Advances in molecular genetics and the prevention and treatment of substance misuse: Implications of association studies of the A1 allele of the D2 dopamine receptor gene

Transition to substance use disorders: impulsivity for reward and learning from reward

Substance dependence constitutes a profound societal burden. Although large numbers of individuals use licit or illicit substances, few transition to dependence. The specific factors influencing this transition are not well understood. Substance-dependent individuals tend to be swayed by the immediate rewards of drug taking, but are often insensitive to delayed negative consequences of their behavior. Dependence is consequently associated with impulsivity for reward and atypical learning from feedback. Behavioral impulsivity is indexed using tasks measuring spontaneous decision-making and capacity to control impulses. While evidence indicates drug taking exacerbates behavioral impulsivity for reward, animal and human studies of drug naïve populations demonstrate it might precede any drug-related problems. Research suggests dependent individuals are also more likely to learn from rewarding (relative to punishing) feedback. This may partly explain why substance-dependent individuals fail to modify their behavior in response to negative outcomes. This enhanced learning from reward may constitute a further pre-existing risk factor for substance dependence. Although impulsivity for reward and preferential learning from rewarding feedback are both underpinned by a compromised dopaminergic system, few studies have examined the relationship between these two mechanisms. The interplay of these processes may help enrich understanding of why some individuals transition to substance dependence.

An Integrated Model of Nature and Nurture Factors that Contribute to Addiction and Recovery

BACKGROUND

In the context of the opioid epidemic and growing awareness of addiction as a public health concern, there are efforts to inform the public, patients, families, and policy makers about the factors that contribute to addiction and facilitate recovery. Several theoretical models provide useful frameworks for this discussion, but each of them has limitations.

OBJECTIVES

This paper presents an accessible yet comprehensive theoretical model that integrates empirical evidence about addiction etiology and recovery using the nature-nurture paradigm.

RESULTS

The model presents substance use along a continuum, and identifies risk and protective factors in multiple domains that have been identified by research. The domains on the nature side of the model include genetic and biological factors, comorbid psychiatric and medical disorders, physiological reinforcement of substance use, and changes to neural mechanisms. The domains on the nurture side of the model include sociocultural factors, environmental factors, personality, emotions, cognitions, psychological reinforcement of substance use, and cognitive and behavioral changes. The progression from increased or decreased substance use to addiction or recovery is mediated by changes in neural mechanisms and cognitive and behavioral changes, which have feedback loops with the physiological and psychological reinforcement.Conclusions/Importance: This model is a useful heuristic, consistent with a public health framework, for discussing addiction and recovery with patients, their families, and the public. This integrated model of nature and nurture factors has the potential to inform clinical practice, consultation, research, prevention programs, educational programs, and public policy.

The D2 dopamine receptor (DRD2) gene is associated with co-morbid depression, anxiety and social dysfunction in untreated veterans with post-traumatic stress disorder

Objective.

To identify clusters of patients with post-traumatic stress disorder (PTSD) according to symptom profile and to examine the association of the A1 allele of the D2 dopamine receptor (DRD2) gene with these clusters.

Method.

Fifty-seven untreated Caucasian Vietnam veterans with PTSD were administered the General Health Questionnaire-28 (GHQ) and the Mississippi Scale for combat-related PTSD. DRD2 allelic status was determined by PCR.

Results.

Subjects with the DRD2 Al allele compared to those without this allele had significantly higher scores on GHQ 2 (anxiety/insomnia), GHQ 3 (social dysfunction) and GHQ 4 (depression). Cluster analysis of the GHQ data identified two primary groups. A high psychopathology cluster (cluster 3), featured by high co-morbid levels of somatic concerns, anxiety/insomnia, social dysfunction and depression, and a low psychopathology cluster (cluster 1), manifested by the reverse pattern. Scores in each of the four GHQ groups were significantly higher in cluster 3 than cluster 1, as was Mississippi Scale PTSD score. DRD2 A1 allele veterans compared to those without this allele were significantly more likely to be found in the high than the low psychopathology cluster group.

Conclusions.

DRD2 variants are associated with severe co-morbid psychopathology in PTSD subjects.

The association between perinatal hypoxia exposure and externalizing symptoms and children's decision making in conditions of uncertainty is moderated by DRD2 genotype

Variants of the DRD2 Taq1A polymorphism, which have been shown to result in functional differences in dopamine D2 receptors (D2R), have been linked to various externalizing outcomes in adults. However, the neurobiological processes that contribute to these associations are not well understood. The current study investigates gene × environment effects on teacher-rated externalizing behaviors and probabilistic decision making in a sample of 333 children (age 9) enrolled in an ongoing longitudinal study. Findings indicate that externalizing behaviors increased as a function of hypoxic exposure only among individuals carrying the A1 (A1+) allele. Results also indicate that willingness to pursue reward under conditions of maximum uncertainty (50% probability) decreased as a function of hypoxic exposure only among A1- individuals. Among A1 carriers, no association between probability decision making and hypoxic exposure emerged. These findings suggest that hypoxia could influence neural development through different biological pathways depending on D2 receptor genotype, and provide insight into the development of individual differences in behavior and decision making.

TAQ1A1 Allele of the DRD2 Gene Region Contribute to Shorter Survival Time in Alcohol Dependent Individuals When Controlling for the Influence of Age and Gender. A Follow-up Study of 18 Years

Aims

To investigate the influence of the A1 allele of the TAQ1A polymorphism in the dopamine D2 receptor (DRD2) gene region on mortality in adult individuals with alcohol dependence.

Methods

The study sample consisted of 359 alcohol-dependent individuals treated for severe alcohol withdrawal symptoms in 1997. Years of survival was studied in an 18-year follow-up. In the analyses, gender and age were controlled for.

Results

At the 18-year follow-up, 53% individuals had deceased. The analyses showed that older age (P < 0.001), male gender (P < 0.05) and carrying the A1 allele (P < 0.01) all significantly and independently contributed to shorten years of survival. Among the deceased individuals, the genotype A1+ was the only significant contributor to shorten years of survival.

Conclusions

An important contribution of the present study is that in alcohol dependence the Taq1A1 allele of the DRD2 gene region is a risk factor for premature death of similar importance as the well-known risk factors of age and gender.

