Association of the ADH2*3 Allele With A Negative Family History Of Alcoholism in African American Young Adults

How do we 'learn' addiction? Risk factors and mechanisms getting addicted to alcohol

BACKGROUND

Alcohol dependence is one of the leading contributors to the burden of disease in the world. A range of genetic and environmental risk factors has been identified to date, and preclinical and clinical studies including imaging studies have identified neuronal networks involved in the development of alcohol dependence.

METHODS

We review genetic and environmental risk factors for the development of alcohol addiction as well as structural and neuronal changes, including their transmitter systems, due to regular alcohol intake.

RESULTS

Stress as well as family background and, in juveniles, the peer group could be identified as environmental risk factors for alcohol dependence. Heritability is estimated at around 50%, and it seems to be comparable in women and men. There is ongoing research on a broad range of putative endophenotypes such as tolerance of the effects of alcohol intake or personal traits like 'impulsivity'. On the neurobiological level, chronic alcohol intake seems to render mesolimbic circuits hypersensitive to alcohol and alter the motivational reward system including dopaminergic neurotransmission.

CONCLUSION

Environmental and genetic risk factors, and especially their interaction, facilitate the development of alcohol dependence. Ongoing alcohol intake results in profound alterations of neuronal systems crucial for motivation, learning, memory and cognition control. Future studies should further combine the knowledge of neurobiological mechanisms and risk factors to develop new prevention strategies.

Evaluation of the influence of alcohol dehydrogenase polymorphisms on alcohol elimination rates in African Americans

INTRODUCTION

The relationship between alcohol dehydrogenase (ADH) polymorphisms and alcohol use disorders in populations of African descent has not been clearly established. This study examined the effect of ADH1B polymorphisms on alcohol metabolism and subjective response, following intravenous (IV) alcohol administration, and the influence of gender, recent drinking history, and family history of alcoholism (FHA), in nondependent African American drinkers.

MATERIALS

The sample included eighty-seven 21- to 35-year-old, light social drinkers of African descent. Participants included 39 sib pairs, 2 sibships with 3 siblings each, and 3 individuals who were not part of a sibship. Participants received infusions via the use of the clamp method that refers to the goal of controlling breath alcohol concentration in 2 randomized sessions at 0.06 g% ethanol and 0 mg% (placebo), and a battery of subjective scales at predefined time points. Dependent measures included alcohol elimination rates (AERs), alcohol disappearance rates (ADRs), subjective measures peak scores, and area under the curve. General linear model and mixed models were performed to examine the relationship between ADH1B genotype, dependent measures, and influence of covariates.

RESULTS

Participants with ADH1B1/1 genotypes showed higher number of drinks (p = 0.023) and drinks per drinking day (p = 0.009) compared with the persons with ADH1B1/3 genotype. AER (adjusted for body weight) was higher in ADH1B*1 homozygotes (p = 0.045) compared with ADH1B1/3 heterozygotes. ADR differed significantly between males and females (p = 0.002), regardless of body weight (p = 0.004) and lean body mass (p < 0.001) adjustments. Although a few subjective measures differed across genotype, all measures were higher in alcohol sessions compared with placebo sessions (p < 0.001). These observations were mediated by drinks per drinking day, gender, and FHA.

CONCLUSIONS

ADH1B polymorphism had a marginal effect on alcohol pharmacokinetics following IV alcohol administration in nondependent drinkers of African descent. Session (alcohol vs. placebo) and ADH1B genotype did, however, influence subjective response to alcohol with some variation by gender, FHA, and drinks per drinking day.

ADH and ALDH polymorphisms and alcohol dependence in Mexican and Native Americans

BACKGROUND

Ethanol is primarily metabolized in the liver by two rate-limiting reactions: conversion of ethanol to acetaldehyde by alcohol dehydrogenase (ADH) and subsequent conversion of acetaldehyde to acetate by aldehyde dehydrogenase (ALDH). ADH and ALDH exist in multiple isozymes that differ in their kinetic properties. Notably, polymorphisms within the genes that encode for these isozymes vary in their allele frequencies between ethnic groups, and thus, they have been considered as candidate genes that may differentially influence risk for the development of alcohol dependence across ethnic groups.

OBJECTIVES AND METHODS

Associations between alcohol dependence and polymorphisms in ADH1B, ADH1C, and ALDH2 were compared in a community sample of Native Americans (n 791) living on reservations and Mexican Americans (n 391) living within the same county.

RESULTS

Two Mexican Americans and no Native Americans possessed one ALDH2*2 allele. Presence of at least one ADH1B*2 allele was found in 7% of the Native Americans and 13% of the Mexican Americans, but was only associated with protection against alcohol dependence in the Mexican Americans. Presence of at least one ADH1B*3 allele was found in 4% of the Native Americans and 2% of the Mexican Americans, but was associated with protection against alcohol dependence only in the Native Americans. No associations between alcohol dependence and polymorphisms in ADH1C were found.

CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE

Polymorphisms in ADH1B are protective against alcoholism in these two populations; however, these findings do not explain the high prevalence of alcoholism in these populations.

