Genetic time-series analysis identifies a major QTL for in vivo alcohol metabolism not predicted by in vitro studies of structural protein polymorphism at the ADH1B or ADH1C loci

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.

Is ADH1C genotype relevant for the cardioprotective effect of alcohol?

The cardioprotective effect of ethanol has been suggested to be linked to one of the ethanol metabolizing enzymes (ADH1C), which constitutes a high V(max) and a low V(max) variant. This has been demonstrated in some studies, while others have not been able to replicate the findings. The aim of the present study was to investigate the relation between the different ADH1C genotypes, death from coronary heart disease (CHD) and alcohol in a material larger than the previously published studies. Eight hundred CHD deaths as well as 1303 controls were genotyped for the high V(max) (γ1) and the low V(max) (γ2) ADH1C variant. Information of alcohol use was available for all subjects. Multiple logistic regression analyses was used to study if the decreased risk of death from CHD in alcohol consuming subjects was more pronounced in subjects homozygous for the γ2 allele (γ2γ2 subjects) compared to γ1γ1 and γ1γ2 subjects. The odds ratio (OR) for death from CHD in alcohol consumers compared to abstainers was similar in the genotype groups, i.e., 0.62 (95% CI: 0.43-0.88) in γ1γ1 subjects and 0.62 (95% CI: 0.42-0.91) in γ2γ2 subjects. Also when stratifying the results by gender and when dividing alcohol consumers into different alcohol consumption groups, there was no difference in the OR between the different genotype groups. This study, which included the largest study group published so far, failed to find any link between the ADH1C genotype and the cardioprotective effects of alcohol.

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.

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.

Molecular genetics of alcohol dependence and related endophenotypes

Alcohol dependence is a worldwide public health problem, and involves both environmental and genetic vulnerability factors. The heritability of alcohol dependence is rather high, ranging between 50% and 60%, although alcohol dependence is a polygenic, complex disorder.

Genome-wide scans on large cohorts of multiplex families, including the collaborative study on genetics of alcoholism (COGA), emphasized the role of many chromosome regions and some candidate genes. The genes encoding the alcohol-metabolizing enzymes, or those involved in brain reward pathways, have been involved. Since dopamine is the main neurotransmitter in the reward circuit, genes involved in the dopaminergic pathway represent candidates of interest. Furthermore, gamma-amino-butyric acid (GABA) neurotransmitter mediates the acute actions of alcohol and is involved in withdrawal symptomatology. Numerous studies showed an association between variants within GABA receptors genes and the risk of alcohol dependence.

In accordance with the complexity of the “alcohol dependence” phenotype, another field of research, related to the concept of endophenotypes, received more recent attention. The role of vulnerability genes in alcohol dependence is therefore re-assessed focusing on different phenotypes and endophenotypes. The latter include brain oscillations, EEG alpha and beta variants and alpha power, and amplitude of P300 amplitude elicited from a visual oddball task.

Recent enhancement on global characterizations of the genome by high-throughput approach for genotyping of polymorphisms and studies of transcriptomics and proteomics in alcohol dependence is also reviewed.

Genetic association in multivariate phenotypic data: power in five models

This article concerns the power of various data analytic strategies to detect the effect of a single genetic variant (GV) in multivariate data. We simulated exactly fitting monozygotic and dizygotic phenotypic data according to single and two common factor models, and simplex models. We calculated the power to detect the GV in twin 1 data in an ANOVA of phenotypic sum scores, in a MANOVA, and in exploratory factor analysis (EFA), in which the common factors are regressed on the genetic variant. We also report power in the full twin model, and power of the single phenotype ANOVA. The results indicate that (1) if the GV affects all phenotypes, the sum score ANOVA and the EFA are most powerful, while the MANOVA is less powerful. Increasing phenotypic correlations further decreases the power of the MANOVA; and (2) if the GV affects only a subset of the phenotypes, the EFA or the MANOVA are most powerful, while sum score ANOVA is less powerful. In this case, an increase in phenotypic correlations may enhance the power of MANOVA and EFA. If the effect of the GV is modeled directly on the phenotypes in the EFA, the power of the EFA is approximately equal to the power of the MANOVA.

