Candidate genes for alcohol dependence: a review of genetic evidence from human studies

Gender-specific interactions between alcohol metabolism genes and severity of quantitative alcohol-related-traits in a Tibetan population

Association between genes influencing alcohol metabolism and alcohol use disorders (AUD) has been extensively studied, but the effect of interactions between these genes and AUD have rarely been tested. Our previous case-control study in a Tibetan population noted that the positive association between c2 allele of cytochrome P4502E1 (CYP2E1) gene and AUD might only exist in males who are homozygotes for 1 alleles of aldehyde dehydrogenase-2 (ALDH2) and alcohol dehydrogenase-1B (ADH1B) genes, but this interaction did not reach statistical significance. Using the same set of data, the present study was aimed at exploring interactions between these genes and quantitative alcohol-related-trait scores (QARTs), and whether these are influenced by gender. The sample included 383 AUD cases with the alcohol use disorders identification test (AUDIT) score ≥10 and 350 normal controls with the AUDIT score ≤5. QARTs were measured using three factors from AUDIT. Possible associations of QARTs with interactions among genotypes of ALDH2 1/ 2, ADH1B1/2 and CYP2E1 c1/c2 and sex were analyzed in AUD cases and normal controls separately. The subjects with 2 alleles of ALDH2 or/and ADH1B had significantly lower scores of alcohol intake among controls but had significantly higher scores of alcohol related problems among cases. The score of alcohol intake in male cases who are homozygous for ALDH2 1 and ADH1B 1 and with CYP2E1 c2 allele was significantly higher than that of other cases. These findings suggest that interactions between genes influencing alcohol metabolism are influenced by gender and might affect QARTs differently between the milder-/non-drinkers and AUD cases.

Drugs and addiction: an introduction to epigenetics

Addiction is a debilitating psychiatric disorder, with a complex aetiology involving the interaction of inherited predispositions and environmental factors. Emerging evidence suggests that epigenetic alterations to the genome, including DNA methylation and histone modifications, are important mechanisms underlying addiction and the neurobiological response to addictive substances. In this review, we introduce the reader to epigenetic mechanisms and describe a potential role for dynamic epigenetic changes in mediating addictive behaviours via long-lasting changes in gene expression. We summarize recent findings from both molecular and behavioural experiments elucidating the role of epigenetic changes in mediating the addictive potential of various drugs of abuse, including cocaine, amphetamine and alcohol. The implications of these findings for molecular studies of addiction and the future development of novel therapeutic interventions are also discussed.

Neural markers of genetic vulnerability to drug addiction

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

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.

Association study of the Ile349val polymorphism of the gene ADH1C and alcohol dependence

OBJECTIVE: The aim of this study was to investigate the polymorphism Ile349Val of the enzyme alcohol dehydrogenase ADH1C gene among individuals with alcohol dependence syndrome (ADS) attending Alcoholics Anonymous (AA) meetings. METHODS: A total of 120 subjects residing in Rio de Janeiro city participated in this study. Subjects were divided into two groups: a group consisting of 54 individuals from the ADS group and 66 individuals that declared not having any alcohol dependence (control group). DNA was extracted from mouth epithelial cells by phenol-chloroform method and further submitted to amplification by polymerase chain reaction (PCR). RESULTS: Our results did not show differences between the genotypes of control individuals and ADS subjects. Nevertheless, we found increased rates of alcoholism in families of ADS subjects as compared to controls. CONCLUSIONS: Our results did not show any genotype difference on the ADH1C gene when control and AA genotypes are compared.

A systematic evaluation and validation of subtypes of adolescent alcohol use motives: genetic and environmental contributions

BACKGROUND

Alcohol use motives are closely associated with specific profiles of alcohol use and reflect a subjectively derived decisional framework based on a motivational style of responding. Adult twin studies typically estimate the heritability of alcohol use motives to be between 7 and 42%, although relatively little is known about genetic and environmental influences upon alcohol use motives in adolescence.

METHODS

Latent class analysis (LCA) models containing 1 through 5 classes were fitted to the data derived from 1,422 adolescent twin and siblings self-reported alcohol use motives. Using twin models, we estimated the genetic, shared, and nonshared environmental influences to the class membership data derived from the LCA.

RESULTS

Four drinking motives classes were identified (family-oriented, social, enhancement/social, and coping/social). The coping/social and enhancement/social classes were differentiated from the social class on measures of depression, delinquency, and aggressive behavior. Analyses indicated that nonadditive genetic factors accounted for 76% of the variance in the coping/social motives class and additive genetic influences accounted for 66% of the variance in the social motives class. There was a moderate contribution of genetic factors and shared environmental factors influencing class membership of enhancement/social motivated drinkers (28 and 20% explained variance, respectively). Substantial shared environmental influences were revealed for membership of the family-oriented class (75%).

CONCLUSIONS

Heritable influences may predispose individuals to drink to cope with negative affect, for social reasons, and to a lesser extent for enhancement. Familial environmental influences shape family-oriented motives for drinking in adolescents.

Evaluating a cognitive model of ALDH2 and drinking behavior

BACKGROUND

Despite evidence for genetic influences on alcohol use and alcohol-related cognitions, genetic factors and endophenotypes are rarely incorporated in cognitive models of drinking behavior. This study evaluated a model of ALDH2 and drinking behavior stipulating cognitive factors and alcohol sensitivity as accounting for genetic influences on drinking outcomes.

METHODS

Participants were Asian-American young adults (n = 171) who completed measures of alcohol cognitions (drinking motives, drinking refusal self-efficacy, and alcohol expectancies), alcohol sensitivity, drinking behavior, and alcohol-related problems as part of a prospective study. Structural equation modeling (SEM) evaluated a model of drinking behavior that stipulated indirect effects of ALDH2 on drinking outcomes through cognitive variables and alcohol sensitivity.

RESULTS

The full model provided an adequate fit to the observed data, with the measurement model explaining 63% of the variance in baseline heavy drinking and 50% of the variance in alcohol-related problems at follow-up. Associations of ALDH2 with cognitive factors and alcohol sensitivity were significant, whereas the association of ALDH2 with drinking was not significant with these factors included in the model. Mediation tests indicated significant indirect effects of ALDH2 through drinking motives, drinking refusal self-efficacy, and alcohol sensitivity.

CONCLUSIONS

Results are consistent with the perspective that genetic influences on drinking behavior can be partly explained by learning mechanisms and implicate cognitive factors as important for characterizing associations of ALDH2 with drinking.

