The interaction between the dopamine transporter gene and age at onset in relation to tobacco and alcohol use among 19-year-olds

Parental drug use disorders and youth psychopathology: Meta-analytic review

Parental drug use disorders (PDUDs) represent a highly prevalent risk factor for youth's development of psychological and substance misuse. However, most research on associations between parental substance use and child mental health focuses on composites of parental drug, alcohol, and tobacco use. PDUDs are associated with a range of legal, health, and environmental risks that make them substantially distinct from tobacco and alcohol misuse, yet associations between PDUDs and youth psychopathology symptoms have yet to be assessed quantitatively using meta-analytic techniques. Accordingly, the present meta-analysis assessed the association between PDUDs and youth's internalizing, externalizing, substance use, and total psychological problems across 30 studies (N = 8433). Meta-analytic findings showed that PDUDs were associated with greater substance use and total psychological problems in youth. Across studies, PDUDs were not associated with broad dimensions of youth internalizing and externalizing symptoms but demonstrated a positive relation with youth ADHD and conduct disorder symptoms. There were significant moderation effects for study quality, symptom informant, and child age, where the association between PDUDs and child symptoms of psychopathology was stronger for older youth, in higher quality studies, and studies using joint parent-child symptom informants. Taken together, the meta-analytic findings suggest that PDUDs present a significant risk factor for youth. Future research targeting the relation between parental drug use and youth psychopathology is warranted for prevention and intervention efforts. Implication of findings, mechanisms of interest, and an agenda for future research are discussed.

Association studies of dopamine synthesis and metabolism genes with multiple phenotypes of heroin dependence

BACKGROUND

Heroin dependence is a complex disease with multiple phenotypes. Classification of heroin users into more homogeneous subgroups on the basis of these phenotypes could help to identify the involved genetic factors and precise treatments. This study aimed to identify the association between genetic polymorphisms of DA synthesis and metabolism genes, including tyrosine hydroxylase (TH), DOPA decarboxylase (DDC), solute carrier family 6 member 3 (SLC6A3) and DA beta-hydroxylase (DBH), with six important phenotypes of heroin dependence.

METHODS

A total of 801 heroin dependent patients were recruited and fourteen potential functional single nucleotide polymorphisms (SNPs) were genotyped by SNaPshot. Associations between SNPs with six phenotypes were mainly assessed by binary logistic regression. Generalized multifactor dimensionality reduction was used to analyze the gene-by-gene and gene-by-environment interactions.

RESULTS

We found that DBH rs1611114 TT genotype had a protective effect on memory impairment after heroin dependence (P = 0.002, OR = 0.610). We also found that the income-rs12666409-rs129915-rs1611114 interaction yielded the highest testing balance accuracy and cross-validation consistency for memory change after heroin dependence.

CONCLUSIONS

Our results suggest that the memory change after heroin dependence was a result of a combination of genetics and environment. This finding could lead to a better understanding of heroin dependence and further improve personalized treatment.

Application of Research Domain Criteria to childhood and adolescent impulsive and addictive disorders: Implications for treatment

The Research Domain Criteria (RDoC) initiative provides a large-scale, dimensional framework for the integration of research findings across traditional diagnoses, with the long-term aim of improving existing psychiatric treatments. A neurodevelopmental perspective is essential to this endeavor. However, few papers synthesizing research findings across childhood and adolescent disorders exist. Here, we discuss how the RDoC framework may be applied to the study of childhood and adolescent impulsive and addictive disorders in order to improve neurodevelopmental understanding and to enhance treatment development. Given the large scope of RDoC, we focus on a single construct highly relevant to addictive and impulsive disorders - initial responsiveness to reward attainment. Findings from genetic, molecular, neuroimaging and other translational research methodologies are highlighted.

