Association of ADH and ALDH genes with alcohol dependence in the Irish Affected Sib Pair Study of alcohol dependence (IASPSAD) sample

On the Neurobiological Role of Oxidative Stress in Alcohol-Induced Impulsive, Aggressive and Suicidal Behavior

Objectives: Alcohol abuse is known to result in behavioral impairments (such as increased impulsivity, aggressive, and suicidal behavior), but the neurobiological basis for these behavioral impairments remains unknown. The objective of this review is to propose a neurobiological basis for alcohol-induced aggression, impulsivity, and suicidal behavior. Methods: Search was done by accessing PubMed/Medline, EBSCO, and PsycINFO databases. The search string used was "(Alcohol OR Alcoholism* OR Alcohol Abuse) AND (Behavior* OR Behavioral Impairment or Disorder) AND (Oxidative Stress OR Reactive Oxygen Species)." The electronic databases were searched for titles or abstracts containing these terms in all published articles between January 1, 1960, and May 31, 2019. The search was limited to studies published in English and other languages involving both animal and human subjects. Articles selected included randomized clinical trials (RCTs), observational studies, meta-analyses, and both systemic and narrative reviews, providing both quantitative and qualitative information with a measure of alcohol abuse or alcoholism as an outcome. Exclusion criteria were unpublished data of any form, including conference proceedings and dissertation. New key terms were identified (new term included: "Antioxidants, Neurotransmitters, Dopamine, Serotonin, GABA, Glutamate. Aggression, Impulsivity, Suicidal Behavior, hippocampus, prefrontal cortex, limbic system, psychiatric disorders, PTSD, Anxiety, Depression. These new terms were searched with Alcohol or Alcoholism or Alcohol Abuse and Oxidative Stress separately resulting in the identification of over 3000 articles. 196 were included in this article. Results: Multiple lines of evidence indicate that oxidative stress (OS) plays a critical underlying role in alcohol toxicity and behavioral impairments. Conclusions/Importance: People diagnosed with PTSD, anxiety disorder, depression, and those with a personality high in psychoticism as measured by the P Scale of the Eysenck Personality Questionnaire, with comorbid alcohol abuse or alcohol use disorder (AUD), may display increased impulsivity, aggression, and suicidal behavior because of the potentiating effect of alcohol-induced OS on their elevated brain oxidative status. Antioxidant therapy should be an integral part of acute alcohol intoxication and AUD treatment. Further research is necessary to fully understand the relationship between OS and alcohol-induced behavioral impairments.

Alcohol Dehydrogenases, Aldehyde Dehydrogenases, and Alcohol Use Disorders: A Critical Review

Alcohol use disorders (AUDs) are complex traits, meaning that variations in many genes contribute to the risk, as does the environment. Although the total genetic contribution to risk is substantial, most individual variations make only very small contributions. By far the strongest contributors are functional variations in 2 genes involved in alcohol (ethanol [EtOH]) metabolism. A functional variant in alcohol dehydrogenase 1B (ADH1B) is protective in people of European and Asian descent, and a different functional variant in the same gene is protective in those of African descent. A strongly protective variant in aldehyde dehydrogenase 2 (ALDH2) is essentially only found in Asians. This highlights the need to study a wide range of populations. The likely mechanism of protection against heavy drinking and AUDs in both cases is alteration in the rate of metabolism of EtOH that at least transiently elevates acetaldehyde. Other ADH and ALDH variants, including functional variations in ADH1C, have also been implicated in affecting drinking behavior and risk for alcoholism. The pattern of linkage disequilibrium in the ADH region and the differences among populations complicate analyses, particularly of regulatory variants. This critical review focuses upon the ADH and ALDH genes as they affect AUDs.

Comparative Metagenomic Analysis of Rhizosphere Microbial Community Composition and Functional Potentials under Rehmannia glutinosa Consecutive Monoculture

Consecutive monoculture of Rehmannia glutinosa, highly valued in traditional Chinese medicine, leads to a severe decline in both quality and yield. Rhizosphere microbiome was reported to be closely associated with the soil health and plant performance. In this study, comparative metagenomics was applied to investigate the shifts in rhizosphere microbial structures and functional potentials under consecutive monoculture. The results showed R. glutinosa monoculture significantly decreased the relative abundances of Pseudomonadaceae and Burkholderiaceae, but significantly increased the relative abundances of Sphingomonadaceae and Streptomycetaceae. Moreover, the abundances of genera Pseudomonas, Azotobacter, Burkholderia, and Lysobacter, among others, were significantly lower in two-year monocultured soil than in one-year cultured soil. For potentially harmful/indicator microorganisms, the percentages of reads categorized to defense mechanisms (i.e., ATP-binding cassette (ABC) transporters, efflux transporter, antibiotic resistance) and biological metabolism (i.e., lipid transport and metabolism, secondary metabolites biosynthesis, transport and catabolism, nucleotide transport and metabolism, transcription) were significantly higher in two-year monocultured soil than in one-year cultured soil, but the opposite was true for potentially beneficial microorganisms, which might disrupt the equilibrium between beneficial and harmful microbes. Collectively, our results provide important insights into the shifts in genomic diversity and functional potentials of rhizosphere microbiome in response to R. glutinosa consecutive monoculture.

A Critical Review of Methods and Results in the Search for Genetic Contributors to Alcohol Sensitivity

Attributes of alcohol sensitivity are present before alcohol use disorders (AUDs) develop, they predict those adverse alcohol outcomes, are familial in nature, and many are heritable. Whether measured by alcohol challenges or retrospective reports of numbers of drinks required for effects, alcohol sensitivity reflects multiple phenotypes, including low levels of alcohol response and alcohol-related stimulation. Identification of genes that contribute to alcohol sensitivity could help identify individuals carrying risks for AUDs through their alcohol responses for whom early intervention might mitigate their vulnerability. Such genes could also improve understanding of biological underpinnings of AUDs, which could lead to new treatment approaches. However, the existing literature points to a wide range of genetic mechanisms that might contribute to alcohol responses, and few such genetic findings have been widely replicated. This critical review describes the potential impact of the diverse methods used to study sensitivity on the diversity of genetic findings that have been reported, places the genetic variants mentioned in the literature into broader categories rather than isolated results, and offers suggestions regarding how to advance the field by interpreting findings in light of the methods used to select research subjects and to measure alcohol sensitivity. To date, the most promising results have been for GABA, glutamate, opioid, dopamine, serotonin, and cholinergic system genes. The more gene variants that can be identified as contributors to sensitivity the better future gene screening platforms or polygenic scores are likely to be.

Association of alcohol dehydrogenase 1C gene *1/*2 polymorphism with alcohol Dependence(AD) in Turkey: A meta-analysis

Previous studies have investigated the association between ADH1C ^*1/^*2 polymorphism and alcohol dependence (AD), but have yielded controversial results in Turkey. Therefore, in an effort to illustrate whether ADH1C ^*1/^*2 polymorphism is associated with AD risk in Turkish population, we used meta analysis to synthetically evaluate the effect of ADH1C ^*1/^*2 polymorphism on AD. Publications were identified by searching in PubMed and EMBASE databases. Four eligible studies involving 400 controls and 421 cases were included in this study. Overall, there is a significant association between ADH1C ^*1/^*2 polymorphism and AD risk in the allelic model (OR = 1.66, 95% CI = 1.05-2.62, P = 0.03) and recessive model (OR = 1.72, 95% CI = 1.14-2.58, P = 0.01), while no significance was discovered in the dominant genetic model, homozygote model and heterozygotemodel. No publication bias was indicated from Begg's and Egger's test. Our meta-analysis results suggested that a potential relationship between ADH1C ^*1/^*2 polymorphism and AD risk in Turkish population. Further studies are confirmed to resolve this question about the etiological mechanisms of the correlation.

Associations between alcohol dehydrogenase genes and alcohol use across early and middle adolescence: Moderation × Preventive intervention

Data from the in-school sample of the PROSPER preventive intervention dissemination trial were used to investigate associations between alcohol dehydrogenase genes and alcohol use across adolescence, and whether substance misuse interventions in the 6th and 7th grades (targeting parenting, family functioning, social norms, youth decision making, and peer group affiliations) modified associations between these genes and adolescent use. Primary analyses were run on a sample of 1,885 individuals and included three steps. First, we estimated unconditional growth curve models with separate slopes for alcohol use from 6th to 9th grade and from 9th to 12th grade, as well as the intercept at Grade 9. Second, we used intervention condition and three alcohol dehydrogenase genes, 1B (ADH1B), 1C (ADH1C), and 4 (ADH4) to predict variance in slopes and intercept. Third, we examined whether genetic influences on model slopes and intercepts were moderated by intervention condition. The results indicated that the increase in alcohol use was greater in early adolescence than in middle adolescence; two of the genes, ADH1B and ADH1C, significantly predicted early adolescent slope and Grade 9 intercept, and associations between ADH1C and both early adolescent slope and intercept were significantly different across control and intervention conditions.