Variation in the ADH1B proximal promoter affects expression

The primary pathway of metabolism of dietary alcohol is via its oxidation in liver by alcohol dehydrogenases (ADH). Differences in the ADH enzyme activity or levels of enzyme present could affect the risk for alcoholism. Regulatory variations have been shown to affect the promoter activity and thereby affect the risk for alcoholism. In this study the functional effects of the two SNPs (rs1159918 and rs1229982) in the proximal promoter region of ADH1B that were associated with alcoholism were explored. We examined the effects of five naturally occurring haplotypes on the promoter activity. We observed that a C to A change at rs1229982 increased promoter activity 1.4-fold.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

ADH single nucleotide polymorphism associations with alcohol metabolism in vivo

We have previously found that variation in alcohol metabolism in Europeans is linked to the chromosome 4q region containing the ADH gene family. We have now typed 103 single nucleotide polymorphisms (SNPs) across this region to test for allelic associations with variation in blood and breath alcohol concentrations after an alcohol challenge. In vivo alcohol metabolism was modelled with three parameters that identified the absorption and rise of alcohol concentration following ingestion, and the rate of elimination. Alleles of ADH7 SNPs were associated with the early stages of alcohol metabolism, with additional effects in the ADH1A, ADH1B and ADH4 regions. Rate of elimination was associated with SNPs in the intragenic region between ADH7 and ADH1C, and across ADH1C and ADH1B. SNPs affecting alcohol metabolism did not correspond to those reported to affect alcohol dependence or alcohol-related disease. The combined SNP associations with early- and late-stage metabolism only account for approximately 20% of the total genetic variance linked to the ADH region, and most of the variance for in vivo alcohol metabolism linked to this region is yet to be explained.

Long-term stability and heritability of telephone interview measures of alcohol consumption and dependence

Alcohol dependence symptoms and consumption measures were examined for stability and heritability. Data were collected from 12,045 individuals (5376 twin pairs, 1293 single twins) aged 19 to 90 years in telephone interviews conducted in three collection phases. Phases 1 and 2 were independent samples, but Phase 3 targeted families of smokers and drinkers from the Phase 1 and 2 samples. The stability of dependence symptoms and consumption was examined for 1158 individuals interviewed in both Phases 1 and 3 (mean interval = 11.0 years). For 1818 individuals interviewed in Phases 2 and 3 (mean interval = 5.5 years) the stability of consumption was examined. Heritability was examined for each collection phase and retest samples from the selected Phase 3 collection. The measures examined were a dependence score, based on DSM-IIIR and DSM-IV criteria for substance dependence, and a quantity x frequency measure. Measures were moderately stable, with test-retest correlations ranging from .58 to .61 for dependence and from .55 to .64 for consumption. However, the pattern of changes over time for dependence suggested that the measure may more strongly reflect recent than lifetime experience. Similar to previous findings, heritabilities ranged from .42 to .51 for dependence and from .31 to .51 for consumption. Consumption was significantly less heritable in the younger Phase 2 cohort (23-39 years) compared to the older Phase 1 cohort (28-90 years).

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

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

Effects of variation at the ALDH2 locus on alcohol metabolism, sensitivity, consumption, and dependence in Europeans

BACKGROUND

The low-activity variant of the aldehyde dehydrogenase 2 (ALDH2) gene found in East Asian populations leads to the alcohol flush reaction and reduces alcohol consumption and risk of alcohol dependence (AD). We have tested whether other polymorphisms in the ALDH2 gene have similar effects in people of European ancestry.

METHODS

Serial measurements of blood and breath alcohol, subjective intoxication, body sway, skin temperature, blood pressure, and pulse were obtained in 412 twins who took part in an alcohol challenge study. Participants provided data on alcohol reactions, alcohol consumption, and symptoms related to AD at the time of the study and subsequently. Haplotypes based on 5 single-nucleotide polymorphisms (SNPs) were used in tests of the effects of variation in the ALDH2 gene on alcohol metabolism and alcohol's effects.

RESULTS

The typed SNPs were in strong linkage disequilibrium and 2 complementary haplotypes comprised 83% of those observed. Significant effects of ALDH2 haplotype were observed for breath alcohol concentration, with similar but smaller and nonsignificant effects on blood alcohol. Haplotype-related variation in responses to alcohol, and reported alcohol consumption, was small and not consistently in the direction predicted by the effects on alcohol concentrations.

CONCLUSIONS

Genetic variation in ALDH2 affects alcohol metabolism in Europeans. However, the data do not support the hypothesis that this leads to effects on alcohol sensitivity, consumption, or risk of dependence.