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.

ADH1B*3 and response to alcohol in African-Americans

BACKGROUND

Variations in the alleles for the alcohol-metabolizing enzymes have been shown to influence risk for alcohol dependence. One variant, ADH1B*3, is observed almost exclusively in populations of African ancestry and has been shown to be associated with reduced rates of alcohol dependence. We conducted an alcohol challenge study to test whether ADH1B*3 is associated with differences in subjective and physiological response to alcohol.

METHOD

We administered a moderate dose of alcohol (0.72 g/kg for males, 0.65 g/kg for females) to a sample of African-American young adults (n = 91; ages 21 to 26). Participants were genotyped for ADH1B, as well as additional polymorphisms that might contribute to alcohol response. Breath alcohol concentration, self-reported sedation and stimulation, and pulse rate were assessed prior to alcohol administration and for 2.5 hours following administration.

RESULTS

ADH1B*3 was associated with higher levels of sedation and a sharper increase in pulse rate immediately following alcohol consumption.

CONCLUSIONS

These findings suggest that the lower rates of alcohol dependence in those with ADH1B*3 alleles may be because of differences in alcohol response, particularly increased sedation.

Associations of ADH and ALDH2 gene variation with self report alcohol reactions, consumption and dependence: an integrated analysis

Alcohol dependence (AD) is a complex disorder with environmental and genetic origins. The role of two genetic variants in ALDH2 and ADH1B in AD risk has been extensively investigated. This study tested for associations between nine polymorphisms in ALDH2 and 41 in the seven ADH genes, and alcohol-related flushing, alcohol use and dependence symptom scores in 4597 Australian twins. The vast majority (4296) had consumed alcohol in the previous year, with 547 meeting DSM-IIIR criteria for AD. There were study-wide significant associations (P<2.3 x 10(-4)) between ADH1B-Arg48His (rs1229984) and flushing and consumption, but only nominally significant associations (P<0.01) with dependence. Individuals carrying the rs1229984 G-allele (48Arg) reported a lower prevalence of flushing after alcohol (P=8.2 x 10(-7)), consumed alcohol on more occasions (P=2.7 x 10(-6)), had a higher maximum number of alcoholic drinks in a single day (P=2.7 x 10(-6)) and a higher overall alcohol consumption (P=8.9 x 10(-8)) in the previous year than those with the less common A-allele (48His). After controlling for rs1229984, an independent association was observed between rs1042026 (ADH1B) and alcohol intake (P=4.7 x 10(-5)) and suggestive associations (P<0.001) between alcohol consumption phenotypes and rs1693482 (ADH1C), rs1230165 (ADH5) and rs3762894 (ADH4). ALDH2 variation was not associated with flushing or alcohol consumption, but was weakly associated with AD measures. These results bridge the gap between DNA sequence variation and alcohol-related behavior, confirming that the ADH1B-Arg48His polymorphism affects both alcohol-related flushing in Europeans and alcohol intake. The absence of study-wide significant effects on AD results from the low P-value required when testing multiple single nucleotide polymorphisms and phenotypes.

Genetic and environmental factors in head and neck cancer genesis

Head and neck squamous cell carcinoma (HNSCC) include squamous cell carcinomas of the oral cavity, pharynx, and larynx. Epidemiologic data suggest that the etiology and pathogenesis of HNSCC are influenced by environmental and lifestyle-related factors, such as tobacco use, ethanol consumption, papilloma virus infection, dietary factors and exposure to toxic substances. DNA repair systems and carcinogen-metabolizing enzymes can increase the risk for HNSCC but no definite causal mechanism has been demonstrated. There are several well-characterized entities that are associated with risk and prognosis of head and neck cancer, including Lynch-II syndrome, Bloom syndrome, Fanconi's anemia, xeroderma pigmentosum, ataxia telangiectasia, and Li-Fraumeni syndrome. This review aims to present the current status in our understanding of HNSCC and highlight controversies relating to the role of several factors in the genesis of the cancer.

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

BACKGROUND

The genes coding for ethanol metabolism enzymes [alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH)] have been widely studied for their influence on the risk to develop alcohol dependence (AD). However, the relation between polymorphisms of these metabolism genes and AD in Caucasian subjects has not been clearly established. The present study examined evidence for the association of alcohol metabolism genes with AD in the Irish Affected Sib Pair Study of alcohol dependence.

METHODS

We conducted a case-control association study with 575 independent subjects who met Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, AD diagnosis and 530 controls. A total of 77 single nucleotide polymorphisms (SNPs) in the seven ADH (ADH1-7) and two ALDH genes (ALDH1A1 and ALDH2) were genotyped using the Illumina GoldenGate protocols. Several statistical procedures were implemented to control for false discoveries.

