D2 dopamine receptor gene in psychiatric and neurologic disorders and its phenotypes

Genetic variations in the interleukin-6 and interleukin-8 genes and the interleukin-6 receptor gene in delirium

OBJECTIVE

The aim of this study was to investigate whether genetic polymorphisms in the interleukin-6 gene (IL6), the IL-6 receptor gene (IL6R), and the IL-8 gene (IL8) were associated with delirium in a population of acutely admitted older patients.

METHODS

This was a prospective cohort study in the Academic Medical Center in Amsterdam, running from April, 2003, through August, 2008. A total of 881 patients, aged 65 years and older, acutely admitted to the medical department or to the surgical department following hip fracture, were included in the study. Delirium was diagnosed by the Confusion Assessment Method. Two single-nucleotide polymorphisms (SNPs) in the IL6 gene, one in the IL6R gene, and one in the IL8 gene were genotyped.

RESULTS

Fifty percent of the 115 surgical patients and 34% of the 605 medical patients experienced delirium. Delirious patients were older (82.8 years vs. 77.6 years) and had more frequent pre-existing functional (64% vs. 36%) or cognitive impairment (83% vs. 26%) (p < 0.001). The determination of polymorphisms had success rates between 87% and 96%. Rs1800697 and rs1800797 in the IL6 gene, rs8192284 in the IL6R gene, and rs4073 in the IL8 gene were not associated with the development of delirium.

CONCLUSION

Recent observations have indicated that IL-6 and IL-8 play a role in delirium in the elderly, but functional genetic variations in the IL6, IL6R, and IL8 genes were not associated with delirium. Still, the inflammatory hypothesis of delirium is gaining ground in the literature on the basis of recent animal research.

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.

Understanding the Global Problem of Drug Addiction is a Challenge for IDARS Scientists

IDARS is an acronym for the International Drug Abuse Research Society. Apart from our scientific and educational purposes, we communicate information to the general and scientific community about substance abuse and addiction science and treatment potential. Members of IDARS are research scientists and clinicians from around the world, with scheduled meetings across the globe. IDARS is developing a vibrant and exciting international mechanism not only for scientific interactions in the domain of addiction between countries but also ultimately as a resource for informing public policy across nations. Nonetheless, a lot more research needs to be done to better understand the neurobiological basis of drug addiction - A challenge for IDARS scientists.

Reward-related genes and personality traits in alcohol-dependent individuals: a pilot case control study

Components of the brain reward system, i.e. the mesolimbic dopamine, laterodorsal cholinergic and ghrelin signaling systems, have been implicated in alcohol reward in preclinical studies. Genetic variants of these systems have previously been linked to alcohol dependence. Here, we genotyped 31 single nucleotide polymorphisms (SNPs): 1 SNP in the dopamine D₂ receptor (DRD2) gene, 20 SNPs in 5 different nicotinic acetylcholine receptor subunit (CHRN*) genes, and 10 SNPs in the genes encoding pro-ghrelin (GHRL) and its receptor (GHSR), in a pilot study of type 1 alcoholics (n = 84) and healthy controls (n = 32). These individuals were characterized using the Temperament and Character Inventory. None of the SNPs were associated with risk of alcohol dependence in this population. The GG genotype of SNP rs13261190 in the CHRNB3 was associated with increased novelty seeking, while SNPs of the ghrelin signaling system were associated with decreased self-directedness (AA of rs495225, GHSR) and alterations in self-transcendence (AA of both rs42451 and rs35680, GHRL). In conclusion, this pilot study suggests that reward-related genes are associated with altered personality scores in type 1 alcohol dependence, which warrants future studies of these associations in larger study samples.

The influence of three genes on whether adolescents use contraception, USA 1994-2002

In a further contribution to recent investigations of the relevance of genetic processes for demographic outcomes, we investigate genetic associations with whether adolescents use contraception. Using data from the National Longitudinal Study of Adolescent Health, we find that variants in the dopamine transporter gene DAT1, the dopamine receptor gene DRD2, and the monoamine oxidase gene MAOA are associated with unprotected sexual intercourse. Consistent with previous analyses of these data, the genotypes DRD2*A1/A2, DRD2*A2/A2, DAT1*9R/10R, and MAOA*2R/ are associated with higher odds of unprotected sexual intercourse than other genotypes at these loci. The DRD2 associations apply to both men and women, whereas the other associations apply to women only. These results are robust to controls for population stratification by continental ancestry, do not vary by contraceptive type, and are consistent with previous research showing that these genetic variants are associated with higher rates of impulsivity.

Cigarette experimentation in Mexican origin youth: psychosocial and genetic determinants

BACKGROUND

Established psychosocial risk factors increase the risk for experimentation among Mexican origin youth. Now, we comprehensively investigate the added contribution of select polymorphisms in candidate genetic pathways associated with sensation seeking, risk taking, and smoking phenotypes to predict experimentation.

METHODS

Participants (N = 1,118 Mexican origin youth) recruited from a large population-based cohort study in Houston, TX, provided prospective data on cigarette experimentation over 3 years. Psychosocial data were elicited twice-baseline and final follow-up. Participants were genotyped for 672 functional and tagging variants in the dopamine, serotonin, and opioid pathways.

RESULTS

After adjusting for gender and age, with a Bayesian False Discovery Probability set at 0.8 and prior probability of 0.05, six gene variants were significantly associated with risk of experimentation. After controlling for established risk factors, multivariable analyses revealed that participants with six or more risk alleles were 2.25 [95% confidence interval (CI), 1.62-3.13] times more likely to have experimented since baseline than participants with five or fewer. Among committed never-smokers (N = 872), three genes (OPRM1, SNAP25, HTR1B) were associated with experimentation as were all psychosocial factors. Among susceptible youth (N = 246), older age at baseline, living with a smoker, and three different genes (HTR2A, DRD2, SLC6A3) predicted experimentation.

CONCLUSIONS

Our findings, which have implications for development of culturally specific interventions, need to be validated in other ethnic groups.

IMPACT

These results suggest that variations in select genes interact with a cognitive predisposition toward smoking. In susceptible adolescents, the impact of the genetic variants appears to be larger than committed never-smokers.

Association of DRD2 and DRD3 polymorphisms with Parkinson's disease in a multiethnic consortium

OBJECTIVE

To examine genetic associations of polymorphisms in the dopamine receptor D2 (DRD2) and D3 (DRD3) genes with risk of Parkinson's disease (PD).

METHODS

The study included 1325 newly diagnosed patients with PD and 1735 controls from a consortium of five North American case-control studies. We collected risk factor information by in-person or telephone interview. Six DRD2 and two DRD3 polymorphisms were genotyped using a common laboratory. Odds ratios were estimated using logistic regression.