First description and evaluation of SNPs in the ADH and ALDH genes in a population of alcoholics in Central-West Brazil

Worldwide, different studies have reported an association of alcohol-use disorder (AUD) with different types of Single Nucleotide Polymorphisms (SNPs) in the genes for aldehyde dehydrogenase (ALDH) and alcohol dehydrogenase (ADH). In Brazil, there is little information about the occurrence of these SNPs in the AUD population and an absence of studies characterizing the population in the Central-West Region of Brazil. Actually, in Brazil, there are more than 4 million people with AUD. Despite the major health hazards of AUD, information on alcohol consumption and its consequences are not well understood. Therefore, it is extremely important to characterize these SNPs for the better understanding of AUD as a genetic disease in the Brazilian population. The present study, unlike other studies in other countries, is done with a subject population that shows a significant amount of racial homogenization. We evaluated the presence of SNPs in the ADH (ADH1B, ADH1C, and ADH4) and ALDH (ALDH2) genes in alcohol users of Goiânia, State of Goiás - Brazil, and then we established a possible relationship with AUD by allelic and genotypic study. This study was conducted with a population of people with AUD (n = 99) from Goiás Alcohol Dependence Recovery Center (GO CEREA) and Psychosocial Care Center for Alcohol and Drugs (CAPS AD), and with a population of people without AUD as controls (n = 100). DNA was extracted from whole-blood samples and the genotyping was performed using TaqMan^® SNP genotyping assays. For characterization and evaluation of SNPs in the population, genotype frequency, allele frequency, haplotype frequency, Hardy-Weinberg equilibrium, and linkage disequilibrium were analyzed. Statistical analyses were calculated by GENEPOP 4.5 and Haploview software. The allele 1 was considered as "wild" (or *1) and allele 2 as mutant (or *2). Significant differences were found for ADH1B*, ADH4*2, and ALDH2*2 SNPs when the genotype and allele frequencies were analyzed. In addition, four haplotypes were observed between ADH1B*2 and ADH1C*2 through linkage disequilibrium analysis. The genetic variants may be associated with protection against AUD in the population studied.

Analysis of the Association of Nonsynonymous Polymorphisms in ADH Genes with Hazardous Drinking in HIV-1-Positive Individuals

BACKGROUND

Hazardous drinking (HD) is a serious health problem in people infected with human immunodeficiency virus type 1 (HIV-1). Single nucleotide polymorphisms (SNPs) in alcohol dehydrogenase (ADH) genes have been associated with HD in different populations, but there were no data about this in HIV-1-positive individuals. This study investigated the association of 4 nonsynonymous SNPs in ADH genes (Arg48His and Arg370Cys in ADH1B gene; Arg272Gln and Ile350Val in ADH1C gene) with HD in people living with HIV-1.

METHODS

This case-control study included 365 HIV-1-positive individuals (121 with HD and 244 without HD). Sociodemographic variables were collected with a standardized individual questionnaire. HD (score ≥8) and binge drinking (BD) (drinks on the same occasion ≥5) were detected with the Alcohol Use Disorders Identification Test. The 4 SNPs were genotyped by the polymerase chain reaction-restriction fragment length polymorphism method. Adjusted odds ratios (aORs) and 95% confidence intervals (CIs) were calculated using logistic regression analysis. The Bonferroni correction was used (considering the 4 SNPs studied).

RESULTS

There were no significant differences in the frequencies of Arg370Cys, Arg272Gln, and Ile350Val polymorphisms between HD cases and controls. Otherwise, Arg/His genotype (rs1229984) in ADH1B gene showed a protective effect against HD (aOR = 0.36; 95% CI: 0.14 to 0.90) and BD (aOR = 0.49; 95% CI: 0.21 to 0.95). Nevertheless, these differences were no longer significant after Bonferroni correction.

CONCLUSIONS

The results of this study suggest a possible effect of the Arg48His genotype on the protection against HD in HIV-1-positive individuals.

Associations Between Genomic Variants in Alcohol Dehydrogenase Genes and Alcohol Symptomatology in American Indians and European Americans: Distinctions and Convergence

BACKGROUND

Higher rates of alcohol use disorders (AUD) have been observed in some Native American populations than other ethnic groups such as European Americans (EAs) in the United States. Previous studies have shown that variation in the alcohol dehydrogenase (ADH) genes may affect the risk for development of AUD and that the prevalence of these variants differs depending on the ancestral origins of a population.

METHODS

In this study, we assessed sequencing variants in the ADH genomic region (ADH1-7) and tested for their associations with AUD phenotypes in 2 independent populations: an American Indian (AI) community sample and an EA cohort from the San Francisco Family Alcohol Study. Association tests were conducted for both common and rare variants using sequencing data for 2 phenotypes: the number of alcohol-related life events and the count of alcohol dependence drinking symptoms. A regularized regression method was used to select the best set of ADH variants associated with phenotypes. Variance component model was incorporated in all analyses to leverage the admixture and relatedness.

RESULTS

Two variants near ADH4 and 2 near ADH1C exhibited significant associations with AUD in AIs; no variant was significant in EAs. Common risk variants in AIs were either absent from or much less frequent in EAs. The feature selection method selected mostly distinct yet often colocated subsets of ADH variants to be associated with AUD phenotypes between the 2 cohorts. In the rare-variant analyses, the only association was observed between the whole region and the alcohol-related life events in AIs.

CONCLUSIONS

Our results suggest that ADH variants, both common and rare, are more likely to impact risk for alcohol-related symptomatology in this AI population than in this EA sample, and ADH variants that might affect AUD are likely different but convergent on similar regions between the 2 populations.

Genetic influences on adolescent behavior

Adolescence is a transitional, developmental phase with marked shifts in behavior, particularly as related to risk-taking and experimentation. Genetic influences on adolescent behavior also show marked changes across this developmental period; in fact, adolescence showcases the dynamic nature of genetic influences on human behavior. Using the twin studies literature on alcohol use and misuse, we highlight several principles of genetic influence on adolescent behavior. We illustrate how genetic influences change (increase) across adolescence, as individuals have more freedom to express their predispositions and to shape their social worlds. We show how there are multiple genetic pathways to risk, and how the environment can moderate the importance of genetic predispositions. Finally, we review the literature aimed at identifying specific genes involved in adolescent behavior and understanding how identified genes impact adolescent outcomes. Ultimately, understanding how genetic predispositions combine with environmental influences to impact pathways of risk and resilience should be translated into improved prevention and intervention efforts; this remains a rich area for future research.

Genetics of alcoholism

Multiple lines of evidence strongly indicate that genetic factors contribute to the risk for alcohol use disorders (AUD). There is substantial heterogeneity in AUD, which complicates studies seeking to identify specific genetic factors. To identify these genetic effects, several different alcohol-related phenotypes have been analyzed, including diagnosis and quantitative measures related to AUDs. Study designs have used candidate gene analyses, genetic linkage studies, genomewide association studies (GWAS), and analyses of rare variants. Two genes that encode enzymes of alcohol metabolism have the strongest effect on AUD: aldehyde dehydrogenase 2 and alcohol dehydrogenase 1B each has strongly protective variants that reduce risk, with odds ratios approximately 0.2-0.4. A number of other genes important in AUD have been identified and replicated, including GABRA2 and alcohol dehydrogenases 1B and 4. GWAS have identified additional candidates. Rare variants are likely also to play a role; studies of these are just beginning. A multifaceted approach to gene identification, targeting both rare and common variations and assembling much larger datasets for meta-analyses, is critical for identifying the key genes and pathways important in AUD.

Drosophila and Caenorhabditis elegans as Discovery Platforms for Genes Involved in Human Alcohol Use Disorder

BACKGROUND

Despite the profound clinical significance and strong heritability of alcohol use disorder (AUD), we do not yet have a comprehensive understanding of the naturally occurring genetic variance within the human genome that drives its development. This lack of understanding is likely to be due in part to the large phenotypic and genetic heterogeneities that underlie human AUD. As a complement to genetic studies in humans, many laboratories are using the invertebrate model organisms (iMOs) Drosophila melanogaster (fruit fly) and Caenorhabditis elegans (nematode worm) to identify genetic mechanisms that influence the effects of alcohol (ethanol) on behavior. While these extremely powerful models have identified many genes that influence the behavioral responses to alcohol, in most cases it has remained unclear whether results from behavioral-genetic studies in iMOs are directly applicable to understanding the genetic basis of human AUD.

