPs) within 8 genes (DRD1, DRD2, DRD3, DRD4, DRD5, BDNF, SLC6A3 and COMT).

Results

This study revealed six new associations involving SNPs within DRD2 gene on chromosome 11. These six SNPs within the DRD2 were found to be most strongly associated with substance addiction in the Jordanian Arabic sample. The strongest statistical evidence for these new association signals were from rs1799732 in the C/−C promoter and rs1125394 in A/G intron 1 regions of DRD2, with the overall estimate of effects returning an odds ratio of 3.37 (χ2 (2, N = 460) = 21, p-value = 0.000026) and 1.78 (χ2 (2, N = 460) = 8, p-value = 0.001), respectively. It has been suggested that DRD2, dopamine receptor D2, plays an important role in dopamine secretion and the signal pathways of dopaminergic reward and drug addiction.

Conclusion

This study is the first to show a genetic link to substance addiction in a Jordanian population of Arab descent. These findings may contribute to our understanding of drug addiction mechanisms in Middle Eastern populations and how to manage or dictate therapy for individuals. Comparative analysis with different ethnic groups could assist further improving our understanding of these mechanisms.

Association of dopamine-related gene alleles, smoking behavior and decline in FEV1 in subjects with COPD: findings from the lung health study

Cigarette smoking is the major risk factor for chronic obstructive pulmonary disease (COPD). Specific dopamine related gene alleles have previously been found to be associated with smoking initiation, maintenance and cessation. We investigated the association between specific dopamine related gene alleles and both change in smoking behavior and lung function change over time in individuals with mild-to-moderate COPD. Subjects included a subset of participants in the Lung Health Study (LHS), a smoking intervention study in smokers with mild to moderate COPD. Smoking status was determined and lung function performed at baseline and annually for 5 years. In post-hoc analyses, we assessed the association of the dopamine receptor (DRD2) TaqI A1(+) allele (A1A1, A1A2 genotypes) and A1(-) allele (A2A2 genotype), and the dopamine transporter (DAT) 9R(+) allele (9R9R and 9R10R genotypes) and 9R(-) allele (10R10R genotype) with both changes in smoking status and lung function in a subset of LHS subjects. No significant associations were noted between variants in these genes and success in smoking cessation. However, in exploratory analyses that did not adjust for multiple comparisons, sustained male (but not female) quitters with the DRD2 A1(-) allele and/or the DAT 9R(+) allele showed an accelerated decline in FEV(1) similar to that of continuing smokers over 5 years after quitting smoking. These preliminary findings suggest that dopamine-related genes may play a role in the progression of COPD, at least in the subset of male ex-smokers whose disease continues to progress despite sustained quitting, and warrants additional confirmatory and mechanistic studies.

Dopamine-system genes, childhood abuse, and clinical manifestations in women with Bulimia-Spectrum Disorders

OBJECTIVE

We explored interaction effects involving polymorphisms of targeted dopamine system genes and selected forms of childhood abuse (sexual, physical and emotional) acting upon severity of binge-eating and psychopathological symptoms in women with Bulimia-Spectrum Disorders (BSDs).

METHODS

Women diagnosed with a BSD (n = 216) were assessed for childhood traumata, eating-disorder (ED) symptoms, and selected psychopathological features (sensation seeking, impulsivity, compulsivity and affective instability), and then provided blood samples for genotyping of main polymorphisms of dopamine-2 receptor (DRD2), dopamine transporter (DAT1) and catechol o-methyltransferase (COMT) genes.

RESULTS

Sensation Seeking was elevated in carriers of the low-function allele of the DRD2 Taq1A polymorphism who also reported childhood sexual abuse, relative to that in individuals showing other combinations of alleles and abuse exposures. In addition, carriers of a low-function allele of COMT scored higher on compulsivity, lower on impulsivity, and marginally lower on frequency of binge-eating than did individuals in whom the allele was absent.

DISCUSSION

Our results suggest that genes acting within the dopamine system may contribute, either directly or indirectly (i.e., in interaction with traumatic childhood experiences), to variations in the presentation of comorbid traits and, possibly, of bulimic symptoms.

Association between temperament in terms of the Regulative Theory of Temperament and DRD4 and DAT1 gene polymorphisms

OBJECTIVES

This is a study of the association between DRD4 exon III VNTR and DAT1 3'-untranslated region polymorphisms on the one hand and temperament assessed with the Formal Characteristics of Behaviour-Temperament Inventory on the other hand.