RESULTS

Among non-Hispanic whites, homozygous carriers of Taq1A DRD2 (rs1800497) polymorphism had an increased risk of PD compared to homozygous wildtype carriers (OR=1.5, 95% CI 1.0-2.3). In contrast, the direction of association for Taq1A polymorphism was opposite for African-Americans, showing an inverse association with PD risk (OR=0.10, 95% CI 0.2-0.7). Among white Hispanics who carried two alleles, the Ser9Gly DRD3 (rs6280) polymorphism was associated with a decreased risk of PD (OR=0.4, 95% CI 0.2-0.8). The inverse association of smoking with PD risk was not modified by any of the DRD2 or DRD3 polymorphisms.

CONCLUSIONS

DRD2 polymorphisms are unlikely to be true disease-causing variants; however, three DRD2 polymorphisms (including Taq1A) may be in linkage disequilibrium with possible disease associated variants in the DRD2-ANKK1-NCAM1-TTC12 gene cluster.

The role of dopamine transporter (SLC6A3) and dopamine D2 receptor/ankyrin repeat and kinase domain containing 1 (DRD2/ANKK1) gene polymorphisms in personality traits

Variations in personality traits are caused by interactions between multiple genes of small effect and environmental factors. To date, gender- and ethnicity-specific variations in personality have been established. In the present study, we aimed to test: (1) the effects of four polymorphisms of dopamine system genes: ANKK1/DRD2 Taq1A, DRD2 rs6275, SLC6A3 40-bp VNTR and rs27072, on personality traits; (2) whether these effects differ between men and women and between Russians and Tatars. A sample of 652 healthy individuals (222 men and 430 women) of Caucasian origin (233 Russians and 419 Tatars) from Russia was subjected to personality traits assessment with Eysenck Personality Inventory (EPI) and Temperament and Character Inventory-125 (TCI-125). The associations between each personality trait and polymorphisms were assessed with regression models adjusted for gender and ethnicity. There were significant effects of ANKK1/DRD2 Taq1A on Neuroticism (p=0.016) and of SLC6A3 rs27072 on Persistence (p=0.021) in both genders. The association between ANKK1/DRD2 Taq1A A2/A2-genotype and higher Novelty Seeking and lower Reward Dependence was shown in men only (p for gender interaction=0.018). In women only, there was a significant association between SLC6A3 10R*G-haplotype and higher Persistence (p=0.002). Our findings provide evidence for a modifying effect of gender on the associations between dopamine system genes and approach-related traits (in men) and Persistence (in women).

Do alcohol-dependent individuals with DRD2 A1 allele have an increased risk of relapse? A pilot study

AIMS

The TaqIA polymorphism of the dopamine D2 receptor (DRD2) gene has been extensively studied in relation to alcoholism, and the TaqI A1 allele appears to be over-represented in alcohol-dependent individuals. In a recent study, this allele has also been associated with a highly increased mortality rate in alcohol-dependent individuals. In the present study, we investigated whether the TaqI A1 allele of the DRD2 gene region was associated with a higher relapse rate in alcohol-dependent individuals.

METHODS

Adult women (n = 10) and men (n = 40) with a diagnosis of alcohol-dependence were recruited from two Swedish 12-step treatment units for alcoholism. Subjects were genotyped for the TaqIA polymorphism. On average, 1&frac12; year after the end of the treatment program, subjects were re-interviewed by using the alcohol-related items from the Addiction Severity Index follow-up version.

RESULTS

Thirty-three (66%) subjects self-reported relapse and 17 (34%) abstinence during the follow-up period. Thirty-sex percent (18/50) were carriers of the A1 allele of the DRD2 gene region, and 64% (32/50) were non-carriers. Among the carriers of the A1 allele, 89% (16/18) reported relapse in contrast to 53% (17/32) in the non-carriers (P = 0.01; odds ratio = 7.1).

CONCLUSION

The present study is, to our knowledge, the first report of an association between the TaqI A1 allele and a substantially increased relapse rate. It should be emphasized that the number of subjects is relatively small, and this investigation should therefore be considered as a pilot study.

The association between the SLC6A3 VNTR 9-repeat allele and alcoholism-a meta-analysis

BACKGROUND

Dopamine transporter gene (SLC6A3) represents a promising candidate involved in the development of alcoholism. This study aimed to explore the association between the 9-repeat allele (A9) of a 40-bp variable number tandem repeat (VNTR) polymorphism in the 3' un-translated region (3' UTR) of the SLC6A3 gene and alcoholism.

METHODS

The SLC6A3 VNTR was genotyped by PCR in unrelated Mexican Americans including 337 controls and 365 alcoholics. Pearson's chi-square test or Fisher's exact test was used to compare the genotype and allele distribution. Meta-analyses were performed for population-based case-control association studies of the SLC6A3 VNTR polymorphism with alcoholism. Data were analyzed under random effect models with the Comprehensive Meta-analysis (v.2) statistical software package.

RESULTS

In Mexican Americans, no significant difference was found in allele and genotype distribution between controls and alcoholics or between controls and alcoholics with alcohol withdrawal seizure (AWS) or delirium tremens (DT) (unadjusted p > 0.05). A total of 13 research articles were included in the meta-analyses. No significant difference of the SLC6A3 VNTR A9 was noted between controls and alcoholics at the genotypic and allelic level when all ethnic populations, only Caucasian populations, or only Asian populations were considered (p > 0.05). Significant associations were observed between SLC6A3 VNTR A9 and alcoholics with AWS or DT at the genotypic as well as allelic level when all ethnic populations or only Caucasian populations were considered (p < 0.05, OR 1.5-2.1).

CONCLUSIONS

Meta-analyses suggest a possible association between the SLC6A3 VNTR A9 and alcoholic subgroup with AWS or DT.

DRD2 and DRD4 in relation to regular alcohol and cannabis use among adolescents: does parenting modify the impact of genetic vulnerability? The TRAILS study

AIMS

The aims of the present study were to determine the direct effect of DRD2 and DRD4, as well as their interaction with parenting (i.e. rejection, overprotection and emotional warmth), on the development of regular alcohol and cannabis use in 1192 Dutch adolescents from the general population.

METHODS

Information was obtained by self-report questionnaires. Perceived rejection, overprotection and emotional warmth were assessed at age 10-12. Regular alcohol and cannabis use were determined at age 15-18 and defined as the consumption of alcohol on 10 or more occasions in the past four weeks, and the use of cannabis on 4 or more occasions in the past four weeks. Models were adjusted for age, sex, parental alcohol or cannabis use, and externalizing behavior.

RESULTS

Carrying the A1 allele of the DRD2 TaqIA polymorphism, or the 7 repeat DRD4, was not directly related to regular alcohol or cannabis use. In addition, adolescent carriers of these genetic risk markers were not more susceptible to the influence of less optimal parenting. Main effects for parenting indicated that overprotection increased the risk of regular alcohol use, whereas the risk of cannabis use was enhanced by parental rejection and buffered by emotional warmth.

