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

Association between opioid and dopamine receptor gene polymorphisms OPRM1 rs1799971, DAT VNTR 9-10 repeat allele, DRD1 rs4532 and DRD2 rs1799732 and alcohol dependence: an ethnicity oriented meta-analysis

OBJECTIVE

We carried out a meta-analysis of four opioid and dopamine candidate gene polymorphisms having conflicting results in prior literature, namely OPRM1 rs1799971, DAT VNTR 9-10 repeat, DRD1 rs4532 and DRD2 rs1799732, to clarify their association with alcohol dependence and further stratified results by ethnicity to analyze possible ethnicity-mediated effects.

METHODS

Inclusion criteria: case-control studies assessing the association between OPRM1 rs1799971, DAT VNTR 9/10 repeat allele, DRD1 rs4532 and DRD2 rs1799732 with alcohol dependence, with sufficient data available to calculate the odds ratio (OR) within a 95% confidence interval. Exclusion criteria: studies of quantitative measures of alcohol consumption, response to medications or analyses of other markers in the candidate genes, studies without controls, animal studies and lack of genotyping data. Information sources were PubMed, Google Scholar and ScienceDirect databases, all of which were searched for articles published till 2021. Heterogeneity between studies and publication bias, subgroup analyses and sensitivity analyses were carried out.

RESULTS

A total of 41 published studies were included in the current meta-analysis. For the OPRM1 gene, there was a statistically significant association in the Asian population with a pooled OR of 1.707 (95% CI, 1.32-2.20 P  < 0.0001) and 1.618 (95% CI, 1.16-2.26 P  = 0.005) in the additive and dominant genetic models. For DAT VNTR 9/10 repeat, a statistically significant association of the risk vs. common allele was observed in AD with a pooled OR of 1.104 (95% CI, 1.00-1.21 P  = 0.046) in the allele model and the additive genetic model in the Caucasian population with pooled OR of 1.152 (95% CI, 1.01-1.31 P  = 0.034).

CONCLUSION

Results indicate that some of the effects may be ethnicity-specific.

OTHER

The meta-analysis has been registered in the CRD PROSPERO (CRD42023411576).

Alcohol in Psoriasis-From Bench to Bedside

Alcohol affects the symptoms, compliance and comorbidities as well as the safety and efficacy of treatments in psoriatic patients. In this review, we aim to summarize and link clinical observations with a molecular background, such as signaling pathways at the cellular level and genetic variations, and to provide an overview of how this knowledge could influence our treatment selection and patient management.

Dysregulation of the histone demethylase KDM6B in alcohol dependence is associated with epigenetic regulation of inflammatory signaling pathways

Epigenetic enzymes oversee long‐term changes in gene expression by integrating genetic and environmental cues. While there are hundreds of enzymes that control histone and DNA modifications, their potential roles in substance abuse and alcohol dependence remain underexplored. A few recent studies have suggested that epigenetic processes could underlie transcriptomic and behavioral hallmarks of alcohol addiction. In the present study, we sought to identify epigenetic enzymes in the brain that are dysregulated during protracted abstinence as a consequence of chronic and intermittent alcohol exposure. Through quantitative mRNA expression analysis of over 100 epigenetic enzymes, we identified 11 that are significantly altered in alcohol‐dependent rats compared with controls. Follow‐up studies of one of these enzymes, the histone demethylase KDM6B, showed that this enzyme exhibits region‐specific dysregulation in the prefrontal cortex and nucleus accumbens of alcohol‐dependent rats. KDM6B was also upregulated in the human alcoholic brain. Upregulation of KDM6B protein in alcohol‐dependent rats was accompanied by a decrease of trimethylation levels at histone H3, lysine 27 (H3K27me3), consistent with the known demethylase specificity of KDM6B. Subsequent epigenetic (chromatin immunoprecipitation [ChIP]–sequencing) analysis showed that alcohol‐induced changes in H3K27me3 were significantly enriched at genes in the IL‐6 signaling pathway, consistent with the well‐characterized role of KDM6B in modulation of inflammatory responses. Knockdown of KDM6B in cultured microglial cells diminished IL‐6 induction in response to an inflammatory stimulus. Our findings implicate a novel KDM6B‐mediated epigenetic signaling pathway integrated with inflammatory signaling pathways that are known to underlie the development of alcohol addiction.

A review of psychosocial factors linked to adolescent substance use

PURPOSE

Informed by ecological theories and models of influence, this review discusses various psychosocial risk and protective factors that contribute to adolescent substance use behavior. Given typical patterns of substance use initiation during this developmental period, an emphasis is placed on alcohol, cigarette, and marijuana use.

FINDINGS

Consistent with bioecological theories, peers and parents tend to have the strongest effect on adolescent substance use behavior. Influences can be both direct, such as offers and availability to use substances, as well as indirect influences, such as the perception of substance use approval. Schools and neighborhoods also contribute to adolescent substance use behavior, but this effect is often less direct. Moreover, the effect of neighborhoods on adolescent behavior reflects both structural components (e.g., neighborhood racial composition, teacher-student ratios) in addition to social process (e.g., neighborhood social cohesion, school connectedness). A review of parallel studies conducted with animals is also provided.

SUMMARY

Adolescent substance use behavior does not occur in a vacuum. Investigations must encompass the relevant social ecologies that affect adolescent behavior, including family, peer, school, and neighborhood contexts to provide a more complete understanding of substance use etiology.

Recent advances in genetic studies of alcohol use disorders

PURPOSE OF REVIEW

Alcohol use disorder (AUD) is a complex genetic disorder with very high heritability. This polygenic disorder not only results in increased morbidity and mortality, it is also a substantial social and economic burden on families and the nation. For past three decades, several genetic studies were conducted to identify genes and pathways associated with AUD. This review aims to summarize past efforts and recent advances in genetic association studies of AUD and related traits.

RECENT FINDINGS

Initial genetic association studies achieved a limted success and suffered from low power due to small sample sizes. AUD is a polygenic trait and data from several thousands individuals was required to identify the genetic factors of small effect sizes. The scenario changed recently with technological advances and significant reduction in cost of the genome wide association analyses (GWAS). This enabled researchers to generate genomic data on mega biobanks and cohorts with access to extensive clinical and non-clinical phenotypes. Public access to data from biobanks and collaborative efforts of researchers lead to identification of several novel loci associated with AUDs and related traits. Efforts are now underway to identify the causal variants under the GWAS loci to identify target genes and biological mechanisms underpining AUDs. Many GWAS variants occur in promoter or enhancer regions of the genes and are involved in regulation of gene expression of causal genes. This, large amounts of "omics" data from projects such as "ENCODE", RoadMap and GTEx is also helping researchers to integrate "multi-omics" data to interpret functional significance of GWAS variants.

SUMMARY

With current review, we aim to present the recent advances in genetic and molecular studies of AUDs. Recent successes in genetic studies of AUDs will definetely motivate researchers and lead to better therapeutic interventions for this complex disorder.

Genetic association between −93A/G polymorphism in the Fyn kinase gene and alcohol dependence in Spanish men

Background

Fyn tyrosine kinase is a member of the Scr family that phosphorylates the NR2A and NR2B subunits of the NMDA receptors reducing the inhibitory effects of ethanol and therefore may regulate the individual sensitivity to ethanol.

Objectives

To investigate whether there is any relationship between the polymorphism at position −93 of the Fyn kinase gene and the susceptibility to develop alcoholism.