RESULTS

All markers with minor allele frequency greater than 0.01 were in Hardy-Weinberg equilibrium. Numerous SNPs in ADH genes showed association with AD, including one marker in the coding region of ADH1C (rs1693482 in exon6, Ile271Gln). Haplotypic association was observed in the ADH5 and ADH1C genes, and in a long haplotype block formed by the ADH1A and ADH1B loci. We detected two significant interactions between pairs of markers in intron 6 of ADH6 and intron 12 of ALDH2 (p = 5 x 10(-5)), and 5' of both ADH4 and ADH1A (p = 2 x 10(-4)).

CONCLUSION

We found evidence for the association of several ADH genes with AD in a sample of Western European origin. The significant interaction effects between markers in ADH and ALDH genes suggest possible epistatic roles between alcohol metabolic enzymes in the risk for AD.

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.

Association of haplotypic variants in DRD2, ANKK1, TTC12 and NCAM1 to alcohol dependence in independent case–control and family samples

There have been many conflicting reports concerning the association of the DRD2 locus with alcohol dependence (AD). To investigate whether these findings could be reconciled by considering the genomic region of DRD2 in greater detail, we conducted two separate association studies of AD in 1220 European-American subjects using family-based (488 subjects) and case-control (318 cases and 414 controls) designs, and 43 single nucleotide polymorphisms mapped to the gene cluster of NCAM1, TTC12, ANKK1 and DRD2. We used a generalized linear model and haplotype score tests for the case-control sample, and the family-based association test for the family sample. Haplotype associations centered on TTC12 exon 3 [rs1893699-rs723077; optimal individual haplotype simulated P-value (P(oihs)) = 0.00021] in both independent samples (family and case-control). Additional AD-associated haplotypes centered around NCAM1 exon 12 in the family sample (P(oihs) = 0.0032), and at exons 2 and 5 of ANKK1 in the case-control sample (P(oihs) = 0.00058). LD contrasts between cases and controls support selection at TTC12 exon 3 and ANKK1 exon 2. The armadillo repeat domains encoded by TTC12 and dopamine interact in the Wnt pathway and may have effects on dopamine cell development in the ventral midbrain. We conclude that risk for AD is attributable in part to variants in four regions within this cluster: exon 3 of TTC12, exon 12/intron13 of NCAM1 and exons 2 and 5 of ANKK1. The complexity of these relationships, many of which replicate between our independent samples, may explain prior inconsistent results.

Alcohol dehydrogenase 1B genotype and fetal alcohol syndrome: a HuGE minireview

Fetal alcohol syndrome (FAS), 1 of the most common developmental disabilities in the United States, occurs at a rate of 0.5-2.0:1000 live births. Animal model, family, and twin studies suggest a genetic component to FAS susceptibility. Alcohol dehydrogenases (ADHs) catalyze the rate-limiting step in alcohol metabolism. Studies of genetic associations with FAS have focused on the alcohol dehydrogenase 1B (ADH1B) gene, comparing mothers and children with the alleles ADH1B*2 or ADH1B*3, associated with faster ethanol metabolism, with those homozygous for ADH1B*1. While most studies have found a protective effect for genotypes containing ADH1B*2 or ADH1B*3, results have been conflicting, and further investigation into the association between the ADH1B genotype and FAS is needed. Whether increased alcohol intake accounts for the elevated risk reported for the ADH1B*1/ADH1B*1 genotype should be addressed, and future studies would benefit from consistent case definitions, enhanced exposure measurements, larger sample sizes, and careful study design.

Overview of the role of alcohol dehydrogenase and aldehyde dehydrogenase and their variants in the genesis of alcohol-related pathology

Alcohol dehydrogenase (ADH) and mitochondrial aldehyde dehydrogenase (ALDH2) are responsible for metabolizing the bulk of ethanol consumed as part of the diet and their activities contribute to the rate of ethanol elimination from the blood. They are expressed at highest levels in liver, but at lower levels in many tissues. This pathway probably evolved as a detoxification mechanism for environmental alcohols. However, with the consumption of large amounts of ethanol, the oxidation of ethanol can become a major energy source and, particularly in the liver, interferes with the metabolism of other nutrients. Polymorphic variants of the genes for these enzymes encode enzymes with altered kinetic properties. The pathophysiological effects of these variants may be mediated by accumulation of acetaldehyde; high-activity ADH variants are predicted to increase the rate of acetaldehyde generation, while the low-activity ALDH2 variant is associated with an inability to metabolize this compound. The effects of acetaldehyde may be expressed either in the cells generating it, or by delivery of acetaldehyde to various tissues by the bloodstream or even saliva. Inheritance of the high-activity ADH β2, encoded by theADH2*2gene, and the inactiveALDH2*2gene product have been conclusively associated with reduced risk of alcoholism. This association is influenced by gene–environment interactions, such as religion and national origin. The variants have also been studied for association with alcoholic liver disease, cancer, fetal alcohol syndrome, CVD, gout, asthma and clearance of xenobiotics. The strongest correlations found to date have been those between theALDH2*2allele and cancers of the oro-pharynx and oesophagus. It will be important to replicate other interesting associations between these variants and other cancers and heart disease, and to determine the biochemical mechanisms underlying the associations.