CONCLUSIONS

Our findings do not support an association between DRD2/DRD4 and regular alcohol and cannabis use in adolescents. Given the substance-specific influences of rejection, overprotection and emotional warmth, these parenting factors might be promising candidates for prevention work.

Differential susceptibility to rearing environment depending on dopamine-related genes: new evidence and a meta-analysis

In the current paper we present new empirical data and meta-analytic evidence for the role of dopamine-related genes as a susceptibility factor interacting with the rearing environment for better and for worse, that is, increasing children's susceptibility to both the adverse effects of unsupportive environments and the beneficial effects of supportive rearing. In Study 1 we examined the readiness of 91 7-year-old children to donate their money to a charity (UNICEF). We tested whether the association between attachment and donating behavior was moderated by the presence of the dopamine receptor D4 (DRD4) 7-repeat allele. The attachment story completion task was used to assess attachment as an index of the quality of the rearing environment. Children with secure attachment representations donated more but only if they had the DRD4 7-repeat allele. In Study 2 we present the results of a meta-analysis of gene-environment studies on children up to 10 years of age involving dopamine-related genes (dopamine receptor D2, DRD4, dopamine transporter). The cumulative negative effects of these "risk genes" and adverse rearing environments have been stressed, but potentially cumulative positive effects of these same genes interacting with positive rearing environments remained largely unnoticed. We examined the associations between negative and positive rearing environments and developmental outcomes as moderated by dopamine-related gene polymorphisms. Children with the less efficient dopamine-related genes did worse in negative environments than the comparisons without the "genetic risk," but they also profited most from positive environments. Findings are discussed in light of evolutionary theory, and illustrated with some practical implications of differential susceptibility.

Psychopathological aspects of dopaminergic gene polymorphisms in adolescence and young adulthood

Dopamine hypotheses of several psychiatric disorders are based upon the clinical benefits of drugs affecting dopamine transporter or receptors, and have prompted intensive candidate gene research within the dopaminergic system during the last two decades. The aim of this review is to survey the most important findings concerning dopaminergic gene polymorphisms in attention deficit hyperactivity disorder (ADHD), Tourette syndrome (TS), obsessive compulsive disorder, and substance abuse. Also, genetic findings of related phenotypes, such as inattention, impulsivity, aggressive behavior, and novelty seeking personality trait are presented, because recent studies have applied quantitative trait measures using questionnaires, symptom scales, or other objective endophenotypes. Unfortunately, genetic variants with minor effects are problematic to detect in these complex inheritance disorders, often leading to contradictory results. The most consistent association findings relate to ADHD and the dopamine transporter and the dopamine D4 receptor genes. Meta-analyses also support the association between substance abuse and the D2 receptor gene. The dopamine catabolizing enzyme genes, such as monoamine oxidase (MAO) A and catechol-O-methyltransferase (COMT) genes, have been linked to aggressive behaviors.

DRD2/ANKK1 TaqI A polymorphism affects corticostriatal activity in response to negative affective facial stimuli

DRD2/ANKK1 TaqI A polymorphism has been suggested to be involved in a reward-related psychiatric disorders. However, the effect of Dopamine receptor D2 (DRD2) on emotional processing has not been investigated yet. We investigated the possible relationship between DRD2/ANKK1 TaqI A polymorphism and corticostriatal response to negative facial stimuli using functional magnetic resonance imaging. All participants were genotyped with regard to the DRD2/ANKK1 TaqI A polymorphism. Our results suggest an association between the DRD2/ANKK1 TaqI A polymorphism and activations in the putamen, the anterior cingulate cortex, and amygdala in response to negative facial stimuli. Furthermore, molecular heterosis at the TaqI polymorphism of DRD2/ANKK1 may play an important role in affective regulation by corticostriatal pathway.

A dopamine gene (DRD2) distinguishes between offenders who have and have not been violently victimized

Research has shown that offenders, on average, are more likely to be violently victimized than nonoffenders. However, a substantial percentage of offenders are not violently victimized. The current study uses data from the National Longitudinal Study of Adolescent Health (Add Health) to investigate whether variants of a polymorphism in the dopamine D2 receptor gene (DRD2) distinguish between offenders who are violently victimized and offenders who are not violently victimized. The results show that offenders who are violently victimized are more likely to carry the DRD2 (A1) risk allele than offenders who have not been violently victimized.

Association study of catechol-O-methyltransferase gene polymorphisms with schizophrenia and psychopathological symptoms in Han Chinese

Although dysfunction of catechol-O-methyltransferase (COMT)-mediated dopamine transmission is implicated in the etiology of schizophrenia, the human COMT gene has not been associated consistently with schizophrenia. The purpose of this study was to investigate whether the COMT gene is associated with the development of schizophrenia and whether the polymorphisms of this gene influence the psychopathological symptoms in patients with schizophrenia. Fourteen polymorphisms of the COMT gene were analyzed in a case-control study of 876 Han Chinese individuals (434 patients and 442 controls). All participants were screened using a Chinese version of the modified Schedule for Affective Disorders and Schizophrenia-Lifetime Version (SADS-L) and all patients met the criteria for schizophrenia. Furthermore, pretreatment of psychopathology was assessed using the Positive and Negative Syndrome Scale (PANSS) in a subset of 224 hospitalized schizophrenia patients, who were drug-naÏve or drug-free, to examine the association between clinical symptomatology and COMT polymorphisms. No significant differences in allele or genotype frequencies were observed between schizophrenia patients and controls, for all variants investigated. Haplotype analysis showed that three haplotype blocks of the COMT gene were not associated with the development of schizophrenia. Moreover, these COMT polymorphisms did not influence the PANSS scores of schizophrenia patients. This study suggests that the COMT gene may not contribute to the risk of schizophrenia and to the psychopathological symptoms of schizophrenia among Han Chinese.