METHODS

In this review, we critically evaluate the utility of the fly and worm models for identifying genes that influence AUD in humans.

RESULTS

Based on results published through early 2015, studies in flies and worms have identified 91 and 50 genes, respectively, that influence 1 or more aspects of behavioral responses to alcohol. Collectively, these fly and worm genes correspond to 293 orthologous genes in humans. Intriguingly, 51 of these 293 human genes have been implicated in AUD by at least 1 study in human populations.

CONCLUSIONS

Our analyses strongly suggest that the Drosophila and C. elegans models have considerable utility for identifying orthologs of genes that influence human AUD.

Genetic variants in or near ADH1B and ADH1C affect susceptibility to alcohol dependence in a British and Irish population

Certain single nucleotide polymorphisms (SNPs) in genes encoding alcohol dehydrogenase (ADH) enzymes confer a significant protective effect against alcohol dependence syndrome (ADS) in East Asian populations. Recently, attention has focused on the role of these SNPs in determining ADS risk in European populations. To further elucidate these associations, SNPs of interest in ADH1B, ADH1C and the ADH1B/1C intergenic region were genotyped in a British and Irish population (ADS cases n = 1076: controls n = 1027) to assess their relative contribution to ADS risk. A highly significant, protective association was observed between the minor allele of rs1229984 in ADH1B and ADS risk [allelic P = 8.4 × 10(-6) , odds ratio (OR) = 0.26, 95 percent confidence interval, 0.14, 0.49]. Significant associations were also observed between ADS risk and the ADH1B/1C intergenic variant, rs1789891 [allelic P = 7.2 × 10(-5) , OR = 1.4 (1.2, 1.6)] and three non-synonymous SNPs rs698, rs1693482 and rs283413 in ADH1C. However, these associations were not completely independent; thus, while the ADH1B rs1229984 minor allele association was independent of those of the intergenic variant rs1789891 and the three ADH1C variants, the three ADH1C variants were not individually independent. In conclusion, the rare ADH1B rs1229984 mutation provides significant protection against ADS in this British and Irish population; other variants in the ADH gene cluster also alter ADS risk, although the strong linkage disequilibrium between SNPs at this location precluded clear identification of the variant(s) driving the associations.

Childhood adversity moderates the effect of ADH1B on risk for alcohol-related phenotypes in Jewish Israeli drinkers

Childhood adversity and genetic variant ADH1B-rs1229984 have each been shown to influence heavy alcohol consumption and disorders. However, little is known about how these factors jointly influence these outcomes. We assessed the main and additive interactive effects of childhood adversity (abuse, neglect and parental divorce) and the ADH1B-rs1229984 on the quantitative phenotypes 'maximum drinks in a day' (Maxdrinks) and DSM-Alcohol Use Disorder (AUD) severity, adjusting for demographic variables, in an Israeli sample of adult household residents (n = 1143) evaluated between 2007 and 2009. Childhood adversity and absence of the protective ADH1B-rs1229984 A allele were associated with greater mean Maxdrinks (mean differences: 1.50; 1.13, respectively) and AUD severity (mean ratios: 0.71; 0.27, respectively). In addition, childhood adversity moderated the ADH1B-rs1229984 effect on Maxdrinks (P < 0.01) and AUD severity (P < 0.05), in that there was a stronger effect of ADH1B-rs1229984 genotype on Maxdrinks and AUD severity among those who had experienced childhood adversity compared with those who had not. ADH1B-rs1229984 impacts alcohol metabolism. Therefore, among those at risk for greater consumption, e.g. those who experienced childhood adversity, ADH1B-rs1229984 appears to have a stronger effect on alcohol consumption and consequently on risk for AUD symptom severity. Evidence for the interaction of genetic vulnerability and early life adversity on alcohol-related phenotypes provides further insight into the complex relationships between genetic and environmental risk factors.

Protective variant associated with alcohol dependence in a Mexican American cohort

Background

Mexican Americans, particularly those born in the United States, are at greater risk for alcohol associated morbidity and mortality. The present study sought to investigate whether specific genetic variants may be associated with alcohol use disorder phenotypes in a select population of Mexican American young adults.

Methods

The study evaluated a cohort of 427 (age 18 – 30 years) Mexican American men (n = 171) and women (n = 256). Information on alcohol dependence was obtained through interview using the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA). For all subjects, DNA was extracted from blood samples, followed by genotyping using an Affymetrix Axiom Exome1A chip.

Results

A protective variant (rs991316) located downstream from the ADH7 (alcohol dehydrogenase 7) gene showed suggestive significance in association with alcohol dependence symptom counts derived from DSM-III-R and DSM-IV criteria, as well as to clustered alcohol dependence symptoms. Additional linkage analysis suggested that nearby variants in linkage disequilibrium with rs991316 were not responsible for the observed association with the alcohol dependence phenotypes in this study.

Conclusions

ADH7 has been shown to have a protective role against alcohol dependence in previous studies involving other ethnicities, but has not been reported for Mexican Americans. These results suggest that variants near ADH7 may play a role in protection from alcohol dependence in this Mexican American cohort.

Association and ancestry analysis of sequence variants in ADH and ALDH using alcohol-related phenotypes in a Native American community sample

Higher rates of alcohol use and other drug-dependence have been observed in some Native American (NA) populations relative to other ethnic groups in the US. Previous studies have shown that alcohol dehydrogenase (ADH) genes and aldehyde dehydrogenase (ALDH) genes may affect the risk of development of alcohol dependence, and that polymorphisms within these genes may differentially affect risk for the disorder depending on the ethnic group evaluated. We evaluated variations in the ADH and ALDH genes in a large study investigating risk factors for substance use in a NA population. We assessed ancestry admixture and tested for associations between alcohol-related phenotypes in the genomic regions around the ADH1-7 and ALDH2 and ALDH1A1 genes. Seventy-two ADH variants showed significant evidence of association with a severity level of alcohol drinking-related dependence symptoms phenotype. These significant variants spanned across the entire 7 ADH gene cluster regions. Two significant associations, one in ADH and one in ALDH2, were observed with alcohol dependence diagnosis. Seventeen variants showed significant association with the largest number of alcohol drinks ingested during any 24-hour period. Variants in or near ADH7 were significantly negatively associated with alcohol-related phenotypes, suggesting a potential protective effect of this gene. In addition, our results suggested that a higher degree of NA ancestry is associated with higher frequencies of potential risk variants and lower frequencies of potential protective variants for alcohol dependence phenotypes.

Genetics and alcoholism

Alcohol is widely consumed; however, excessive use creates serious physical, psychological and social problems and contributes to the pathogenesis of many diseases. Alcohol use disorders (that is, alcohol dependence and alcohol abuse) are maladaptive patterns of excessive drinking that lead to serious problems. Abundant evidence indicates that alcohol dependence (alcoholism) is a complex genetic disease, with variations in a large number of genes affecting a person's risk of alcoholism. Some of these genes have been identified, including two genes involved in the metabolism of alcohol (ADH1B and ALDH2) that have the strongest known affects on the risk of alcoholism. Studies continue to reveal other genes in which variants affect the risk of alcoholism or related traits, including GABRA2, CHRM2, KCNJ6 and AUTS2. As more variants are analysed and studies are combined for meta-analysis to achieve increased sample sizes, an improved picture of the many genes and pathways that affect the risk of alcoholism will be possible.