Novelty seeking mediates the effect of DRD3 variation on onset age of amphetamine dependence in Han Chinese population

The dopamine receptor D3 (DRD3) gene, one of the candidate genes for amphetamine dependence (AD), is involved in the mesolimbic dopaminergic system, implicated as the underlying mechanism of addiction. Our case-control study aimed to investigate whether the DRD3 gene is associated with the susceptibility to AD and specific personality traits in AD patients. A total of 1060 unrelated Han Chinese subjects (559 AD patients and 501 controls) were screened using the same assessment tool and genotyped for eight DRD3 polymorphisms. All patients met the DSM-IV-TR criteria for AD, and personality traits of 539 were assessed using a Tridimensional Personality Questionnaire. Furthermore, AD individuals were divided into four clinical subgroups based on gender and psychosis status, to reduce the clinical heterogeneity. We found that the ATA haplotype combination for SNPs rs324029, rs6280, and rs9825563, respectively, was significantly associated with total AD patients (p = 0.0003 after 10,000 permutations). Similar results were observed in the both male and non-psychosis subgroup but not in other subgroups. In addition, DRD3 rs9825563 may influence onset age of drug use, partially mediated by novelty seeking in the non-psychosis AD group. In conclusion, DRD3 is a potential genetic factor in the susceptibility to AD and is associated with onset age of drug use through interaction with novelty seeking in a specific patient group in the Han Chinese population.

The dopamine transporter role in psychiatric phenotypes

The dopamine transporter (DAT) is one of the most relevant and investigated neurotransmitter transporters. DAT is a plasma membrane protein which plays a homeostatic role, controlling both extracellular and intracellular concentrations of dopamine (DA). Since unbalanced DA levels are known to be involved in numerous mental disorders, a wealth of investigations has provided valuable insights concerning DAT role into normal brain functioning and pathological processes. Briefly, this extensive but non-systematic review discusses what is recently known about the role of SLC6A3 gene which encodes the dopamine transporter in psychiatric phenotypes. DAT protein, SLC6A3 gene, animal models, neuropsychology, and neuroimaging investigations are also concisely discussed. To conclude, current challenges are reviewed in order to provide perspectives for future studies.

Environmental risks outweigh dopaminergic genetic risks for alcohol use and abuse from adolescence through early adulthood

BACKGROUND

Alcohol use is a primary public health concern, particularly among adolescents and young adults. Based on the rapidly growing field of gene-environment models, this study assessed the combined role of environmental and dopamine-related genetic correlates of early alcohol use and abuse.

METHODS

Multilevel growth models assessed trajectories of alcohol use and intoxication and ordered logistic regressions assessed alcohol use disorder among a sample of 12,437 youth from the nationally representative Add Health study who were followed from mid-adolescence through early adulthood.

RESULTS

Endogenous and exogenous stressful life events and social norms supportive of alcohol use from parents and peers were significant predictors of alcohol use, intoxication, and alcohol use disorder, with consistent patterns across males and females. In contrast, a dopamine-system genetic risk score (GRS) was not associated with alcohol use trajectories nor alcohol use disorder in early adulthood, although weak connections emerged between the GRS and growth trajectories of intoxication, indicating that higher GRS predicted more frequent episodes of intoxication during the transition to adulthood but not during adolescence or later 20s. No evidence of gene-environment interactions emerged.

CONCLUSIONS

Results extend a substantial body of prior research primarily assessing single genetic polymorphisms in the dopamine system, suggesting that dopaminergic GRSs may be associated with more problematic alcohol behaviors at some developmental periods, but further, that social norms and stressful life experiences are more consistent correlates of early and problematic alcohol use among youth. These environmental factors present potential targets for research manipulating contexts to identify causal pathways.