Short Summary

We investigated the influence of A1 allele of the TAQ1A polymorphism in DRD2 receptor gene region on mortality in alcohol-dependent individuals in an 18-year follow-up. Age, gender and the A1 allele contributed to shorten years of survival. Among the deceased, the A1+ was the only contributor to shorten years of survival.

The association of insertions/deletions (INDELs) and variable number tandem repeats (VNTRs) with obesity and its related traits and complications

BACKGROUND

Despite the fact that insertions/deletions (INDELs) are the second most common type of genetic variations and variable number tandem repeats (VNTRs) represent a large portion of the human genome, they have received far less attention than single nucleotide polymorphisms (SNPs) and larger forms of structural variation like copy number variations (CNVs), especially in genome-wide association studies (GWAS) of complex diseases like polygenic obesity. This is exemplified by the vast amount of review papers on the role of SNPs and CNVs in obesity, its related traits (like anthropometric measurements, biochemical variables, and eating behavior), and its related complications (like hypertension, hypertriglyceridemia, hypercholesterolemia, and insulin resistance-collectively known as metabolic syndrome). Hence, this paper reviews the types of INDELs and VNTRs that have been studied for association with obesity and its related traits and complications. These INDELs and VNTRs could be found in the obesity loci or genes from the earliest GWAS and candidate gene association studies, like FTO, genes in the leptin-proopiomelanocortin pathway, and UCP2/3. Given the important role of the brain serotonergic and dopaminergic reward system in obesity susceptibility, the association of INDELs and VNTRs in these neurotransmitters' metabolism and transport genes with obesity is also reviewed. Next, the role of INS VNTR in obesity and its related traits is questionable, since recent large-scale studies failed to replicate the earlier positive associations. As obesity results in chronic low-grade inflammation of the adipose tissue, the proinflammatory cytokine gene IL1RA and anti-inflammatory cytokine gene IL4 have VNTRs that are implicated in obesity. A systemic proinflammatory state in combination with activation of the renin-angiotensin system and decreased nitric oxide bioavailability as found in obesity leads to endothelial dysfunction. This explains why VNTR and INDEL in eNOS and ACE, respectively, could be predisposing factors of obesity. Finally, two novel genes, DOCK5 and PER3, which are involved in the regulation of the Akt/MAPK pathway and circadian rhythm, respectively, have VNTRs and INDEL that might be associated with obesity.

SHORT CONCLUSION

In conclusion, INDELs and VNTRs could have important functional consequences in the pathophysiology of obesity, and research on them should be continued to facilitate obesity prediction, prevention, and treatment.

Pathways In and Out of Substance Use Among Homeless-Emerging Adults

Although high rates of alcohol and drug use have been found among homeless young people, less is known about who is responsible for their initiation, the reasons for their continued use, and why some individuals eventually transition out of using whereas others do not. Based on qualitative interviews with 40 homeless individuals 19 to 21 years of age in the Midwest, results revealed that the majority of respondents were initiated into substance use by friends and acquaintances, although family also played a significant role. Almost one half of respondents reported using substances to cope with early family abuse, stress, and life on the streets. Additionally, the majority indicated that they had no intentions of quitting. Substance misuse that is left untreated may lead to chemical dependency among homeless emerging adults and may contribute to long-term homelessness.

Parental Substance Abuse As an Early Traumatic Event. Preliminary Findings on Neuropsychological and Personality Functioning in Young Drug Addicts Exposed to Drugs Early

Parental substance use is a major risk factor for child development, heightening the risk of drug problems in adolescence and young adulthood, and exposing offspring to several types of traumatic events. First, prenatal drug exposure can be considered a form of trauma itself, with subtle but long-lasting sequelae at the neuro-behavioral level. Second, parents' addiction often entails a childrearing environment characterized by poor parenting skills, disadvantaged contexts and adverse childhood experiences (ACEs), leading to dysfunctional outcomes. Young adults born from/raised by parents with drug problems and diagnosed with a Substance Used Disorder (SUD) themselves might display a particularly severe condition in terms of cognitive deficits and impaired personality function. This preliminary study aims to investigate the role of early exposure to drugs as a traumatic event, capable of affecting the psychological status of young drug addicts. In particular, it intends to examine the neuropsychological functioning and personality profile of young adults with severe SUDs who were exposed to drugs early in their family context. The research involved three groups, each consisting of 15 young adults (aged 18–24): a group of inpatients diagnosed with SUDs and exposed to drugs early, a comparison group of non-exposed inpatients and a group of non-exposed youth without SUDs. A neuropsychological battery (Esame Neuropsicologico Breve-2), an assessment procedure for personality disorders (Shedler-Westen Assessment Procedure-200) and the Symptom CheckList-90-Revised were administered. According to present preliminary results, young drug addicts exposed to drugs during their developmental age were characterized by elevated rates of neuropsychological impairments, especially at the expense of attentive and executive functions (EF); personality disorders were also common but did not differentiate them from non-exposed youth with SUDs. Alternative multi-focused prevention and intervention programs are needed for children of drug-misusing parents, addressing EF and adopting a trauma-focused approach.

The Neurobiology of "Food Addiction" and Its Implications for Obesity Treatment and Policy

There is a growing view that certain foods, particularly those high in refined sugars and fats, are addictive and that some forms of obesity can usefully be treated as a food addiction. This perspective is supported by a growing body of neuroscience research demonstrating that the chronic consumption of energy-dense foods causes changes in the brain's reward pathway that are central to the development and maintenance of drug addiction. Obese and overweight individuals also display patterns of eating behavior that resemble the ways in which addicted individuals consume drugs. We critically review the evidence that some forms of obesity or overeating could be considered a food addiction and argue that the use of food addiction as a diagnostic category is premature. We also examine some of the potential positive and negative clinical, social, and public policy implications of describing obesity as a food addiction that require further investigation.

Candidate gene-environment interaction research: reflections and recommendations

Studying how genetic predispositions come together with environmental factors to contribute to complex behavioral outcomes has great potential for advancing the understanding of the development of psychopathology. It represents a clear theoretical advance over studying these factors in isolation. However, research at the intersection of multiple fields creates many challenges. We review several reasons why the rapidly expanding candidate gene-environment interaction (cG×E) literature should be considered with a degree of caution. We discuss lessons learned about candidate gene main effects from the evolving genetics literature and how these inform the study of cG×E. We review the importance of the measurement of the gene and environment of interest in cG×E studies. We discuss statistical concerns with modeling cG×E that are frequently overlooked. Furthermore, we review other challenges that have likely contributed to the cG×E literature being difficult to interpret, including low power and publication bias. Many of these issues are similar to other concerns about research integrity (e.g., high false-positive rates) that have received increasing attention in the social sciences. We provide recommendations for rigorous research practices for cG×E studies that we believe will advance its potential to contribute more robustly to the understanding of complex behavioral phenotypes.