Replication of genome wide association studies of alcohol dependence: support for association with variation in ADH1C

Genome-wide association studies (GWAS) have revealed many single nucleotide polymorphisms (SNPs) associated with complex traits. Although these studies frequently fail to identify statistically significant associations, the top association signals from GWAS may be enriched for true associations. We therefore investigated the association of alcohol dependence with 43 SNPs selected from association signals in the first two published GWAS of alcoholism. Our analysis of 808 alcohol-dependent cases and 1,248 controls provided evidence of association of alcohol dependence with SNP rs1614972 in the ADH1C gene (unadjusted p = 0.0017). Because the GWAS study that originally reported association of alcohol dependence with this SNP [1] included only men, we also performed analyses in sex-specific strata. The results suggest that this SNP has a similar effect in both sexes (men: OR (95%CI) = 0.80 (0.66, 0.95); women: OR (95%CI) = 0.83 (0.66, 1.03)). We also observed marginal evidence of association of the rs1614972 minor allele with lower alcohol consumption in the non-alcoholic controls (p = 0.081), and independently in the alcohol-dependent cases (p = 0.046). Despite a number of potential differences between the samples investigated by the prior GWAS and the current study, data presented here provide additional support for the association of SNP rs1614972 in ADH1C with alcohol dependence and extend this finding by demonstrating association with consumption levels in both non-alcoholic and alcohol-dependent populations. Further studies should investigate the association of other polymorphisms in this gene with alcohol dependence and related alcohol-use phenotypes.

Common variants at 12q24 are associated with drinking behavior in Han Chinese

BACKGROUND

Alcohol consumption is heritable, but genetic susceptibility to drinking behavior has not been investigated widely in genome-wide association studies.

OBJECTIVE

We aimed to identify susceptibility loci for drinking behavior (drinkers compared with nondrinkers) in Han Chinese.

DESIGN

We performed 2 genome-wide association studies including 1420 drinkers and 3590 nondrinkers in discovery, followed by a de novo replication analysis comprising 4896 drinkers and 13,293 nondrinkers. DNA samples of the subjects were collected for genotyping.

RESULTS

The association results of drinking behavior (drinkers or nondrinkers) showed a cluster of single nucleotide polymorphisms at 12q24 in discovery (P < 5 × 10(-8)), with the strongest association for rs11066280 near C12orf51 (P-combined = 3.26 × 10(-215)). Moreover, we observed the association with drinking behavior for a functional variant in ALDH2 at 12q24 (rs671, P-discovery = 5.17 × 10(-35)). We also identified the association between rs11066280 and daily alcohol intake among drinkers (P-combined = 4.01 × 10(-21)).

CONCLUSION

Our data indicate that common variants at 12q24 may contribute to the susceptibility of drinking behavior in Han Chinese.

NCK2 is significantly associated with opiates addiction in African-origin men

Substance dependence is a complex environmental and genetic disorder with significant social and medical concerns. Understanding the etiology of substance dependence is imperative to the development of effective treatment and prevention strategies. To this end, substantial effort has been made to identify genes underlying substance dependence, and in recent years, genome-wide association studies (GWASs) have led to discoveries of numerous genetic variants for complex diseases including substance dependence. Most of the GWAS discoveries were only based on single nucleotide polymorphisms (SNPs) and a single dichotomized outcome. By employing both SNP- and gene-based methods of analysis, we identified a strong (odds ratio = 13.87) and significant (P value = 1.33E - 11) association of an SNP in the NCK2 gene on chromosome 2 with opiates addiction in African-origin men. Codependence analysis also identified a genome-wide significant association between NCK2 and comorbidity of substance dependence (P value = 3.65E - 08) in African-origin men. Furthermore, we observed that the association between the NCK2 gene (P value = 3.12E - 10) and opiates addiction reached the gene-based genome-wide significant level. In summary, our findings provided the first evidence for the involvement of NCK2 in the susceptibility to opiates addiction and further revealed the racial and gender specificities of its impact.

Large scale association analysis for drug addiction: results from SNP to gene

Many genetic association studies used single nucleotide polymorphisms (SNPs) data to identify genetic variants for complex diseases. Although SNP-based associations are most common in genome-wide association studies (GWAS), gene-based association analysis has received increasing attention in understanding genetic etiologies for complex diseases. While both methods have been used to analyze the same data, few genome-wide association studies compare the results or observe the connection between them. We performed a comprehensive analysis of the data from the Study of Addiction: Genetics and Environment (SAGE) and compared the results from the SNP-based and gene-based analyses. Our results suggest that the gene-based method complements the individual SNP-based analysis, and conceptually they are closely related. In terms of gene findings, our results validate many genes that were either reported from the analysis of the same dataset or based on animal studies for substance dependence.

Association of alcohol dehydrogenase polymorphisms and life-style factors with excessive alcohol intake within the Spanish population (EPIC-Spain)

AIMS

To analyse associations between alcohol dehydrogenase (ADH) polymorphisms and alcohol intake in Spanish men and women.

DESIGN AND SETTINGS

We analysed the relationship between 21 genetic variants in ADH genes and excessive alcohol intake in both men and women. Single nucleotide polymorphisms (SNPs) were genotyped using a customized array and a sex-stratified analysis was performed.

MEASUREMENTS

Ethanol intake was calculated using a validated dietary history questionnaire.

PARTICIPANTS

Heavy consumers of alcohol (≥70 g/day in men, ≥42 g/day in women) (653 cases) and very low or non-consumers (<2 g/day) (880 controls) from the Spanish cohort of the European Prospective Investigation into Cancer (EPIC).

FINDINGS

We found statistically significant associations between alcohol intake and known life-style factors; namely, smoking and food energy intake (meat and fruit/seeds) in both men and women, as well as with physical activity in women and educational level in men. Additionally, we found that a non-synonymous coding SNP in ADH1B (rs1229984) is associated inversely with excessive alcohol intake in men [odds ratio (OR) = 0.19, 95% confidence interval (CI) = 0.11-0.33; P = 4.77E(-10) ) and women (OR = 0.48, 95% CI = 0.27-0.83; P = 0.0067). Furthermore, ADH6 rs3857224 was found associated with heavy alcohol intake in women (OR = 1.61, 95% CI = 1.21-2.14; P = 1.01E(-3) ), but not in men.

CONCLUSIONS

In the Spanish population, the single nucleotide polymorphism of alcohol dehydrogenase ADH1B, rs1229984, is associated inversely with alcohol intake in both men and women. Another polymorphism of ADH6, rs3857224, is associated with heavy alcohol intake in women.

Fetal alcohol exposure and IQ at age 8: evidence from a population-based birth-cohort study

Background

Observational studies have generated conflicting evidence on the effects of moderate maternal alcohol consumption during pregnancy on offspring cognition mainly reflecting problems of confounding. Among mothers who drink during pregnancy fetal alcohol exposure is influenced not only by mother’s intake but also by genetic variants carried by both the mother and the fetus. Associations between children’s cognitive function and both maternal and child genotype at these loci can shed light on the effects of maternal alcohol consumption on offspring cognitive development.

Methods

We used a large population based study of women recruited during pregnancy to determine whether genetic variants in alcohol metabolising genes in this cohort of women and their children were related to the child’s cognitive score (measured by the Weschler Intelligence Scale) at age 8.

Findings

We found that four genetic variants in alcohol metabolising genes in 4167 children were strongly related to lower IQ at age 8, as was a risk allele score based on these 4 variants. This effect was only seen amongst the offspring of mothers who were moderate drinkers (1–6 units alcohol per week during pregnancy (per allele effect estimates were −1.80 (95% CI = −2.63 to −0.97) p = 0.00002, with no effect among children whose mothers abstained during pregnancy (0.16 (95%CI = −1.05 to 1.36) p = 0.80), p-value for interaction  = 0.009). A further genetic variant associated with alcohol metabolism in mothers was associated with their child’s IQ, but again only among mothers who drank during pregnancy.

Further clarification of the contribution of the ADH1C gene to vulnerability of alcoholism and selected liver diseases

The alcohol dehydrogenase 1C (ADH1C) subunit is an important member of the alcohol dehydrogenase family, a set of genes that plays a major role in the catabolism of ethanol. Numerous association studies have provided compelling evidence that ADH1C gene variation (formerly ADH3) is associated with altered genetic susceptibility to alcoholism and alcohol-related liver disease, cirrhosis, or pancreatitis. However, the results have been inconsistent, partially, because each study involved a limited number of subjects, and some were underpowered. Using cumulative data over the past two decades, this meta-analysis (6,796 cases and 6,938 controls) considered samples of Asian, European, African, and Native American origins to examine whether the aggregate genotype provide statistically significant evidence of association. The results showed strong evidence of association between ADH1C Ile350Val (rs698, formerly ADH1C *1/*2) and alcohol dependence (AD) and abuse in the combined studies. The overall allelic (Val vs. Ile or *2 vs. *1) P value was 1 × 10(-8) and odds ratio (OR) was 1.51 (1.31, 1.73). The Asian populations produced stronger evidence of association with an allelic P value of 4 × 10(-33) [OR 2.14 (1.89, 2.43)] with no evidence of heterogeneity, and the dominant and recessive models revealed even stronger effect sizes. The strong evidence remained when stricter criteria and sub-group analyses were applied, while Asians always showed stronger associations than other populations. Our findings support that ADH1C Ile may lower the risk of AD and alcohol abuse as well as alcohol-related cirrhosis in pooled populations, with the strongest and most consistent effects in Asians.