The SLC6A3 gene possibly affects susceptibility to late-onset alcohol dependence but not specific personality traits in a Han Chinese population

Dopaminergic dysfunction has an important role in the pathoetiology of alcohol dependence (AD). The purpose of this study was to determine whether the solute carrier family 6 member 3 (SLC6A3) gene (also known as the dopamine transporter DAT gene) was associated with AD, and whether variants in the SLC6A3 locus were associated with specific personality traits in patients with AD. Sixteen polymorphisms in SLC6A3 were analyzed using 637 patients with AD and 523 healthy controls. To reduce clinical heterogeneity, patients were classified into two subgroups: early-onset AD (EOAD) and late-onset AD (LOAD). The Tridimensional Personality Questionnaire was used to assess the personality traits novelty seeking (NS) and harm avoidance (HA) in the patients with AD. Using allele frequency and genotype distribution comparisons and logistic regression analysis, we found evidence of association between rs6350 and AD (P < 0.05). Following subgroup analysis, we confirmed evidence of an association in patients with LOAD (P = 0.003), but not in patients with EOAD. Heterozygous carriers of the A allele have a nearly 3 times greater risk to develop LOAD compared to individuals who do not have an A allele. Although we found that patients with AD had higher NS and HA scores compared to controls (P < 0.001), we did not find evidence of association between SLC6A3 polymorphisms and either NS or HA in patients with AD using linear regression analysis. The findings from our study indicate that the SLC6A3 gene may have a role in susceptibility to late-onset AD in the Han Chinese population.

[Combination of DAT and DBH gene polymorphisms with a family history of alcohol use disorders increases the risk of withdrawal seizures and delirium tremens during alcohol withdrawal in alcohol-dependent men]

AIM

To explore the genetic influence of a family history of alcohol use disorders and the dopamine transporter SLC6A3 (DAT1) and dopamine beta-hydroxylase (DBH) gene polymorphisms on the risk of severe complications (withdrawal seizures (AWS) and delirium tremens (DT)) during alcohol withdrawal in alcohol-dependent men.

MATERIAL AND METHODS

We investigated the effects of 3 previously reported candidate genetic variations: 40-bp variable number tandem repeat (VNTR) polymorphism and C/T exon 15 (rs27072) in the 3' untranslated region (3' UTR) of the SLC6A3(DAT1) gene, and -1021 C/T (rs1611115) of DBH gene in 266 alcohol-dependent Russian male inpatients in two groups by presence (SC group: AWS, DT, AWS+DT, n=130) or absence (n=136) of severe complications diagnosed by ICD-10 during current alcohol withdrawal. Clinically important information and a family history of alcohol use disorders (FH) were obtained by semi-structured interview.

RESULTS

Patients in SC group more often have positive FH (54.6% vs. 33%, p=0.001) and their age at first alcohol use (FAU) was lower (16±3.53y.o vs. 17±1.66 y.o, p=0.001). Logistic regression revealed that FH predicts severe complications in total (р=0.001) and DT (р=0.003), FAU independently predicts severe complications in total (р=0.008), AWS (р=0.04), DT (р=0.032), AWS+DT (р=0.048) and every year of delay alcohol use decreases the risk by 18-30%. The gene polymorphisms interact with FAU to decrease the FAU influence on the risk of AWS (T variant of DAT (rs27072), р=0.04), (AWS+DT) and DT (T variant of DBH (rs1611115), р=0.023 and р=0.06). The T variant of DAT (rs27072) is associated with FAU (p=0.007) and increases the risk of (AWS+DT) (р=0.036), but decreases the risk of AWS (р=0.038) and of DT (р=0.021) too, but only in interaction with positive FH. The 9 repeat variant (9R) of DAT VNTR is associated with AWS (p=0.009), but the risk of AWS (р=0.004) and of SC in total (р=0.001) are elevated only in 9R carriers with positive FH. The 9R independently increases the risk of DT (р=0.048) and the effect become more robust in 9R carriers with high density of FH (р=0.014). The gene x gene interaction decreases the risk of DT (р=0.055). According to an analysis of total cohort of patients, the T variant of DBH (rs1611115) is associated with any kind of manifestation of delirium in alcohol-dependent men (p=0.039).

CONCLUSION

This study demonstrate the genetic influence of a family history of alcohol use disorders and DAT and DBH gene polymorphisms on the risk of withdrawal seizures and delirium tremens. The interaction of genetic variations with positive family history provides the most robust effect, the interaction of genetic variations with the age at first alcohol use may «protect» their carriers from negative influence of this «behavioral» risk factor. Replication in large cohorts of patients is necessary to verify these findings for subsequent use in prevention programs.