Impulsivity-related cognition in alcohol dependence: Is it moderated by DRD2/ANKK1 gene status and executive dysfunction?

Perceived impaired control over alcohol use is a key cognitive construct in alcohol dependence that has been related prospectively to treatment outcome and may mediate the risk for problem drinking conveyed by impulsivity in non-dependent drinkers. The aim of the current study was to investigate whether perceived impaired control may mediate the association between impulsivity-related measures (derived from the Short-form Eysenck Personality Questionnaire-Revised) and alcohol-dependence severity in alcohol-dependent drinkers. Furthermore, the extent to which this hypothesized relationship was moderated by genetic risk (Taq1A polymorphism in the DRD2/ANKK1 gene cluster) and verbal fluency as an indicator of executive cognitive ability (Controlled Oral Word Association Test) was also examined. A sample of 143 alcohol-dependent inpatients provided an extensive clinical history of their alcohol use, gave 10ml of blood for DNA analysis, and completed self-report measures relating to impulsivity, impaired control and severity of dependence. As hypothesized, perceived impaired control (partially) mediated the association between impulsivity-related measures and alcohol-dependence severity. This relationship was not moderated by the DRD2/ANKK1 polymorphism or verbal fluency. These results suggest that, in alcohol dependence, perceived impaired control is a cognitive mediator of impulsivity-related constructs that may be unaffected by DRD2/ANKK1 and neurocognitive processes underlying the retrieval of verbal information.

Dopamine and glucose, obesity, and reward deficiency syndrome

Obesity as a result of overeating as well as a number of well described eating disorders has been accurately considered to be a world-wide epidemic. Recently a number of theories backed by a plethora of scientifically sound neurochemical and genetic studies provide strong evidence that food addiction is similar to psychoactive drug addiction. Our laboratory has published on the concept known as Reward Deficiency Syndrome (RDS) which is a genetic and epigenetic phenomena leading to impairment of the brain reward circuitry resulting in a hypo-dopaminergic function. RDS involves the interactions of powerful neurotransmitters and results in abnormal craving behavior. A number of important facts which could help translate to potential therapeutic targets espoused in this focused review include: (1) consumption of alcohol in large quantities or carbohydrates binging stimulates the brain’s production of and utilization of dopamine; (2) in the meso-limbic system the enkephalinergic neurons are in close proximity, to glucose receptors; (3) highly concentrated glucose activates the calcium channel to stimulate dopamine release from P12 cells; (4) a significant correlation between blood glucose and cerebrospinal fluid concentrations of homovanillic acid the dopamine metabolite; (5) 2-deoxyglucose (2DG), the glucose analog, in pharmacological doses is associated with enhanced dopamine turnover and causes acute glucoprivation. Evidence from animal studies and fMRI in humans support the hypothesis that multiple, but similar brain circuits are disrupted in obesity and drug dependence and for the most part, implicate the involvement of DA-modulated reward circuits in pathologic eating behaviors. Based on a consensus of neuroscience research treatment of both glucose and drug like cocaine, opiates should incorporate dopamine agonist therapy in contrast to current theories and practices that utilizes dopamine antagonistic therapy. Considering that up until now clinical utilization of powerful dopamine D2 agonists have failed due to chronic down regulation of D2 receptors newer targets based on novel less powerful D2 agonists that up-regulate D2 receptors seems prudent. We encourage new strategies targeted at improving DA function in the treatment and prevention of obesity a subtype of reward deficiency.

Hatching the behavioral addiction egg: Reward Deficiency Solution System (RDSS)™ as a function of dopaminergic neurogenetics and brain functional connectivity linking all addictions under a common rubric

BACKGROUND

Following the first association between the dopamine D2 receptor gene polymorphism and severe alcoholism, there has been an explosion of research reports in the psychiatric and behavioral addiction literature and neurogenetics. With this increased knowledge, the field has been rife with controversy. Moreover, with the advent of Whole Genome-Wide Studies (GWAS) and Whole Exome Sequencing (WES), along with Functional Genome Convergence, the multiple-candidate gene approach still has merit and is considered by many as the most prudent approach. However, it is the combination of these two approaches that will ultimately define real, genetic allelic relationships, in terms of both risk and etiology. Since 1996, our laboratory has coined the umbrella term Reward Deficiency Syndrome (RDS) to explain the common neurochemical and genetic mechanisms involved with both substance and non-substance, addictive behaviors.

METHODS

This is a selective review of peer-reviewed papers primary listed in Pubmed and Medline.

RESULTS

A review of the available evidence indicates the importance of dopaminergic pathways and resting-state, functional connectivity of brain reward circuits.

DISCUSSION

Importantly, the proposal is that the real phenotype is RDS and impairments in the brain's reward cascade, either genetically or environmentally (epigenetically) induced, influence both substance and non-substance, addictive behaviors. Understanding shared common mechanisms will ultimately lead to better diagnosis, treatment and prevention of relapse. While, at this juncture, we cannot as yet state that we have "hatched the behavioral addiction egg", we are beginning to ask the correct questions and through an intense global effort will hopefully find a way of "redeeming joy" and permitting homo sapiens live a life, free of addiction and pain.

Association of dopamine receptor gene polymorphism and psychological personality traits in liability for opioid addiction

There is a clear evidence that same psychoactive substance may cause various individual physiological reactions in same environmental conditions. Although there is a general attitude on equal liability to opioid addiction, latest genetic analysis findings imply there are certain quantifiable factors that could lead to elevated individual liability towards development of opioid addiction. The goal of this study was to investigate association of certain personality traits and genetic factors (separately and in combination) with heroin addiction. Total of 200 individuals participated in the study: 100 patients on Metadone Maintenance Treatment (MMT) and 100 age and sex matched healthy volunteers. All were medically examined, interviewed and psychologically evaluated using Eysenck personality questionnaire (EPQ) and genotyped for DRD2 (rs1800497) using PCR-RFLP method. Overrepresentation of certain personality traits (neuroticism, psychoticism and extraversion/ intraversion), together with environemental risk factors such as: upbringing within incomplete families and familial history of psychotropic substances abuse, are associated with high-risk development of opioid addiction.