Network analysis of EtOH-related candidate genes

Recently, we collected many large-scale datasets for alcohol dependence and EtOH response in five organisms and deposited them in our EtOH-related gene resource database (ERGR, http://bioinfo.mc.vanderbilt.edu/ERGR/). Based on multidimensional evidence among these datasets, we prioritized 57 EtOH-related candidate genes. To explore their biological roles, and the molecular mechanisms of EtOH response and alcohol dependence, we examined the features of these genes by the Gene Ontology (GO) term-enrichment test and network/pathway analysis. Our analysis revealed that these candidate genes were highly enriched in alcohol dependence/alcoholism and highly expressed in brain or liver tissues. All the significantly enriched GO terms were related to neurotransmitter systems or EtOH metabolic processes. Using the Ingenuity Pathway Analysis system, we found that these genes were involved in networks of neurological disease, cardiovascular disease, inflammatory response, and small molecular metabolism. Many key genes in signaling pathways were in the central position of these networks. Furthermore, our protein-protein interaction (PPI) network analysis suggested some novel candidate genes which also had evidence in the ERGR database. This study demonstrated that our candidate gene selection is effective and our network/pathway analysis is useful for uncovering the molecular mechanisms of EtOH response and alcohol dependence. This approach can be applied to study the features of candidate genes of other complex traits/phenotypes.

Using a pharmacokinetic model to relate an individual's susceptibility to alcohol dependence to genotypes

BACKGROUND/AIMS

Population-based studies have successfully identified genes affecting common diseases, but have not provided a molecular mechanism. We describe an approach for alcohol dependence connecting a mechanistic model at the molecular level with disease risk at the population level, and investigate how this model implies statistical gene-gene interactions that affect disease risk.

METHODS

We develop a pharmacokinetic model describing how genetic variations in ADH1B, ADH1C, ADH7, ALDH2, and TAS2R38 affect consumption behavior, and alcohol and acetaldehyde levels over time in various tissues of individuals with a particular genotype to predict their susceptibility to alcohol dependence.

RESULTS

We show that there is good agreement between the observed genotype/haplotype frequencies and those predicted by the model among cases and controls. Based on this framework, we show that we expect to observe statistical interactions among these genes for a reasonably large sample size when logistic regression models are used to relate genotype effects and disease risk.

CONCLUSION

Our model exemplifies mechanistic modeling of how genes interact to influence an individual's susceptibility to alcohol dependence. We anticipate that this general approach could also be applied to study other diseases at the molecular level.

MAOA interacts with the ALDH2 gene in anxiety-depression alcohol dependence

BACKGROUND

Alcohol dependence is usually comorbid with anxiety disorder, depressive disorder, or both; this comorbidity may increase drinking behavior. We previously hypothesized that anxiety-depressive alcohol dependence (ANX/DEP ALC) was a genetically specific subtype of alcohol dependence. ANX/DEP ALC may be related to dopamine and serotonin, which are catalyzed by monoamine oxidase A (MAOA) and acetaldehyde dehydrogenase 2 (ALDH2). The aim of this study was to determine whether the interaction between the MAOA and the ALDH2 genes is associated with ANX/DEP ALC.

METHODS

We recruited 383 Han Chinese men in Taiwan: 143 ANX/DEP ALC and 240 healthy controls. The diagnosis of ANX/DEP ALC (alcohol dependence with a past or current history of anxiety, depressive disorder, or both) was made using DSM-IV criteria. Genotypes of ALDH2 and MAOA-uVNTR (variable number of tandem repeat located upstream) were determined using PCR-RFLP.

RESULTS

The ALDH2, but not the MAOA-uVNTR, polymorphism was associated with ANX/DEP ALC. After stratifying the MAOA-uVNTR polymorphism, we found a stronger association between the ALDH2*1/*2 and *2/*2 genotypes and the controls in the MAOA-uVNTR 4-repeat subgroup. Logistic regression significantly associated the interaction between ALDH2 and MAOA variants with ANX/DEP ALC.

CONCLUSION

We conclude that the MAOA and ALDH2 genes interact in ANX/DEP ALC. Although the MAOA gene alone is not associated with ANX/DEP ALC, we hypothesize that different variants of MAOA-uVNTR polymorphisms modify the protective effects of the ALDH2*2 allele on ANX/DEP ALC in Han Chinese in Taiwan.

OPRM1 SNP (A118G): involvement in disease development, treatment response, and animal models

Endogenous opioids acting at mu-opioid receptors mediate many biological functions. Pharmacological intervention at these receptors has greatly aided in the treatment of acute and chronic pain, in addition to other uses. However, the development of tolerance and dependence has made it difficult to adequately prescribe these therapeutics. A common single nucleotide polymorphism (SNP), A118G, in the mu-opioid receptor gene can affect opioid function and, consequently, has been suggested to contribute to individual variability in pain management and drug addiction. Investigation into the role of A118G in human disease and treatment response has generated a large number of association studies across various disease states as well as physiological responses. However, characterizing the functional consequences of this SNP and establishing if it causes or contributes to disease phenotypes have been significant challenges. In this manuscript, we will review a number of association studies as well as investigations of the functional impact of this gene variant. In addition, we will describe a novel mouse model that was generated to recapitulate this SNP in mice. Evaluation of models that incorporate known human genetic variants into a tractable system, like the mouse, will facilitate the understanding of discrete contributions of SNPs to human disease.

Interaction among genes influencing ethanol metabolism and sex is association with alcohol use disorders in a Tibet population

Associations between alcohol use disorders and polymorphisms of genes influencing ethanol metabolism have been widely reported, but gene-gene and gene-sex interaction studies have rarely been examined. Using a set of samples collected during an epidemiological study of alcohol use disorders AUDs in a Tibetan population in China, we performed a case-control study to investigate the relationship between the functional polymorphisms of genes influencing ethanol metabolism and AUDs. The sample included 383 individuals with an AUDIT score >or=10 and 350 control subjects with the AUDIT score <or=5. All participants were genotyped for ALDH2*1/*2, ADH1B*1/*2, and CYP2E1*c1/c2*. Data were analyzed employing an integrated strategy using MDR, SPSS, and UNPHASED software. The MDR analysis showed that the four-factor model including ADH1B*1/*2, ALDH2*1/*2, and CYP2E1*c1/*c2 polymorphisms, and sex was the most accurate model associated with AUDs with the highest OR 3.299. It also revealed that CYP2E1 *c1/*c2 polymorphism interacted significantly with sex. Independent analysis confirmed that both ADH2*2 and ALDH2*2 allele were significantly associated with AUDs (OR: 0.441 for ADH2*2 and 0.137 for ALDH2*2). CYP2E1*c2 was positively associated with AUDs only in males homozygotic for ALDH2*1 and ADH1B*1 (OR: 2.585). Cumulative association analysis showed the number of protective alleles and genotypes were negatively associated with AUDs. In conclusion, ALDH2*2 and ADH1B*2 alleles were not only independently associated with AUDs but also demonstrated cumulative dosage effects. However the positive association between CYP2E1*c2 allele and AUDs might only exist in males homozygotic for ALDH2*1 and ADH1B*1.

Dopamine D2 receptor polymorphisms and susceptibility to alcohol dependence in Indian males: a preliminary study

Background

Dopamine is an important neurotransmitter involved in reward mechanism in the brain and thereby influences development and relapse of alcohol dependence. The dopamine D2 receptor (DRD2) gene on chromosome 11 (q22-q23) has been found to be associated with increased alcohol consumption through mechanisms involving incentive salience attributions and craving in alcoholic patients. Therefore, we investigated the association of three single nucleotide polymorphisms (SNP) in DRD2 gene with alcohol dependence in the north Indian subjects.