Twin study of the relationship between adolescent attention-deficit/hyperactivity disorder and adult alcohol dependence

OBJECTIVE

Adolescent problem behaviors such as conduct disorder and attention-deficit/hyperactivity disorder (ADHD) are often associated with alcohol problems in adulthood, particularly alcohol dependence. This association is partly a result of shared genetic liability. However, it is unclear whether ADHD, or an ADHD subtype, shares genetic influences with alcohol dependence beyond those also shared by conduct disorder.

METHOD

We evaluated phenotypic associations between adolescent conduct disorder and ADHD phenotypes with adult alcohol dependence in a population-based sample of adult male twins (N = 1,774). We then assessed genetic and environmental relationships among phenotypes using structural equation modeling.

RESULTS

Individually, conduct disorder and each ADHD factor were associated with adult alcohol dependence. Results from twin modeling indicate that a genetic factor common to conduct disorder and ADHD also loads strongly onto alcohol dependence. Even after controlling for genetic factors shared with conduct disorder and other ADHD factors, the hyperactivity component of ADHD shared significant residual genetic influences with alcohol dependence.

CONCLUSIONS

Most of the genetically mediated association between adolescent ADHD and adult alcohol dependence is shared with conduct disorder, reflecting a generalized risk to externalizing behaviors. The significant residual genetic covariance between the ADHD factor hyperactivity/impulsivity and alcohol dependence implies that impulsive behaviors less destructive/harmful than those manifested by conduct disorder can be indicative of genetic risk for adult alcohol dependence. However, the ADHD factors inattention and forgetfulness are not uniquely predictive of genetic/environmental risk for alcohol dependence.

The genetics of substance dependence

A large segment of the population suffers from addiction to alcohol, smoking, or illicit drugs. Not only do substance abuse and addiction pose a threat to health, but the consequences of addiction also impose a social and economic burden on families, communities, and nations. Genome-wide linkage and association studies have been used for addiction research with varying degrees of success. The most well-established genetic factors associated with alcohol dependence are in the genes encoding alcohol dehydrogenase (ADH), which oxidizes alcohol to acetaldehyde, and aldehyde dehydrogenase (ALDH2), which oxidizes acetaldehyde to acetate. Recently emerging genetic studies have linked variants in the genes encoding the α3, α5, and β4 nicotinic acetylcholine receptor subunits to smoking risk. However, the influence of these well-established genetic variants accounts for only a small portion of the heritability of alcohol and nicotine addiction, and it is likely that there are both common and rare risk variants yet to be identified. Newly developed DNA sequencing technologies could potentially advance the detection of rare variants with a larger impact on addiction risk.

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.

Association between in vivo alcohol metabolism and genetic variation in pathways that metabolize the carbon skeleton of ethanol and NADH reoxidation in the alcohol challenge twin study

BACKGROUND

Variation in alcohol metabolism affects the duration of intoxication and alcohol use. While the majority of genetic association studies investigating variation in alcohol metabolism have focused on polymorphisms in alcohol or aldehyde dehydrogenases, we have now tested for association with genes in alternative metabolic pathways that catalyze the carbon skeleton of ethanol (EtOH) and NADH reoxidation.

METHODS

Nine hundred fifty single nucleotide polymorphisms (SNPs) spanning 14 genes (ACN9, ACSS1, ACSS2, ALDH1A1, CAT, CYP2E1, GOT1, GOT2, MDH1, MDH2, SLC25A10, SLC25A11, SLC25A12, SLC25A13) were genotyped in 352 young adults who participated in an alcohol challenge study. Traits tested were blood alcohol concentration (BAC), breath alcohol concentration (BrAC), peak alcohol concentration, and rates of alcohol absorption and elimination. Allelic association was tested using quantitative univariate and multivariate methods.

RESULTS

A CYP2E1 promoter SNP (rs4838767, minor allele frequency 0.008) exceeded the threshold for study-wide significance (4.01 × 10(-5) ) for 2 early BAC, 8 BrAC measures, and the peak BrAC. For each phenotype, the minor C allele was related to a lower alcohol concentration, most strongly for the fourth BrAC (p = 2.07 × 10(-7) ) explaining ~8% of the phenotypic variance. We also observed suggestive patterns of association with variants in ALDH1A1 and on chromosome 17 near SLC25A11 for aspects of blood and breath alcohol metabolism. An SNP upstream of GOT1 (rs2490286) reached study-wide significance for multivariate BAC metabolism (p = 0.000040).

CONCLUSIONS

Overall, we did not find strong evidence that variation in genes coding for proteins that further metabolize the carbon backbone of acetaldehyde, or contribute to mechanisms for regenerating NAD from NADH, affects alcohol metabolism in our European-descent subjects. However, based on the breath alcohol data, variation in the promoter of CYP2E1 may play a role in preabsorptive or early hepatic alcohol metabolism, but more samples are required to validate this finding.

Strong protective effect of the aldehyde dehydrogenase gene (ALDH2) 504lys (*2) allele against alcoholism and alcohol-induced medical diseases in Asians

Alcohol is oxidized to acetaldehyde, which in turn is oxidized to acetate. The aldehyde dehydrogenase 2 gene (ALDH2) is the most important gene responsible for acetaldehyde metabolism. Individuals heterozygous or homozygous for the lys (A or *2) allele at the single nucleotide polymorphism (SNP) glu504lys (rs671) of ALDH2 have greatly reduced ability to metabolize acetaldehyde, which greatly decreases their risk for alcohol dependence (AD). Case-control studies have shown association between this SNP and alcohol dependence as well as alcohol-induced liver disease. However, some studies have produced insignificant results. Using cumulative data from the past 20 years predominately from Asian populations (from both English and Chinese publications), this meta-analysis sought to examine and update whether the aggregate data provide new evidence of statistical significance for the proposed association. Our results (9,678 cases and 7,331 controls from 53 studies) support a strong association of alcohol abuse and dependence, with allelic P value of 3 × 10(-56) and OR of 0.23 (0.2, 0.28) under the random effects model. The dominant model (lys-lys + lys-glu vs. glu-glu) also showed strong association with P value of 1 × 10(-44) and OR of 0.22 (0.18, 0.27). When stricter criteria and various sub-group analyses were applied, the association remained strong (for example, OR = 0.23 (0.18, 0.3) and P = 2 × 10(-28) for the alcoholic patients with alcoholic liver disease, cirrhosis, or pancreatitis). These findings provide confirmation of the involvement of the human ALDH2 gene in the pathogenesis of AD as well as alcohol-induced medical illnesses in East-Asians.

Ethanol metabolism and osmolarity modify behavioral responses to ethanol in C. elegans

BACKGROUND

Ethanol (EtOH) is metabolized by a 2-step process in which alcohol dehydrogenase (ADH) oxidizes EtOH to acetaldehyde, which is further oxidized to acetate by aldehyde dehydrogenase (ALDH). Although variation in EtOH metabolism in humans strongly influences the propensity to chronically abuse alcohol, few data exist on the behavioral effects of altered EtOH metabolism. Here, we used the nematode Caenorhabditis elegans to directly examine how changes in EtOH metabolism alter behavioral responses to alcohol during an acute exposure. Additionally, we investigated EtOH solution osmolarity as a potential explanation for contrasting published data on C. elegans EtOH sensitivity.

METHODS

We developed a gas chromatography assay and validated a spectrophotometric method to measure internal EtOH in EtOH-exposed worms. Further, we tested the effects of mutations in ADH and ALDH genes on EtOH tissue accumulation and behavioral sensitivity to the drug. Finally, we tested the effects of EtOH solution osmolarity on behavioral responses and tissue EtOH accumulation.

RESULTS

Only a small amount of exogenously applied EtOH accumulated in the tissues of C. elegans and consequently their tissue concentrations were similar to those that intoxicate humans. Independent inactivation of an ADH-encoding gene (sodh-1) or an ALDH-encoding gene (alh-6 or alh-13) increased the EtOH concentration in worms and caused hypersensitivity to the acute sedative effects of EtOH on locomotion. We also found that the sensitivity to the depressive effects of EtOH on locomotion is strongly influenced by the osmolarity of the exogenous EtOH solution.