Double dissociation of dopamine genes and timing in humans

A number of lines of evidence implicate dopamine in timing [Rammsayer, T. H. Neuropharmacological approaches to human timing. In S. Grondin (Ed.), Psychology of time (pp. 295-320). Bingley, UK: Emerald, 2008; Meck, W. H. Neuropharmacology of timing and time perception. Brain Research, Cognitive Brain Research, 3, 227-242, 1996]. Two human genetic polymorphisms are known to modulate dopaminergic activity. DRD2/ANKK1-Taq1a is a D(2) receptor polymorphism associated with decreased D(2) density in the striatum [Jönsson, E. G., Nothen, M. M., Grunhage, F., Farde, L., Nakashima, Y., Propping, P., et al. Polymorphisms in the dopamine D(2) receptor gene and their relationships to striatal dopamine receptor density of healthy volunteers. Molecular Psychiatry, 4, 290-296, 1999]; COMT Val158Met is a functional polymorphism associated with increased activity of the COMT enzyme such that catabolism of synaptic dopamine is greater in pFC [Meyer-Lindenberg, A., Kohn, P. D., Kolachana, B., Kippenhan, S., McInerney-Leo, A., Nussbaum, R., et al. Midbrain dopamine and prefrontal function in humans: Interaction and modulation by COMT genotype. Nature Neuroscience, 8, 594-596, 2005]. To investigate the role of dopamine in timing, we genotyped 65 individuals for DRD2/ANKK1-Taq1a, COMT Val158Met, and a third polymorphism, BDNF Val66Met, a functional polymorphism affecting the expression of brain-derived neurotrophic factor [Egan, M. F., Kojima, M., Callicott, J. H., Goldberg, T. E., Kolachana, B. S., Bertolino, A., et al. The BDNF val66met polymorphism affects activity-dependent secretion of BDNF and human memory and hippocampal function. Cell, 112, 257-269, 2003]. Subjects were tested on a temporal discrimination task with sub- and supra-second intervals (500- and 2000-msec standards) as well as a spontaneous motor tempo task. We found a double dissociation for temporal discrimination: the DRD2/ANKK1-Taq1a polymorphism (A1+ allele) was associated with significantly greater variability for the 500-msec duration only, whereas the COMT Val158Met polymorphism (Val/Val homozygotes) was associated with significantly greater variability for the 2000-msec duration only. No differences were detected for the BDNF Vall66Met variant. Additionally, the DRD2/ANKK1-Taq1a polymorphism was associated with a significantly slower preferred motor tempo. These data provide a potential biological basis for the distinctions between sub- and supra-second timing and suggest that BG are integral for the former whereas pFC is implicated in the latter.

Risky alcohol use in adolescence: the role of genetics (DRD2, SLC6A4) and coping motives

BACKGROUND

Drinking to cope (i.e., drinking to forget or alleviate negative feelings) has been found to be associated with adolescents' heavy drinking and alcohol-related problems. Additionally, it is widely accepted that genetic factors are involved in alcohol use and dependence. Studies are only beginning to reveal, however, which specific genotypes are related to drinking behaviors, and it is unknown whether they may interact with coping motives in predicting adolescents' risky drinking. The aim of this study was to examine relationships between the dopamine D2 receptor gene (DRD2) Taq1A polymorphism (rs1800497), a serotonin transporter gene (SLC6A4) polymorphism (5-HTTLPR), coping motives, and adolescents' binge drinking and alcohol-related problems.

METHODS

Participants in this cross-sectional study were 282 Dutch adolescents (mean age 17.4, 47% men) who had consumed alcohol at least once in their life.

RESULTS

Coping motives were positively related to both binge drinking and alcohol-related problems, while DRD2 and SLC6A4 genotypes were not. DRD2, but not the SLC6A4 genotype, interacted with coping motives. The link between coping motives and alcohol outcomes was stronger among those carrying the DRD2 risk (A1) allele.

CONCLUSIONS

This study extends the present literature by providing additional insight into the etiological factors of adolescent drinking behavior. An interaction between a vulnerability gene (DRD2) and a cognitive factor (coping drinking) was found to be related to adolescents' binge drinking and alcohol-related problems.

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.

Rethinking the genetic basis for comorbidity of schizophrenia and type 2 diabetes

The co-occurrence of schizophrenia (SCZ) and type 2 diabetes mellitus (T2D) has been well documented. This review article focuses on the hypothesis that the co-occurrence of SCZ and T2D may be, at least in part, driven by shared genetic factors. Previous genetic studies of T2D and SCZ evidence have disclosed a number of overlapped risk loci. However, the putative common genetic factors for SCZ and T2D remain inconclusive due to inconsistent findings. A systemic review of methods of identifying genetic loci contributing to the comorbidity link between SCZ and T2D is hence needed. In the current review article, we have discussed several different approaches to localizing the shared susceptibility genes for these two diseases. To begin with, one could start with probing the gene involved in both glucose and dopamine metabolisms. Additionally, hypothesis-free genome-wide association studies (GWAS) may provide more clues to the common genetic basis for these two diseases. Genetic similarities inferred from GWAS may shed some light on the genetic mechanism underlying the comorbidity link between SCZ and T2D. Meanwhile, endophenotypes (e.g., adiponectin level in T2D and working memory in SCZ) may serve as alternative phenotypes that are more directly influenced by genes than target diseases. Hence, endophenotypes of these diseases may be more tractable to identification. To summarize, novel approaches are needed to dissect the complex genetic basis of the comorbidity of SCZ and T2D.

Brief communication: Allelic and haplotypic structure at the DRD2 locus among five North Indian caste populations

The dopamine D2 receptor (DRD2) gene, with its known human-specific derived alleles that can facilitate haplotype reconstruction, presents an important locus for anthropological studies. The three sites (TaqIA, TaqIB, and TaqID) of the DRD2 gene are widely studied in various world populations. However, no work has been previously published on DRD2 gene polymorphisms among North Indian populations. Thus, the present study attempts to understand the genetic structure of North Indian upper caste populations using the allele and haplotype frequencies and distribution patterns of the three TaqI sites of the DRD2 gene. Two hundred forty-six blood samples were collected from five upper caste populations of Himachal Pradesh (Brahmin, Rajput and Jat) and Delhi (Aggarwal and Sindhi), and analysis was performed using standard protocols. All three sites were found to be polymorphic in all five of the studied populations. Uniform allele frequency distribution patterns, low heterozygosity values, the sharing of five common haplotypes, and the absence of two of the eight possible haplotypes observed in this study suggest a genetic proximity among the selected populations. The results also indicate a major genetic contribution from Eurasia to North Indian upper castes, apart from the common genetic unity of Indian populations. The study also demonstrates a greater genetic inflow among North Indian caste populations than is observed among South Indian caste and tribal populations.

The ANKK1 protein associated with addictions has nuclear and cytoplasmic localization and shows a differential response of Ala239Thr to apomorphine

The TaqIA single-nucleotide polymorphism (SNP), which is the most widely studied genetic polymorphism in addictions, is located at the gene that encodes the RIP kinase ANKK1 near the gene for dopamine receptor D2. The TaqIA SNP is in strong linkage disequilibrium with the SNP rs7118900, which changes the alanine at position 239 to threonine in the ANKK1 protein (Ala239/A2; Thr239/A1). In silico analysis has predicted that this polymorphic substitution creates an additional phosphorylation site in the kinase domain of ANKK1. To investigate the contribution of ANKK1 to the pathophysiology of TaqIA-associated phenotypes, we analyzed transfected HEK293T cells with the human ANKK1-kinase(Ala239) and ANKK1-kinase(Thr239) variants tagged with GFP. We observed that the ANKK1-kinase is located in both the nucleus and the cytoplasm, suggesting that there is nucleocytoplasmic shuttling of this putative signal transducer. In addition, we found that the Ala239Thr ANKK1-kinase polymorphism exhibited strong expression differences in both the nucleus and the cytoplasm at basal level and when stimulated with the dopamine agonist apomorphine. Specifically, the ANKK1-kinase(Thr239) variant showed the highest level of basal protein expression, while ANKK1-kinase(Ala239) was 0.64-fold lower. After treatment with apomorphine, ANKK1-kinase(Ala239) showed a 2.4-fold increment in protein levels, whereas a 0.67-fold reduction was observed in ANKK1-kinase(Thr239). Thus, here we provide the first evidence of functional ANKK1 differences that are marked by TaqIA and could be associated with vulnerability to addiction.