Methods

We studied the distribution of genotypes and alleles of the polymorphism −93A/G (137346 T/C) in the 5′ UTR region of the fyn gene in 207 male heavy drinkers (119 with alcohol dependence and 88 with alcohol abuse) and 100 control subjects from Castilla y León (Spain).

Results

The frequency of G allele carriers was higher in alcohol dependents than in alcohol abusers (47.9% vs 30.6%; p = 0.015; OR = 2.077; 95% CI 1.165–3.704).

Conclusion

Our results show that the −93G allele of Fyn kinase gene is associated with higher risk to develop alcohol dependence in Spanish men.

The Role of Epigenetics in Addiction: Clinical Overview and Recent Updates

Addiction is an international public health problem. It is a polygenic disorder best understood by accounting for the interplay between genetic and environmental factors. A recent way of perceiving this interaction is through epigenetics, which help grasp the neurobiological changes that occur in addiction and explain its relapsing-remitting nature. It is now known that every cell has a different way of expressing its phenotype, despite a universal DNA sequence. This is particularly true in the central nervous system where environmental factors influence this expression. Three major epigenetic processes have been found to participate in the perpetuation of addiction by changing the state of the chromatin and the degree of gene transcription: histone acetylation and methylation, DNA methylation, and noncoding RNAs. In the animal model literature, substantial evidence exists about the role of these epigenetic changes in the different phases of substance use disorders. This book chapter is a non-systematic literature review of the recent publications tackling the topic of epigenetics in addiction. Even though this evidence remains scarce and relatively poorly systematized, it is a promising foundation for future research of molecules that target specific brain regions and their functions to address core behavioral changes seen in addiction.

How alcohol drinking affects our genes: an epigenetic point of view

This work highlights recent studies in epigenetic mechanisms that play a role in alcoholism, which is a complex multifactorial disorder. There is a large body of evidence showing that alcohol can modify gene expression through epigenetic processes, namely DNA methylation and nucleosomal remodeling via histone modifications. In that regard, chronic exposure to ethanol modifies DNA and histone methylation, histone acetylation, and microRNA expression. The alcohol-mediated chromatin remodeling in the brain promotes the transition from use to abuse and addiction. Unravelling the multiplex pattern of molecular modifications induced by ethanol could support the development of new therapies for alcoholism and drug addiction targeting epigenetic processes.

Serial Progression from Attention-Deficit/Hyperactivity Disorder to Alcohol Use Disorder: Serial Multiple Mediated Effects of Externalizing Disorders and Depression

Objective

Externalizing disorders such as attention-deficit/hyperactivity disorder (ADHD), conduct disorder and antisocial personality disorder, as well as depression are common comorbidities in alcohol use disorder (AUD). The current study focused on the temporal relationship between the onsets of these disorders and AUD, and investigated the serial multiple mediator model of externalizing disorders (e.g., ADHD) and depression on AUD.

Methods

We analyzed the mediated effects of the Adult ADHD Self-Report Scale (ASRS), the Barratt Impulsiveness Scale motor (BIS_M) and the Beck Depression Inventory (BDI) on Korean version of the Alcohol Dependence Scale (ADS_K) using the multiple-step multiple mediation procedure regression analysis. In addition, we comparatively analyzed different clinical characteristics in relation to conduct problems.

Results

The multiple-step multiple mediation procedure found the serial multiple mediated effects of the BIS_M and the BDI on the relationship between the ASRS and the ADS_K. Also, the group with conduct problem was significantly high in ADHD symptoms, depression, anxiety, impulsivity, legal problems and alcohol-related problems, compared to the group without conduct problems.

Conclusion

To sum up, the results of this study show that ADHD symptoms in childhood could exert significant effects on the severity of AUD in adulthood, and both disorders might be mediated by the externalizing disorders characterized by the core feature of motor impulsivity, and depression serially. Thus, the treatment of preceding disorders in accordance with developmental stages is an overarching clinical component for preventing the subsequent development of AUD and for its treatment.

Genetics of alcohol use disorder: a review

Alcohol use disorder (AUD) represents a significant and ongoing public health concern with 12-month prevalence estimates of ∼5.6%. Quantitative genetic studies suggest a heritability of approximately 50% for AUD, and as a result, significant efforts have been made to identify specific variation within the genome related to the etiology of AUD. Given the limited number of replicable findings that have emerged from genome-wide linkage and candidate gene association studies, more recent efforts have focused on the use of genome-wide association studies (GWAS). These studies have suggested that hundreds of variants across the genome, most of small effect (R² < 0.002), contribute to the genetic etiology of AUD. The present review describes the initial, though limited, successes of GWAS to identify loci related to risk for AUD as well as other etiologically relevant traits (e.g. alcohol consumption). In addition, 'Post-GWAS' approaches that rely on GWAS data to estimate the heritability and co-heritability of traits, test causal relations between traits, and aid in gene discovery are described. Together, the described research findings illustrate the importance of molecular genetic research on AUD as we seek to better understand the mechanisms through which genetic variation leads to increased risk for AUD.

The association between the nicotinic acetylcholine receptor α4 subunit gene (CHRNA4) rs1044396 and Internet gaming disorder in Korean male adults

The primary aim of this study was to investigate the genetic predisposition of Internet gaming disorder (IGD), and the secondary aim was to compare the results to those of alcohol dependence (AD). Two independent case-control studies were conducted. A total of 30 male participants with IGD, diagnosed according to the 5^th edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) criteria, and 30 sex-matched controls participated in study 1. We designed targeted exome sequencing (TES) to test for 72 candidate genes that have been implicated in the pathogenesis of addiction. The genes included seven neurotransmitter (dopamine, serotonin, glutamate, r-aminobutyric acid (GABA), norepinephrine, acetylcholine, and opioid) system genes. A total of 31 male in-patients with AD and 29 normal male controls (NC) were enrolled in study 2. The same 72 genes included in study 1 and ten additional genes related to alcohol-metabolic enzyme were selected as the target genes, and we identified the genetic variants using the same method (TES). The IGD group had a lower frequency of the T allele of rs1044396 in the nicotinic acetylcholine receptor alpha 4 subunit (CHRNA4), and this variant represents a protective allele against IGD. However, we did not find a significant difference in the polymorphisms of the 72 genes that encode neurotransmitter systems between the AD and NC groups. This study demonstrated that rs1044396 of CHRNA4 was significantly associated with IGD.

Review: Genetic research on alcohol use outcomes in African American populations: A review of the literature, associated challenges, and implications

BACKGROUND AND OBJECTIVES

There have been remarkable advances in understanding genetic influences on complex traits; however, individuals of African descent have been underrepresented in genetic research.

METHODS

We review the limitations of existing genetic research on alcohol phenotypes in African Americans (AA) including both twin and gene identification studies, possible reasons for underrepresentation of AAs in genetic research, the implications of the lack of racially diverse samples, and special considerations regarding conducting genetic research in AA populations.

RESULTS

There is a marked absence of large-scale AA twin studies so little is known about the genetic epidemiology of alcohol use and problems among AAs. Individuals of African descent have also been underrepresented in gene identification efforts; however, there have been recent efforts to enhance representation. It remains unknown the extent to which genetic variants associated with alcohol use outcomes in individuals of European and African descent will be shared. Efforts to increase representation must be accompanied by careful attention to the ethical, legal, and social implications of genetic research. This is particularly true for AAs due to the history of abuse by the biomedical community and the persistent racial discrimination targeting this population.

CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE

Lack of representation in genetic studies limits our understanding of the etiological factors that contribute to substance use and psychiatric outcomes in populations of African descent and has the potential to further perpetuate health disparities. Involving individuals of diverse ancestry in discussions about genetic research will be critical to ensure that all populations benefit equally from genetic advances. (Am J Addict 2017;26:486-493).

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.

GABRB1 Single Nucleotide Polymorphism Associated with Altered Brain Responses (but not Performance) during Measures of Impulsivity and Reward Sensitivity in Human Adolescents

Variations in genes encoding several GABA_A receptors have been associated with human drug and alcohol abuse. Among these, a number of human studies have suggested an association between GABRB1, the gene encoding GABA_A receptor β1 subunits, with Alcohol dependence (AD), both on its own and comorbid with other substance dependence and psychiatric illnesses. In the present study, we hypothesized that the GABRB1 genetically-associated increased risk for developing alcoholism may be associated with impaired behavioral control and altered sensitivity to reward, as a consequence of altered brain function. Exploiting the IMAGEN database (Schumann et al., 2010), we explored in a human adolescent population whether possession of the minor (T) variant of the single nucleotide polymorphism (SNP) rs2044081 is associated with performance of tasks measuring aspects of impulsivity, and reward sensitivity that are implicated in drug and alcohol abuse. Allelic variation did not associate with altered performance in either a stop-signal task (SST), measuring one aspect of impulsivity, or a monetary incentive delay (MID) task assessing reward anticipation. However, increased functional magnetic resonance imaging (fMRI) blood-oxygen-level dependent (BOLD) response in the right hemisphere inferior frontal gyrus (IFG), left hemisphere caudate/insula and left hemisphere inferior temporal gyrus (ITG) during MID performance was higher in the minor (T) allelic group. In contrast, during SST performance, the BOLD response found in the right hemisphere supramarginal gyrus, right hemisphere lingual and left hemisphere inferior parietal gyrus indicated reduced responses in the minor genotype. We suggest that β1-containing GABA_A receptors may play a role in excitability of brain regions important in controlling reward-related behavior, which may contribute to susceptibility to addictive behavior.

Exploration of a Polygenic Risk Score for Alcohol Consumption: A Longitudinal Analysis from the ALSPAC Cohort

BACKGROUND

Uncertainty remains about the true extent by which alcohol consumption causes a number of health outcomes. Genetic variants, or combinations of variants built into a polygenic risk score (PGRS), can be used in an instrumental variable framework to assess causality between a phenotype and disease outcome of interest, a method known as Mendelian randomisation (MR). We aimed to identify genetic variants involved in the aetiology of alcohol consumption, and develop a PGRS for alcohol.

METHODS

Repeated measures of alcohol consumption from mothers and their offspring were collected as part of the Avon Longitudinal Study of Parents and Children. We tested the association between 89 SNPs (identified from either published GWAS data or from functional literature) and repeated measures of alcohol consumption, separately in mothers (from ages 28-48) and offspring (from ages 15-21) who had ever reported drinking. We modelled log units of alcohol using a linear mixed model and calculated beta coefficients for each SNP separately. Cross-validation was used to determine an allelic score for alcohol consumption, and the AVENGEME algorithm employed to estimate variance of the trait explained.

RESULTS

Following correction for multiple testing, one SNP (rs1229984) showed evidence for association with alcohol consumption (β = -0.177, SE = 0.042, p = <0.0001) in the mothers. No SNPs showed evidence for association in the offspring after correcting for multiple testing. The optimal allelic score was generated using p-value cut offs of 0.5 and 0.05 for the mothers and offspring respectively. These scores explained 0.3% and 0.7% of the variance.

CONCLUSION

Our PGRS explains a modest amount of the variance in alcohol consumption and larger sample sizes would be required to use our PGRS in an MR framework.

An investigation of child maltreatment and epigenetic mechanisms of mental and physical health risk

In the present investigation, differential methylation analyses of the whole genome were conducted among a sample of 548 school-aged low-income children (47.8% female, 67.7% Black, M age = 9.40 years), 54.4% of whom had a history of child maltreatment. In the context of a summer research camp, DNA samples via saliva were obtained. Using GenomeStudio, Methylation Module, and the Illumina Custom Model, differential methylation analyses revealed a pattern of greater methylation at low methylation sites (n = 197 sites) and medium methylation sites (n = 730 sites) and less methylation at high methylation sites (n = 907 sites) among maltreated children. The mean difference in methylation between the maltreated and nonmaltreated children was 6.2%. The relative risk of maltreatment with known disease biomarkers was also investigated using GenoGo MetaCore Software. A large number of network objects previously associated with mental health, cancer, cardiovascular systems, and immune functioning were identified evidencing differential methylation among maltreated and nonmaltreated children. Site-specific analyses were also conducted for aldehyde dehydrogenase 2 (ALDH2), ankyrin repeat and kinase domain containing 1 (ANKK1), and nuclear receptor subfamily 3, group C, member 1 (NR3C1) genes, and the results highlight the importance of considering gender and the developmental timing of maltreatment. For ALDH2, the results indicated that maltreated girls evidenced significantly lower methylation compared to nonmaltreated girls, and maltreated boys evidenced significantly higher methylation compared to nonmaltreated boys. Moreover, early onset-not recently maltreated boys evidenced significantly higher methylation at ALDH2 compared to nonmaltreated boys. Similarly, children with early onset-nonrecent maltreatment evidenced significantly higher methylation compared to nonmaltreated children at ANKK1. The site-specific results were not altered by controlling for genotypic variation of respective genes. The findings demonstrate increased risk for adverse physical and mental health outcomes associated with differences in methylation in maltreated children and indicate differences among maltreated children related to developmental timing of maltreatment and gender in genes involved in mental health functioning.

miR-181a is a negative regulator of GRIA2 in methamphetamine-use disorder

A previous study reported that the miR-181a level in serum was significantly different between patients with methamphetamine-use disorder and healthy controls and that chronic methamphetamine use down-regulates the expression of miR-181a. Bioinformatic analysis predicted that miR-181a might bind the 3′-UTRs of the mRNA transcripts of the human glutamate receptor genes GRIA2 and GABRA1. In this study, we measured the expression of GRIA2 and GABRA1 in patients with methamphetamine-use disorder. In addition, we examined whether miR-181a down-regulates GRIA2 and GABRA1 in a cell-based assay. We further examined the effects of chronic methamphetamine exposure on the expression of miR-181a, GRIA2 and GABRA1. The results demonstrated that serum GRIA2 is higher in patients with methamphetamine-use disorder than in healthy controls. Dual luciferase reporter assays and a cell-based model of methamphetamine exposure also showed that miR-181a directly regulates expression of GRIA2. This study supports the evidence that miR-181a and the glutamate AMPA receptor gene GRIA2 play a critical role in methamphetamine-use disorder.