METHODS

The study was run on 418 participants (314 women and 104 men) aged 18 to 55 years sampled from healthy male and female volunteers recruited from inhabitants of the Warsaw metropolis.

RESULTS

Main effects of sex were found for briskness (F(1,417) = 9.05, P = .003, η(2) = 0.022), perseveration (F(1,417) = 37.83, P < .001, η(2) = 0.085), sensory sensitivity (F(1,417) = 14.16, P < .001, η(2) = 0.003), and emotional reactivity (F(1,417) = 34.67, P < .001, η(2) = 0.078). A significant main effect of DAT1 variant was also found for sensory sensitivity (F(1,417) = 7.36, P = .007, η(2) = 0.018). No main effects of DRD4 on any of the analyzed temperament traits were found. A significant interaction of sex and DRD4 variant was found for sensory sensitivity (F(1,417) = 5.68, P = .018, η(2) = 0.014). No significant 3-way interactions (DAT1 × DRD4 × sex) were found.

CONCLUSIONS

A significant main effect of DAT1 polymorphism on sensory sensitivity and a significant interactive sex/DRD4 effect on that same trait were found.

DAT by perceived MC interaction on human prefrontal activity and connectivity during emotion processing

BACKGROUND

Maternal care (MC) and dopamine modulate brain activity during emotion processing in inferior frontal gyrus (IFG), striatum and amygdala. Reuptake of dopamine from the synapse is performed by the dopamine transporter (DAT), whose abundance is predicted by variation in its gene (DAT 3'VNTR; 10 > 9-repeat alleles). Here, we investigated the interaction between perceived MC and DAT 3'VNTR genotype on brain activity during processing of aversive facial emotional stimuli.

METHODS

Sixty-one healthy subjects were genotyped for DAT 3'VNTR and categorized in low and high MC individuals. They underwent functional magnetic resonance imaging while performing a task requiring gender discrimination of facial stimuli with angry, fearful or neutral expressions.

RESULTS

An interaction between facial expression, DAT genotype and MC was found in left IFG, such that low MC and homozygosity for the 10-repeat allele are associated with greater activity during processing of fearful faces. This greater activity was also inversely correlated with a measure of emotion control as scored with the Big Five Questionnaire. Moreover, MC and DAT genotype described a double dissociation on functional connectivity between IFG and amygdala.

CONCLUSION

These findings suggest that perceived early parental bonding may interact with DAT 3'VNTR genotype in modulating brain activity during emotionally relevant inputs.

In vitro study methodologies to investigate genetic aspects and effects of drugs used in attention-deficit hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is one of the most common psychiatric disorders in children and adolescents, with up to 5 % affected worldwide. Twin and family studies on ADHD show its high familiality with heritability estimated around 70 %, but, to date, no specific polymorphism or gene was found to be specifically affected. Psychostimulants (amphetamine, methylphenidate) and non-psychostimulants (atomoxetine) are used successfully in ADHD therapy, but many of their mechanisms of action and their adverse effects are not yet fully understood. Therefore, both genetic findings and therapeutic interventions should be further investigated. One easy platform for such studies is in vitro analyses, which encompass neuronal cell culture studies, transfections of genetic constructs, binding and electrophysiology analyses. In this review, different methods will be referred in particular to ADHD findings, and new techniques will be mentioned for future studies of drug or genetic effects in vitro.

The androgen receptor facilitates inhibition of human dopamine transporter (DAT1) reporter gene expression by HESR1 and HESR2 via the variable number of tandem repeats

A functional genetic polymorphism in the 3'-untranslated region (UTR) within exon 15 of the human DAT gene (DAT1) has been described. This 3'-UTR contains a variable number of tandem repeats (VNTR) 40 bp in length; many association studies of psychiatric or developmental disorders with this VNTR have been conducted. We previously demonstrated that HESR1 (the Hairy/enhancer of split related transcriptional factor 1 with YRPW motif) and HESR2 reduced DAT reporter gene expression via this 3'-UTR. VNTR allele-dependent altered reporter gene expression was also observed. In the present study, we wanted to clarify the molecular characterization of HESR1 and HESR2, focusing on its cis-element and co-factor. Deletion of the VNTR domain increased reporter gene expression both with and without transfection of HESRs, suggesting that the VNTR inhibits DAT expression, and is responsive to HESRs. In the presence of transfected androgen receptor (AR), activity of the luciferase reporter with the nine-repeat allele (9r) decreased, while that with the ten-repeat allele (10r), the most frequent in the population, increased significantly. Furthermore, co-expression of HESR1 or HESR2 with AR increased the inhibitory effect of the HESRs. Our data indicate that a functional modification occurs when the HESRs are coupled with AR. This HESR-AR interaction could be the molecular basis of sexual dimorphisms in DAT expression, or other dopamine-related behavioral traits.