Genomic screen for substance dependence and body mass index in southwest California Indians

Substance abuse and obesity are health disparities that may afflict Native Americans more than some other ethnic groups. One theoretical assumption concerning Native people is that the long history of dependence on foraging and subsistence agriculture may have led to selective enrichment of traits that improve genetic fitness, so called 'thrifty' or 'fat sparing' genes. We have speculated that this same selective pressure may have enriched for genetic variants that increase the risk for consumption of alcohol and drugs of abuse. Here, we report the results of a genome scan that compared findings for two consumption phenotypes: 'any drug dependence and/or regular tobacco use' and body mass index (BMI) in southwest California (SWC) Indian families. Variance component analyses from SOLAR were used to generate log of the odds ratio (LOD) scores. Evidence for linkage was found on chromosome 6 for both the 'any drug' (LOD score = 3.3) and BMI (LOD score = 2.3) phenotypes. Bivariate analyses of the two phenotypes revealed a combined LOD score of 4.1 at that location. Additional loci on chromosomes 6, 15, 16 and 21 were found for the 'any drug' phenotype, and on chromosomes 8, 16 and 18 for BMI (LOD scores ranged between 1.2 and 2.3). These results provide suggestive evidence for linkage for substance abuse and BMI in this Mission Indian population and, furthermore, provide preliminary data suggesting that 'consumption phenotypes' may share some genetic determinants.

Association of the ADHIB*3 Allele With Alcohol-Related Phenotypes in Trinidad

BACKGROUND

Two of the class I alcohol dehydrogenase (ADH) genes located on chromosome 4 (ADH1B and ADH1C) encode for multiple isozymes that differ in their kinetic properties. At the ADH1B locus, 3 polymorphisms are present (ADH1B(*)1, ADH1B(*)2, ADH1B(*)3). ADH1B(*)2 (found mostly in individuals of East Asian and Jewish descent) and ADH1B(*)3 (found mostly in individuals of African decent) alleles encode for a more active enzyme variants than ADH1B(*)1 and the presence of these alleles has been associated with protection from alcohol dependence. The relationship between these alleles and alcohol-associated phenotypes has not been previously investigated in individuals living in the Caribbean.

METHODS

One hundred thirty-three alcohol-dependent individuals of either East Indian or African ancestry and 98 controls matched by age, sex, education, and ethnicity participated in the study. A structured interview [the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA)] was used to gather information on demographics, psychiatric diagnoses, personal drinking, and drug use history. Leukocyte DNA extracted from a blood sample obtained from each participant was genotyped at the ADH1B locus. Serum levels of the liver enzymes alanine and aspartate aminotransferase (ALT, AST), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), and gamma-glutamyl transferase (GGT) as well as the presence of HIV, hepatitis B surface antigen, and antihepatitis C virus antibody were also assayed. The specific aim of the study was to investigate the associations between ADH1B alleles and alcohol dependence, drinking history, and liver function in individuals from the 2 major ethnic groups of Trinidad (individuals of African and East Indian ancestry).

RESULTS

Twenty-eight of the Afro-Trinidadian (Afro-TT) participants (41%) and 1 Indo-Trinidadian (Indo-TT) (>1%) had at least 1 ADH1B(*)3 allele and 3 Afro-TT were homozygous for the allele. African participants with at least 1 ADH1B(*)3 allele were found to be significantly less likely to be alcohol dependent (p<0.018), and to have lower alcohol consumption levels (p<0.05). Among those participants who were alcohol dependent, ADH1B(*)3 was associated with significantly higher levels of ALT (p<0.05).

CONCLUSIONS

This study suggests, in this sample of Trinidadians, that the ADH1B(*)3 allele is associated with protection from the development of alcoholism but is also associated with enhanced risk for elevated serum ALT levels in those individuals who do become alcohol dependent.

Involvement of cannabinoid CB2 receptor in alcohol preference in mice and alcoholism in humans

We tested if cannabinoid type 2 receptor (CB2) in the central nervous system plays a role in alcohol abuse/dependence in animal model and then examined an association between the CB2 gene polymorphism and alcoholism in human. Mice experiencing more alcohol preference by drinking showed reduced Cb2 gene expression, whereas mice with little preference showed no changes of it in ventral midbrain. Alcohol preference in conjunction with chronic mild stress were enhanced in mice treated with CB2 agonist JWH015 when subjected to chronic stress, whereas antagonist AM630 prevented development of alcohol preference. There is an association between the Q63R polymorphism of the CB2 gene and alcoholism in a Japanese population (P=0.007; odds ratio 1.25, 95% CI, (1.06-1.47)). CB2 under such environment is associated with the physiologic effects of alcohol and CB2 antagonists may have potential as therapies for alcoholism.

Associations of variations in alcohol dehydrogenase genes with the level of response to alcohol in non-Asians

BACKGROUND

Risk and protective factors for alcohol use disorders (AUDs) are complex and reflect both environmental and genetic factors. Genetic components account for about 50% of the variation and influence several phenotypes, including the level of response (LR) to alcohol as well as alcohol-metabolizing enzyme polymorphisms. Variations in the ADH1B and ADH1C genes may influence the LR to alcohol by increasing levels of acetaldehyde during alcohol metabolism, although most data on this question come from Asian populations.