Methods

In a retrospective analysis, genetic association of three polymorphisms from DRD2 gene with alcohol dependence was investigated using a case-control approach. Alcohol dependence was determined by DSM-IV criteria and a total of 90 alcoholics and 60 healthy unrelated age-matched control subjects were recruited. Odds ratio and confidence interval was calculated to determine risk conferred by a predisposing allele/genotype/haplotype. Logistic regression analysis was carried out to correlate various clinical parameters with genotypes, and to study pair-wise interactions between SNPs.

Results

The study showed a significant association of -141C Ins allele and a trend of association of TaqI A1 allele of DRD2 with alcohol dependence. Haplotype with the predisposing -141C Ins and TaqI A1 alleles (-141C Ins-A-A1) seems to confer ≈ 2.5 times more risk to develop alcohol dependence.

Conclusions

The study provides preliminary insight into genetic risk to alcohol dependence in Indian males. Two polymorphisms namely, -141C Ins/Del and TaqI A in DRD2 gene may have clinical implications among Indian alcoholic subjects.

A cognitive model for the intergenerational transference of alcohol use behavior

A family history of alcoholism has shown to be one of the greatest consistent risk factors in the intergenerational transference of alcohol problems. Whereas a large number of studies have attempted to identify the processes responsible for this interfamilial transfer, the mechanisms remain unclear. Family, twin and adoption studies, and environmental theories have resulted in a number of unanswered questions regarding the extent that these factors influence the transmission of alcohol behavior. Recently, cognitive theories have suggested that the observation of parental drinking habits contributes to the child's beliefs and expectations of alcohol's effects. A hypothesised cognitive model will be proposed suggesting that the mechanism for the transference of particular drinking styles from parent to offspring may be further explained by the transference of alcohol cognitions, in particular, alcohol expectancies and drinking refusal self-efficacy. This review focuses on research of bio/psycho/social factors that perpetuate alcohol misuse across generations, and will delineate the proposed cognitive mechanisms for the interfamilial transference of alcohol problems and discuss the implications of the proposed model.

Identifying quantitative trait loci (QTLs) and genes (QTGs) for alcohol-related phenotypes in mice

Alcoholism is a complex clinical disorder with genetic and environmental contributions. Although no animal model duplicates alcoholism, models for specific factors, such as the withdrawal syndrome, are useful to identify potential genetic determinants of liability in humans. Murine models have been invaluable to identify quantitative trait loci (QTLs) that influence a variety of alcohol responses. However, the QTL regions are typically large, at least initially, and contain numerous genes, making identification of the causal quantitative trait gene(s) (QTGs) challenging. Here, we present QTG identification strategies currently used in the field of alcohol genetics and discuss relevance to alcoholic human populations.

Preferential ethanol consumption in Drosophila models features of addiction

Alcohol addiction is a common affliction with a strong genetic component [1]. Although mammalian studies have provided significant insight into the molecular mechanisms underlying ethanol consumption [2], other organisms such as Drosophila melanogaster are better suited for unbiased, forward genetic approaches to identify novel genes. Behavioral responses to ethanol, such as hyperactivity, sedation, and tolerance, are conserved between flies and mammals [3, 4], as are the underlying molecular pathways [5-9]. However, few studies have investigated ethanol self-administration in flies [10]. Here we characterize ethanol consumption and preference in Drosophila. Flies prefer to consume ethanol-containing food over regular food, and this preference increases over time. Flies are attracted to the smell of ethanol, which partially mediates ethanol preference, but are averse to its taste. Preference for consuming ethanol is not entirely explained by attraction to either its sensory or caloric properties. We demonstrate that flies can exhibit features of alcohol addiction. First, flies self-administer ethanol to pharmacologically relevant concentrations. Second, flies will overcome an aversive stimulus in order to consume ethanol. Third, flies rapidly return to high levels of ethanol consumption after a period of imposed abstinence. Thus, ethanol preference in Drosophila provides a new model for studying aspects of addiction.

Alcoholism and dampened temporal limbic activation to emotional faces

BACKGROUND

Excessive chronic drinking is accompanied by a broad spectrum of emotional changes ranging from apathy and emotional flatness to deficits in comprehending emotional information, but their neural bases are poorly understood.

METHODS

Emotional abnormalities associated with alcoholism were examined with functional magnetic resonance imaging in abstinent long-term alcoholic men in comparison to healthy demographically matched controls. Participants were presented with emotionally valenced words and photographs of faces during deep (semantic) and shallow (perceptual) encoding tasks followed by recognition.

RESULTS

Overall, faces evoked stronger activation than words, with the expected material-specific laterality (left hemisphere for words, and right for faces) and depth of processing effects. However, whereas control participants showed stronger activation in the amygdala and hippocampus when viewing faces with emotional (relative to neutral) expressions, the alcoholics responded in an undifferentiated manner to all facial expressions. In the alcoholic participants, amygdala activity was inversely correlated with an increase in lateral prefrontal activity as a function of their behavioral deficits. Prefrontal modulation of emotional function as a compensation for the blunted amygdala activity during a socially relevant face appraisal task is in agreement with a distributed network engagement during emotional face processing.

CONCLUSIONS

Deficient activation of amygdala and hippocampus may underlie impaired processing of emotional faces associated with long-term alcoholism and may be a part of the wide array of behavioral problems including disinhibition, concurring with previously documented interpersonal difficulties in this population. Furthermore, the results suggest that alcoholics may rely on prefrontal rather than temporal limbic areas in order to compensate for reduced limbic responsivity and to maintain behavioral adequacy when faced with emotionally or socially challenging situations.

Associations of cohort and socio-demographic correlates with transitions from alcohol use to disorders and remission in metropolitan China

AIMS

To examine socio-demographic associations of transitions from alcohol use to disorders and of remission from disorders in metropolitan China.

DESIGN AND SETTING

Face-to-face interviewing by trained lay-interviewers on a multi-staged, clustered sample from the general population of Beijing and Shanghai, China.

PARTICIPANTS

A total of 5201 adults aged 18-70 years and with household registration.

MEASUREMENTS

World Mental Health version of Composite International Diagnostic Interview.

FINDINGS

Lifetime prevalence estimates for alcohol use, regular use (at least 12 drinks in a year), DSM-IV abuse and dependence with abuse were 65.4%, 39.5% (60.4% of ever-drinkers), 4.6% (11.6% of regular users) and 0.9% (20.4% of lifetime alcohol abusers), respectively. These estimates were higher among respondents from the recent cohort; 64.3% and 36.9% respondents with a history of lifetime abuse and dependence respectively had remitted. The number of socio-demographic associations for the onset of each transitional stage decreased from alcohol use to alcohol dependence. Onset of ever-use was more common in respondents who were male, 18-50 years of age, with middle education level and never married, but less common among the previously married and students. First onset of regular use among those with ever-use was more common in respondents who were male, less than 50 years of age and never married, but less common in students. Being male and less than 50 years of age was associated with more alcohol abusers among regular users.