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.

Young people in drug treatment in Ireland: their views on substance use aetiology, trajectory, parents' role in substance use and coping skills

OBJECTIVES

The aim of the current study was to gain insight into the process of initiation and progression to problematic use among young people who reach clinically significant levels of substance use requiring treatment.

METHOD

Twenty young people, aged between 15 and 19 years from two different drug treatment centres in Ireland were interviewed regarding their views on their pathway into substance use, their progress to more problematic use, their perception of their parents' role, if any, in their trajectory and their typical coping style before treatment. Content analysis was conducted on the resulting narratives.

RESULTS

The use of substances to cope with life stressors emerged as a prominent theme at initial and problematic stages of use. Multiple maladaptive coping approaches were reported. Both direct and indirect influences from parents in their substance use problem were cited. However, some participants reported that parents had no causal role in their substance use trajectory, in particular regarding mothers.

CONCLUSIONS

The current findings suggest that substance misuse is a multi-determined problem and a number of intervention strategies are suggested to delay onset and related harms associated with adolescent substance use.

[Stabilization of remission in patients with opioid dependence with naltrexone implant: a pharmacogenetic approach]

AIM

To evaluate the effect of opioid receptor genes and dopamine system genes polymorphisms on treatment outcomes of opioid dependence with implantable and oral naltrexone.

MATERIAL AND METHODS

Authors carried out a randomized double-blind, double-dummy, placebo-controlled clinical trial. Three hundred and six patients with opioid dependence were randomized into 3 equal treatment groups. The first group received implantation of 1000 mg naltrexone every 2 months during 6 months + oral naltrexone placebo; the second group - placebo implant every 2 months + oral naltrexone (50mg/day) and the third group - placebo implant + oral naltrexone placebo. It was genotyped polymorphisms in the following genes: mu-opioid receptor (OPRM1), kappa-opioid receptor (OPRK1), catechol-O-methyltransferase (COMT), dopamine receptors types 2 (DRD2) and 4 (DRD4), dopamine-beta-hydroxylase, and dopamine transporter (DAT1).

RESULTS

Regardless of treatment several polymorphisms of these genes were associated with high risk of relapse: an allele L (2R) DRD4 120bp (p=0.05; OR (95% CI)=3.3(1.1-10.1)); an allele С DRD2 NcoI (р=0,051; OR (95% CI)=2,86 (1,09-7,52)); the genotype 9.9 DAT VNTR 40bp (р=0,04; OR (95% CI)=1,4 (1,3-1,5)); on the contrary, (СС+СТ)-(ТТ)) variants of OPRK1-DRD2Ncol increased a chance to complete treatment program (р=0,004; OR (95% CI)=7.4 (1.8-30.4)), Kaplan-Meier survival analysis (р=0,016). The probability of completing treatment program by the carriers of these variants was higher in the oral naltrexone group (p=0.016), lower in the double placebo group (p=0.015), but did not influence on treatment outcomes in the naltrexone-implant group.

CONCLUSION

Naltrexone-implant is a highly effective medication for treatment of opioid dependence and its effectiveness exceeds that of oral naltrexone and placebo. The study has shown the joint influence of opioid receptor genes and genes of dopaminergic system on treatment outcomes of opioid dependence. Genetic analysis is useful for determining potential responders to naltrexone treatment of opioid dependence.

Genetic influence of dopamine receptor, dopamine transporter, and nicotine metabolism on smoking cessation and nicotine dependence in a Japanese population

Background

This study investigated whether polymorphisms of the ankyrin repeat and kinase domain containing 1 gene (ANKK1), which is adjacent to the dopamine D2 receptor gene (DRD2), and the dopamine transporter (SLC6A3) and cytochrome P450 2A6 (CYP2A6) genes influence smoking cessation and nicotine dependence in a Japanese population. In 96 current and former smokers, genotyping frequencies for the ANKK1/DRD2 TaqIA, SLC6A3 VNTR, and CYP2A6 polymorphisms were subjected to chi-square analysis, and regression analyses were used to determine the association of the genotypes of current smokers with a Heavy Smoking Index, in addition to evaluating the effect of the subjects’ smoking history on the association.