Dopamine transporter (DAT1) VNTR polymorphism and alcoholism in two culturally different populations of south India

It is well established that the central dopaminergic reward pathway is likely involved in alcohol intake and the progression of alcohol dependence. Dopamine transporter (DAT1) mediates the active re-uptake of DA from the synapse and is a principal regulator of dopaminergic neurotransmission. The gene for the human DAT1 displays several polymorphisms, including a 40-bp variable number of tandem repeats (VNTR) ranging from 3 to 16 copies in the 3'-untranslated region (UTR) of the gene. To assess the role of this gene in alcoholism, we genotyped the VNTR of DAT1 gene in a sample of 206 subjects from the Kota population (111 alcohol dependence cases and 95 controls) and 142 subjects from Badaga population (81 alcohol dependence cases and 61 controls). Both populations inhabit a similar environmental zone, but have different ethnic histories. Phenotype was defined based on the DSM-IV criteria. Genotyping was performed using PCR and electrophoresis. The association of DAT1 with alcoholism was tested by using the Clump v1.9 program which uses the Monte Carlo method. In both Kota and Badaga populations, the allele A10 was the most frequent allele followed by allele A9. The genotypic distribution is in Hardy-Weinberg equilibrium in both cases and control groups of Kota and Badaga populations. The DAT1 VNTR was significantly associated with alcoholism in Badaga population but not in Kota population. Our results suggest that the A9 allele of the DAT gene is involved in vulnerability to alcoholism, but that these associations are population specific.

Molecular variation at the SLC6A3 locus predicts lifetime risk of PTSD in the Detroit Neighborhood Health Study

Recent work suggests that the 9-repeat (9R) allele located in the 3'UTR VNTR of the SLC6A3 gene increases risk of posttraumatic stress disorder (PTSD). However, no study reporting this association to date has been based on population-based samples. Furthermore, no study of which we are aware has assessed the joint action of genetic and DNA methylation variation at SLC6A3 on risk of PTSD. In this study, we assessed whether molecular variation at SLC6A3 locus influences risk of PTSD. Participants (n = 320; 62 cases/258 controls) were drawn from an urban, community-based sample of predominantly African American Detroit adult residents, and included those who had completed a baseline telephone survey, had provided blood specimens, and had a homozygous genotype for either the 9R or 10R allele or a heterozygous 9R/10R genotype. The influence of DNA methylation variation in the SLC6A3 promoter locus was also assessed in a subset of participants with available methylation data (n = 83; 16 cases/67 controls). In the full analytic sample, 9R allele carriers had almost double the risk of lifetime PTSD compared to 10R/10R genotype carriers (OR = 1.98, 95% CI = 1.02-3.86), controlling for age, sex, race, socioeconomic status, number of traumas, smoking, and lifetime depression. In the subsample of participants with available methylation data, a significant (p = 0.008) interaction was observed whereby 9R allele carriers showed an increased risk of lifetime PTSD only in conjunction with high methylation in the SLC6A3 promoter locus, controlling for the same covariates. Our results confirm previous reports supporting a role for the 9R allele in increasing susceptibility to PTSD. They further extend these findings by providing preliminary evidence that a "double hit" model, including both a putatively reduced-function allele and high methylation in the promoter region, may more accurately capture molecular risk of PTSD at the SLC6A3 locus.