Current considerations regarding food addiction

"Food addiction" is an emerging area, and behavioral and biological overlaps have been observed between eating and addictive disorders. Potential misconceptions about applying an addiction framework to problematic eating behavior may inhibit scientific progress. Critiques of "food addiction" that focus on descriptive differences between overeating and illicit drugs are similar to early criticisms of the addictiveness of tobacco. Although food is necessary for survival, the highly processed foods associated with addictive-like eating may provide little health benefit. Individual differences are important in determining who develops an addiction. If certain foods are addictive, the identification of possible risk factors for "food addiction" is an important next step. Not all treatments for addiction require abstinence. Addiction interventions that focus on moderation or controlled use may lead to novel approaches to treating eating-related problems. Finally, addiction-related policies that focus on environmental (instead of educational) targets may have a larger public health impact in reducing overeating.

Family history of mental illness or alcohol abuse and the irritable bowel syndrome

OBJECTIVE

We have observed that many patients with IBS drink very little alcohol and postulated that this may reflect membership in families affected by alcoholism and mental illness. We aimed to evaluate whether a family history of substance or alcohol abuse, or psychiatric illness, is associated with IBS.

METHODS

A valid GI questionnaire was mailed to a randomly selected population-based cohort to identify IBS and healthy controls. The electronic medical record was reviewed to record the subjects' self-reported personal and family health histories.

RESULTS

A total of 2300 subjects responded (response rate 55%; IBS 13%, n=287); 230 subjects with IBS and 318 controls were eligible. Family history of alcohol/substance abuse was reported by 33% of cases and 25% of controls (OR=1.4, 95% CI=1.0-2.1, p=0.06). Family history of psychiatric illness was reported by 37% of cases and 22% of controls (OR=2.0, 95% CI=1.3-2.9, p<0.001). In the absence of a personal history of alcohol use, a family history of alcohol/substance abuse was predictive of IBS status (OR adjusted for age and gender=1.5, 95% CI=1.0-2.3, p=0.05). In the absence of a personal history of alcohol use, reporting both a family history of alcohol/substance abuse and anxiety/depression/mental illness was clearly predictive of IBS status (OR=2.5, 95% CI=1.4-4.5; p<0.005). Substance abuse as a child was associated with an increased risk of IBS (OR=2.3, 95% CI=1.1-4.8; p<0.03).

CONCLUSION

IBS is independently associated with a family history of psychiatric illness and may be linked to a family history of alcohol/substance abuse.

Genetics of alcoholism

Alcohol use and alcohol use disorders are substantially heritable. Variants in genes coding for alcohol metabolic enzymes have long been known to influence consumption. More recent studies in family-based samples have implicated GABRA2, nicotinic receptor genes such as CHRNB3, and a number of other specific single genes as associated with alcohol use disorders. The growing use of genetic analyses, in particular studies using polygenic risk scores; neurobiologic pathways; and methods for quantifying gene × gene and gene × environment interactions have also contributed to an evolving understanding of the genetic architecture of alcohol use disorders. Additionally, the study of behavioral traits associated with alcohol dependence such as impulsivity and sensation seeking, and the influences of demographic factors (i.e., sex and ethnicity) have significantly enhanced the genetics of alcoholism literature. This article provides a brief overview of the current topically relevant findings in the field to date and includes areas of research still requiring attention.

GABA Receptors Genes Polymorphisms and Alcohol Dependence: No Evidence of an Association in an Italian Male Population

Objective

The genes encoding for gamma-aminobutyric acid (GABA) A and B receptors may be considered as candidates for alcoholism; genetic alterations at this level may produce structural and functional diversity and thus play a role in the response to alcohol addiction treatment. To investigate these aspects further, we conducted a preliminary genetic association study on a population of Italian male alcohol addicts, focusing on GABA A and B receptors.

Methods

A total of 186 alcohol-dependent subjects (in the first phase 139, then 47 more samples) and 182 controls were genotyped for 25 single nucleotide polymorphisms (SNPs) of genes encoding the alpha-1 subunit of GABA A receptor (GABRA1) and subunits 1 and 2 of GABA B receptor (GABBR1 and GABBR2). The chi-squared test for allele and genotype distributions and Hardy-Weinberg equilibrium analysis of both subjects and controls were performed. Bonferroni's correction for multiple comparisons was applied.

Results

Preliminary results comparing 139 alcohol-dependent subjects and 182 controls showed differences in genotype distribution in the former for SNP rs29253, located in the intron region of the GABBR1 gene. In order to clarify the meaning of this association, 47 more samples from alcohol-dependent subjects were tested for this SNP only: the previously found association was not confirmed.

Conclusion

The lack of significant differences between the two groups does not provide evidence that GABRA 1 and GABBR1 and 2 genes are candidates for alcoholism in this population. Further studies with larger samples are needed, together with investigation of other components of the GABA pathway.

Association between Fok I vitamin D receptor gene (VDR) polymorphism and impulsivity in alcohol-dependent patients

Vitamin D appears to have an important role in the modulation of the central nervous system. Vitamin D exerts its biological effects through its interaction with the vitamin D receptor (VDR). Located on chromosome 12 (12q13.1), the VDR gene has many different polymorphisms. Some of them are known to affect the VDR function, such as FokI (rs2228570, T/C) single nucleotide polymorphism. We aimed to explore a potential relationship between FokI VDR polymorphism and impulsiveness in alcohol-dependent (AD) patients. The study population consisted of 148 patients diagnosed with alcohol dependence (DSM-IV criteria) and 212 healthy controls. DNA was extracted from whole blood samples using the standard procedure. Genotypes were analyzed using a real-time PCR method. We found that FokI VDR gene polymorphism was associated with impulsivity [Barratt Impulsiveness Scale (BIS)-11 total score; P = 0.014], and with attentional impulsivity (BIS-11 subscale; P = 0.002) in the male AD patients. Our results suggest that CC FokI genotype of the VDR gene is associated with a higher level of impulsivity in these patients. This finding supports the hypothesis that impulsiveness, which significantly contributes to development of alcohol dependence, has a genetic background.

Serotonin transporter gene promoter polymorphism (5-HTTLPR) and alcohol use in general population: interaction effect with birth cohort

RATIONALE AND OBJECTIVE

Prevalence of alcohol use is markedly influenced by socioeconomic conditions and is therefore subject to cohort effects. The common genetic variation 5-HTTLPR (serotonin transporter gene-linked polymorphic region) has been related to several aspects of alcohol use and addiction but with mixed results, probably due to different environmental interaction effects. We aimed at assessing whether the association between alcohol use and 5-HTTLPR genotype is subject to cohort effects as birth cohorts may be raised in significantly different environments.

METHODS

We used the database of the Estonian Children Personality Behaviour and Health Study (beginning in 1998). Cohorts of initially 9-year-old (recalled at ages 15 and 18) and 15-year-old (recalled at ages 18 and 25) children provided self-reports on their alcohol use in all data collection waves (complete data available n = 1,075).

RESULTS

A significant genotype × gender × cohort interaction effect on the age of consuming the first alcoholic drink was found [F(2, 1,063) = 7.2, p < 0.001]. Females with the s/s genotype in the older cohort were the latest experimenters with alcohol, while the s/s females of younger cohort had tried alcohol earlier than any other group. In males, there was no significant cohort × genotype interaction, but the 5-HTTLPR genotype was associated with alcohol use, the s/s subjects reporting the highest consumption.

CONCLUSION

Expression of genetic vulnerability to alcohol use is influenced by birth cohort effects. The 5-HTTLPR genotype is associated with alcohol consumption in general population, but the effect depends on gender and birth cohort.