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.

The ADH1B and DRD2 gene polymorphism may modify the protective effect of the ALDH2 gene against heroin dependence

Understanding the influences of genes involved in dopamine and serotonin metabolism, such as the aldehyde dehydrogenase 2 (ALDH2) and alcohol dehydrogenase 1B (ADH1B) genes, is critical for understanding addictive behavior. In addition, dopamine D2 receptor (DRD2) gene may also interact with the dopamine metabolizing genes and link to addiction. Therefore, we investigated the association between the ALDH2, ADH1B and DRD2 polymorphisms and heroin dependence. Heroin-dependent Han Chinese patients (n=304) and healthy controls (n=335) were recruited. Genotypes of ALDH2, ADH1B and DRD2 polymorphisms were analyzed using a polymerase chain reaction with restriction fragment length polymorphism. The frequency of the ALDH2*1/*1 genotype was significantly lower in heroin-dependent patients than in controls, but the frequency of ADH1B and DRD2 genotypes was not significantly different. Further stratification of the ALDH2 gene with the ADH1B gene showed that the protective effect of ALDH2*1/*1 existed only in patients who also carried the ADH1B*1/*1 and ADH1B*1/*2 genotype. Logistic regression analysis showed a significant interaction between ALDH2 and ADH1B (P=0.022) and DRD2, ALDH2 and ADH1B in patients (P=0.037). The ALDH2*1/*1, ADH1B*1/*1, and ADH1B*1/*2 genotypes may interact and protect their carriers against heroin dependence and the protective effect may be varied by the DRD2 gene polymorphism. We conclude that the protective effect of the ALDH2 polymorphism against heroin dependence may be modified by the ADH1B and DRD2 polymorphism.

Dopamine genes (DRD2/ANKK1-TaqA1 and DRD4-7R) and executive function: their interaction with obesity

Obesity is a multifactorial disease caused by the interaction between genotype and environment, and it is considered to be a type of addictive alteration. The A1 allele of the DRD2/ANKK1-TaqIA gene has been associated with addictive disorders, with obesity and with the performance in executive functions. The 7 repeat allele of the DRD4 gene has likewise been associated with the performance in executive functions, as well as with addictive behaviors and impulsivity. Participants were included in the obesity group (N = 42) if their body mass index (BMI) was equal to or above 30, and in the lean group (N = 42) if their BMI was below 25. The DRD2/ANKK1-TaqIA and DRD4 VNTR polymorphisms were obtained. All subjects underwent neuropsychological assessment. Eating behavior traits were evaluated. The 'DRD2/ANKK1-TaqIA A1-allele status' had a significant effect on almost all the executive variables, but no significant 'DRD4 7R-allele status' effects were observed for any of the executive variables analyzed. There was a significant 'group' x 'DRD2/ANKK1-TaqIA A1-allele status' interaction effect on LN and 'group' x 'DRD4 7R-allele status' interaction effect on TMT B-A score. Being obese and a carrier of the A1 allele of DRD2/ANKK1-TaqIA or the 7R allele of DRD4 VNTR polymorphisms could confer a weakness as regards the performance of executive functions.

Genetics of dopamine receptors and drug addiction

Dopamine plays a key role in reward behavior, yet the association of drug dependence as a chronic, relapsing disorder with the genes encoding the various dopaminergic receptor subtypes remains difficult to delineate. In the context of subsequent genome-wide association (GWAS) research and post-GWAS investigations, we summarize the novel data that link genes encoding molecules involved in the dopaminergic system (dopamine receptors, transporter and enzymes in charge of its metabolism) to drug addiction. Recent reports indicate that the heritability of drug addiction should be high enough to allow a significant role for a specific set of genes, and the available genetic studies, which might not be already conclusive because of the heterogeneity of designs, methods and recruited samples, should support the idea of a significant role of at least one gene related to dopaminergic system. Evolutionary changes in primates and non-primate animals of genes coding for molecules involved in dopaminergic system highlight why addictive disorders are mainly limited to humans. Restricting the analyses to more specific intermediate phenotypes (or endophenotypes) such as attention allocation, stress reactivity, novelty seeking, behavioral disinhibition and impulsivity, instead of the broad addictive disorder concept can be instrumental to identify novel genes associated with these traits in the context of genome-wide studies.

The aldehyde dehydrogenase 2 gene is associated with heroin dependence

BACKGROUND

Determining the influences of genes involved in metabolizing dopamine and encoding dopamine receptors, such as the aldehyde dehydrogenase 2 (ALDH2) and dopamine D2 receptor/ankyrin repeat and kinase domain containing 1 (DRD2/ANKK1) genes, is critical for understanding addictive behavior. Therefore, we investigated the association between the ALDH2 and DRD2/ANKK1 Taq IA polymorphisms and heroin dependence.

METHODS

Heroin-dependent Han Chinese patients (250) and healthy controls (312) were recruited. ALDH2 and DRD2/ANKK1 Taq IA polymorphisms were genotyped.

RESULTS

The frequency of ALDH2*1/*2 and *2/*2 genotypes was significantly higher in heroin-dependent patients than in controls, but the frequency of DRD2 Taq IA genotypes was not significantly different. Logistic regression analysis showed no significant interaction between ALDH2 and DRD2 Taq IA genotypes in patients.

CONCLUSIONS

The ALDH2 polymorphism, but not the DRD2, was associated with heroin dependence.

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.

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.

Cognitive effects of nicotine: genetic moderators

Cigarette smoking is the main preventable cause of death in developed countries, and the development of more effective treatments is necessary. Cumulating evidence suggests that cognitive enhancement may contribute to the addictive actions of nicotine. Several studies have demonstrated that nicotine enhances cognitive performance in both smokers and non-smokers. Genetic studies support the role of both dopamine (DA) and nicotinic acetylcholine receptors (nAChRs) associated with nicotine-induced cognitive enhancement. Based on knockout mice studies, beta2 nAChRs are thought to be essential in mediating the cognitive effects of nicotine. alpha7nAChRs are associated with attentional and sensory filtering response, especially in schizophrenic individuals. Genetic variation in D2 type DA receptors and the catechol-O-methyltransferase enzyme appears to moderate cognitive deficits induced by smoking abstinence. Serotonin transporter (5-HTT) gene variation also moderates nicotine-induced improvement in spatial working memory. Less is known about the contribution of genetic variation in DA transporter and D4 type DA receptor genetic variation on the cognitive effects of nicotine. Future research will provide a clearer understanding of the mechanism underlying the cognitive-enhancing actions of nicotine.