CONCLUSION

This study was the first to reveal in a Chinese population that qualitatively different risk factors might operate during the different stages of progression from alcohol use to disorders. Further research is needed to clarify the mechanisms underlying these differences in order to guide prevention programmes.

Genome-wide association study of alcohol dependence

CONTEXT

Alcohol dependence is a serious and common public health problem. It is well established that genetic factors play a major role in the development of this disorder. Identification of genes that contribute to alcohol dependence will improve our understanding of the mechanisms that underlie this disorder.

OBJECTIVE

To identify susceptibility genes for alcohol dependence through a genome-wide association study (GWAS) and a follow-up study in a population of German male inpatients with an early age at onset.

DESIGN

The GWAS tested 524,396 single-nucleotide polymorphisms (SNPs). All SNPs with P < 10(-4) were subjected to the follow-up study. In addition, nominally significant SNPs from genes that had also shown expression changes in rat brains after long-term alcohol consumption were selected for the follow-up step.

SETTING

Five university hospitals in southern and central Germany.

PARTICIPANTS

The GWAS included 487 male inpatients with alcohol dependence as defined by the DSM-IV and an age at onset younger than 28 years and 1358 population-based control individuals. The follow-up study included 1024 male inpatients and 996 age-matched male controls. All the participants were of German descent.

MAIN OUTCOME MEASURES

Significant association findings in the GWAS and follow-up study with the same alleles.

RESULTS

The GWAS produced 121 SNPs with nominal P < 10(-4). These, together with 19 additional SNPs from homologues of rat genes showing differential expression, were genotyped in the follow-up sample. Fifteen SNPs showed significant association with the same allele as in the GWAS. In the combined analysis, 2 closely linked intergenic SNPs met genome-wide significance (rs7590720, P = 9.72 x 10(-9); rs1344694, P = 1.69 x 10(-8)). They are located on chromosome region 2q35, which has been implicated in linkage studies for alcohol phenotypes. Nine SNPs were located in genes, including the CDH13 and ADH1C genes, that have been reported to be associated with alcohol dependence.

CONCLUSIONS

This is the first GWAS and follow-up study to identify a genome-wide significant association in alcohol dependence. Further independent studies are required to confirm these findings.

The relationship between serotonin receptor 1B polymorphisms A-161T and alcohol dependence

BACKGROUND

Several studies have suggested that the serotonin receptor 1B gene (5HT1B) may be important in the pathogenesis of alcohol dependence (alcoholism; ALC; AD). We examined whether 5HT1B gene A-161T polymorphisms (rs130058) are a susceptibility factor for total AD and subgroups of AD. We further explored correlation of this 5HT1B gene variant between anxiety-depression alcoholism (ANX/DEP ALC) and antisocial alcoholism (antisocial ALC) subgroups because of the high comorbidity of anxiety-depression, antisocial personality disorder, and AD.

METHODS

We recruited 522 Han Chinese in Taiwan for this study: 322 AD patients and 200 controls. The patient group was recruited primarily from medical teaching hospitals; patients with antisocial alcoholism were recruited from Taiwanese prisons. Individuals with AD were classified into 3 homogeneous clinical subgroups -- pure alcoholism (pure ALC), ANX/DEP ALC, and antisocial ALC -- using DSM-IV diagnosis. The 5HT1B gene A-161T polymorphism was determined using PCR-RFLP.

RESULTS

No significant differences in genotypic and allelic frequencies were found between controls and the total AD group or between controls and the 3 AD subgroups. However, there were significant differences in the 5HT1B gene A-161T polymorphism at both the genotype and allelic levels between the ANX/DEP ALC and antisocial ALC subgroups.

CONCLUSIONS

This study suggests that the 5HT1B gene A-161T polymorphism alone is not a risk factor for increasing susceptibility to either AD or its subtypes. However, 5HT1B gene A-161T polymorphisms might be one of the common genetic factors between the ANX/DEP ALC and antisocial ALC subgroups.

TPH2 gene variants and anxiety during alcohol detoxification outcome

Clinical outcome of alcoholism may be partly under genetic control. The serotonergic system is involved in alcohol intake, and it has been widely investigated in alcohol dependence. Recently, attention has been focused on the neuronal tryptophan hydroxylase 2 gene (TPH2). TPH2 variants have been consistently associated with anxiety-related traits; since anxiety is critical for alcohol dependence treatment, in the present paper we investigated 9 SNPs within the THP2 gene in anxiety symptoms during the detoxification procedure. The sample comprised 68 alcohol-dependent patients who where evaluated with the Hamilton Rating Scale for Anxiety, before and after the detoxification procedure. Other psychopathological indicators of outcome, such as depression and anxiety sub-features were also investigated. We did not observe a role for TPH2 variants in the efficacy of treatment in relieving anxiety and other psychopathological symptoms. However, a haplotype that included the promoter rs4570625 polymorphism (associated with anxiety-related traits in previous studies) showed an association with the severity of anxiety symptoms on admission. This preliminary finding, although obtained on a small sample, may provide further support for a role of the TPH2 gene in emotional behaviors. Furthermore, the present study suggests the possible functional significance of the promoter rs4570625 polymorphism. The present preliminary results are of interest in alcoholism, given that comorbidity with anxiety represents a critical problem in treatment settings and response to detoxification.

Altering the relative abundance of GABA A receptor subunits changes GABA- and ethanol-responses in Xenopus oocytes

BACKGROUND

Variations in GABRA2 and GABRG3, genes encoding the alpha2 and gamma3 subunits of the pentameric GABA(A) receptor, are associated with the risk of developing alcoholism in adults, conduct disorder at younger ages, and with differences in electroencephalographic power in the beta frequency range. The SNPs associated with alcoholism did not alter the coding of these genes, and extensive DNA sequencing of GABRA2 did not find coding changes in the high-risk haplotypes. Therefore, we hypothesize that the associations arise from differences in gene expression.

METHODS

Here we report studies in Xenopus oocytes to examine the functional effects of altering the relative abundance of these 2 receptor subunits on GABA current and response to ethanol, as a model of potential effects of regulatory differences.

RESULTS

When human alpha2beta2gamma3 subunits are co-expressed, increasing the amount of the alpha2 subunit mRNA increased GABA current; in contrast, increasing the amount of the gamma3 subunit decreased GABA currents. Acute ethanol treatment of oocytes injected with a 1:1:1 or 2:2:1 ratio of alpha2:beta2:gamma3 subunit mRNAs resulted in significant potentiation of GABA currents, whereas ethanol inhibited GABA currents in cells injected with a 6:2:1 ratio. Overnight treatment with ethanol significantly reduced GABA currents in a manner dependent on the ratio of subunits.

CONCLUSIONS

These studies demonstrate that changes in relative expression of GABA(A) receptor subunits alter the response of the resulting channels to GABA and to ethanol.