Association between copy number variation losses and alcohol dependence across African American and European American ethnic groups

BACKGROUND

Copy number variations (CNVs) are structural genetic mutations consisting of segmental gains or losses in DNA sequence. Although CNVs contribute substantially to genomic variation, few genetic and imaging studies report association of CNVs with alcohol dependence (AD). Our purpose is to find evidence of this association across ethnic populations and genders. This work is the first AD-CNV study across ethnic groups and the first to include the African American (AA) population.

METHODS

This study considers 2 CNV data sets, one for discovery (2,345 samples) and the other for validation (239 samples), both including subjects with AD and healthy controls of European and African ancestry. Our analysis assesses the association between AD and CNV losses across ethnic groups and gender by examining the effect of overall losses across the whole genome, collective losses within individual cytogenetic bands, and specific losses in CNV regions.

RESULTS

Results from the discovery data set showed an association between CNV losses within 16q12.2 and AD diagnosis (p = 4.53 × 10(-3) ). An overlapping CNV region from the validation data set exhibited the same direction of effect with respect to AD (p = 0.051). This CNV region affects the genes CES1p1 and CES1, which are members of the carboxylesterase (CES) family. The enzyme encoded by CES1 is a major liver enzyme that typically catalyzes the decomposition of ester into alcohol and carboxylic acid and is involved in drug or xenobiotics, fatty acid, and cholesterol metabolisms. In addition, the most significantly associated CNV region was located at 9p21.2 (p = 1.9 × 10(-3) ) in our discovery data set. Although not observed in the validation data set, probably due to small sample size, this result might hold potential connection to AD given its connection with neuronal death. In contrast, we did not find any association between AD and the overall total losses or the collective losses within individual cytogenetic bands.

CONCLUSIONS

Overall, our study provides evidence that the specific CNVs at 16q12.2 contribute to the development of alcoholism in AA and European American populations.

Variation of types of alcoholism: review and subtypes identified in Han Chinese

Alcoholism, as it has been hypothesized, is caused by a highly heterogeneous genetic load. Since 1960, many reports have used the bio-psycho-social approach to subtype alcoholism; however, no subtypes have been genetically validated. We reviewed and compared the major single-gene, multiple-gene, and gene-to-gene interaction studies on alcoholism published during the past quarter-century, including many recent studies that have made contributions to the subtyping of alcoholism. Four subtypes of alcoholism have been reported: [1] pure alcoholism, [2] anxiety/depression alcoholism, [3] antisocial alcoholism, and [4] mixed alcoholism. Most of the important studies focused on three genes: DRD2, MAOA, and ALDH2. Therefore, our review focuses on these three genes.

RNA-Seq reveals novel transcriptional reorganization in human alcoholic brain

DNA microarrays have been used for over a decade to profile gene expression on a genomic scale. While this technology has advanced our understanding of complex cellular function, the reliance of microarrays on hybridization kinetics results in several technical limitations. For example, knowledge of the sequences being probed is required, distinguishing similar sequences is difficult because of cross-hybridization, and the relatively narrow dynamic range of the signal limits sensitivity. Recently, new technologies have been introduced that are based on novel sequencing methodologies. These next-generation sequencing methods do not have the limitations inherent to microarrays. Next-generation sequencing is unique since it allows the detection of all known and novel RNAs present in biological samples without bias toward known transcripts. In addition, the expression of coding and noncoding RNAs, alternative splicing events, and expressed single nucleotide polymorphisms (SNPs) can be identified in a single experiment. Furthermore, this technology allows for remarkably higher throughput while lowering sequencing costs. This significant shift in throughput and pricing makes low-cost access to whole genomes possible and more importantly expands sequencing applications far beyond traditional uses (Morozova & Marra, 2008) to include sequencing the transcriptome (RNA-Seq), providing detail on gene structure, alternative splicing events, expressed SNPs, and transcript size (Mane et al., 2009; Tang et al., 2009; Walter et al., 2009), in a single experiment, while also quantifying the absolute abundance of genes, all with greater sensitivity and dynamic range than the competing cDNA microarray technology (Mortazavi, Williams, McCue, Schaeffer, & Wold, 2008).

Genetic differences in response to alcohol

The level of response to alcohol, which reflects individual differences in sensitivity to the pharmacologic effects of alcohol, is considered to be an important endophenotype of alcohol use disorder (AUD). By comparing monozygotic and dizygotic twins, the heritability of the level of response to alcohol has been estimated to be 60%. Many genes have been implicated as potential contributors toward heavy drinking, alcohol-related problems, and AUD through a low level of response to alcohol, each with a small effect. Identified are genes for gamma-aminobutyric acid (GABA) receptors, serotonin transporter, opioid receptor, and nicotinic acetylcholine receptor, but the most well-characterized genes that have a strong impact on the level of response to alcohol are those for alcohol-metabolizing enzymes. Although two genetic variations in alcohol and aldehyde dehydrogenases, which have been the most intensively studied, exist almost exclusively in Asian populations, studies on the effect of genetic variations in alcohol-metabolizing enzymes on the response to alcohol are gradually expanding in non-Asian populations. In this chapter, we focus on genetic studies in humans. After analyzing the overall influence of genetic factors on the response to alcohol, we explore individual genes that may influence the response to alcohol. Lastly, we review studies examining the effects of genetic variations in alcohol-metabolizing enzymes on the level of response to alcohol.

The role of sociodemographic factors in the risk of transition from alcohol use to disorders and remission in singapore

AIMS

The aim of the study was to define predictors of transition from alcohol use to disorders, and their remission, among adults residing in Singapore.

METHODS

The Singapore Mental Health Study was a cross-sectional survey conducted from December 2009 to December 2010. Information on alcohol use, regular use, DSM-IV criteria for abuse and dependence, and remission among 6616 respondents was obtained with the Composite International Diagnostic Interview.

RESULTS

The prevalence of lifetime alcohol use (drinking at least once in the lifetime) and regular use (ever drinking at least 12 drinks in a 12-month period) was 66.6 and 32%, respectively. Of the regular drinkers, 10.1% progressed into alcohol abuse; 6.9% of abusers turned to alcohol dependence and 16.6 and 7.1% of those with history of alcohol abuse and/or dependence subsequently reported remission defined as cessation of alcohol use and the absence of any symptoms for at least 2 years before interview. Transitions to regular use and to dependence were associated with younger age, Indian ethnicity and an early age of onset of drinking, and women had a higher risk than men of transition from abuse to dependence. Remissions were associated with older age, Malay ethnicity and late age of onset.

CONCLUSION

The rates of alcohol use and transition to disorders were lower than in other developing countries that have been studied. Sociodemographic predictors include younger age of onset of drinking, something that intervention programs and preventive strategies in Singapore should note.

NKAIN1-SERINC2 is a functional, replicable and genome-wide significant risk gene region specific for alcohol dependence in subjects of European descent

OBJECTIVE

We aimed to identify novel, functional, replicable and genome-wide significant risk regions specific for alcohol dependence using genome-wide association studies (GWASs).

METHODS

A discovery sample (1409 European-American cases with alcohol dependence and 1518 European-American controls) and a replication sample (6438 European-Australian family subjects with 1645 alcohol dependent probands) underwent association analysis. Nineteen other cohorts with 11 different neuropsychiatric disorders served as contrast groups. Additional eight samples underwent expression quantitative locus (eQTL) analysis.