Results

Genotyping results suggested that nicotine dependence among current smokers homozygous for the SLC6A3 10r allele was lower than that of smokers carrying the minor alleles, and that the CYP2A6 polymorphism might mediate this association. Furthermore, the age at which current smokers began smoking might moderate the association between their genetic polymorphisms and nicotine dependence.

Conclusions

This study provides preliminary findings on the influence of genetic variants on the smoking phenotypes in a Japanese population.

Epigenetic alteration of the dopamine transporter gene in alcohol-dependent patients is associated with age

Chronic alcohol abuse and dependence are associated with dysfunctional dopaminergic neurotransmission in mesocorticolimbic circuits. Genetic and environmental factors have been shown to modulate susceptibility to alcohol dependence, and both may act through epigenetic mechanisms that can modulate gene expression, e.g. DNA methylation at CpG sites. Recent studies have suggested that DNA methylation patterns may change over time. However, few data are available concerning the rate of these changes in specific genes. A recent study found that hypermethylation of the promoter of the dopamine transporter (DAT) gene was positively correlated with alcohol dependence and negatively correlated with alcohol craving. The aim of the present study was to replicate these findings in a larger sample of alcohol-dependent patients and population-based controls matched for age and sex. No difference in methylation level was observed between patients and controls, and no difference in methylation level was observed before and after alcohol withdrawal in patients. However, patients with more severe craving showed a trend towards lower DAT methylation levels (P = 0.07), which is consistent with previous findings. Furthermore, in our overall sample, DAT methylation levels increased with age. Interestingly, a separate analysis of patients suggested that this finding was mainly driven by the patient group. Although the present data do not clarify whether chronic alcohol abuse is responsible for this phenomenon or merely enhances an ageing-specific process, our findings suggest that hypermethylation in alcohol-dependent patients is a consequence, rather than a cause, of the disorder.

Environmental smoking and smoking onset in adolescence: the role of dopamine-related genes. Findings from two longitudinal studies

Although environmental smoking (i.e., paternal and maternal smoking, sibling smoking, and peer smoking) is one of the most important factors for explaining adolescent smoking behavior, not all adolescents are similarly affected. The extent to which individuals are vulnerable to smoking in their environment might depend on genetic factors. The aim of this study was to examine the interplay between environmental smoking and genes encoding components of the dopaminergic system (i.e., dopamine receptor D2, D4, and dopamine transporter DAT1) in adolescent smoking onset. Data from two longitudinal studies were used. Study 1 consisted of 991 non-smoking early adolescents (mean age = 12.52, SD = .57) whereas study 2 consisted of 365 non-smoking middle to late adolescents (mean age = 14.16, SD = 1.07) who were followed for 16 and 48 months, respectively. Logistic regression analyses were conducted using Mplus. In study 1, we found positive associations between parents' and friends' smoking at the first measurement and smoking status 16 months later. In study 2 we found a positive association between friends' smoking and smoking onset 48 months later. Neither study demonstrated any interaction effects of the DRD2, DRD4, or DAT1 genotypes. In conclusion, the effects of environmental smoking on smoking onset are similar for adolescent carriers and non-carriers of these specific genes related to the dopaminergic system.

Stress, substance abuse, and addiction

Experiencing stressful life events is reciprocally associated with substance use and abuse. The nature of these relationships varies based on the age of stress exposure and stage of substance use involvement. This chapter reviews the developmental and biological processes involved in the relationship of stress exposure and substance use initiation, substance use maintenance and relapse, and response to substance abuse treatment. Special emphasis is given to describing the various stress-related mechanisms involved in substance use and abuse, highlighting the differences between each of these phases of drug use and drawing upon current research to make suggestions for treatments of substance use disorder (SUD) patients. Stress is inherent to the experience of life and, in many situations, unavoidable. Through ongoing research and treatment development, there is the potential to modify the relationship of stress with ongoing substance use and abuse.