CONCLUSIONS

Our results indicate that EtOH metabolism via ADH and ALDH has a statistically discernable but surprisingly minor influence on EtOH sedation and internal EtOH accumulation in worms. In contrast, the osmolarity of the medium in which EtOH is delivered to the animals has a more substantial effect on the observed sensitivity to EtOH.

Different phenotypic and genotypic presentations in alcohol dependence: age at onset matters

OBJECTIVE

Several theoretical typology models have been proposed to classify alcoholism into more homogeneous subtypes using various criteria, for which age at onset of alcohol dependence is shared across many models. We investigated the evidence for the distinction between early- versus late-onset alcoholism by examining relevant phenotypic and genotypic variables.

METHOD

Data are from 1,248 individuals with alcohol dependence, who were interviewed to collect detailed clinical information. Early versus late onset of alcohol dependence was defined by the age at onset of 22 years. Odds ratio (OR) and Cohen's d were calculated as effect size for comparisons of clinical features between the two groups. We adjusted interviewed age and gender in logistic regression models. Case-control genetic analyses were conducted for the association between HTR1B, SLC6A4, DRD2, and OPRμ1 genes and subgroups of alcohol dependence using a sample of 530 controls screened for alcohol problems.

RESULTS

Early-onset alcoholism exhibited significantly (p < .01) different clinical characteristics from late-onset alcoholism, including higher severity in alcohol dependence symptoms (d = 0.22) and maximum drinking quantity within 24 hours (d = 0.40), more rapid progression from regular drinking to meet alcohol dependence diagnosis (d = 1.73), higher expectancies for alcohol (d = 0.22-0.47), more comorbidity with externalizing disorders (ORs = 2.8-2.9), and greater prevalence of family alcohol use problems (d = 0.26-0.43). In addition, markers in the HTR1B and OPRμ1 genes showed genetic associations with subgroups of alcohol dependence (ORs = 1.5-2.4).

CONCLUSIONS

Our findings support that subgroups of alcohol dependence defined by onset age have phenotypic and genetic differences. The early-onset subgroup had more severe features for almost every aspect we examined. Coupled with genetic association findings, age at onset of alcohol dependence may serve as a simple but important clinical marker with implications for future etiological research and intervention.

Association of a genetic polymorphism of the alcohol-metabolizing enzyme ADH1C with alcohol dependence: results of a case-control study

OBJECTIVE

Alcohol dependence causes serious problems which may be influenced by genetic factors associated with alcohol metabolism. The aim was to investigate the allelic and genotypic difference in distribution of a polymorphism in alcohol dehydrogenase 1C gene (ADH1C) between alcohol-dependent individuals and controls, and to examine if these genotypes were associated with the age at which the patient became alcohol-dependent.

METHODS

We conducted a case-control study including 90 alcohol-dependent cases and 100 historic controls. The genomic DNA was isolated and the alleles were analyzed with an RFLP.

RESULTS

The ADH1C*1 allele frequencies were 0.89 (95% CI 0.84-0.91) in controls and 0.68 (95% CI 0.61-0.74) in alcohol-dependent patients. The frequencies of the ADH1C*2 allele were 0.11 (95% CI 0.07-0.14) and 0.32 (95% CI 0.25-0.38) among controls and alcohol-dependent patients, respectively (p < 0.0001). The ADH1C*1/*1 genotype frequency was significantly higher in the control group (77%) compared to that of the alcohol-dependents (51%, p < 0.0001). The ADH1C*1/*2 genotype frequency was significantly lower in the control group (23%) compared to that of the alcohol-dependents (42%, p < 0.0001). We obtained no statistically significant difference among the ADH1C genotype groups regarding age.

CONCLUSIONS

These findings suggest that a significantly higher presence of ADH1C*2 allele is associated with alcohol dependence in a Turkish population. Studies with other related polymorphisms are needed to more precisely estimate the association of alcohol dependence with ADH1C.

Confirmation of prior evidence of genetic susceptibility to alcoholism in a genome-wide association study of comorbid alcoholism and bipolar disorder

OBJECTIVES

Alcoholism and affective disorders are both strongly comorbid and heritable. We have investigated the genetic comorbidity between bipolar affective disorder and alcoholism.

METHODS

A genome-wide allelic association study of 506 patients from the University College London bipolar disorder case-control sample and 510 ancestrally matched supernormal controls. One hundred forty-three of the bipolar patients fulfilled the Research Diagnostic Criteria diagnosis of alcoholism. A total of 372 193 single nucleotide polymorphisms (SNPs) were genotyped. Genes previously shown to be associated with alcoholism and addiction phenotypes were then tested for association in the bipolar alcoholic sample using gene-wise permutation tests of all SNPs genotyped within a 50-kb region flanking each gene.

RESULTS

Several central nervous system genes showed significant (P<0.05) gene-wise evidence of association with bipolar alcoholism. The genes implicated, which replicated genes previously shown to be associated with alcoholism were: cadherin 11, collagen type 11 α2, neuromedin U receptor 2, exportin7, and semaphorin-associated protein 5A. The SNPs most strongly implicated in bipolar alcoholism, but, which did not meet conventional genome-wide significance criteria were the insulin-like growth factor-binding protein 7, carboxypeptidase O, cerebellin 2, and the cadherin 12 genes.

CONCLUSION

We have confirmed the role of some genes previously shown to be associated with alcoholism in the comorbid bipolar alcoholism subgroup. In this subgroup, bipolar disorder may lower the threshold for the phenotypic expression of these alcoholism susceptibility genes. We also show that some genes may independently increase susceptibility to affective disorder and alcoholism.

Strong association of the alcohol dehydrogenase 1B gene (ADH1B) with alcohol dependence and alcohol-induced medical diseases

BACKGROUND

The alcohol dehydrogenase 1B gene (ADH1B) is hypothesized to affect predisposition to alcohol dependence (AD) and abuse. A variant of the ADH1B gene (rs1229984 or Arg48His; previously referred to as Arg [*1] and His [*1]) has been reported to be associated with reduced rates of alcohol and drug dependence. Different studies have produced inconclusive results regarding association between rs1229984 (or rs2066702) and substance dependence.

METHODS

Using the cumulative association study literature from the past 21 years from both English- and Chinese-language publications, this meta-analysis seeks to clarify the contradictory findings and to examine whether the aggregate data provide new evidence of significant association.

RESULTS

The results, based on a large sample size (9638 cases and 9517 controls), suggested strong associations with alcohol dependence and abuse as well as alcohol-induced liver diseases, with an allelic (Arg vs. His) p value being 1 × 10(-36) and odds ratio (OR) (95% confidence intervals [CI]) 2.06 (1.84-2.31) under the random effects model. The dominant and recessive models produced larger ORs of 2.17 and 3.05, respectively. When more stringent criteria and subgroup analyses were imposed, the associations remained consistent and were strongest in various Asian groups (allelic p = 7 × 10(-42) and OR (95% CI) = 2.24 [1.99-2.51] with ORs of 2.16 and 4.11 for dominant and recessive models, respectively).

CONCLUSIONS

Our findings provide further strong evidence for the involvement of the ADH1B gene in the pathogenesis of alcohol dependence and abuse as well as for some alcohol-induced medical diseases in the multiple ethnic populations--in particular, certain Asian populations.

Stable genetic effects on symptoms of alcohol abuse and dependence from adolescence into early adulthood

Relatively little is known about how genetic influences on alcohol abuse and dependence (AAD) change with age. We examined the change in influence of genetic and environmental factors which explain symptoms of AAD from adolescence into early adulthood. Symptoms of AAD were assessed using the four AAD screening questions of the CAGE inventory. Data were obtained up to six times by self-report questionnaires for 8,398 twins from the Netherlands Twin Register aged between 15 and 32 years. Longitudinal genetic simplex modeling was performed with Mx. Results showed that shared environmental influences were present for age 15-17 (57%) and age 18-20 (18%). Unique environmental influences gained importance over time, contributing 15% of the variance at age 15-17 and 48% at age 30-32. At younger ages, unique environmental influences were largely age-specific, while at later ages, age-specific influences became less important. Genetic influences on AAD symptoms over age could be accounted for by one factor, with the relative influence of this factor differing across ages. Genetic influences increased from 28% at age 15-17 to 58% at age 21-23 and remained high in magnitude thereafter. These results are in line with a developmentally stable hypothesis that predicts that a single set of genetic risk factors acts on symptoms of AAD from adolescence into young adulthood.