METHODS

This study evaluated associations of ADH1B and ADH1C genotypes in a non-Asian sample. Participants (N = 117, 69.2% female) were 18- to 29-year-old men and women, primarily Caucasian (70.1%) and black (26.5%), recruited in San Diego, California. The Semi-Structured Assessment for the Genetics of Alcoholism Interview was used to assess demographic, substance use, and psychiatric history information, and the Family History Assessment Module was used to determine first-degree family history of alcohol dependence. An alcohol challenge paradigm was used to gather data on the LR to alcohol over 210 minutes.

RESULTS

Participants with the ADH1B*1/*2 genotype had a higher LR to alcohol early in the alcohol challenge (i.e., 30, 60, and 90 minutes after drinking) as measured by both alcohol-related changes in subjective feelings of intoxication and body sway, even when controlling for sex and Russian/Eastern European ancestry. A similar trend was seen for ADH1C*1/*1 genotype, although the results were not significant.

CONCLUSIONS

These findings suggest that studies searching for genes relating to the LR to alcohol as a vulnerability factor for AUDs should consider controlling for ADH1B genotype, as the ADH1B*2 allele could obscure the impact of other genetic polymorphisms.

Diplotype trend regression analysis of the ADH gene cluster and the ALDH2 gene: multiple significant associations with alcohol dependence

The set of alcohol-metabolizing enzymes has considerable genetic and functional complexity. The relationships between some alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) genes and alcohol dependence (AD) have long been studied in many populations, but not comprehensively. In the present study, we genotyped 16 markers within the ADH gene cluster (including the ADH1A, ADH1B, ADH1C, ADH5, ADH6, and ADH7 genes), 4 markers within the ALDH2 gene, and 38 unlinked ancestry-informative markers in a case-control sample of 801 individuals. Associations between markers and disease were analyzed by a Hardy-Weinberg equilibrium (HWE) test, a conventional case-control comparison, a structured association analysis, and a novel diplotype trend regression (DTR) analysis. Finally, the disease alleles were fine mapped by a Hardy-Weinberg disequilibrium (HWD) measure (J). All markers were found to be in HWE in controls, but some markers showed HWD in cases. Genotypes of many markers were associated with AD. DTR analysis showed that ADH5 genotypes and diplotypes of ADH1A, ADH1B, ADH7, and ALDH2 were associated with AD in European Americans and/or African Americans. The risk-influencing alleles were fine mapped from among the markers studied and were found to coincide with some well-known functional variants. We demonstrated that DTR was more powerful than many other conventional association methods. We also found that several ADH genes and the ALDH2 gene were susceptibility loci for AD, and the associations were best explained by several independent risk genes.

Genetic associations of alcohol and aldehyde dehydrogenase with alcohol dependence and their mechanisms of action

Two alcohol dehydrogenase genes (ADHIB and ADH1C on chromosome 4) and one aldehyde dehydrogenase gene (ALDH2 on chromosome 12) exhibit functional polymorphisms that are associated with lower rates of alcohol dependence. The ALDH2*2 allele,found almost exclusively in Asian populations, has the strongest relationship. The ADH1B*2, ADH1B*3, and ADHlC*i alleles, found in varying prevalence in different ethnic groups, have also been associated with lower rates of alcohol dependence. Studies of the ADHIBand ADH1C haplotypes, however, have shown that ADH1C*I is in linkage disequilibrium with ADHiB*2, and the ADH1C*i allele does not appear to have significant unique associations with alcohol dependence. The hypothesized mechanism underlying the associations of the ADH1B and ALDH2 polymorphisms with alcohol dependence is that the isoenzymes encoded by these alleles lead to an accumulation of acetaldehyde during alcohol metabolism. Based on their kinetic properties, ALDH2 *2 theoretically should lead to a slower removal of acetaldehyde than ALDH2*1, whereas ADH1B*2 and ADH1B*3 should lead to a more rapid production of acetaldehyde than ADHIB*I. It is further hypothesized that elevations in acetaldehyde cause more intense reactions to alcohol and lead to lower levels of alcohol intake. Data are consistent with the hypothesis that elevations in acetaldehyde, increased sensitivity to alcohol, and lower levels of drinking reflect the mechanism by which the ALDH2*2 allele reduces risk for alcohol dependence. There is also some evidence supporting this mechanism for the ADH1B*2 and ADHIB*3 alleles, but the results are less consistent. These findings highlight the value of trying to elucidate the mechanism by which genes ultimately give rise to differences in alcohol dependence through the examination of mediating behaviors.