Smoking-specific parenting and smoking onset in adolescence: the role of genes from the dopaminergic system (DRD2, DRD4, DAT1 genotypes)

Although only few studies have shown direct links between dopaminergic system genes and smoking onset, this does not rule out the effect of a gene-environment interaction on smoking onset. Therefore, the aim of this study was to examine the associations between smoking-specific parenting (i.e., frequency and quality of communication and house rules) and smoking onset while considering the potential moderating role of dopaminergic system genes (i.e., DRD2, DRD4, and DAT1 genotypes). Data from five annual waves of the 'Family and Health' project were used. At time 1, the sample comprised 365 non-smoking adolescents (200 younger adolescents, mean age = 13.31, SD = .48; 165 older adolescents, mean age = 15.19, SD = .57). Advanced longitudinal analyses were used (i.e., logistic regression analyses, (dual) latent growth curves, and cross-lagged path models). The results showed a direct effect of quality of communication on smoking onset. No direct effects were found for frequency of communication and house rules. Furthermore, no direct and moderating effects of the DRD2, DRD4, or DAT1 genotypes were found. In conclusion, the findings indicated that the effects of smoking-specific parenting on smoking are similar for adolescent carriers and non-carriers of the dopaminergic system genes.

Review of risk and protective factors of substance use and problem use in emerging adulthood

This review examines the evidence for longitudinal predictors of substance use and abuse in emerging adulthood. Nationally representative data from the 2007 National Survey on Drug use and Health suggest that many substance use problems reach their peak prevalence during emerging adulthood (usually defined as the period from age 18 to age 26). This stage of development is characterized by rapid transitions into new social contexts that involve greater freedom and less social control than experienced during adolescence. Concurrent with this newfound independence is an increase in rates of substance use and abuse. Understanding the risk and protective factors associated with emerging adult substance use problems is an important step in developing interventions targeting those problems. While multiple reviews have examined risk and protective factors for substance use during adolescence, and many of these earlier predictors may predict emerging adult substance use, few studies have focused primarily on the emerging adult outcomes examining predictors from both adolescence and emerging adulthood. This review used the databases PubMed and PsycInfo to identify articles pertaining to longitudinal predictors of substance use problems in emerging adulthood, building from the conceptual framework presented in a review on risk and protective factors for adolescent substance abuse by Hawkins and colleagues (Hawkins, Catalano, & Miller, 1992). Predictors identified as predictors of substance use in adolescence, sometimes decreased in strength and in one case reversed direction. Unique predictors in emerging adulthood were also identified. Implications for prevention science during adolescence and emerging adulthood are discussed as well as suggestions for future research.

Role of novelty seeking personality traits as mediator of the association between COMT and onset age of drug use in Chinese heroin dependent patients

BACKGROUND

Personality traits such as novelty seeking (NS) are associated with substance dependence but the mechanism underlying this association remains uncertain. Previous studies have focused on the role of the dopamine pathway.

OBJECTIVE

Examine the relationships between allelic variants of the catechol-O-methyltransferase (COMT) gene, NS personality traits, and age of onset of drug use in heroin-dependent subjects in China.

METHODS

The 478 heroin dependent subjects from four drug rehabilitation centers in Shanghai who were genotyped for eight tagging single nucleotide polymorphisms (SNP) on the COMT gene completed the NS subscale from the Temperament and Character Inventory. Multivariate analyses were used to assess the potential mediating role of NS personality traits in the association between COMT gene variants and the age of onset of heroin use.

PRINCIPAL FINDINGS AND CONCLUSIONS

In the univariate analysis the COMT rs737866 gene variants were independently associated with both NS and age of onset of drug use: those with the TT genotype had higher NS subscale scores and an earlier onset age of heroin use than individuals with CT or CC genotypes. In the multivariate analysis the inclusion of the NS subscore variable weakened the relationship between the COMT rs737866 TT genotype and an earlier age of onset of drug use. Our findings that COMT is associated with both NS personality traits and with the age of onset of heroin use helps to clarify the complex relationship between genetic and psychological factors in the development of substance abuse.