Association of alcohol dehydrogenase genes with alcohol-related phenotypes in a Native American community sample

BACKGROUND

Previous linkage studies, including a study of the Native American population described in the present report, have provided evidence for linkage of alcohol dependence and related traits to chromosome 4q near a cluster of alcohol dehydrogenase (ADH) genes, which encode enzymes of alcohol metabolism.

METHODS

The present study tested for associations between alcohol dependence and related traits and 22 single-nucleotide polymorphisms (SNPs) spanning the 7 ADH genes. Participants included 586 adult men and women recruited from 8 contiguous Native American reservations. A structured interview was used to assess DSM-III-R alcohol dependence criteria as well as a set of severe alcohol misuse symptoms and alcohol withdrawal symptoms.

RESULTS

No evidence for association with the alcohol dependence diagnosis was observed, but an SNP in exon 9 of ADH1B (rs2066702; ADH1B*3) and an SNP at the 5' end of ADH4 (rs3762894) showed significant evidence of association with the presence of withdrawal symptoms (p = 0.0018 and 0.0012, respectively). Further, a haplotype analysis of these 2 SNPs suggested that the haplotypes containing either of the minor alleles were protective against alcohol withdrawal relative to the ancestral haplotype (p = 0.000006).

CONCLUSIONS

These results suggest that variants in the ADH1B and ADH4 genes may be protective against the development of some symptoms associated with alcohol dependence.

Haplotype-based study of the association of alcohol-metabolizing genes with alcohol dependence in four independent populations

BACKGROUND

Ethanol is metabolized by 2 rate-limiting reactions: alcohol dehydrogenases (ADH) convert ethanol to acetaldehyde that is subsequently metabolized to acetate by aldehyde dehydrogenases (ALDH). Approximately 50% of East Asians have genetic variants that significantly impair this pathway and influence alcohol dependence (AD) vulnerability. We investigated whether variation in alcohol metabolism genes might alter the AD risk in four non-East Asian populations by performing systematic haplotype association analyses to maximize the chances of capturing functional variation.

METHODS

Haplotype-tagging SNPs were genotyped using the Illumina GoldenGate platform. Genotypes were available for 40 SNPs across the ADH genes cluster and 24 SNPs across the two ALDH genes in four diverse samples that included cases (lifetime AD) and controls (no Axis 1 disorders). The case control sample sizes were the following: Finnish Caucasians: 232, 194; African Americans: 267, 422; Plains American Indians: 226, 110; and Southwestern American (SW) Indians: 317, 72.

RESULTS

In all four populations, as well as HapMap populations, 5 haplotype blocks were identified across the ADH gene cluster: (i) ADH5-ADH4; (ii) ADH6-ADH1A-ADH1B; (iii) ADH1C; (iv) intergenic; (v) ADH7. The ALDH1A1 gene was defined by 4 blocks and ALDH2 by 1 block. No haplotype or SNP association results were significant after correction for multiple comparisons; however, several results, particularly for ALDH1A1 and ADH4, replicated earlier findings. There was an ALDH1A1 block 1 and 2 (extending from intron 5 to the 3' UTR) yin yang haplotype (haplotypes that have opposite allelic configuration) association with AD in the Finns driven by SNPs rs3764435 and rs2303317, respectively, and an ALDH1A1 block 3 (including the promoter region) yin yang haplotype association in SW Indians driven by 5 SNPs, all in allelic identity. The ADH4 SNP rs3762894 was associated with AD in Plains Indians.

CONCLUSIONS

The systematic evaluation of alcohol-metabolizing genes in four non-East Asian populations has shown only modest associations with AD, largely for ALDH1A1 and ADH4. A concentration of signals for AD with ALDH1A1 yin yang haplotypes in several populations warrants further study.

Genetic and Environmental Risk Factors for Adolescent-Onset Substance Use Disorders

Substance dependence disorders are chronic relapsing disorders with immense societal consequences. Twin and family studies have found that there are critical genetic and environmental components in the inheritance of substance use disorders, and modern advances in genetics are making it possible to identify specific variants that may predispose an individual to these disorders. Adolescence is a crucial period for initiation, experimentation, and the establishment of more regular patterns of use of alcohol and other drugs. Adolescent substance use is a known risk factor for the development of later alcohol and substance use problems, as well as related externalizing disorders such as antisocial personality disorder. Understanding the early risk factors and processes that make these youths vulnerable to substance use disorders is crucial to the development of effective strategies for prevention. This article reviews the genetic origins of adolescent substance use problems and the potential this field of research offers for prevention.

Associations between ADH gene variants and alcohol phenotypes in Dutch adults

Recently, Macgregor et al. (2009) demonstrated significant associations of ADH polymorphisms with reactions to alcohol and alcohol consumption measures in an Australian sample. The aim of the present study was to replicate these findings in a Dutch sample. Survey data on alcohol phenotypes came from 1,754 unrelated individuals registered with the Netherlands Twin Register. SNPs in the ADH gene cluster located on chromosome 4q (n = 491) were subdivided in seven gene sets: ADH5, ADH4, ADH6, ADH1A, ADH1B, ADH1C and ADH7. Within these sets associations of SNPs with alcohol consumption measures, age at onset variables, reactions to alcohol and problem drinking liability were examined. Of the original 38 SNPs studied by Macgregor et al. (2009), six SNPs were not available in our dataset, because one of them had a minor allele frequency < .01 (rs1229984) and five could not be imputed. The remaining SNP associations with alcohol phenotypes as identified by Macgregor et al. (2009) were not replicated in the Dutch sample, after correcting for multiple genotype and phenotype testing. Significant associations were found however, for reactions to alcohol with a SNP in ADH5 (rs6827292, p = .001) and a SNP just upstream of ADH5 (rs6819724, p = .0007) that is in strong LD with rs6827292. Furthermore, an association between age at onset of regular alcohol use and a SNP just upstream of ADH7 (rs2654849, p = .003) was observed. No significant associations were found for alcohol consumption and problem drinking liability. Although these findings do not replicate the earlier findings at the SNP level, the results confirm the role of the ADH gene cluster in alcohol phenotypes.

A systematic gene-based screen of chr4q22-q32 identifies association of a novel susceptibility gene, DKK2, with the quantitative trait of alcohol dependence symptom counts

Studies of alcohol dependence (AD) have consistently found evidence of linkage on chromosome 4q21-q32. A genome-wide linkage scan in the Irish Affected Sib Pair Study of Alcohol Dependence (IASPSAD) sample also provided its strongest evidence of linkage on chromosome 4q22-q32 using an index of AD severity based on the count of DSM-IV AD symptoms (ADSX; LOD = 4.59). We conducted a systematic, gene-centric association study using 518 LD-tagging single nucleotide polymorphisms (SNPs) in the 65 known and predicted genes within the 1-LOD interval surrounding the linkage peak. Case-only regression analysis with the quantitative variable of ADSX was performed in the 562 genetically independent cases; nominal support for association was demonstrated by 32 tagging SNPs in 14 genes. We did not observe study-wide significance, but gene-wise correction for multiple testing with the Nyholt procedure yielded empirical evidence of association with two genes, DKK2 (dickkopf homolog 2) (P = 0.007) and EGF (epidermal growth factor) (P = 0.025) in the IASPSAD sample. Three SNPs in DKK2 (rs427983; rs419558; rs399087) demonstrated empirical significance. Assessment of possible replication in 847 cases of European descent from a large independent sample, the Collaborative Study of the Genetics of Alcoholism, yielded replication for DKK2 but not EGF. We observed genotypic and phenotypic replication for DKK2 with the three SNPs yielding significant association with ADSX in the IASPSAD sample. Haplotype-specific expression measurements in post-mortem tissue samples suggested a functional role for DKK2. This evidence notwithstanding, replication is needed before confidence can be placed in these findings.