RESULTS

A genome-wide significant risk gene region (NKAIN1-SERINC2) was identified in a meta-analysis of the discovery and replication samples. This region was enriched with 74 risk SNPs (unimputed); half of them had significant cis-acting regulatory effects. The distributions of -log(p) values for the SNP-disease associations or SNP-expression associations in this region were consistent throughout eight independent samples. Furthermore, imputing across the NKAIN1-SERINC2 region, we found that among all 795 SNPs in the discovery sample, 471 SNPs were nominally associated with alcohol dependence (1.7×10(-7)≤p≤0.047); 53 survived region- and cohort-wide correction for multiple testing; 92 SNPs were replicated in the replication sample (0.002≤p≤0.050). This region was neither significantly associated with alcohol dependence in African-Americans, nor with other non-alcoholism diseases. Finally, transcript expression of genes in NKAIN1-SERINC2 was significantly (p<3.4×10(-7)) associated with expression of numerous genes in the neurotransmitter systems or metabolic pathways previously associated with alcohol dependence.

CONCLUSION

NKAIN1-SERINC2 may harbor a causal variant(s) for alcohol dependence. It may contribute to the disease risk by way of neurotransmitter systems or metabolic pathways.

Association study of DRD2 and MAOA genes with subtyped alcoholism comorbid with bipolar disorder in Han Chinese

BACKGROUND

Several studies have hypothesized that genes involved in the dopamine system, including dopamine type-2 receptor (DRD2)-related TaqIA polymorphism and monoamine oxidase-A upstream variable number tandem repeat (uVNTR), may be associated with alcoholism. But their results were contradictory because of alcoholism's heterogeneity. Therefore, we examined whether the DRD2TaqIA and MAOA-uVNTR gene polymorphisms are susceptibility factors for alcoholism comorbid with bipolar disorder (ALC+BP) in Han Chinese in Taiwan.

METHODS

We recruited 101 Han Chinese men with comorbid alcoholism and bipolar disorder, and 328 healthy male controls from the community. Genotyping was done using PCR-RFLP.

RESULTS

There were no significant differences in the genotypic frequencies of the DRD2TaqIA or the MAOA-uVNTR polymorphisms between the 2 groups. The MAOA-uVNTR 3-repeat had a significant protective effect on the ALC+BP (odds ratio=0.432, p=0.035) but not on the healthy controls. However, the interaction between the MAOA-uVNTR 3-repeat and DRD2 A1/A2 was a risk factor in the ALC+BP (odds ratio=3.451, p=0.018).

CONCLUSIONS

We indicated the impact of the association between MAOA-uVNTR 3-repeat and DRD2 A1/A2 with ALC+BP.

Serotonin 2A receptor gene (HTR2A) polymorphism in alcohol-dependent patients

BACKGROUND

The serotonergic (5-HT) dysfunction has been frequently described in subjects with alcohol dependence (AD). In the present study, a potential relationship between T102C polymorphism in the 5-HT receptor subtype 2Agene (HTR2A) and alcohol dependence was examined.

METHODS

Genotypes were analyzed in 150 AD patients diagnosed with DSM-IV criteria and in 80 healthy controls.

RESULTS

The genetic analysis showed that the frequency of 102C allele and C102C genotype in AD subjects was significantly higher than in controls. Moreover, AD patients homozygous for C allele had significantly lower age at onset of alcohol problems than subjects having at least one T allele.

CONCLUSION

The results suggest a potential role of the T102C HTR2A polymorphism in development of alcohol dependence.

Current perspectives on the neurobiology of drug addiction: a focus on genetics and factors regulating gene expression

Drug addiction is a chronic, relapsing disorder defined by cyclic patterns of compulsive drug seeking and taking interspersed with episodes of abstinence. While genetic variability may increase the risk of addictive behaviours in an individual, exposure to a drug results in neuroadaptations in interconnected brain circuits which, in susceptible individuals, are believed to underlie the transition to, and maintenance of, an addicted state. These adaptations can occur at the cellular, molecular, or (epi)genetic level and are associated with synaptic plasticity and altered gene expression, the latter being mediated via both factors affecting translation (epigenetics) and transcription (non coding microRNAs) of the DNA or RNA itself. New advances using techniques such as optogenetics have the potential to increase our understanding of the microcircuitry mediating addictive behaviours. However, the processes leading to addiction are complex and multifactorial and thus we face a major contemporary challenge to elucidate the factors implicated in the development and maintenance of an addicted state.

Association of genetic copy number variations at 11 q14.2 with brain regional volume differences in an alcohol use disorder population

This study investigates the relationship between genetic copy number variations and brain volume differences in an alcohol use disorder (AUD) population. We hypothesized that copy number variations may influence subject's risk for alcohol use disorders through variations in regional gray and white matter brain volumes. Since genetic influences upon behavior are the result of many complicated interactions we focus on differences in brain volume as a putative intermediate phenotype between genetic variation and behavior. Copy number variation, alcohol use assessments and brain structural magnetic resonance images from 283 subjects, 199 male and 84 females who were enrolled in two AUD studies were obtained and analyzed using a combination of the Freesurfer image analysis suite and independent component analysis. Because brain volume varies by age we compared participant's volume variation with that derived from a control cohort of 75 subjects. In addition we also regressed out the possible brain volume changes induced by long term alcohol consumption. Small cerebral cortex, cerebellar and caudate along with large cerebral white matter and 5th ventricle volumes are shown to be significantly associated with increased AUD severity. When these volume variations are compared with control subject volumes; the variations seen in subjects with AUD are markedly different from normal aging effects. CNVs at 11 q14.2 are marginally (p < 0.05 uncorrected) correlated with such brain volume variations and the correlation holds true after controlling for long-term alcohol consumption; deletion carriers have smaller cerebral cortex, cerebellar, caudate and larger cerebral white matter and 5th ventricle volumes than insertion carriers or subjects with no variation in this region. Similarly, deletion carriers also demonstrate higher AUD severity scores than insertion carriers or subjects with no variation. The results presented here suggest that copy number variation and in particular the variation at chromosome 11 q14.2 may have an impact in brain volume variation, potentially influencing AUD behavior.

A comparison of Val81Met and other polymorphisms of alcohol metabolising genes in patients and controls in Northern Spain

The aim of this paper is to study polymorphism in the TH, ADH1B, ADH1C, ALDH2 and CYP2E1 genes so as to ascertain whether it is associated with excessive consumption of alcohol. The SNPs rs6356 of TH, rs1229984, rs2066702 of ADH1B; rs698, rs1693482 of ADH1C; rs671 of ALDH2; rs72559710, rs55897648, rs6413419, rs3813867, rs2031920, rs6413432 of CYP2E1 were studied in a sample of 172 high-level patients and 150 fully non-drinkers controls. Genotyping was performed using Rt-PCR with Taqman probes. SNPs located at ALDH2 and CYP2E1 showed no heterozygosity. Frequency distribution showed significant differences between the two groups studied for loci TH and ADH1B. The genotype Val/Val of TH locus increased in risk 1.988 times (95% CI: 1.006-3.930) that the subjects carrying the genotype Met/Met; and the genotype ADH1B*1/*1 of ADH1B locus increased in risk 3.811 times (CI: 1.660-8.749) that the subjects carrying the genotype ADH1B*1/*2. Alleles Val and ADH1B*1 may therefore increase the risk of the onset and development of this illness.