Integrative strategies to identify candidate genes in rodent models of human alcoholism

The search for genes underlying alcohol-related behaviours in rodent models of human alcoholism has been ongoing for many years with only limited success. Recently, new strategies that integrate several of the traditional approaches have provided new insights into the molecular mechanisms underlying ethanol's actions in the brain. We have used alcohol-preferring C57BL/6J (B6) and alcohol-avoiding DBA/2J (D2) genetic strains of mice in an integrative strategy combining high-throughput gene expression screening, genetic segregation analysis, and mapping to previously published quantitative trait loci to uncover candidate genes for the ethanol-preference phenotype. In our study, 2 genes, retinaldehyde binding protein 1 (Rlbp1) and syntaxin 12 (Stx12), were found to be strong candidates for ethanol preference. Such experimental approaches have the power and the potential to greatly speed up the laborious process of identifying candidate genes for the animal models of human alcoholism.

New findings on the genetic influences on alcohol use and dependence

PURPOSE OF REVIEW

Alcohol dependence is a complex disorder with a well documented highly hereditary nature. This article reviews the recent advances in our understanding of the direct and indirect genetic influences on alcohol use and dependence.

RECENT FINDINGS

Recent findings can be summarized as follows: (a) twin studies have defined and estimated the risks of general and specific alcohol-related vulnerabilities. (b) Linkage studies have provided largely inconsistent findings, though several chromosomal regions have been implicated. (c) Quantitative trait loci analyses in animals have identified that the Mpdz gene predisposes to alcohol dependence and withdrawal. (d) Examination of family-based samples has identified several genes including GABRA2 and CHRM2 thought to be associated with alcohol dependence.

SUMMARY

Despite great advances in understanding of genetic vulnerability in alcohol use disorders, only two gene complexes, ADH and ALDH2, have been identified as having defined effects on alcohol use and liability to dependence in humans. New genes associated with increased risks for the disorder will certainly be added to this list in the near future. Neurobiological analyses of the effects of these genes will surely contribute to further understanding of the cause of alcohol dependence and the interindividual differences in risks.

Genomic screen for loci associated with tobacco usage in Mission Indians

Background

The prevalence of tobacco usage in Native American adults and adolescents is higher than any other racial or ethnic group, yet biological risk and protective factors underlying tobacco use in this ethnic group remain unknown. A genome scan for loci associated with tobacco use phenotypes was performed with data collected from a community sample of Mission Indians residing in Southwest California.

Methods

A structured diagnostic interview was used to define two tobacco use phenotypes: 1) any regular tobacco usage (smoked daily for one month or more) and 2) persistent tobacco usage (smoked at least 10 cigarettes a day for more than one year). Heritability was determined and a linkage analysis was performed, using genotypes for a panel 791 microsatellite polymorphisms, for the two phenotypes using variance component methods implemented in SOLAR.

Results

Analyses of multipoint variance component LOD scores for the two tobacco use phenotypes revealed two scores that exceeded 2.0 for the regular use phenotype: one on chromosomes 6 and one on 8. Four other loci on chromosomes 1,7,13, and 22 were found with LOD scores between 1.0 and 1.5. Two loci of interest were found on chromosomes 1 and 4 for the persistent use phenotype with LOD scores between 1.3–1.5. Bivariate linkage analysis was conducted at the site on chromosome 4 for persistent tobacco use and an alcohol drinking severity phenotype previously identified at this site. The maximum LOD score for the bivariate analysis for the region was 3.4, however, there was insufficient power to exclude coincident linkage.

Conclusion

While not providing evidence for linkage to specific chromosomal regions these results identify regions of interest in the genome in this Mission Indian population, for tobacco usage, some of which were identified in previous genome scans of non-native populations. Additionally, these data lend support for the hypothesis that cigarette smoking, alcohol dependence and other consumptive behaviors may share some common risk and/or protective factors in this Mission Indian population.

The level of response to alcohol in daughters of alcoholics and controls

BACKGROUND

The low level of response (LR) to alcohol is a genetically influenced characteristic related to the development of alcohol use disorders (AUDs). This phenotype is found in men with a family history (FH) of alcoholism, predicts future AUDs, and has heritabilities as high as 60%. However, despite evidence of genetic influences for AUDs in both sexes, the majority of studies evaluating differences in LR across high- and low-risk groups have been conducted on males, and it is unclear how generalizable these results are to women.

METHODS

Twenty-five women who are family history positive (FHP) for alcohol dependence were matched with 25 women with no FH of alcoholism (FHN) on factors that may impact LR. Using an alcohol challenge paradigm, data on the reaction to a moderate dose of alcohol were gathered over a period of 3.5 h. Assessments included breath alcohol concentrations (BrACs), the Subjective High Assessment Scale (SHAS), as well as body sway or static ataxia.

RESULTS

Family history positives reported lower subjective intoxication than FHNs. In addition, when body sway scores were corrected for skewness, FHPs had significantly lower scores on alcohol-related changes in lateral sway. These differences remained after considering the effects of drinking history and BrAC values.

CONCLUSIONS

This study evaluated the LR to alcohol in the largest sample of alcohol challenges in matched FHP and FHN women to date. Overall, the findings are consistent with most data from earlier investigations of smaller sized samples of FHP women. The results suggest that, similar to sons of alcoholics, a low LR to alcohol might also be characteristic of daughters of alcoholics.