The genetics of alcoholism: identifying specific genes through family studies

Alcoholism is a complex disorder with both genetic and environmental risk factors. Studies in humans have begun to elucidate the genetic underpinnings of the risk for alcoholism. Here we briefly review strategies for identifying individual genes in which variations affect the risk for alcoholism and related phenotypes, in the context of one large study that has successfully identified such genes. The Collaborative Study on the Genetics of Alcoholism (COGA) is a family-based study that has collected detailed phenotypic data on individuals in families with multiple alcoholic members. A genome-wide linkage approach led to the identification of chromosomal regions containing genes that influenced alcoholism risk and related phenotypes. Subsequently, single nucleotide polymorphisms (SNPs) were genotyped in positional candidate genes located within the linked chromosomal regions, and analyzed for association with these phenotypes. Using this sequential approach, COGA has detected association with GABRA2, CHRM2 and ADH4; these associations have all been replicated by other researchers. COGA has detected association to additional genes including GABRG3, TAS2R16, SNCA, OPRK1 and PDYN, results that are awaiting confirmation. These successes demonstrate that genes contributing to the risk for alcoholism can be reliably identified using human subjects.

Structural model analysis of multiple quantitative traits

We introduce a method for the analysis of multilocus, multitrait genetic data that provides an intuitive and precise characterization of genetic architecture. We show that it is possible to infer the magnitude and direction of causal relationships among multiple correlated phenotypes and illustrate the technique using body composition and bone density data from mouse intercross populations. Using these techniques we are able to distinguish genetic loci that affect adiposity from those that affect overall body size and thus reveal a shortcoming of standardized measures such as body mass index that are widely used in obesity research. The identification of causal networks sheds light on the nature of genetic heterogeneity and pleiotropy in complex genetic systems.

Disease states are often associated with multiple, correlated traits that may result from shared genetic and nongenetic factors. Genetic analysis of multiple traits can reveal a network of effects in which each trait is influenced by more than one genetic locus (heterogeneity) and different traits share one or more loci in common (pleiotropy). Physiological interactions independent of genetic factors may also contribute to the observed correlations. Structural equation modeling is proposed as a statistical method to characterize the architecture of multiple trait genetic systems. Application of structural equation modeling to body size, adiposity, and bone geometry traits illustrates how the effects of a genetic locus can be decomposed along direct and indirect paths that may be mediated through interactions with other traits. Using this technique the authors identify adiposity loci that act independently of loci affecting overall body size.

The genetics of alcohol dependence

Alcohol dependence is a common, complex disorder, which affects millions of people worldwide and causes considerable burden in terms of interpersonal and societal costs. Family, twin, and adoption studies have convincingly demonstrated that genes play an important role in the development of alcohol dependence, with heritability estimates in the range of 50% to 60% for both men and women. A number of studies are under way to identify specific genes involved in the predisposition toward alcohol dependence, and there is reason to be enthusiastic about recent progress. Several associated susceptibility genes are reviewed here, including genes involved in alcohol metabolism, as well as genes involved in GABAergic, endogenous opioid, dopaminergic, cholinergic, and serotonergic transmission. The next challenge will be to further characterize the risk associated with these susceptibility genes, examining how they may be related to comorbid disorders, developmental trajectories of risk, and potential moderation by environmental factors.

Association of alcohol dehydrogenase genes with alcohol dependence: a comprehensive analysis

Linkage evidence indicated that gene(s) located on chromosome 4q, in the region of the alcohol dehydrogenase (ADH) genes, affected risk for alcoholism. We genotyped 110 single nucleotide polymorphisms (SNPs) across the seven ADH genes and analyzed their association with alcoholism in a set of families with multiple alcoholic members, using the pedigree disequilibrium test. There was strong evidence that variations in ADH4 are associated with alcoholism: 12 SNPs were significantly associated. The region of strongest association ran from intron 1 to 19.5 kb beyond the 3' end of the gene. Haplotype tag SNPs were selected for the block in the ADH4 gene that provided evidence of association and subsequently used in association analysis; the haplotype was significantly associated with alcoholism (P=0.01) There was weaker evidence that variations in ADH1A and ADH1B might also play a role in modifying risk. Among African-Americans, there was evidence that the ADH1B*3 allele was protective.