DAT1 polymorphism is associated with risk taking in the Balloon Analogue Risk Task (BART)

Twin-studies suggest that a significant portion of individual differences in the propensity to take risks resides in people’s genetic make-up and there is evidence that variability in dopaminergic systems relates to individual differences in risky choice. We examined the link between risk taking in a risk taking task (the Balloon Analogue Risk Task, BART) and a variable number tandem repeat (VNTR) polymorphism in the 3′UTR of the dopamine transporter gene (SLC6A3/DAT1). Behavior in BART is known to be associated with activity in striatal reward-processing regions, and DAT1 is assumed to modulate striatal dopamine levels. We find that carriers of DAT1 alleles, which presumably result in lower striatal dopamine availability, showed more risk taking, relative to carriers of the alleles associated with higher striatal dopamine availability. Our analyses suggest that the mechanism underlying this association is diminished sensitivity to rewards among those who take more risks. Overall, our results support the notion that a behavioral genetic approach can be helpful in uncovering the basis of individual differences in risk taking.

An imaging genetics approach to understanding social influence

Normative social influences shape nearly every aspect of our lives, yet the biological processes mediating the impact of these social influences on behavior remain incompletely understood. In this Hypothesis, we outline a theoretical framework and an integrative research approach to the study of social influences on the brain and genetic moderators of such effects. First, we review neuroimaging evidence linking social influence and conformity to the brain's reward system. We next review neuroimaging evidence linking social punishment (exclusion) to brain systems involved in the experience of pain, as well as evidence linking exclusion to conformity. We suggest that genetic variants that increase sensitivity to social cues may predispose individuals to be more sensitive to either social rewards or punishments (or potentially both), which in turn increases conformity and susceptibility to normative social influences more broadly. To this end, we review evidence for genetic moderators of neurochemical responses in the brain, and suggest ways in which genes and pharmacology may modulate sensitivity to social influences. We conclude by proposing an integrative imaging genetics approach to the study of brain mediators and genetic modulators of a variety of social influences on human attitudes, beliefs, and actions.

The influence of five monoamine genes on trajectories of depressive symptoms across adolescence and young adulthood

The influence of five monoamine candidate genes on depressive symptom trajectories in adolescence and young adulthood were examined in the Add Health genetic sample. Results indicated that, for all respondents, carriers of the dopamine receptor D4 5-repeat allele were characterized by distinct depressive symptom trajectories across adolescence and early adulthood. Similarly, for males, individuals with the monoamine oxidase A 3.5-repeat allele exhibited unique depressive symptom trajectories. Specifically, the trajectories of those with the dopamine receptor D4 5-repeat allele were characterized by rising levels in the transition to adulthood, while their peers were experiencing a normative drop in depressive symptom frequency. Conversely, males with the monoamine oxidase A 3.5-repeat allele were shown to experience increased distress in late adolescence. An empirical method for examining a wide array of allelic combinations was employed, and false discovery rate methods were used to control the risk of false positives due to multiple testing. Special attention was given to thoroughly interrogate the robustness of the putative genetic effects. These results demonstrate the value of combining dynamic developmental perspectives with statistical genetic methods to optimize the search for genetic influences on psychopathology across the life course.

Dopamine transporter binding in social anxiety disorder: the effect of treatment with escitalopram

Social anxiety disorder (SAD) is characterised by fear of social or performance situations where the individual is exposed to unfamiliar people or to possible scrutiny by others. The literature on dopamine ligands and dopamine genotypes in SAD is however inconsistent. In this study we measured the effects of SSRI pharmacotherapy on dopamine transporter (DAT) binding in patients with SAD, also addressing variability in DAT genotype. Adult subjects meeting DSM-IV criteria for generalised SAD were studied before and after 12 weeks of pharmacotherapy with the selective serotonin reuptake inhibitor (SSRI) escitalopram. DAT single photon emission computed tomography (SPECT) using (123)I-FP-CIT was performed at baseline, and repeated at 12 weeks. Striatal DAT binding was analysed for changes following therapy, and for correlations with clinical efficacy, in the whole group as well as for a subgroup with the A10/A10 DAT genotype. The study included 14 subjects (9 male, 5 female) with a mean (SD) age of 41 (±13) years. The subjects' Liebowitz Social Anxiety Scale (LSAS) score was significantly decreased following pharmacotherapy. In the combined group the left caudate and left putamen showed clusters of increased DAT binding after therapy. The left caudate changes were also observed in the subgroup of 9 A10/A10 homozygotes. However no correlation was found between improved symptoms and DAT binding. The changes found in DAT binding in the caudate and putamen may be due to serotonergic activation of dopamine function by SSRI therapy. This is consistent with previous work indicating decreased DAT binding in SAD, and increased DAT binding after SSRI administration.