Associations of ALDH2 and ADH1B genotypes with alcohol-related phenotypes in Asian young adults

BACKGROUND

Associations of ALDH2 and ADH1B genotypes with alcohol use have been evaluated largely using case-control studies, which typically focus on adult samples and dichotomous diagnostic outcomes. Relatively fewer studies have evaluated ALDH2 and ADH1B in relation to continuous drinking outcomes or at different developmental stages. This study examined additive and interactive effects of ALDH2 and ADH1B genotypes on drinking behavior in a mixed-gender sample of Asian young adults, focusing on continuous phenotypes (e.g., heavy episodic and hazardous drinking, alcohol sensitivity, drinking consequences) whose expression is expected to precede the onset of alcohol use disorders.

METHODS

The sample included 182 Chinese- and Korean-American young adults ages 18 years and older (mean age = 20 years). Effects of ALDH2, ADH1B and ethnicity were estimated using generalized linear modeling.

RESULTS

The ALDH2*2 allele predicted lower reported rates of alcohol use and drinking consequences as well as greater reported sensitivity to alcohol. There were significant ethnic group differences in drinking outcomes, such that Korean ethnicity predicted higher drinking rates and lower alcohol sensitivity. ADH1B status was not significantly related to drinking outcomes.

CONCLUSIONS

Ethnicity and ALDH2 status, but not ADH1B status, consistently explained significant variance in alcohol consumption in this relatively young sample. Results extend previous work by showing an association of ALDH2 genotype with drinking consequences. Findings are discussed in the context of possible developmental and population differences in the influence of ALDH2 and ADH1B variations on alcohol-related phenotypes.

Gene-Environment Interactions: Peers' Alcohol Use Moderates Genetic Contribution to Adolescent Drinking Behavior

Social context is increasingly recognized as essential for understanding complex human outcomes even among geneticists who focus on genetic influences. These outcomes typically involve multiple genes, multiple environmental factors, and the interactions between the two. In this paper, we propose a conceptual framework for gene-environment interaction and show how the interaction can be tested empirically using a sample of MZ twin, DZ twins, and full siblings. We test the hypothesis that the genetic contribution to adolescent drinking depends on the drinking behavior of their friends, using a sample of clusters of siblings and their friends from Add Health. Our analysis has yielded evidence supporting the gene-environment interaction hypothesis. High levels of alcohol use by one's best friend or among one's friends tend to bring about higher levels of genetic contribution to alcohol use. Lower levels of alcohol use by one's best friend or among one's friends tend to suppress the level of genetic contribution to alcohol use. Our findings suggest that friend behavior might be a particularly important environmental moderator of the expression of genetic disposition for adolescent drug use, smoking, dietary habits, and risky sexual behavior. Subsequent studies of these behaviors that use non-DNA twin samples or DNA measures of genetic variants should investigate peer influence as a significant environmental moderator.

A serotonin transporter gene polymorphism (5-HTTLPR), drinking-to-cope motivation, and negative life events among college students

OBJECTIVE

This study was performed to examine whether a polymorphism (5-HTTLPR) in the serotonin transporter gene was related to college students' reports of relief drinking (drinking-to-cope motives) and whether it moderated the associations between negative life events and drinking to cope. We examined reward drinking (drinking-to-enhance motives) as a comparison and to see whether these effects varied across gender.

METHOD

Using an Internet-based survey, college students (N = 360; 192 women) self-reported on drinking motives and negative life events for up to 4 years. Study participants provided saliva for genotyping the triallelic (LA vs LG or S) variants of 5-HTTLPR.

RESULTS

Among men, individuals with two risk alleles (LG or S), compared with individuals with the LA/LA allele, displayed lower drinking-to-cope motives. Among women, individuals with one risk allele (either LG or S), compared with individuals with the LA/LA allele, displayed stronger drinking-to-enhance motives. The association between yearly changes in negative life events and drinking-to-cope motives varied across 5-HTTLPR genotype and gender and was strongest in the positive direction for women with the LA/LA variant.

CONCLUSIONS

Our findings are not consistent with prior speculation that stronger positive associations between life stress and alcohol use among individuals with the LG or S allele are the result of increased use of alcohol as a method for coping with stress. The importance of examining gender differences in the relations between 5-HTTLPR, substance use, and related constructs is also noted.

Molecular analyses and identification of promising candidate genes for loci on mouse chromosome 1 affecting alcohol physical dependence and associated withdrawal

We recently mapped quantitative trait loci (QTLs) with large effects on predisposition to physical dependence and associated withdrawal severity following chronic and acute alcohol exposure (Alcdp1/Alcw1) to a 1.1-Mb interval of mouse chromosome 1 syntenic with human chromosome 1q23.2-23.3. Here, we provide a detailed analysis of the genes within this interval and show that it contains 40 coding genes, 17 of which show validated genotype-dependent transcript expression and/or non-synonymous coding sequence variation that may underlie the influence of Alcdp1/Alcw1 on ethanol dependence and associated withdrawal. These high priority candidates are involved in diverse cellular functions including intracellular trafficking, oxidative homeostasis, mitochondrial respiration, and extracellular matrix dynamics, and indicate both established and novel aspects of the neurobiological response to ethanol. This work represents a substantial advancement toward identification of the gene(s) that underlies the phenotypic effects of Alcdp1/Alcw1. Additionally, a multitude of QTLs for a variety of complex traits, including diverse behavioral responses to ethanol, have been mapped in the vicinity of Alcdp1/Alcw1, and as many as four QTLs on human chromosome 1q have been implicated in human mapping studies for alcoholism and associated endophenotypes. Thus, our results will be primary to further efforts to identify genes involved in a wide variety of behavioral responses to alcohol and may directly facilitate progress in human alcoholism genetics.

Review. Genetics of addictions: strategies for addressing heterogeneity and polygenicity of substance use disorders

Addictions are common psychiatric disorders that exert high cost to the individual and to society. Addictions are a result of the interplay of multiple genetic and environmental factors. They are characterized by phenotypic and genetic heterogeneity as well as polygenicity, implying a contribution of different neurobiological mechanisms to the clinical diagnosis. Therefore, treatments for most substance use disorders are often only partially effective, with a substantial proportion of patients failing to respond. To address heterogeneity and polygenicity, strategies have been developed to identify more homogeneous subgroups of patients and to characterize genes contributing to their phenotype. These include genetic linkage and association studies as well as functional genetic analysis using endophenotypes and animal behavioural experimentation. Applying these strategies in a translational context aims at improving therapeutic response by the identification of subgroups of addiction patients for individualized, targeted treatment strategies. This article aims to discuss strategies addressing heterogeneity and polygenicity of substance use disorders by presenting results of recent research on genetic and environmental components of addiction. It will also introduce the European IMAGEN study that aims to integrate methodical approaches discussed in order to identify the genetic and neurobiological basis of behavioural traits relevant to the development of addictions.