Functionality of allelic variations in human alcohol dehydrogenase gene family: assessment of a functional window for protection against alcoholism

Alcohol dehydrogenase (ADH) catalyses the rate-determining reaction in ethanol metabolism. Genetic association studies of diverse ethnic groups have firmly demonstrated that the allelic variant ADH1B*2 significantly protects against alcoholism but that ADH1C*1, which is in linkage with ADH1B*2, produces a negligible protection. The influence of other potential candidate genes/alleles within the human ADH family, ADH1B*3 and ADH2, remains unclear or controversial. To address this question, functionalities of ADH1B3 and ADH2 were assessed at a physiological level of coenzyme and substrate range. Ethanol-oxidizing activities of recombinant ADH1B1, ADH1B2, ADH1B3, ADH1C1, ADH1C2 and ADH2 were determined at pH 7.5 in the presence of 0.5 mm NAD with 2-50 mm ethanol. The activity differences between ADH1B2 and ADH1B1 were taken as a threshold for effective protection against alcoholism and those between ADH1C1 and ADH1C2 as a threshold for null protection. Over 2-50 mm ethanol, the activities of ADH1B3 were found 2.9-23-fold lower than those of ADH1B2, largely attributed to the Km effect (ADH1B2, 1.8 mm; ADH1B3, 61 mm). Strikingly, the ADH1B3 activity was only 84% that of ADH1B1 at a low ethanol concentration, 2 mm, but increased 10-fold at 50 mm. Corrected for relative expression levels of the enzyme in liver, the hepatic ADH2 activities were estimated to be 18-97% those of ADH1B1 over 2-50 mm ethanol and were 28-140% of the activity differences between ADH1C1 and ADH1C2. The assessment based on the proposed functional window for the human ADH gene family indicates that ADH1B*3 may show some degree of protection against alcoholism and that the ADH2 functional variants appear to be negligible for this protection.

Association of ALDH1 promoter polymorphisms with alcohol-related phenotypes in southwest California Indians

BACKGROUND

Cytosolic aldehyde dehydrogenase (ALDH1A1) is an important enzyme in the metabolism of acetaldehyde and the synthesis of retinoic acid. Two polymorphisms in the promoter region of ALDH1A1-ALDH1A1*2 and ALDH1A1*3-have recently been identified and described in small samples of Asian, Caucasian, and African individuals. The aim of this study was to determine the prevalence of these polymorphisms in a sample of Southwest California Indians and to test for associations with alcohol dependence and other substance-related behaviors.

METHODS

The participants in this study were 463 adult men and women recruited from 8 contiguous Indian reservations. A structured interview was used to gather information on demographics, psychiatric diagnoses, and personal drinking and drug use history. A blood sample was obtained from each participant, and leukocyte DNA was extracted and used to genotype for the presence of the ALDH1A1 promoter polymorphisms.

RESULTS

Twenty-seven participants (6%) possessed ALDH1A1*2 (frequency, 0.03), two participants possessed ALDH1A1*3, and one participant displayed both of these alleles. Individuals with an ALDH1A1*2 allele had lower rates of alcohol dependence and regular tobacco use than those without this allele. Individuals with ALDH1A1*2 also reported a significantly lower maximum number of drinks ever consumed in a 24-hr period, reported drinking fewer drinks per occasion when they first started drinking regularly, and reported lower expectations of alcohol's effects compared with individuals without this allele.

CONCLUSIONS

Results from this study suggest that ALDH1A1*2 may be associated with protection from the development of alcohol and other substance use disorders.

Alcohol and gene interactions

Alcohol use produces both desirable and undesirable effects, ranging from short-term euphoria and reduction in cardiovascular risk, to violence, accidents, dependence and liver disease. Outcomes are affected by the amount of alcohol used (which is itself affected by genetic variation) and also by the drinker's genes. Genetic effects have been most clearly demonstrated for alcohol dependence, and several of the genes for which variation leads to increased dependence risk have been identified. These include genes for enzymes involved in alcohol metabolism (alcohol dehydrogenase and aldehyde dehydrogenase), and genes for receptors affected by alcohol (particularly γ-aminobutyric acid receptors). Many other gene/dependence associations have been reported but not fully substantiated. Genetic effects on phenotypes other than alcohol dependence are less well understood, and need to be clarified before a full picture of gene-alcohol interactions can be achieved.