Polymorphisms in dopamine system genes are associated with individual differences in attention in infancy

Knowledge about the functional status of the frontal cortex in infancy is limited. This study investigated the effects of polymorphisms in four dopamine system genes on performance in a task developed to assess such functioning, the Freeze-Frame task, at 9 months of age. Polymorphisms in the catechol-O-methyltransferase (COMT) and the dopamine D4 receptor (DRD4) genes are likely to impact directly on the functioning of the frontal cortex, whereas polymorphisms in the dopamine D2 receptor (DRD2) and dopamine transporter (DAT1) genes might influence frontal cortex functioning indirectly via strong frontostriatal connections. A significant effect of the COMT valine(1)methionine (Val 158 Met) polymorphism was found. Infants with the Met/Met genotype were significantly less distractible than infants with the Val/Val genotype in Freeze-Frame trials presenting an engaging central stimulus. In addition, there was an interaction with the DAT1 3; variable number of tandem repeats polymorphism; the COMT effect was present only in infants who did not have two copies of the DAT1 10-repeat allele. These findings indicate that dopaminergic polymorphisms affect selective aspects of attention as early as infancy and further validate the Freeze-Frame task as a frontal cortex task.

Genetic diagnostics of functional variants of the human dopamine D2 receptor gene

INTRODUCTION

The importance of dopamine D2 receptors (DRD2) for central nervous dopaminergic signalling makes variants in the DRD2 gene potential modulators of the risk or course of various behavioural, psychiatric or neurologic diseases (e.g. addiction, schizophrenia, Parkinson's disease). We developed Pyrosequencing genetic screening assays for single nucleotide polymorphisms spanning the whole range of the DRD2 gene locus up to the functionally related ankyrin repeat and kinase domain containing 1 gene (ANKK1) located at approximately 10 kb downstream of DRD2.

METHODS

Assays for 11 genetic variants with reported functional association were developed in DNA samples from 300 unrelated healthy Caucasians and validated by independent conventional sequencing.

RESULTS

In all DNA samples the DRD2/ANKK1 genetic variants were identified correctly as verified by the control samples. The observed frequencies of homozygous, heterozygous and noncarriers of the minor alleles were in agreement with the Hardy-Weinberg equilibrium. Observed minor allele frequencies were DRD2 rs12364283T>C: 6.5%, rs1799978A>G: 4.8%, rs1799732C del: 14.2%, rs4648317C>T: 12.8%, rs1079597G>A: 13.8%, rs1076560G>T: 14.5%, rs1800496C>T: 0.2%, rs1801028C>G: 3.0%, rs6275C>T: 32.7%, rs6277C>T: 53.0% and ANKK1 rs1800497C>T: 17.5%.

CONCLUSION

The presently developed Pyrosequencing assays are provided to facilitate further research toward personalized approaches to pathophysiological conditions involving behavioural, psychiatric and neurologic disorders including addiction, schizophrenia and Parkinson's disease.

Addressing tobacco use disorder in smokers in early remission from alcohol dependence: the case for integrating smoking cessation services in substance use disorder treatment programs

Despite the declining overall rate of cigarette smoking in the general population in the United States, the prevalence of smoking is estimated to be as high as 80% among treatment-seeking alcoholics. The serious adverse health effects of tobacco and heavy alcohol use are synergistic and recent evidence suggests that smoking slows the process of cognitive recovery following alcohol abstinence. In addition, substantial evidence shows that treatment for tobacco dependence does not jeopardize alcohol abstinence. In this paper, we focus on the impact and treatment implications of tobacco dependence among treatment-seeking alcoholics through a review of five areas of research. We begin with brief reviews of two areas of research: studies investigating the genetic and neurobiological vulnerability of comorbid tobacco and alcohol dependence and studies investigating the consequences of comorbid dependence on neurobiological and cognitive functioning. We then review literature on the effects of smoking cessation on drinking urges and alcohol use and the effectiveness of smoking cessation interventions with alcoholic smokers. Finally, we offer recommendations for research with an emphasis on clinical research for enhancing smoking cessation outcomes in this population.

Shared brain vulnerabilities open the way for nonsubstance addictions: carving addiction at a new joint?

For more than half a century, since the beginning of formal diagnostics, our psychiatric nosology has compartmentalized the compulsive pursuit of substance (e.g., alcohol, cocaine, heroin, nicotine) from nonsubstance (e.g., gambling, food, sex) rewards. Emerging brain, behavioral, and genetic findings challenge this diagnostic boundary, pointing to shared vulnerabilities underlying the pathological pursuit of substance and nonsubstance rewards. Working groups for the fifth revision of the Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-V), are thus considering whether the nosologic boundaries of addiction should be redrawn to include nonsubstance disorders, such as gambling. This review discusses how neurobiological data from problem gambling, obesity, and "normal" states of attachment (romantic infatuation, sexual attraction, maternal bonds) may help us in the task of carving addictions "at a new joint." Diagnostic recarving may have a positive effect on addiction research, stimulating discovery of "crossover" pharmacotherapies with benefit for both substance and nonsubstance addictions.

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.

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.

Haplotype frequencies at the DRD2 locus in populations of the East European Plain

Background

It was demonstrated previously that the three-locus RFLP haplotype, TaqI B-TaqI D-TaqI A (B-D-A), at the DRD2 locus constitutes a powerful genetic marker and probably reflects the most ancient dispersal of anatomically modern humans.

Results

We investigated TaqI B, BclI, MboI, TaqI D, and TaqI A RFLPs in 17 contemporary populations of the East European Plain and Siberia. Most of these populations belong to the Indo-European or Uralic language families. We identified three common haplotypes, which occurred in more than 90% of chromosomes investigated. The frequencies of the haplotypes differed according to linguistic and geographical affiliation.

Conclusion

Populations in the northwestern (Byelorussians from Mjadel'), northern (Russians from Mezen' and Oshevensk), and eastern (Russians from Puchezh) parts of the East European Plain had relatively high frequencies of haplotype B2-D2-A2, which may reflect admixture with Uralic-speaking populations that inhabited all of these regions in the Early Middle Ages.