ERGR: An ethanol-related gene resource

Over the last decade rapid progress has been made in the study of ethanol-related traits including alcohol abuse and dependence, and behavioral responses to ethanol in both humans and animal models. To collect, curate, integrate these results so as to make them easily accessible and interpretable for researchers, we developed ERGR, a comprehensive ethanol-related gene resource. We collected and curated more than 30 large-scale data sets including linkage, association and microarray gene expression from the literature and 21 mouse QTLs from public databases. At present, the ERGR deposits ethanol-related information of ∼7000 genes from five organisms: human (3311), mouse (2129), rat (679), fly (614) and worm (228). ERGR provides gene annotations and orthologs, detailed gene study information (e.g. fold changes of gene expression, P-values), and both the text and BLAST searches. Moreover, ERGR has data integration tools such as for data union and intersection, and candidate gene selection based on evidence in multiple datasets or organisms. The ERGR database is evolving with new data releases. More functions will also be added. ERGR has a user-friendly web interface with browse and search functions at multiple levels. It is freely available at http://bioinfo.vipbg.vcu.edu/ERGR/.

Comparisons of structural and functional abnormalities in mouse b-wave mutants

In the most simplistic view, the retinal circuit can be divided into vertical excitatory pathways that use glutamate as their neurotransmitter and lateral inhibitory pathways in the outer and inner synaptic layers that modulate excitation via glycine and GABA. Within the vertical excitatory pathways, the visual signal is initiated in the rod, cone or both photoreceptors, depending on the adaptation state of the retina. This signal is transmitted to the rest of the retina through the bipolar cells, which can be subdivided based on: the photoreceptor that provides their input, their dendritic and axonal morphology, and the polarity of their response evoked by a luminance increment, e.g. depolarizing or hyperpolarizing responses. The polarity of this response is controlled by the type of glutamatergic postsynaptic receptor that is expressed on their dendritic terminals. Hyperpolarizing bipolar cells express AMPA/kainate receptors, whereas depolarizing bipolar cells (DBCs) express the metabotropic glutamate receptor 6 (Grm6). The electroretinogram (ERG) is a non-invasive method used to assess overall retinal function. The initiation of the visual signal in the photoreceptors is reflected in the ERG a-wave and the ensuing depolarization of DBCs in the b-wave. When there is failure of signal transmission from photoreceptors to DBCs or signalling within DBCs, the ERG a-wave is present, while the b-wave is absent or significantly reduced. This ERG phenotype has been found in the human population and is referred to as congenital stationary night blindness. Until recently, it had been assumed that the absence of a b-wave was indicative of a lack of signalling through the On pathway, leaving the Off pathway unaffected. Here we review recent findings that demonstrate that many mouse mutants share a no b-wave ERG phenotype but their retinal morphology and RGC responses differ significantly, suggesting very different effects of the underlying mutations on output from the DBCs to the rest of the retinal circuit.

Addiction science and its genetics

AIM

To assess the progress and impact of genetic studies in the addictions arena and to present this information in a form accessible to the general readership of Addiction.

METHODS

Review of the evidence that genes are involved in addiction, approaches to their identification, current findings and the potential implications.

RESULTS

Family, twin and adoption studies provide strong evidence that addiction runs in families and that this is determined in part by genetic factors. Two main molecular genetic approaches, namely linkage and association, have been adopted to identify the specific genes involved. Both methods are fraught with problems. Linkage is limited by issues of sensitivity, and association by false positives. Perhaps the strongest finding in psychiatric genetics to date is the impressive effect that a single genetic variant, in the aldehyde dehydrogenase 2 gene, has on drinking behaviour and reducing the risk of developing alcohol dependence. Other findings are currently less robust; however, the implications of elucidating the genetic underpinning of addiction will be profound.

CONCLUSIONS

Addiction genetics is a developing science that has yet to prove its worth in the clinical setting.

Association between the nociceptin receptor gene (OPRL1) single nucleotide polymorphisms and alcohol dependence

OPRL1 encodes the nociceptin receptor, which has been shown to be involved in alcohol dependence in previous studies. In the present study, we investigated the association between genetic polymorphisms of OPRL1 and alcohol dependence in a Scandinavian population. We genotyped 15 single nucleotide polymorphisms (SNPs) spanning the OPRL1 locus and found that SNP rs6010718 was significantly associated with both Type I and Type II alcoholics (P < 0.05). Linkage disequilibrium and haplotype analysis identified two haplotype blocks in this region. Furthermore, two haplotypes composed of five tag SNPs showed significant association with alcohol dependence. These findings suggest that genetic variants of the OPRL1 gene play a role in alcohol dependence in the Scandinavian population, warranting further investigation at the OPRL1 locus.

Approach to the genetics of alcoholism: A review based on pathophysiology

Alcohol dependence is a common disorder with a heterogenous etiology. The results of family, twin and adoption studies on alcoholism are reviewed. These studies have revealed a heritability of alcoholism of over 50%. After evaluating the results, it was epidemiologically stated that alcoholism is heterogenous complex disorder with a multiple genetic background. Modern molecular genetic techniques allow examining specific genes involved in the pathophysiology of complex diseases such as alcoholism. Strategies for gene identification are introduced to the reader, including family-based and association studies. The susceptibility genes that are in the focus of this article have been chosen because they are known to encode for underlying mechanisms that are linked to the pathophysiology of alcoholism or that are important for the pharmacotherapeutic approaches in the treatment of alcohol dependence. Postulated candidate genes of the metabolism of alcohol and of the involved neurotransmitter systems are introduced. Genetic studies on alcoholism examining the metabolism of alcohol and the dopaminergic, GABAergic, glutamatergic, opioid, cholinergic and serotonergic neurotransmitter systems as well as the neuropeptide Y are presented. The results are critically discussed followed by a discussion of possible consequences.

Under the influence of genetics: how transdisciplinarity leads us to rethink social pathways to illness

This article describes both sociological and genetic theories of illness causation and derives propositions expected under each and under a transdisciplinary theoretical frame. The authors draw propositions from three theories -- fundamental causes, social stress processes, and social safety net theories -- and tailor hypotheses to the case of alcohol dependence. Analyses of a later wave of the Collaborative Study on the Genetics of Alcoholism reveal a complex interplay of the GABRA2 gene with social structural factors to produce cases meeting DSM/ICD diagnoses. Only modest evidence suggests that genetic influence works through social conditions and experiences. Further, women are largely unaffected in their risk for alcohol dependence by allele status at this candidate gene; family support attenuates genetic influence; and childhood deprivation exacerbates genetic predispositions. These findings highlight the essential intradisciplinary tension in the role of proximal and distal influences in social processes and point to the promise of focusing directly on dynamic, networked sequences that produce different pathways to health and illness.

Alcohol: effects on neurobehavioral functions and the brain

Alcoholism results from an interplay between genetic and environmental factors, and is linked to brain defects and associated cognitive, emotional, and behavioral impairments. A confluence of findings from neuroimaging, physiological, neuropathological, and neuropsychological studies of alcoholics indicate that the frontal lobes, limbic system, and cerebellum are particularly vulnerable to damage and dysfunction. An integrative approach employing a variety of neuroscientific technologies is essential for recognizing the interconnectivity of the different functional systems affected by alcoholism. In that way, relevant experimental techniques can be applied to assist in determining the degree to which abstinence and treatment contribute to the reversal of atrophy and dysfunction.