Fetal ADH2*3, maternal alcohol consumption, and fetal growth

There is some evidence suggesting the allele for alcohol dehydrogenase 2*3 (ADH2*3) is associated with a protective effect against alcohol-related intrauterine growth retardation (IUGR). This study was conducted to explore the affect of the ADH2*3 allele on fetal growth. Bloodspots (n = 1016) belonging to individual infants of a subgroup of the Baltimore-Washington Infant Study (BWIS) were assayed for the presence of the ADH2*3 allele by a polymerase chain reaction (PCR)-based method. Infants genotyped for ADH2*3 were those for whom bloodspots were identified and obtained from the Maryland Newborn Screening Program. The effect of ADH2*3 and maternal alcohol consumption on intrauterine growth was explored by multivariable linear regression analysis. Twenty-six percent of the 306 blood spots belonging to African-American infants were positive for ADH2*3 (4% were homozygous and 22% were heterozygous). Only a small percentage of bloodspots for Caucasian (1.3%) were positive for the ADH2*3 allele. Consequently, further analysis concentrated on gene-exposure interactions for African-American infants. It was found that the incidence of being small-for-gestation-age (SGA) was lower for ADH2*3-positive infants (2.5% versus 8.8%; p = .08). SGA infants had elevated odds for being ADH2*3 negative (OR: 3.15, 95% C.I.: 0.70-14.26) and for being born to mothers that consumed alcohol during pregnancy (OR: 2.31, 95% C.I.: 0.77-6.91). A negative trend between maternal alcohol consumption and mean offspring birthweight was found; however, ADH2*3 did not have a significant impact on mean birthweight for infants born to mothers that drank during pregnancy. These results could be interpreted as possible support for the hypothesis that ADH2 genotype in the infant may impact risk for alcohol-related IUGR. However, this study has limitations in that it is a "nested study of convenience" and involves a relatively small number of infants born to mothers reporting moderate to heavy alcohol use during pregnancy.

Genomic screen for loci associated with alcohol dependence in Mission Indians

Alcohol dependence is a leading cause of morbidity and mortality in Native Americans, yet biological factors underlying the disorder in this ethnic group remain elusive. This study's aims were to map susceptibility loci for DSM-III-R alcohol dependence and two narrower alcohol-related phenotypes in Mission Indian families. Each participant gave a blood sample and completed an interview using the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA) that was used to make alcohol dependence diagnoses and the narrower phenotypes of withdrawal, and drinking severity. Genotypes were determined for a panel 791 microsatellite polymorphisms. Analyses of multipoint variance component LOD scores for the dichotomous DSM-III-R phenotype revealed no peak LOD scores that exceeded 2.0 at any chromosome location. Two chromosomes, 4 and 12, had peak LOD scores that exceeded 2 for the alcohol use severity phenotype and three chromosomes 6, 15, 16 were found to have peaks with LOD scores that exceeded 2 for the withdrawal phenotype. Evidence for linkage to chromosomes 4 and 15, and 16 have been reported previously for alcohol related phenotypes whereas no evidence has as yet been reported for chromosomes 6 and 12. Combined linkage and association analysis suggest that alcohol dehydrogenase 1B gene polymorphisms are partially responsible for the linkage result on chromosome 4 in this population. These results corroborate the importance of several chromosomal regions highlighted in prior segregation studies in alcoholism and further identify new regions of the genome that may be unique to either the restricted phenotypes evaluated or this population of Mission Indians.

Genetic polymorphism in ethanol metabolism: acetaldehyde contribution to alcohol abuse and alcoholism

Acetaldehyde, the first product of ethanol metabolism, has been speculated to be involved in many pharmacological and behavioral effects of ethanol. In particular, acetaldehyde has been suggested to contribute to alcohol abuse and alcoholism. In the present paper, we review current data on the role of acetaldehyde and ethanol metabolism in alcohol consumption and abuse. Ethanol metabolism involves several enzymes. Whereas alcohol dehydrogenase metabolizes the bulk of ethanol within the liver, other enzymes, such as cytochrome P4502E1 and catalase, also contributes to the production of acetaldehyde from ethanol oxidation. In turn, acetaldehyde is metabolized by the enzyme aldehyde dehydrogenase. In animal studies, acetaldehyde is mainly reinforcing particularly when injected directly into the brain. In humans, genetic polymorphisms of the enzymes alcohol dehydrogenase and aldehyde dehydrogenase are also associated with alcohol drinking habits and the incidence of alcohol abuse. From these human genetic studies, it has been concluded that blood acetaldehyde accumulation induces unpleasant effects that prevent further alcohol drinking. It is therefore speculated that acetaldehyde exerts opposite hedonic effects depending on the localization of its accumulation. In the periphery, acetaldehyde is primarily aversive, whereas brain acetaldehyde is mainly reinforcing. However, the peripheral effects of acetaldehyde might also be dependent upon its peak blood concentrations and its rate of accumulation, with a narrow range of blood acetaldehyde concentrations being reinforcing.

Gender, ethnicity and genetics in cardiovascular disease: part 1: Basic principles

Prior to 1993, most drug efficacy and safety trials were conducted in white males, although gender and racial differences in pharmacodynamics and pharmacokinetics have been documented since the early 1900s. Over the last 2 decades, supported by the FDA and legislation, attempts to include more women and minorities in clinical drug trials have been made, with limited success. Yet, there are important differences in pathophysiology and pharmacogenetics, as well as pharmacotherapeutic effectiveness. This is the first of 2 articles that review the basic scientific principles of such differences. In particular, genetic polymorphisms of cardiovascular candidate genes and drug metabolism are described. The pharmacodynamic and pharmacokinetic variations among genders and ethnicities are summarized.