Individual Differences in Nucleus Accumbens Dopamine Receptors Predict Development of Addiction-Like Behavior: A Computational Approach

Clinical and experimental observations show individual differences in the development of addiction. Increasing evidence supports the hypothesis that dopamine receptor availability in the nucleus accumbens (NAc) predisposes drug reinforcement. Here, modeling striatal-midbrain dopaminergic circuit, we propose a reinforcement learning model for addiction based on the actor-critic model of striatum. Modeling dopamine receptors in the NAc as modulators of learning rate for appetitive—but not aversive—stimuli in the critic—but not the actor—we define vulnerability to addiction as a relatively lower learning rate for the appetitive stimuli, compared to aversive stimuli, in the critic. We hypothesize that an imbalance in this learning parameter used by appetitive and aversive learning systems can result in addiction. We elucidate that the interaction between the degree of individual vulnerability and the duration of exposure to drug has two progressive consequences: deterioration of the imbalance and establishment of an abnormal habitual response in the actor. Using computational language, the proposed model describes how development of compulsive behavior can be a function of both degree of drug exposure and individual vulnerability. Moreover, the model describes how involvement of the dorsal striatum in addiction can be augmented progressively. The model also interprets other forms of addiction, such as obesity and pathological gambling, in a common mechanism with drug addiction. Finally, the model provides an answer for the question of why behavioral addictions are triggered in Parkinson's disease patients by D2 dopamine agonist treatments.

Depression and obesity: do shared genes explain the relationship?

BACKGROUND

Studies have found a modest association between depression and obesity, especially in women. Given the substantial genetic contribution to both depression and obesity, we sought to determine whether shared genetic influences are responsible for the association between these two conditions.

METHODS

Data were obtained from 712 monozygotic and 281 dizygotic female twin pairs who are members of the community-based University of Washington Twin Registry. The presence of depression was determined by self-report of doctor-diagnosed depression. Obesity was defined as body mass index of > or =30 kg/m(2), based on self-reported height and weight. Generalized estimating regression models were used to assess the age-adjusted association between depression and obesity. Univariate and bivariate structural equation models estimated the components of variance attributable to genetic and environmental influences.

RESULTS

We found a modest phenotypic association between depression and obesity (odds ratio=1.6, 95% confidence interval=1.2-2.1). Additive genetic effects contributed substantially to depression (57%) and obesity (81%). The best-fitting bivariate model indicated that 12% of the genetic component of depression is shared with obesity.

CONCLUSIONS

The association between depression and obesity in women may be in part due to shared genetic risk for both conditions. Future studies should examine the genetic, environmental, social, and cultural mechanisms underlying the relationship between this association.

Individual differences in the neurophysiology of reward and the obesity epidemic

The obesity epidemic has unfolded in a matter of decades, not millennia, and therefore cannot be attributed to a drift in the genome. Rather, the temporal characteristics of the epidemic more closely track environmental and lifestyle changes, such as reduced physical activity, increased availability of palatable and energy-dense foods and drinks, and increased acceptance of eating outside of meal time (among others). One important observation is that not everyone is becoming obese. This suggests that individual factors interact with recent environmental changes to predispose some to overeat. One hypothesis that has been gaining traction in the neuroscience community is that individual differences in the neural encoding of foods may predispose some to overeat in the presence of a surplus of energy-dense, palatable foods and drinks. The aim of this review is to highlight several possible ways by which individual differences in the neurophysiology of food reward may lead to overeating.

Interaction between dopamine D2 receptor genotype and parental rule-setting in adolescent alcohol use: evidence for a gene-parenting interaction

Association studies investigating the link between the dopamine D2 receptor gene (DRD2) and alcohol (mis)use have shown inconsistent results. This may be due to lack of attention for environmental factors. High levels of parental rule-setting are associated with lower levels of adolescent alcohol use and delay of initiation of drinking. We tested whether DRD2 TaqI A (rs1800497) genotype interacts with alcohol-specific parenting practices in predicting the uptake of regular adolescent alcohol use. Non-regular drinkers were selected from a Dutch, nationwide sample of 428 adolescents (mean age 13.4 years at baseline) and participated in a prospective, community-based study with three annual waves. Parental rule-setting was directly and inversely related to adolescent alcohol use over time. For DRD2 genotype no significant main effect was found. DRD2 genotype interacted with parental rule-setting on adolescent alcohol use over time: adolescents, with parents highly permissive toward alcohol consumption and carrying a genotype with the DRD2 A1 (rs1800497T) allele, used significantly more alcohol over time than adolescents without these characteristics. The DRD2 genotype may pose an increased risk for alcohol use and abuse, depending on the presence of environmental risk factors, such as alcohol-specific parenting.

D1 and D2 dopamine receptor-mediated inhibition of activated normal T cell proliferation is lost in jurkat T leukemic cells

Dopamine is a catecholamine neurotransmitter, which plays an important role in the regulation of T cell functions. In activated T cells from normal volunteers, stimulation of D(1) and D(2) dopamine receptors inhibit cell proliferation and cytokine secretion. However, there is no report yet regarding the regulatory role of D(1) and D(2) dopamine receptors in abnormally proliferating T cells. The present study investigates the expression and effect of activation of these dopamine receptors in Jurkat cells, a leukemic T cell line showing uncontrolled proliferation. Like normal human T cells, in Jurkat cells, D(1) and D(2) dopamine receptors are also expressed; however, unlike activated normal T cells, stimulation of these dopamine receptors in Jurkat cells fails to inhibit their T cell receptor-induced proliferation. This alteration is due to failure of D(1) dopamine receptor-mediated activation of cyclic AMP signaling and a missense mutation at the third cytoplasmic loop of D(2) dopamine receptors affecting inhibition of phosphorylation of ZAP-70, an important downstream protein transducing signal from the T cell receptor. These results help to understand the biology of abnormal proliferation of T cells in pathophysiological conditions where dopamine plays an important role.