Additive effects of the dopamine D2 receptor and dopamine transporter genes on the error-related negativity in young children

The error-related negativity (ERN) is a negative deflection in the event-related potential that occurs approximately 50 ms following the commission of an error at fronto-central electrode sites. Previous models suggest dopamine plays a role in the generation of the ERN. We recorded event-related potentials (ERPs) while 279 children aged 5-7 years completed a simple Go/No-Go task; the ERN was examined in relation to the dopamine D2 receptor (DRD2) and dopamine transporter (DAT1) genes. Results suggest an additive effect of the DRD2 and DAT1 genotype on ERN magnitude such that children with at least one DRD2 A1 allele and children with at least one DAT1 9 allele have an increased (i.e. more negative) ERN. These results provide further support for the involvement of dopamine in the generation of the ERN.

Association of the ALDH1A1*2 promoter polymorphism with alcohol phenotypes in young adults with or without ALDH2*2

BACKGROUND

Prior studies suggest a possible association of a promoter polymorphism in the ALDH1A1 gene ( ALDH1A1*2 ) with alcohol use or dependence. The aim of this study was to examine the association of ALDH1A1*2 with drinking behaviors in Asian young adults and to examine ALDH2 genotype as a potential moderator of these associations.

METHODS

Asian young adults (n = 951) were recruited from 2 college sites for studies of genetic associations with alcohol use behavior. Participants completed comprehensive background questionnaires on demographics and drinking behavior. Fingertip blood samples were obtained for DNA extraction and analysis.

RESULTS

Participants with the ALDH2*1/*2 genotype reported significantly lower levels (frequency and quantity) of drinking within the last 90 days, fewer numbers of heavy drinking episodes within the last 90 days, and lower lifetime maximum consumption levels compared with ALDH2*1/*1 participants. There were no significant main effects of ALDH1A1*2 on any drinking variables, nor was there a significant interaction between ALDH2 and ALDH1A1 genotypes on drinking outcomes.

CONCLUSIONS

The association of ALDH2*2 with reduced alcohol consumption replicates previous findings across numerous studies. Although ALDH1A1*2 was not associated with drinking levels, the lack of an ALDH1A1*2 effect in ALDH2*2 individuals is consistent with the only other study that has examined these associations in East Asian populations.

Genetic variations in the dopaminergic system and alcohol use: a system-level analysis

Alcohol use is highly heritable and has been associated with many gene variants, including those related to dopamine (DA). However, single gene association studies have shown inconsistent and small effects. Using a system-level approach, the current study aimed to estimate the overall effect of genetic variations in the DA system on alcohol use among male drinkers. One hundred seventy-six male college students who reported to have ever drunk alcohol were enrolled. Alcohol use was measured using the Alcohol Use Disorders Identification Test. Ninety-eight representative polymorphisms in all major DA neurotransmitter genes were genotyped. Using analysis of variance, we identified six single-nucleotide polymorphisms (SNP)s that made statistically significant contributions to alcohol use. Next, main effects and interactions of these SNPs were assessed using multiple regression. The final model accounted for approximately 20% of the variance for alcohol use. Finally, permutation analyses ascertained the probability of obtaining these findings by chance to be low, p ranging from 0.024 to 0.048. These results confirmed that DA-related gene variants made strong contributions to reported alcohol use and suggest that multiple regression can be a promising way to explore the genetic basis for multi-gene-determined human behaviors.

Genome-wide association study of alcohol dependence implicates KIAA0040 on chromosome 1q

Previous studies using SAGE (the Study of Addiction: Genetics and Environment) and COGA (the Collaborative Study on the Genetics of Alcoholism) genome-wide association study (GWAS) data sets reported several risk loci for alcohol dependence (AD), which have not yet been well replicated independently or confirmed by functional studies. We combined these two data sets, now publicly available, to increase the study power, in order to identify replicable, functional, and significant risk regions for AD. A total of 4116 subjects (1409 European-American (EA) cases with AD, 1518 EA controls, 681 African-American (AA) cases, and 508 AA controls) underwent association analysis. An additional 443 subjects underwent expression quantitative trait locus (eQTL) analysis. Genome-wide association analysis was performed in EAs to identify significant risk genes. All available markers in the genome-wide significant risk genes were tested in AAs for associations with AD, and in six HapMap populations and two European samples for associations with gene expression levels. We identified a unique genome-wide significant gene--KIAA0040--that was enriched with many replicable risk SNPs for AD, all of which had significant cis-acting regulatory effects. The distributions of -log(p) values for SNP-disease and SNP-expression associations for all markers in the TNN-KIAA0040 region were consistent across EAs, AAs, and five HapMap populations (0.369 ≤ r ≤ 0.824; 2.8 × 10⁻⁹ ≤ p ≤ 0.032). The most significant SNPs in these populations were in high LD, concentrating in KIAA0040. Finally, expression of KIAA0040 was significantly (1.2 × 10⁻¹¹ ≤ p ≤1 .5 × 10⁻⁶) associated with the expression of numerous genes in the neurotransmitter systems or metabolic pathways previously associated with AD. We concluded that KIAA0040 might harbor a causal variant for AD and thus might directly contribute to risk for this disorder. KIAA0040 might also contribute to the risk of AD via neurotransmitter systems or metabolic pathways that have previously been implicated in the pathophysiology of AD. Alternatively, KIAA0040 might regulate the risk via some interactions with flanking genes TNN and TNR. TNN is involved in neurite outgrowth and cell migration in hippocampal explants, and TNR is an extracellular matrix protein expressed primarily in the central nervous system.

Interaction between the DRD4 VNTR polymorphism and proximal and distal environments in alcohol dependence during emerging and young adulthood

The manifestation of alcohol dependence at different developmental stages may be associated with different genetic and environmental factors. Taking a developmental approach, we characterized interaction between the dopamine receptor 4 variable number tandem repeat (DRD4 VNTR) polymorphism and developmentally specific environmental factors (childhood adversity, college/Greek organization involvement, and delayed adult role transition) on alcohol dependence during emerging and young adulthood. Prospective data were obtained from a cohort of 234 White individuals (56% women, 44% men) who were followed up at ages 18 through 34. A longitudinal hierarchical factor model was estimated to model a traitlike persistent alcohol dependence factor throughout emerging and young adulthood and 2 residual statelike alcohol dependence factors limited to emerging adulthood and young adulthood, respectively. We accounted for those alcohol dependence factors by modeling 3 two-way interaction effects between the DRD4 VNTR polymorphism and the 3 developmentally specific environment factors. Carriers of the DRD4 long allele showed greater susceptibility to environmental effects; they showed more persistent symptoms of alcohol dependence as childhood adversity increased and more alcohol dependence symptoms limited to emerging adulthood as college/Greek organization involvement increased. Alcohol dependence among noncarriers of the long allele, however, did not differ as a function of those environments. Although replication is necessary, these findings highlight the importance of repeated phenotypic assessments across development and modeling both distal and proximal environments and their interaction with genetic susceptibility at specific developmental stages.

Could a continuous measure of individual transmissible risk be useful in clinical assessment of substance use disorder? Findings from the National Epidemiological Survey on Alcohol and Related Conditions

OBJECTIVE

Toward meeting the need for a measure of individual differences in substance use disorder (SUD) liability that is grounded in the multifactorial model of SUD transmission, this investigation tested to what degree transmissible SUD risk is better measured using the continuous Transmissible Liability Index (TLI) (young adult version) compared to alternative contemporary clinical methods.