SNP- and haplotype analysis of the tryptophan hydroxylase 2 gene in alcohol-dependent patients and alcohol-related suicide

Several lines of evidence indicate that disturbances of the central serotonergic system are involved in the pathophysiology of alcohol dependence and suicidal behavior. Recent studies have indicated that a newly identified second isoform of the tryptophan hydroxylase gene (TPH2) is preferentially involved in the rate limiting synthesis of neuronal serotonin. Genetic variations in the TPH2 gene have been associated with an increased risk for major depression and suicidal behavior. We performed single SNP (single nucleotide polymorphism), linkage disequilibrium and haplotype studies on 353 alcohol-dependent patients of whom 102 individuals had a history of at least one suicide attempt and 305 healthy controls with 20 SNPs covering the entire gene region of TPH2. Neither single SNP-, nor haplotype analysis could detect significant associations with alcohol dependence and/or suicidal behavior among alcohol-dependent patients. One major haplotype block of strong linkage disequilibrium between introns 5 and 8 of the TPH2 gene has been found in alcoholics and controls, which is in concordance with recent reports. In conclusion, our results suggest that single SNPs, respectively, haplotypes of the TPH2 gene are unlikely to play a major role in the pathophysiology of alcohol dependence or the alcoholism-related phenotype suicidal behavior. Further analysis are needed to confirm these results.

Gene-lifecourse interaction for alcohol consumption in adolescence and young adulthood: five monoamine genes

Association analysis has suggested that common sequence variants of genes that affect monoamine function can affect substance use and abuse. Demonstration of these associations has been inconsistent because of limited sample sizes and phenotype definition. Drawing on the life course perspective, we predicted a stronger association between the polymorphisms in 5HTT, DAT1, DRD4, DRD2, and MAOA and alcohol consumption in young adulthood than adolescence. This analysis tested for the gene-lifecourse interaction for the frequency of alcohol consumption in a nationally representative non-alcohol-dependent sample of 2,466 individuals that were visited during adolescence and young adulthood for four times between 1994 and 2002. All five genes are significantly associated with the frequency of alcohol consumption, with the genotype effects ranging 7%-20% of the mean score of alcohol consumption and their P values being 0.014, 0.0003, 0.003, 0.007, 0.005, and 0.003, respectively. The association is only observed in the life stage of young adulthood and not in adolescence. This analysis has demonstrated the potential usefulness of the life course perspective in genetic studies of human behaviors such as alcohol consumption.

Genetic variation in catechol-O-methyltransferase (COMT) and obesity in the prostate, lung, colorectal, and ovarian (PLCO) cancer screening trial

Catechol-O-methyltransferase (COMT) is an important modulator in the catabolism of extraneural dopamine, which plays an important role in drug reward mechanisms. It is hypothesized that genetic variations in the COMT gene, which can result in a three to fourfold difference in COMT enzyme activity, may be associated with several reward-motivated behaviors. The aim of our study was to examine the relationship between COMT polymorphisms with smoking, obesity and alcohol. Three single nucleotide polymorphisms (SNPs) in COMT were genotyped in 2,371 participants selected randomly from the screening arm of the PLCO Cancer Screening Trial after stratifying by sex, age, and smoking status. Smoking, obesity, and alcohol consumption were assessed by questionnaire. SNP and haplotype associations were estimated using odds ratios (ORs) and 95% confidence intervals (CIs) derived from conditional logistic regression models, adjusted for race/ethnicity. The COMT Ex4-76C > G (Leu136Leu) polymorphism was statistically significantly associated with individuals who had >30% increases in BMI from ages 20 to 50 years, compared to those with 0-5% increase in BMI (0-5%) over the same age period: (CC is referent; OR(CG )= 1.42, OR(GG )= 1.46, P (trend )= 0.06). By sex, the increased risk was further pronounced among females (OR(CG )= 1.50, OR(GG )= 2.10, P (trend )= 0.03). Consistent with our analyses of single polymorphisms, individuals whose BMI increased >30% from ages 20 to 50 years were more likely than individuals with 0-5% increases in BMI to possess COMT haplotypes [COMT Ex3-104C > T-COMT Ex4-76 C > G-COMT Ex4-12 A > G] that included the variant allele for COMT Ex4-76 C > G: C-G-G (T-C-A is referent: OR(C-G-G )= 1.33, 95% CI 1.01-1.77) and C-G-A (OR(C-G-A )= 1.79, 95% CI 0.72-4.49). We observed no association between any of the COMT polymorphisms with smoking behavior or alcohol intake. The COMT Ex4-76C > G (Leu136Leu) polymorphism appears to play a role in large increases in BMI. The null association with smoking and alcohol and the pronounced association with increasing BMI among women further implicates COMT's role in estrogen metabolism as a potentially culpable pathway. Our results support a need for comprehensive evaluation of COMT variations and their functional relevance as COMT may be an important molecular target to evaluate for new treatments regarding obesity.

Ethanol-induced effects on opioid peptides in adult male Wistar rats are dependent on early environmental factors

The vulnerability to develop alcoholism is dependent on both genetic and environmental factors. The neurobiological mechanisms underlying these factors are not fully understood but individual divergence in the endogenous opioid peptide system may contribute. We have previously reported that early-life experiences can affect endogenous opioids and also adult voluntary ethanol intake. In the present study, this line of research was continued and the effects of long-term voluntary ethanol drinking on the opioid system are described in animals reared in different environmental settings. Rat pups were subjected to 15 min (MS15) or 360 min (MS360) of daily maternal separation during postnatal days 1-21. At 10 weeks of age, male rats were exposed to voluntary ethanol drinking in a four-bottle paradigm with 5%, 10% and 20% ethanol solution in addition to water for 2 months. Age-matched controls received water during the same period. Immunoreactive (ir) Met-enkephalin-Arg6Phe7 (MEAP) and dynorphin B (DYNB) peptide levels were thereafter measured in the pituitary gland and several brain areas. In water-drinking animals, lower ir MEAP levels were observed in the MS360 rats in the hypothalamus, medial prefrontal cortex, striatum and the periaqueductal gray, whereas no differences were seen in ir DYNB levels. Long-term ethanol drinking induced lower ir MEAP levels in MS15 rats in the medial prefrontal cortex and the periaqueductal gray, whereas higher levels were detected in MS360 rats in the hypothalamus, striatum and the substantia nigra. Chronic voluntary drinking affected ir DYNB levels in the pituitary gland, hypothalamus and the substantia nigra, with minor differences between MS15 and MS360. In conclusion, manipulation of the early environment caused changes in the opioid system and a subsequent altered response to ethanol. The altered sensitivity of the opioid peptides to ethanol may contribute to the previously reported differences in ethanol intake between MS15 and MS360 rats.