Individual differences and the neural representations of reward expectation and reward prediction error

Reward expectation and reward prediction errors are thought to be critical for dynamic adjustments in decision-making and reward-seeking behavior, but little is known about their representation in the brain during uncertainty and risk-taking. Furthermore, little is known about what role individual differences might play in such reinforcement processes. In this study, it is shown behavioral and neural responses during a decision-making task can be characterized by a computational reinforcement learning model and that individual differences in learning parameters in the model are critical for elucidating these processes. In the fMRI experiment, subjects chose between high- and low-risk rewards. A computational reinforcement learning model computed expected values and prediction errors that each subject might experience on each trial. These outputs predicted subjects' trial-to-trial choice strategies and neural activity in several limbic and prefrontal regions during the task. Individual differences in estimated reinforcement learning parameters proved critical for characterizing these processes, because models that incorporated individual learning parameters explained significantly more variance in the fMRI data than did a model using fixed learning parameters. These findings suggest that the brain engages a reinforcement learning process during risk-taking and that individual differences play a crucial role in modeling this process.

Neither single-marker nor haplotype analyses support an association between the dopamine transporter gene and heroin dependence in Han Chinese

Much evidence suggests that dysfunction of dopamine transporter-mediated dopamine transmission may be involved in the pathophysiology of substance abuse and dependence. The aim of this study was to examine whether the dopamine transporter gene (DAT1; SLC6A3) is associated with the development of heroin dependence (HD) and whether DAT1 influences personality traits in patients with HD. Polymorphisms of DAT1 were analyzed in a case-control study of 1046 Han Chinese (615 patients and 431 controls). All participants were screened using a Chinese version of the modified Schedule of Affective Disorder and Schizophrenia-Lifetime and all patients met the criteria for HD. Furthermore, a Chinese version of the Tridimensional Personality Questionnaire (TPQ) was used to assess personality traits in the patient group and examine the association between their personality traits and DAT1 polymorphisms. Of the patient group, 271 completed the TPQ. No statistically significant differences in allele or genotype frequencies of all investigated variants between HD patients and controls were observed. In haplotype analyses, four haplotype blocks of DAT1 were not associated with the development of HD. These DAT1 polymorphisms did not influence novelty seeking and harm avoidance scores in HD patients. This study suggests that the DAT1 gene may not contribute to the risk of HD and specific personality traits in HD among the Han Chinese population.

Heart-type fatty acid binding protein regulates dopamine D2 receptor function in mouse brain

Fatty acid binding proteins (FABPs) are essential for energy production and long-chain polyunsaturated fatty acid-related signaling in the brain and other tissues. Of various FABPs, heart-type fatty acid binding protein (H-FABP, FABP3) is highly expressed in neurons of mature brain and plays a role in arachidonic acid incorporation into brain and heart cells. However, the precise function of H-FABP in brain remains unclear. We previously demonstrated that H-FABP is associated with the dopamine D(2) receptor long isoform (D2LR) in vitro. Here, we confirm that H-FABP binds to dopamine D(2) receptor (D2R) in brain extracts and colocalizes immunohistochemically with D2R in the dorsal striatum. We show that H-FABP is highly expressed in acetylcholinergic interneurons and terminals of glutamatergic neurons in the dorsal striatum of mouse brain but absent in dopamine neuron terminals and spines in the same region. H-FABP knock-out (KO) mice showed lower responsiveness to methamphetamine-induced sensitization and enhanced haloperidol-induced catalepsy compared with wild-type mice, indicative of D2R dysfunction. Consistent with the latter, aberrant increased acetylcholine (ACh) release and depolarization-induced glutamate (Glu) release were observed in the dorsal striatum of H-FABP KO mice. Furthermore, phosphorylation of CaMKII (Ca(2+)/calmodulin-dependent protein kinase II) and ERK (extracellular signal-regulated kinase) was significantly increased in the dorsal striatum. We confirmed elevated ERK phosphorylation following quinpirole-mediated D2R stimulation in H-FABP-overexpressing SHSY-5Y human neuroblastoma cells. Together, H-FABP is highly expressed in ACh interneurons and glutamatergic terminals, thereby regulating dopamine D2R function in the striatum.

Dopamine and binge eating behaviors

Central dopaminergic mechanisms are involved in the motivational aspects of eating and food choices. This review focuses on human and animal data investigating the importance of dopamine on binge eating behaviors. Early work examining dopamine metabolites in the cerebrospinal fluid and plasma of bulimic individuals suggested decreased dopamine turnover during the active phase of the illness. While neuroimaging studies of dopamine mechanisms in bulimia nervosa (BN) and binge eating disorder (BED) are limited, genetic studies in humans have implicated an increased frequency of dopamine transporter and associated D2 receptor polymorphisms with binge pathology. Recent studies in rodent models of dietary-induced binge eating (DIBE) have investigated plausible dopamine mechanisms involved in sustaining binge eating behaviors. In DIBE models, highly palatable foods (fats, sugars and their combination), as well as restricted access conditions appear to promote ingestive responses and result in sustained dopamine stimulation within the nucleus accumbens. Taken together with studies on the comorbidity of illicit drug use and eating disorders, the data reviewed here support a role for dopamine in perpetuating the compulsive feeding patterns of BN and BED. As such, we propose that sustained stimulation of the dopamine systems by bingeing promoted by preexisting conditions (e.g., genetic traits, dietary restraint, stress, etc.) results in progressive impairments of dopamine signaling. To disrupt this vicious cycle, novel research-based treatment options aiming at the neural substrates of compulsive eating patterns are necessary.

Longitudinal examination of obesity and cognitive function: results from the Baltimore longitudinal study of aging

BACKGROUND

Obesity indices (i.e. BMI, waist-to-hip ratio) show differential relationships to other health outcomes, though their association to neurocognitive outcome is unclear.

METHODS

We examined whether central obesity would be more closely associated with cognitive function in 1,703 participants from the Baltimore Longitudinal Study of Aging.

RESULTS

Longitudinal mixed-effects regression models showed multiple obesity indices were associated with poorer performance in a variety of cognitive domains, including global screening measures, memory, and verbal fluency tasks. Obesity was associated with better performance on tests of attention and visuospatial ability. An obesity index by age interaction emerged in multiple domains, including memory and attention/executive function.

CONCLUSION

Obesity indices showed similar associations to cognitive function, and further work is needed to clarify the physiological mechanisms that link obesity to poor neurocognitive outcome.

Epigenetics and biomarkers in the staging of neuropsychiatric disorders

Epigenetics, or alterations in the phenotype or gene expression due to mechanisms other than changes in the underlying DNA sequence, reflects the sensitivity and responsiveness of human and animal brains in constantly varying circumstances regulating gene expression profiles that define the biomarkers and present the ultimate phenotypical outcomes, such as cognition and emotion. Epigenetics is associated with functionally relevant alterations to the genome in such a fashion that under the particular conditions of early, adolescent, and adult life, environmental signals may activate intracellular pathways that remodel the "epigenome," triggering changes in gene expression and neural function. Thus, genetic influences in neuropsychiatric disorders that are subject to clinical staging, epigenetics in schizophrenia, epigenetic considerations in the expression of sensorimotor gating resulting from disease conditions, biomarkers of drug use and addiction, current notions on the role of dopamine in schizophrenia spectrum disorders, and the discrete interactions of biomarkers in persistent memory were to greater or lesser extents reflected upon. The relative contributions of endophenotypes and epistasis for mediating epigenetic phenomena and the outcomes as observed in the analysis of biomarkers appear to offer a multitude of interactive combinations to further complicate the labyrinthine machinations of diagnosis, intervention, and prognosis.