METHOD

Data from 9535 18- to 30-year-olds in the 2001-2002 National Epidemiologic Survey on Alcohol and Related Conditions, a U.S. representative sample, were used to compute TLI scores and test hypotheses. Other variables were SUDs of each DSM-IV drug class, clinical predictors of SUD treatment outcomes, treatment seeking and usage, age of onset of SUDs and substance use (SU), and eligibility for SUD clinical trials.

RESULTS

TLI scores account for variation in SUD risk over and above parental lifetime SUD, conduct and antisocial personality disorder criteria and frequency of SU. SUD risk increases two- to four-fold per standard deviation increment in TLI scores. The TLI is associated with SUD treatment seeking and usage, younger age of onset of SU and SUD, and exclusion from traditional clinical trials of SUD treatment.

CONCLUSIONS

The TLI can identify persons with high versus low transmissible SUD risk, worse prognosis of SUD recovery and to whom extant SUD clinical trials results may not generalize. Recreating TLI scores in extant datasets facilitates etiology and applied research on the full range of transmissible SUD risk in development, treatment and recovery without obtaining new samples.

Association of polymorphisms in HTR2A, HTR1A and TPH2 genes with suicide attempts in alcohol dependence: a preliminary report

We investigated a relationship between selected polymorphisms: rs6313 in HTR2A, rs6295 in HTR1A and rs1386494 in TPH2, and suicidal behaviour in 150 alcohol-dependent patients. There was a significant association between more frequent C102C genotype in HTR2A and suicide attempts in alcoholic females. No differences in genotype distribution in HTR1A and TPH2 SNPs were found between patients with and without suicide attempts.

Positive and negative effects of alcohol and nicotine and their interactions: a mechanistic review

Nicotine and alcohol are two of the most commonly abused legal substances. Heavy use of one drug can often lead to, or is predictive of, heavy use of the other drug in adolescents and adults. Heavy drinking and smoking alone are of significant health hazard. The combination of the two, however, can result in synergistic adverse effects particularly in incidences of various cancers (e.g., esophagus). Although detrimental consequences of smoking are well established, nicotine by itself might possess positive and even therapeutic potential. Similarly, alcohol at low or moderated doses may confer beneficial health effects. These opposing findings have generated considerable interest in how these drugs act. Here we will briefly review the negative impact of drinking-smoking co-morbidity followed by factors that appear to contribute to the high rate of co-use of alcohol and nicotine. Our main focus will be on what research is telling us about the central actions and interactions of these drugs, and what has been elucidated about the mechanisms of their positive and negative effects. We will conclude by making suggestions for future research in this area.

Identifying neurobiological phenotypes associated with alcohol use disorder severity

Although numerous studies provide general support for the importance of genetic factors in the risk for alcohol use disorders (AUDs), candidate gene and genome-wide studies have yet to identify a set of genetic variations that explain a significant portion of the variance in AUDs. One reason is that alcohol-related phenotypes used in genetic studies are typically based on highly heterogeneous diagnostic categories. Therefore, identifying neurobiological phenotypes related to neuroadaptations that drive the development of AUDs is critical for the future success of genetic and epigenetic studies. One such neurobiological phenotype is the degree to which exposure to alcohol taste cues recruits the basal ganglia, prefrontal cortex, and motor areas, all of which have been shown to have a critical role in addictive behaviors in animal studies. To that end, this study was designed to examine whether cue-elicited responses of these structures are associated with AUD severity in a large sample (n=326) using voxelwise and functional connectivity measures. Results suggested that alcohol cues significantly activated dorsal striatum, insula/orbitofrontal cortex, anterior cingulate cortex, and ventral tegmental area. AUD severity was moderately correlated with regions involved in incentive salience such as the nucleus accumbens and amygdala, and stronger relationships with precuneus, insula, and dorsal striatum. The findings indicate that AUDs are related to neuroadaptations in these regions and that these measures may represent important neurobiological phenotypes for subsequent genetic studies.

Addiction-like behavior in Drosophila

Alcohol abuse is a pervasive problem known to be influenced by genetic factors, yet our understanding of the mechanisms underlying alcohol addiction is far from complete. Drosophila melanogaster has been established as a model for studying the molecular mechanisms that mediate the acute and chronic effects of alcohol. However, the Drosophila model has not yet been extended to include more complex alcohol-related behaviors such as self-administration. We recently established a paradigm to characterize ethanol consumption and preference in flies. We demonstrated that flies prefer to consume ethanol-containing food over regular food, and this preference exhibits several features of alcohol addiction: flies increase ethanol consumption over time, they consume ethanol to pharmacologically relevant concentrations, they will overcome an aversive stimulus in order to consume ethanol, and they exhibit relapse after a period of ethanol deprivation. Thus, ethanol preference in flies provides a new model for studying important aspects of addiction and their underlying mechanisms. One mutant that displayed decreased ethanol preference, krasavietz, may represent a first step toward uncovering those mechanisms.

Ethanol-induced effects on the dopamine and serotonin systems in adult Wistar rats are dependent on early-life experiences

Some individuals control their ethanol consumption throughout life, but others escalate their intake to levels that increase the risk for addiction. The early environment influences the individual response to ethanol and affects the underlying physiological processes that lead to a transition from a voluntary to a compulsive use of ethanol. However, the neurobiological substrates for these processes are not understood. The present study aimed to test the hypothesis that early environmental experiences affect the neurobiological effects that are induced by voluntary ethanol consumption. Rat pups were subjected to three different rearing environments: conventional animal facility rearing or separation from dam and littermates for either 15 or 360min. In adulthood, the rats were exposed to a two-bottle free choice between ethanol and water for seven weeks. Tissue levels of dopamine, 5-hydroxytryptamine (5-HT) and their metabolites were measured in brain areas that have been implicated in reward and addiction processes. Differences in ethanol-induced effects were noted in 5-HT-related measurements in the nucleus accumbens and ventral tegmental area and in dopamine-related measurements in the dorsal raphe nucleus (DRN). These results provided evidence of an early environmental impact on interactive neuronal circuits between the DRN and reward pathways. The amygdala, a key area in addiction processes, was particularly sensitive to early-life conditions. The animals that experienced the longest separation differed from the others; they had low basal 5-HT levels and responded with an increase in 5-HT after ethanol. These altered responses to initial ethanol consumption as a result of early environmental factors may affect the transition from habitual to compulsive drinking and contribute to individual vulnerability or resilience to addiction.

The influence of gene-environment interactions on alcohol consumption and alcohol use disorders: a comprehensive review

Since 2005, a rapidly expanding literature has evaluated whether environmental factors such as socio-cultural context and adversity interact with genetic influences on drinking behaviors. This article critically reviews empirical research on alcohol-related genotype-environment interactions (GxE) and provides a contextual framework for understanding how genetic factors combine with (or are shaped by) environmental factors to influence the development of drinking behaviors and alcohol use disorders. Collectively, evidence from twin, adoption, and molecular genetic studies indicates that the degree of importance of genetic influences on risk for drinking outcomes can vary in different populations and under different environmental circumstances. However, methodological limitations and lack of consistent replications in this literature make it difficult to draw firm conclusions regarding the nature and effect size of alcohol-related GxE. On the basis of this review, we describe several methodological challenges as they relate to current research on GxE in drinking behaviors and provide recommendations to aid future research.