Dopamine D2 receptor genotype is associated with increased mortality at a 10-year follow-up of alcohol-dependent individuals

AIMS

Because the TAQ1 A1 allele may be associated with alcohol-related medical illnesses, and medical illnesses in alcohol-dependent individuals are associated with increased mortality, we test the hypothesis that the TAQ1 A1 allele of the DRD2 gene is associated with increased mortality in alcohol-dependent individuals.

METHODS

Following an index treatment episode, a 10-year follow-up study in 366 alcohol-dependent individuals was performed. The TAQ1 A1/A2 DRD2 genotype and allele frequencies were compared between those deceased and those still living at the 10-year point. In addition, the genotype and allele frequencies of these alcohol-dependent individuals were compared to that in 578 control subjects.

RESULTS

The prevalence of the A1 allele differed between the deceased and living patients and the controls: 47% of the deceased were A1+, compared to 37% of the living patients and 32% of the controls. The frequency of the TAQ1 A1/A2 genotype also differed between the groups. Thus, 43% had the A1/A2 genotype in comparison with 32% in the living patients and 29% in the controls. The TAQ 1 A1 allele frequency differed between the groups. The frequency of A1 allele was 25% in the deceased patients compared to 21% in the living patients and 17% in the controls.

CONCLUSION

The TAQ I A1 allele of the DRD2 gene (or DRD2 gene region) was associated with increased mortality over a 10-year period in alcohol-dependent individuals.

The TaqI A DRD2 polymorphism in type II alcohol dependence: a marker of age at onset or of a familial disease?

Cloninger's type II is a severe, early-onset, male-limited, and genetically influenced, impulsive form of alcoholism. Significant association has been reported between the A1 allele of the D2 dopamine receptor (DRD2) gene, substance misuse and personality traits of impulsivity and novelty seeking. We assessed the association between the TaqI A DRD2 gene polymorphism with Cloninger's typology and family history of alcohol abuse, which is thought to be more frequent in type II alcoholics. Fifty-one male alcohol-dependent patients were discriminated between type I and type II according to age at onset of alcohol-related problems and interviewed about family history of alcoholism. The associations between DRD2 (A1 or A2 alleles), family history, and typology were assessed by Pearson's chi-square test. Although typology was not associated with the studied polymorphism, a higher rate of general family history of alcohol abuse was still observed in type II patients (chi(2)(1)=4.53; P=.033). Furthermore, the A1 allele of the DRD2 was significantly associated with paternal history of alcoholism (chi(2)(1)=4.66; P=.031) and male, first-degree, collateral history of alcoholism (chi(2)(1)=4.40; P=.036). Age at onset of alcohol-related problems as main discriminator between type I and type II alcohol dependence does not seem to be associated by the TaqI A DRD2 polymorphism. However, the A1 allele of the DRD2 may be a marker of male familial alcoholism, which has been associated with type II alcohol dependence.

Gender effect on association between DRD2 polymorphism and substance dependence in a Spanish sample

Our aim was to examine a possible association between substance dependence and the TaqIA polymorphism of the D2 dopamine receptor (DRD2), a single nucleotide polymorphism (SNP) located at the 3' UTR region of the DRD2 gene. A case-control design stratified by gender was used to analyze the genotypes of this SNP in a sample of 125 substance-dependent patients according to DSM-IV and 203 blood donors recruited as controls in two general city hospitals in Madrid, Spain. Genomic DNA from peripheral blood samples was amplified through PCR to identify the variants of the SNP in the DRD2 gene. Analyses performed with Chi(2) tests revealed that the A1 allele (A1/A1 and A1/A2 genotypes) of the Taq 1A SNP of the DRD2 gene was significantly associated with substance dependence in males, but not in the whole sample. Male patients had significantly higher rates of the A1-containing genotypes than male controls. The finding of an association between substance dependence and the DRD2 gene TaqIA SNP only in males suggests the existence of gender-specific differences in the genetic underpinnings of substance dependence.

D2 dopamine receptor (DRD2) gene, P300, and personality in children of alcoholics

The D2 dopamine receptor (DRD2) gene has been associated with alcoholism and other drug use disorders. Reduced P300 amplitude has been noted in individuals with psychiatric disorders. Personality variables are also associated with reduced P300 amplitude. The current study was conducted to determine whether variants of the DRD2 would show differential relationships among P300 amplitude and personality traits. The study consisted of 101 adolescent children of alcoholics; 39 carried the A1(+) genotype (A1A1, A1A2) and 62 carried the A1(-) genotype (A2A2). The A1(+) genotype group had higher IQ and Self-Directedness scores than the A1(-) genotype group. As predicted, the negative relationship between Novelty Seeking and Harm Avoidance was present in A1(-) but not A1(+) participants. Additionally, in A1(+) but not in A1(-) participants, there was a negative relationship between Novelty Seeking and Self-Directedness and a positive relationship between P300 amplitude and Cooperativeness. The results suggest that in adolescent children of alcoholics, dopaminergic genetic determinants are critical modifiers of the relationship between neurocognitive and personality endophenotypes proposed as vulnerability markers for substance use disorders.

Cortical NMDA receptor expression in human chronic alcoholism: influence of the TaqIA allele of ANKK1

Real-time RT-PCR normalized to GAPDH was used to assay N-methyl-D-aspartate (NMDA) receptor NR1, NR2A and NR2B subunit mRNA in human autopsy cortex tissue from chronic alcoholics with and without comorbid cirrhosis of the liver and matched controls. Subunit expression was influenced by the subject's genotype. The TaqIA polymorphism selectively modulated NMDA receptor mean transcript expression in cirrhotic-alcoholic superior frontal cortex, in diametrically opposite ways in male and female subjects. Genetic make-up may differentially influence vulnerability to brain damage by altering the excitation: inhibition balance, particularly in alcoholics with comorbid cirrhosis of the liver. The TaqIA polymorphism occurs within the poorly characterised ankyrin-repeat containing kinase 1 (ANKK1) gene. Using PCR, ANKK1 mRNA transcript was detected in inferior temporal, occipital, superior frontal and primary motor cortex of control human brain. ANKK1 expression may mediate the influence of the TaqIA polymorphism on phenotype.