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.

An integrated genome research network for studying the genetics of alcohol addiction

Alcohol drinking is highly prevalent in many cultures and contributes to the global burden of disease. In fact, it was shown that alcohol constitutes 3.2% of all worldwide deaths in the year 2006 and is linked to more than 60 diseases, including cancers, cardiovascular diseases, liver cirrhosis, neuropsychiatric disorders, injuries and foetal alcohol syndrome. Alcoholism, which has been proven to have a high genetic load, is one potentially fatal consequence of chronic heavy alcohol consumption, and may be regarded as one of the most prevalent neuropsychiatric diseases afflicting our society today. The aim of the integrated genome research network 'Genetics of Alcohol Addiction'--which is a German inter-/trans-disciplinary life science consortium consisting of molecular biologists, behavioural pharmacologists, system biologists with mathematicians, human geneticists and clinicians--is to better understand the genetics of alcohol addiction by identifying and validating candidate genes and molecular networks involved in the aetiology of this pathology. For comparison, addictive behaviour to other drugs of abuse (e.g. cocaine) is studied as well. Here, we present an overview of our research consortium, the current state of the art on genetic research in the alcohol field, and list finally several of our recently published research highlights. As a result of our scientific efforts, better insights into the molecular and physiological processes underlying addictive behaviour will be obtained, new targets and target networks in the addicted brain will be defined, and subsequently, novel and individualized treatment strategies for our patients will be delivered.

The Role of Genetics in Nicotine Dependence: Mapping the Pathways from Genome to Syndrome

Nicotine dependence continues to be a major public health problem worldwide and there is unequivocal evidence that genetics play a substantial role in its etiology. This review provides an overview of the evidence for genetic influences and recent advances in the field. Traditional quantitative genetics studies have revealed nicotine dependence is heritable and molecular genetics studies are providing increasing evidence that the genes responsible for nicotine's pharmacokinetics and pharmacodynamics are particularly important. Despite considerable progress, a number of significant complexities and challenges remain. These include determining the specificity of genetic influences and clarifying the role of interactive contributions. One promising strategy for addressing these issues is an intermediate phenotype approach that attempts to identify the intervening proximal mechanisms that confer differential genetic risk. Understanding these mechanisms may permit more precision in understanding genetic influences and may also identify novel targets for intervention or prevention.

Incorporating age at onset of smoking into genetic models for nicotine dependence: evidence for interaction with multiple genes

Nicotine dependence is moderately heritable, but identified genetic associations explain only modest portions of this heritability. We analyzed 3369 SNPs from 349 candidate genes and investigated whether incorporation of SNP-by-environment interaction into association analyses might bolster gene discovery efforts and prediction of nicotine dependence. Specifically, we incorporated the interaction between allele count and age at onset of regular smoking (AOS) into association analyses of nicotine dependence. Subjects were from the Collaborative Genetic Study of Nicotine Dependence and included 797 cases ascertained for Fagerström nicotine dependence and 811 non-nicotine-dependent smokers as controls, all of European descent. Compared with main effect models, SNP x AOS interaction models resulted in higher numbers of nominally significant tests, increased predictive utility at individual SNPs and higher predictive utility in a multi-locus model. Some SNPs previously documented in main effect analyses exhibited improved fits in the joint analysis, including rs16969968 from CHRNA5 and rs2314379 from MAP3K4. CHRNA5 exhibited larger effects in later-onset smokers, in contrast with a previous report that suggested the opposite interaction (Weiss et al. 2008). However, a number of SNPs that did not emerge in main effect analyses were among the strongest findings in the interaction analyses. These include SNPs located in GRIN2B (P = 1.5 x 10(-5)), which encodes a subunit of the N-methyl-D-aspartate receptor channel, a key molecule in mediating age-dependent synaptic plasticity. Incorporation of logically chosen interaction parameters, such as AOS, into genetic models of substance use disorders may increase the degree of explained phenotypic variation and constitutes a promising avenue for gene discovery.