ADH1A variation predisposes to personality traits and substance dependence

Human personality traits are strong predictors or characteristics of many psychiatric disorders including substance dependence (SD). Recently, significant associations between alcohol dehydrogenase type 1A gene (ADH1A) and SD have been reported, which led us to investigate the impact of ADH1A variation on personality traits and risk of SD. Five hundred fifty-eight subjects with SD [398 European-Americans (EAs) and 160 African-Americans (AAs)], 517 college students (384 EAs and 133 European-origin Hispanics), and 448 healthy subjects (385 EAs, 48 AAs, and 15 European-origin Hispanics) participated. Personality traits were assessed in 247 subjects with SD (179 EAs and 68 AAs), all 517 college students, and 332 healthy subjects (285 EAs, 40 AAs, and 7 European-origin Hispanics). The relationships between ADH1A and personality traits were comprehensively examined using stepwise multivariate analysis of covariance (MANCOVA), and then decomposed by stepwise analysis of covariance (ANCOVA). The relationship between ADH1A and SD was examined using stepwise logistic regression analysis. Admixture effects on analyses were considered. Overall, Agreeableness and Conscientiousness were associated with the diplotypes, haplotypes, genotypes, and/or alleles of ADH1A in three of four phenotype groups including EA SD subjects, healthy subjects, and AA SD subjects (1.7 x 10(-4) <or= P <or= 0.055), but not college students. Neuroticism was associated with diplotype, haplotypes and genotypes in AA SD subjects (0.001 <or= P <or= 0.031). In addition, SD was associated with diplotypes, haplotypes, genotypes, and/or alleles of ADH1A (0.008 <or= P <or= 0.060). The present study demonstrates that the ADH1A variation may contribute to the genetic component of variation in personality traits and SD.

Genome-wide association study of alcohol dependence implicates a region on chromosome 11

BACKGROUND

Alcohol dependence is a complex disease, and although linkage and candidate gene studies have identified several genes associated with the risk for alcoholism, these explain only a portion of the risk.

METHODS

We carried out a genome-wide association study (GWAS) on a case-control sample drawn from the families in the Collaborative Study on the Genetics of Alcoholism. The cases all met diagnostic criteria for alcohol dependence according to the Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition; controls all consumed alcohol but were not dependent on alcohol or illicit drugs. To prioritize among the strongest candidates, we genotyped most of the top 199 single nucleotide polymorphisms (SNPs) (p < or = 2.1 x 10(-4)) in a sample of alcohol-dependent families and performed pedigree-based association analysis. We also examined whether the genes harboring the top SNPs were expressed in human brain or were differentially expressed in the presence of ethanol in lymphoblastoid cells.

RESULTS

Although no single SNP met genome-wide criteria for significance, there were several clusters of SNPs that provided mutual support. Combining evidence from the case-control study, the follow-up in families, and gene expression provided strongest support for the association of a cluster of genes on chromosome 11 (SLC22A18, PHLDA2, NAP1L4, SNORA54, CARS, and OSBPL5) with alcohol dependence. Several SNPs nominated as candidates in earlier GWAS studies replicated in ours, including CPE, DNASE2B, SLC10A2, ARL6IP5, ID4, GATA4, SYNE1, and ADCY3.

CONCLUSIONS

We have identified several promising associations that warrant further examination in independent samples.

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.

A method for mapping intralocus interactions influencing excessive alcohol drinking

Excessive alcohol (ethanol) consumption is the hallmark of alcohol use disorders. The F1 hybrid cross between the C57BL/6J (B6) and FVB/NJ (FVB) inbred mouse strains consumes more ethanol than either progenitor strain. The purpose of this study was to utilize ethanol-drinking data and genetic information to map genes that result in overdominant (or heterotic) ethanol drinking. About 600 B6 x FVB F2 mice, half of each sex, were tested for ethanol intake and preference in a 24-h, two-bottle water versus ethanol choice procedure, with ascending ethanol concentrations. They were then tested for ethanol intake in a Drinking in the Dark (DID) procedure, first when there was no water choice and then when ethanol was offered versus water. DNA samples were obtained and genome-wide QTL analyses were performed to search for single QTLs (both additive and dominance effects) and interactions between pairs of QTLs, or epistasis. On average, F2 mice consumed excessive amounts of ethanol in the 24-h choice procedure, consistent with high levels of consumption seen in the F1 cross. Consumption in the DID procedure was similar or higher than amounts reported previously for the B6 progenitor. QTLs resulting in heightened consumption in heterozygous compared to homozygous animals were found on Chrs 11, 15, and 16 for 24-h choice 30% ethanol consumption, and on Chr 11 for DID. No evidence was found for epistasis between any pair of significant or suggestive QTLs. This indicates that the hybrid overdominance is due to intralocus interactions at the level of individual QTL.

Oral cancer and polymorphism of ethanol metabolising genes

Oral cancer is the sixth most common cancer worldwide and a major health problem in some parts of the world. Epidemiological studies have shown that habitual alcohol consumption could be a risk factor in oral carcinogenesis, although the true involvement of alcohol is unknown. Via alcohol dehydrogenase (ADH) and cytochrome P450 oxidase (CYP) alcohol is metabolized to acetaldehyde, a highly toxic compound, which plays an important role in carcinogenesis. Subsequently, and during the metabolizing process, acetaldehyde becomes acetate by acetaldehyde dehydrogenase (ALDH). Therefore, acetaldehyde levels are determined mainly by the action of ADH, CYP and ALDH. Recently, several studies have found that certain polymorphisms of genes encoding these enzymes confer a higher or lower metabolic activity and therefore different risk for certain malignancies such as oral cancer. In this review, we analyze the polymorphisms of alcohol metabolising enzymes in relation susceptibility to an oral cancer.

A non-synonymous variant in ADH1B is strongly associated with prenatal alcohol use in a European sample of pregnant women

Pregnant women are advised to abstain from alcohol despite insufficient evidence on the fetal consequences of moderate prenatal alcohol use. Mendelian randomization could help distinguish causal effects from artifacts due to residual confounding and measurement errors; however, polymorphisms reliably associated with alcohol phenotypes are needed. We aimed to test whether alcohol dehydrogenase (ADH) gene variants were associated with alcohol use before and during pregnancy. Ten variants in four ADH genes were genotyped in women from South-West England. Phenotypes of interest were quantity and patterns of alcohol consumption before and during pregnancy, including quitting alcohol following pregnancy recognition. We tested single-locus associations between genotypes and phenotypes with regression models. We used Bayesian models (multi-locus) to take account of linkage disequilibrium and reanalyzed the data with further exclusions following two conservative definitions of ‘white ethnicity’ based on the woman's reported parental ethnicity or a set of ancestry-informative genetic markers. Single-locus analyses on 7410 women of white/European background showed strong associations for rs1229984 (ADH1B). Rare allele carriers consumed less alcohol before pregnancy [odds ratio (OR) = 0.69; 95% confidence interval (CI): 0.56–0.86, P = 0.001], were less likely to have ‘binged’ during pregnancy (OR = 0.55, 95% CI: 0.38–0.78, P = 0.0009), and more likely to have abstained in the first trimester of gestation (adjusted OR = 1.42, 95% CI: 1.12–1.80, P = 0.004). Multi-locus models confirmed these results. Sensitivity analyses did not suggest the presence of residual population stratification. We confirmed the established association of rs1229984 with reduced alcohol consumption over the life-course, contributing new evidence of an effect before and during pregnancy.

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.

Raf Kinase Inhibitory Protein protects cells against locostatin-mediated inhibition of migration

BACKGROUND

Raf Kinase Inhibitory Protein (RKIP, also PEBP1), a member of the Phosphatidylethanolamine Binding Protein family, negatively regulates growth factor signaling by the Raf/MAP kinase pathway. Since an organic compound, locostatin, was reported to bind RKIP and inhibit cell migration by a Raf-dependent mechanism, we addressed the role of RKIP in locostatin function.

METHODS/FINDINGS

We analyzed locostatin interaction with RKIP and examined the biological consequences of locostatin binding on RKIP function. NMR studies show that a locostatin precursor binds to the conserved phosphatidylethanolamine binding pocket of RKIP. However, drug binding to the pocket does not prevent RKIP association with its inhibitory target, Raf-1, nor affect RKIP phosphorylation by Protein Kinase C at a regulatory site. Similarly, exposure of wild type, RKIP-depleted HeLa cells or RKIP-deficient (RKIP(-/-)) mouse embryonic fibroblasts (MEFs) to locostatin has no effect on MAP kinase activation. Locostatin treatment of wild type MEFs causes inhibition of cell migration following wounding. RKIP deficiency impairs migration further, indicating that RKIP protects cells against locostatin-mediated inhibition of migration. Locostatin treatment of depleted or RKIP(-/-) MEFs reveals cytoskeletal disruption and microtubule abnormalities in the spindle.

CONCLUSIONS/SIGNIFICANCE

These results suggest that locostatin's effects on cytoskeletal structure and migration are caused through mechanisms independent of its binding to RKIP and Raf/MAP kinase signaling. The protective effect of RKIP against drug inhibition of migration suggests a new role for RKIP in potentially sequestering toxic compounds that may have deleterious effects on cells.