Behavioral phenotypes of impulsivity related to the ANKK1 gene are independent of an acute stressor

BACKGROUND

The A1 allele of the ANKK1 TaqIA polymorphism (previously reported as located in the D2 dopamine receptor (DRD2) gene) is associated with reduced DRD2 density in the striatum and with clinical disorders, particularly addiction. It was hypothesized that impulsivity represents an endophenotype underlying these associations with the TaqIA and that environmental stress would moderate the strength of the gene-behavior relationship.

METHODS

TaqIA genotyping was conducted on 72 healthy young adults who were randomly allocated to either an acute psychosocial stress or relaxation induction condition. Behavioral phenotypes of impulsivity were measured using a card-sorting index of reinforcement sensitivity and computerized response inhibition and delay discounting tasks.

RESULTS

Separate analyses of variance revealed associations between the A1 allele and two laboratory measures of impulsivity. The presence of the TaqIA allele (A1+) was associated with slower card-sorting in the presence of small financial reinforcers, but was overcome in a second administration after either a five-minute rest or psychosocial stress induction. A1+ participants also demonstrated significantly poorer response inhibition and faster response times on a computerized stop inhibition task, independent of acute stress exposure.

CONCLUSION

These findings indicate the A1 allele is associated with an endophenotype comprising both a "rash impulsive" behavioral style and reinforcement-related learning deficits. These effects are independent of stress.

[Genetic factors of alcohol-dependence]

INTRODUCTION

Alcohol dependence is a complex and multifactorial disease resulting both from neurobiological mechanisms and environmental factors. It is frequently associated with comorbid psychiatric disorders or with specific personality or behavioral features. Although action can be taken on the environment in order to decrease the risk of the illness, current methods used to prevent or to treat this pathology show moderate efficacy: problematic consumption of ethanol in the general population as well as relapse rates under treatment in dependent patients remain indeed very high.

LITERATURE FINDINGS

It is therefore of major importance to broaden our knowledge of alcohol dependence and its comorbidities so as to improve both their prevention and treatment. In this perspective, recent progress in the field of neurosciences may contribute to achieve this goal. Precisely, genetics is a promising way benefiting from many advances in genetic epidemiology, cellular and molecular biology, neuroimaging and pharmacology. In parallel with a better understanding of the neurobiology of addictions and associated behaviors, these techniques led to the identification of brain mechanisms in which a genetic variation may influence the individual vulnerability towards alcohol dependence. Moreover, there is growing evidence that alcoholism results from the interaction of genetic and environmental factors influencing both its expression and its course. Given the fact that alcohol-dependence seems highly heritable (50 to 60% of the variance in both men and women), this review assesses the role of some of the genomic regions linked with the disease, as well as the principal variants of candidate genes identified as specifically involved in the predisposition. Polymorphisms of genes influencing alcohol metabolism, GABAergic, dopaminergic and serotonergic neurotransmission seem, indeed, at stake in the development of alcohol-dependence and its related features such as personality, behavior, impulse control or craving. In the future, a better characterization of the links between genotypes and phenotypes will probably increase our ability to treat alcoholic patients.

Association of dopamine and opioid receptor genetic polymorphisms with response to methadone maintenance treatment

BACKGROUND

Genetic variations of the dopamine and opioid receptors could influence the response to methadone maintenance treatment (MMT).

METHODS

We included 238 MMT patients according to their response to treatment and methadone dosing, along with 217 subjects without substance dependence. All were genotyped for polymorphisms of the dopamine D1, D2, micro-opioid and delta-opioid receptor genes.

RESULTS

The polymorphisms of the micro-opioid (118A>G), delta-opioid (921T>C), dopamine D1 (DdeI) and D2 (TaqI A) receptor genes were not associated with response to MMT and methadone dosing, whereas an association was found with the dopamine D2 receptor (DRD2) 957C>T polymorphism. The 957CC carriers were more frequently non-responders to treatment (OR=2.4; p=0.02) and presented a fourfold shorter period of negative urine screening (p=0.02). No significant differences in allele frequencies were observed between the MMT patients and the control group, suggesting no association of the analyzed polymorphisms with opioid dependence.

CONCLUSIONS

These results suggest that DRD2 genotype may contribute to the understanding of the interindividual variability to the response to MMT.

The A1 allele of the D2 dopamine receptor gene region, alcohol expectancies and drinking refusal self-efficacy are associated with alcohol dependence severity

Psychological risk and genetic risk for alcohol dependence are rarely examined in concert. The current study used path analysis (via structural equation modelling) to explore the relationship between the A(1) allele of the D2 dopamine receptor DRD2 gene region, age of problem drinking onset, alcohol expectancy and drinking refusal self-efficacy towards alcohol consumption and dependence severity. One hundred and forty-three (93 male, 50 female) alcohol dependent inpatients provided an extensive clinical history, including age of onset of problem drinking and quantity and frequency of alcohol consumption. The Drinking Expectancy Profile and the Alcohol Dependence Scale were completed, and 10 milliliters of blood were obtained for genetic analysis. The results showed that the posited model fitted the data set well and support the pattern of direct (allele status to drinking) and indirect (allele status influenced by psychosocial variables) relationships hypothesised for the model. A formal test of mediation showed some support for a psychosocial mediational model. The results are discussed in terms of a possible developmental trajectory that involves both genetic risk that influences brain dopamine activity and reinforcement expectancies that both operate via diminished drinking refusal self-efficacy. The prevention and treatment possibilities that arise from understanding this trajectory are examined.

A preliminary study: novelty seeking, frontal executive function, and dopamine receptor (D2) TaqI A gene polymorphism in patients with methamphetamine dependence

INTRODUCTION

Dopamine receptor polymorphisms have been associated with specific patterns of novelty seeking (NS) temperamental nature and frontal executive function. In addition, carriers of dopamine receptor type 2 (DRD2)-TaqI A1 have been hypothesized to be potentially vulnerable to addictive behaviors. In the present study, the association between dopamine D2 polymorphisms, NS, and frontal executive function was studied.

METHODS

Thirty-seven methamphetamine (MA)-dependent subjects and 40 healthy comparison subjects participated in the current study. The severity of addiction, NS temperament, and frontal executive functions were measured using the Addiction Severity Index, the NS subscale in the Temperament and Character Inventory, and the Wisconsin Card Sorting Test, respectively. All subjects were genotyped with regard to DRD2-TaqI polymorphisms.