The association of the dopamine transporter gene and the dopamine receptor 2 gene with delirium, a meta-analysis

Delirium is the most common neuropsychiatric syndrome in elderly ill patients. Previously, associations between delirium and the dopamine transporter gene (solute carrier family 6, member 3 (SLC6A3)) and dopamine receptor 2 gene (DRD2) were found. The aim of this study was to validate whether markers of the SLC6A3 and DRD2 genes are were associated with delirium in independent populations. Six European populations collected DNA of older delirious patients. Associations were determined per population and results were combined in a meta-analysis. In total 820 medical inpatients, 185 cardiac surgery patients, 134 non-cardiac surgery patients and 502 population-based elderly subjects were included. Mean age was 82 years (SD 7.5 years), 598 (36%) were male, 665 (41%) had pre-existing cognitive impairment, and 558 (34%) experienced delirium. The SLC6A3 rs393795 homozygous AA genotype was more frequent in patients without delirium in all populations. The meta-analysis showed an Odds Ratio (OR) for delirium of 0.4 (95% confidence interval (C.I.) 0.2-0.6, P = 0.0003) for subjects with AA genotype compared to the AG and GG genotypes. SLC6A3 marker rs1042098 showed no association with delirium. In meta-analysis the DRD2 rs6276 homozygous GG genotype showed an OR of 0.8 for delirium (95% C.I. 0.6-1.1, P = 0.24). When subjects were stratified for cognitive status the rs6276 GG genotype showed ORs of 0.6 (95% C.I. 0.4-1.0, P = 0.06) and 0.8 (95% C.I. 0.5-1.5, P = 0.51) for delirium in patients with and without cognitive impairment, respectively. In independent cohorts, a variation in the SLC6A3 gene and possibly the DRD2 gene were found to protect for delirium.

Pharmacogenetics of D2 dopamine receptor gene in prolactin-secreting pituitary adenomas

IMPORTANCE OF THE FIELD

Dopamine-agonists are the treatment of choice of prolactin-secreting pituitary adenomas (PRL-omas). Their actions on D2 dopamine receptor (DRD2) and the clinical outcome may be affected by polymorphisms.

AREAS COVERED IN THIS REVIEW

PRL-omas are well-differentiated endocrine tumors expressing DRD2. The dopamine-agonist cabergoline (CB), normalizes prolactin and reduces tumor size in about 80 - 90% of patients. DRD2 polymorphisms correlate with neuropsychiatric disorders, in particular alcoholism and schizophrenia. This review describes the DRD2 polymorphisms, their functional effects, and their impact on susceptibility and response to dopamine-agonists treatment. Searching PubMed database for pertinent articles we found that some DRD2 polymorphisms, particularly TaqIA, TaqIB and NcoI, are associated with different receptor binding in brain areas. One study carried out in patients with PRL-omas found a correlation between NcoI and TaqIA and resistance to CB. In particular, resistant patients had higher prevalence of NcoI-T allele than the responsive patients, while the commonest haplotype (having TaqIA2 allele) was associated with better response.

WHAT THE READER WILL GAIN

This review deals with the connection between DRD2 polymorphisms and PRL-oma treatment and suggests hypotheses for further studies.

TAKE HOME MESSAGE

Only one study was carried out to analyze the role of DRD2 polymorphisms in PRLomas response to CB. Further studies, including pituitary and hypothalamus in vivo determination of DRD2 binding according to DRD2 genotypes, investigation of possible post-receptorial mechanisms involved, as well as population studies in collaboration with psychiatrists and neurologists, are needed.

Reward circuitry responsivity to food predicts future increases in body mass: moderating effects of DRD2 and DRD4

OBJECTIVE

To determine whether responsivity of reward circuitry to food predicts future increases in body mass and whether polymorphisms in DRD2 and DRD4 moderate these relations.

DESIGN

The functional magnetic resonance imaging (fMRI) paradigm investigated blood oxygen level dependent activation in response to imagined intake of palatable foods, unpalatable foods, and glasses of water shown in pictures. DNA was extracted from saliva samples using standard salting-out and solvent precipitation methods.

PARTICIPANTS

Forty-four adolescent female high school students ranging from lean to obese.

MAIN OUTCOME

Future increases in body mass index (BMI).

RESULTS

Weaker activation of the frontal operculum, lateral orbitofrontal cortex, and striatum in response to imagined intake of palatable foods, versus imagined intake of unpalatable foods or water, predicted future increases in body mass for those with the DRD2 TaqIA A1 allele or the DRD4-7R allele. Data also suggest that for those lacking these alleles, greater responsivity of these food reward regions predicted future increases in body mass.

DISCUSSION

This novel prospective fMRI study indicates that responsivity of reward circuitry to food increases risk for future weight gain, but that genes that impact dopamine signaling capacity moderate the predictive effects, suggesting two qualitatively distinct pathways to unhealthy weight gain based on genetic risk.

Association between dopaminergic polymorphisms and borderline personality traits among at-risk young adults and psychiatric inpatients

BACKGROUND

In the development of borderline personality disorder (BPD) both genetic and environmental factors have important roles. The characteristic affective disturbance and impulsive aggression are linked to imbalances in the central serotonin system, and most of the genetic association studies focused on serotonergic candidate genes. However, the efficacy of dopamine D2 receptor (DRD2) blocking antipsychotic drugs in BPD treatment also suggests involvement of the dopamine system in the neurobiology of BPD.

METHODS

In the present study we tested the dopamine dysfunction hypothesis of impulsive self- and other-damaging behaviors: borderline and antisocial traits were assessed by Structured Clinical Interview for Diagnosis (SCID) for DSM-IV in a community-based US sample of 99 young adults from low-to-moderate income families. For the BPD trait analyses a second, independent group was used consisting of 136 Hungarian patients with bipolar or major depressive disorder filling out self-report SCID-II Screen questionnaire. In the genetic association analyses the previously indicated polymorphisms of the catechol-O-methyl-transferase (COMT Val158Met) and dopamine transporter (DAT1 40 bp VNTR) were studied. In addition, candidate polymorphisms of the DRD2 and DRD4 dopamine receptor genes were selected from the impulsive behavior literature.