Gene-environment correlations: a review of the evidence and implications for prevention of mental illness

Family studies have demonstrated genetic influences on environmental exposure: the phenomenon of gene-environment correlation (rGE). A few molecular genetic studies have confirmed the results, but the identification of rGE in studies that measure genes and environments faces several challenges. Using examples from studies in psychology and psychiatry, we integrate the behavioral and molecular genetic literatures on rGE, describe challenges in identifying rGE and discuss the implications of molecular genetic findings of rGE for future research on gene-environment interplay and for attempts to prevent disease by reducing environmental risk exposure. Genes affect environments indirectly, via behavior and personality characteristics. Associations between individual genetic variants and behaviors are typically small in magnitude, and downstream effects on environmental risk are further attenuated by behavioral mediation. Genotype-environment associations are most likely to be detected when the environment is behaviorally modifiable and highly specified and a plausible mechanism links gene and behavior. rGEs play an important causal role in psychiatric illness. Although research efforts should concentrate on elucidating the genetic underpinnings of behavior rather than the environment itself, the identification of rGE may suggest targets for environmental intervention even in highly heritable disease. Prevention efforts must address the possibility of confounding between rGE and gene-environment interaction (G x E).

Sleep electroencephalographic spectral power after withdrawal from alcohol in alcohol-dependent patients

BACKGROUND

Dysfunctional hyperarousal is suspected to be a neurophysiological determinant of relapse in abstinent alcohol-dependent patients. In the present study, we used spectral power analysis of the sleep electroencephalographic (EEG) to quantify brain activity during sleep in patients during subacute withdrawal as well as in control subjects. Our hypothesis was that the subgroup of patients who relapsed within the 3 months to follow-up would exhibit-increased dysfunctional arousal manifested by higher-frequency (beta) EEG power during sleep.

METHODS

Twenty-six alcohol-dependent in-patients were examined with polysomnography over 2 nights 2 to 3 weeks after withdrawal. At the 3-month clinical follow-up assessment, 12 of them had relapsed and 14 abstained. The control group consisted of 23 healthy subjects similar to the patients with alcohol dependence in age and gender distribution. Spectral sleep EEG analysis was performed on both nights (adaptation and baseline) of all subjects. Logarithmic artifact-controlled spectral band power of sleep stage 2 and rapid eye movement (REM) sleep was analyzed for Group, Gender, and Age effects using multiple analyses of covariance. Three groups were compared with the Group factor: relapsers, abstainers, and controls.

RESULTS

Generally, both Group and Age effects were significant for the second, baseline night for the visually scored sleep parameters, while spectral EEG parameters showed significant differences in the adaptation night. In the adaptation night, a significant enhancement in the beta2 band (24-32 Hz) was seen in REM sleep in relapsers relative to both abstainers and controls.

CONCLUSIONS

The beta2 increase could be interpreted as a sign of dysfunctional arousal during REM sleep "unmasked" by the additional stressor of sleep environment adaptation. Its determinants are likely to be both premorbid and drinking history related.

Mutation screen of the GAD2 gene and association study of alcoholism in three populations

Synaptic actions of gamma-amino butyric acid (GABA) have been implicated in many facets of ethanol's effects and risk for alcoholism. We examined whether variation in glutamate decarboxylase-2 (GAD2), a gene encoding for a major enzyme in the synthesis of GABA, contributes to risk of alcohol dependence (AD). We screened GAD2 for sequence variants using dHPLC in a population of 96 individuals. Several single nucleotide polymorphisms (SNPs), including four rare non-synonymous polymorphisms, were identified. Thirteen SNPs located in the GAD2 gene were genotyped in a sample of 113 Russian males with AD and 100 Russian male controls. These analyses revealed a modest association between the functional GAD2 -243 A > G SNP (rs2236418) and AD (allele P = 0.038, genotype P = 0.008). An additional sample of 138 Russian males with AD were genotyped for the GAD2 -243 A > G. These analyses supported an association of this polymorphism with AD (combined sample allele P = 0.038, genotype P = 0.0009). We extended these findings to additional populations: a sample of 538 college students assessed using the AUDIT and a sample of European-American (EA) AD subjects (n = 235) and controls (n = 310). Analyses in these populations did not support a role for GAD2 in alcoholism. In summary, the results of an extensive search for an association of GAD2 with AD suggest that variation in GAD2 is not a major risk factor for AD in EAs. The functional promoter GAD2 -243 A > G variant may influence risk for AD in some populations, or its role may be limited to susceptibility to severe AD.

How gene–stress–behavior interactions can promote adolescent alcohol use: The roles of predrinking allostatic load and childhood behavior disorders

A variety of environmental and genetic factors modulating the risk for alcoholism have been described, which predominantly act by interacting with each other. For example, the family, peers and society determine the level of exposure to stress and alcohol, while genes modulate how sensitive an individual responds to both. The resulting behaviors feed back to the social environment, modulating and in the worst case increasing further stress exposure. We here review neurobiological evidence how such a process of mutual interaction can involve and affect drinking. In at-risk adolescents it may have been in force for many years before they have their first alcoholic drink, increasing their risk for addiction by generating allostatic load. As an example, psychiatric disorders involving attention deficit, hyperactivity, or disruptive behaviors first evolve during childhood and are influenced by all the above factors. They are also strongly associated with harmful adolescent drinking and later alcohol use disorders. One important implication of this concept is that issues such as family adversity, adolescent psychiatric disorders, or adolescent drinking might not only be associated with, but causally related to, the risk for later addiction. They are targets for preventive interventions, which should start as early as possible in subjects at-risk.

Genetic Polymorphisms Related to Delirium Tremens: A Systematic Review

BACKGROUND

Delirium tremens (DT) is one of the more severe complications of alcohol withdrawal (AW), with a 5 to 10% lifetime risk for alcohol-dependent patients. The 2 most important neurosystems involved in AW are gamma-aminobutyric acid and glutamate. It is unknown whether these neurosystems are involved in the pathophysiology of DT as well. The candidate gene approach in DT could contribute to this knowledge and demonstrate a possible genetic predisposition for DT. The purpose of this study is to give an overview of all studied genetic polymorphisms in the diverse candidate genes related to DT and to summarize what these studies contribute to insights into the pathophysiology of DT.

METHODS

The inclusion criteria for this literature study were articles in English analyzing the association between a genetic polymorphism and DT without other AW syndromes. Studies were identified until February 2006 in MEDLINE and EMBASE databases.

RESULTS

We found 25 studies dealing with 30 polymorphisms, located in 19 different genes. Positive associations were found in 3 different candidate genes involved in the dopamine transmission, 1 gene involved in the glutamate pathway, 1 neuropeptide gene, and 1 cannabinoid gene. Two candidate genes involved in the dopamine transmission, dopamine receptor D3, and solute carrier family 6, were each associated with DT in 2 different study populations. The other 4 positive associations were not replicated in other studies.

CONCLUSIONS

A total of 8 positive associations out of 30 polymorphisms makes a genetic base for DT plausible. Understanding the pathophysiological process of the development of DT has, indeed, been augmented by the reviewed genetic association studies. These studies suggest that the regulation of dopaminergic neurotransmission may play an important role.