RESULTS

The prevalence of DRD2-TaqI A1 allele polymorphisms was greater in the MA-abuser group than in the comparison group. Patients with MA dependence also had higher NS characteristics and high scores in total trials, errors, and perseverative errors of the Wisconsin Card Sorting Test than comparison subjects. Within patients with MA dependence, the subgroup of DRD2-TaqI A1 carrier had greater NS scores relative to those without, whereas there was only a trend level of lower frontal executive function in the first subgroup.

CONCLUSION

In the present study, the MA-dependent patients with DRD2-TaqI A1 allele had significantly greater NS scores and lower frontal executive function with a trend level than those without. These preliminary results suggest that MA-dependent patients may have the possibility of genetic and biogenic vulnerability to MA.

Antipsychotic-induced tardive dyskinesia and polymorphic variations in COMT, DRD2, CYP1A2 and MnSOD genes: a meta-analysis of pharmacogenetic interactions

Despite accumulating evidence pointing to a genetic basis for tardive dyskinesia, results to date have been inconsistent owing to limited statistical power and limitations in molecular genetic methodology. A Medline, EMBASE and PsychINFO search for literature published between 1976 and June 2007 was performed, yielding 20 studies from which data were extracted for calculation of pooled estimates using meta-analytic techniques. Evidence from pooled data for genetic association with tardive dyskinesia (TD) showed (1) in COMT(val158met), using Val-Val homozygotes as reference category, a protective effect for Val-Met heterozygotes (OR=0.63, 95% CI: 0.46-0.86, P=0.004) and Met carriers (OR=0.66, 95% CI: 0.49-0.88, P=0.005); (2) in Taq1A in DRD2, using the A1 variant as reference category, a risk-increasing effect for the A2 variant (OR=1.30, 95% CI: 1.03-1.65, P=0.026), and A2-A2 homozygotes using A1-A1 as reference category (OR=1.80, 95% CI: 1.03-3.15, P=0.037); (3) in MnSOD Ala-9Val, using Ala-Ala homozygotes as reference category, a protective effect for Ala-Val (OR=0.37, 95% CI: 0.17-0.79, P=0.009) and for Val carriers (OR=0.49, 95% CI: 0.24-1.00, P=0.047). These analyses suggest multiple genetic influences on TD, indicative of pharmacogenetic interactions. Although associations are small, the effects underlying them may be subject to interactions with other loci that, when identified, may have acceptable predictive power. Future genetic research will take advantage of new genomic knowledge. Molecular Psychiatry (2008) 13, 544-556; doi:10.1038/sj.mp.4002142; published online 8 January 2008.

Association study of dopamine receptor D2 TaqI A polymorphism and reward-related personality traits in healthy Korean young females

BACKGROUND

Genetic factors make a significant contribution to the determination of human personality traits. We aimed to investigate the possible relationship between dopamine receptor D2 (DRD2) TaqI A polymorphism and the reward-related personality traits as measured by the Carver and White Behavioral Inhibition System/Behavioral Approach System (BIS/BAS) scales and Cloninger's Temperament and Character Inventory (TCI).

METHODS

The sample consisted of 267 female healthy Korean unrelated university students (age: 23.12 +/- 3.22 years) and they filled out the BIS/BAS scales and the TCI. Genomic DNA was isolated from whole blood and genotyped with the fluorescence polarization detection method. The effect of the independent variables (DRD2 genotypes) on the dependent variables were analyzed by multivariate and subsequent univariate ANOVA.

RESULTS

We found significant associations between the A1 allele of the DRD2 TaqI A polymorphism and a high BAS-RR score (reward responsiveness). No significant association was observed between DRD2 polymorphisms and other factors of the BIS/BAS scales and TCI.

CONCLUSION

These findings suggest the notion that DRD2 TaqI A polymorphism contributes to high reward sensitivity, which measures anticipation and positive response towards reward.

The genetics of nicotine addiction liability: ethical and social policy implications

AIM

To assess the promise and risks of technological applications of genetic research on liability to develop nicotine dependence.

METHODS

We reviewed (i) the evidence on the genetics of nicotine dependence; (ii) the technical feasibility of using genetic information to reduce smoking uptake and increase cessation; and (iii) policy and ethical issues raised by the uses of genetic information on addiction liability.

RESULTS

(i) Despite evidence from twin studies that genes contribute to addiction susceptibility, research to date has not identified commonly occurring alleles that are strongly predictive of developing nicotine addiction. Nicotine addiction is likely to involve multiple alleles of small effect that interact with each other and with the environment. (ii) Population screening for susceptibility alleles is unlikely to be effective or cost-effective. Tailoring of smoking cessation treatments with genetic information is more plausible but results to date have been disappointing. Population health strategies such as increased taxation and reduced opportunities to smoke are more efficient in reducing cigarette smoking. Tobacco harm reduction policies applied to populations may also play a role in reducing tobacco-related harm. (iii) Future uses of genomic information on addiction risk will need to assess the risks of medicalising addiction (e.g. pessimism about capacity to quit) and community concerns about genetic privacy.

CONCLUSIONS

Nicotine genomics is a very new and underdeveloped field. On the evidence to date, its advocates would be wise to avoid extravagant claims about its preventive applications.

Ten good reasons to consider biological processes in prevention and intervention research

Most contemporary accounts of psychopathology acknowledge the importance of both biological and environmental influences on behavior. In developmental psychopathology, multiple etiological mechanisms for psychiatric disturbance are well recognized, including those operating at genetic, neurobiological, and environmental levels of analysis. However, neuroscientific principles are rarely considered in current approaches to prevention or intervention. In this article, we explain why a deeper understanding of the genetic and neural substrates of behavior is essential for the next generation of preventive interventions, and we outline 10 specific reasons why considering biological processes can improve treatment efficacy. Among these, we discuss (a) the role of biomarkers and endophenotypes in identifying those most in need of prevention; (b) implications for treatment of genetic and neural mechanisms of homotypic comorbidity, heterotypic comorbidity, and heterotypic continuity; (c) ways in which biological vulnerabilities moderate the effects of environmental experience; (d) situations in which Biology x Environment interactions account for more variance in key outcomes than main effects; and (e) sensitivity of neural systems, via epigenesis, programming, and neural plasticity, to environmental moderation across the life span. For each of the 10 reasons outlined we present an example from current literature and discuss critical implications for prevention.