RESULTS

The DRD2 TaqI B1-allele and A1-allele were associated with borderline traits in the young adult sample (p = 0.001, and p = 0.005, respectively). Also, the DRD4 -616 CC genotype appeared as a risk factor (p = 0.02). With severity of abuse accounted for in the model, genetic effects of the DRD2 and DRD4 polymorphisms were still significant (DRD2 TaqIB: p = 0.001, DRD2 TaqIA: p = 0.008, DRD4 -616 C/G: p = 0.002). Only the DRD4 promoter finding was replicated in the independent sample of psychiatric inpatients (p = 0.007). No association was found with the COMT and DAT1 polymorphisms.

CONCLUSIONS

Our results of the two independent samples suggest a possible involvement of the DRD4 -616 C/G promoter variant in the development of BPD traits. In addition, an association of the DRD2 genetic polymorphisms with impulsive self-damaging behaviors was also demonstrated.

The ANKK1 gene associated with addictions is expressed in astroglial cells and upregulated by apomorphine

BACKGROUND

TaqIA, the most widely analyzed genetic polymorphism in addictions, has traditionally been considered a gene marker for association with D2 dopamine receptor gene (DRD2). TaqIA is located in the coding region of the ANKK1 gene that overlaps DRD2 and encodes a predicted kinase ANKK1. The ANKK1 protein nonetheless had yet to be identified. This study examined the ANKK1 expression pattern as a first step to uncover the biological bases of TaqIA-associated phenotypes.

METHODS

Northern blot and quantitative reverse-transcriptase polymerase chain reaction analyses were performed to analyze the ANKK1 mRNA. To study ANKK1 protein expression, we developed two polyclonal antibodies to a synthetic peptides contained in the putative Ser/Thr kinase domain.

RESULTS

We demonstrate that ANKK1 mRNA and protein were expressed in the adult central nervous system (CNS) in human and rodents, exclusively in astrocytes. Ankk1 mRNA level in mouse astrocyte cultures was upregulated by apomorphine, suggesting a potential relationship with the dopaminergic system. Developmental studies in mice showed that ANKK1 protein was ubiquitously located in radial glia in the CNS, with an mRNA expression pick around embryonic Day 15. This time expression pattern coincided with that of the Drd2 mRNA. On induction of differentiation by retinoic acid, a sequential expression was found in human neuroblastoma, where ANKK1 was expressed first, followed by that of DRD2. An opposite time expression pattern was found in rat glioma.

CONCLUSIONS

Spatial and temporal regulation of the expression of ANKK1 suggest an involvement of astroglial cells in TaqIA-related neuropsychiatric phenotypes both during development and adult life.

Association of promoter variants of human dopamine transporter gene with schizophrenia in Han Chinese

OBJECTIVE

Although dopamine was implicated in the etiology of schizophrenia, the human dopamine transporter gene (DAT1; SLC6A3) has not consistently been associated with schizophrenia. The purpose of this study was to examine whether six polymorphisms within the DAT1 gene are associated with schizophrenia.

METHODS

Six polymorphisms of the DAT1 gene (3 SNPs [rs6413429, rs2652511, and rs2975226] in the promoter region, one SNP [rs6347] in exon 9, and one SNP [rs27072]/one variable number tandem repeat [VNTR] in exon 15) were analyzed in 352 Chinese patients with schizophrenia and in 311 healthy controls. Pretreatment psychopathology was assessed using the Positive and Negative Syndrome Scale in a subset of 160 hospitalized schizophrenia patients who were drug-free or drug-naïve.

RESULTS

A statistically significant difference in two polymorphisms (rs2652511 and rs2975226) and a promoter region haplotype (rs2652511, rs2975226, and rs6413429) was found between patients and healthy controls. No association with schizophrenia was found for other polymorphisms and another haplotype (3' region). Symptoms severity (PANSS global, positive, negative and general symptoms scores) was similar regardless of DAT1 polymorphism.

CONCLUSION

The promoter region of the DAT1 gene may play a role in increasing susceptibility to schizophrenia, but does not affect the severity of psychotic symptoms in Han Chinese.

Effect of the TaqIA polymorphism on ethanol response in the brain

Acute ethanol administration increases striatal dopamine release and decreases cerebral glucose metabolism. The A1 allele of the ANKK1 TaqIa polymorphism is associated with lower dopaminergic tone and greater risk for alcoholism, but the mechanisms are unclear. We hypothesized that ethanol would be more reinforcing in men with the A1 allele (A1+) than in men without it (A1-), as indicated by decreased anxiety and fatigue and altered activity in associated brain regions. In a pilot study, A1+ and A1- men (6/group) drank ethanol (0.75 ml/kg) or placebo beverages on each of 2 days. Positron emission tomography with [F-18]fluorodeoxyglucose (FDG) was used to assess regional cerebral glucose metabolism as a measure of relative brain activity while participants performed a vigilance task. Significant findings were as follows: Ethanol decreased anxiety and fatigue in A1+ men but increased them in A1- men. Ethanol increased activity in the striatum and insula of A1+ men, but reduced activity in the anterior cingulate of A1- men. Reduced anxiety and fatigue in A1+ men were significantly associated with greater activity within a right orbitofrontal region previously implicated in cognitive control, and less activity in structures associated with anxiety (amygdala), fatigue (thalamus), and craving/reinforcement (striatum). In contrast, anxiety and fatigue changes were unrelated to brain activity in A1- men. Although these results require replication in a larger sample, alcohol-induced negative reinforcement may explain the greater risk for alcoholism associated with the A1 allele.

Neurobehavioral evidence for changes in dopamine system activity during adolescence

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

Functional neuroimaging of reward circuitry responsivity to monetary gains and losses in posttraumatic stress disorder

BACKGROUND

Clinical impressions and preclinical work suggest that posttraumatic stress disorder (PTSD) might be associated with dysfunctional reward processing. To pursue this issue, we administered a validated passive-viewing monetary reward task during functional magnetic resonance imaging (fMRI) to subjects with chronic PTSD and to mentally healthy individuals.

METHODS

The protocol evaluated fMRI signal changes that anticipated or accompanied monetary gains and losses under varying conditions of controlled expectation. The "expectancy phase" entailed presentation of a promising, unpromising, or intermediate Wheel of Fortune-type spinner, whereas the "outcome phase" was defined by the arrow landing on one of three sectors of that spinner, thereby determining the subjects' gain or loss for that trial.

RESULTS

Neuroimaging data from 20 PTSD and 26 healthy subjects withstood quality control procedures and were included. In voxelwise and anatomically defined region-of-interest analyses, when gains were contrasted to losses, between-group comparison revealed smaller bilateral striatal activations in the PTSD subjects. In the PTSD group, less striatal activation to gains versus losses was associated with more self-reported motivational and social deficits.

CONCLUSIONS

The present data support the hypothesis that PTSD is associated with abnormal processing of monetary outcomes and that this alteration might be related to some aspects of emotional numbing.