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

Impact of Alcohol-Induced Facial Flushing Phenotype on Alcohol Consumption among Korean Adults: A Two-Year Cross-Sectional Study

BACKGROUND

Alcohol-induced facial flushing phenotype (flushing) is common among East Asians. Despite a small intake of alcohol, they experience heightened levels of acetaldehyde, a group-1 carcinogen, which in turn causes unpleasant symptoms such as redness, acting as a robust protective mechanism against consuming alcohol. However, some individuals with this genetic trait exhibit weakened alcohol restraint, which increases the risk of developing alcohol-related cancers, such as esophageal and head/neck cancer, by more than ten times. Although this flushing phenomenon is crucial for public health, there is a paucity of studies that have comprehensively investigated the effect of flushing or its genotype on alcohol consumption in a large group of East Asians while controlling for various sociodemographic and health-related variables at a country level.

OBJECTIVE

This two-year cross-sectional study aimed to explore the effect of flushing on drinking behavior in Koreans and to examine whether the effect varies across sociodemographic and health-related factors.

METHODS

We used data from the Korea National Health and Nutrition Examination Survey 2019-2020 conducted by the Korea Disease Control and Prevention Agency. Our sample comprised 10,660 Korean adults. The study investigated the association of 26 variables, including flushing, with drinking frequency and amount. The effect of flushing was examined with and without adjusting for the other 25 variables using multinomial logistic regression analysis. Additionally, we tested the interaction effect with flushing and conducted a simple effect analysis. To ensure unbiased results, we employed complex sample design elements, including strata, clusters, and weights, to obtain unbiased results for the Rao-Scott χ2 test, t-test, and multinomial logistic regression analysis.

RESULTS

The suppressive effect of flushing was significant across all pronounced categories of alcohol consumption at the significance level of .001 in 2019. The ranges of the standardized regression slopes and odds ratios were -6.70 ≥  ≥ -11.25 and 0.78 ≥ OR ≥ 0.50 for frequency; -5.37 ≥  ≥ -17.64 and 0.73 ≥ OR ≥ 0.36 for amount, respectively. The effect became somewhat stronger when adjusted for confounders. The effect also exhibited an overall stronger trend as the severity of alcohol consumption increased. The betas and odds ratios were consistently smaller in 2020 compared to the previous year. A simple effect analysis revealed a diminished alcohol-suppressive effect of flushing on alcohol consumption for specific groups (e.g., those with low levels of education, limited family support, physical labor, or health-related issues).

CONCLUSIONS

Our findings suggest that flushing suppresses drinking in Koreans overall but has little or no effect in certain vulnerable populations. Therefore, health authorities should conduct targeted epidemiological studies to assess drinking patterns and disease profiles, particularly regarding alcohol-related cancers, and establish effective preventive measures tailored to this population.

CLINICALTRIAL

Hypomethylation of Long Interspersed Nucleotide Elements and Aldehyde Dehydrogenase in Patients of Alcohol Use Disorder with Cirrhosis

Alcohol use disorder (AUD) and cirrhosis are key outcomes of excessive alcohol use, and a genetic influence in these outcomes is increasingly recognized. While 80-90% of heavy alcohol users show evidence of fatty liver, only 10-20% progress to cirrhosis. There is currently no clear understanding of the causes of this difference in progression. The aim of this study is to evaluate genetics and epigenetics at the aldehyde dehydrogenase (ALDH2) locus in patients with AUD and liver complications. Study participants were inpatients from the clinical services of Gastroenterology and Psychiatry at St. John's Medical College Hospital (SJMCH) and the National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore, India. Men diagnosed as having AUD with cirrhosis (AUDC+ve, N = 136) and AUD without cirrhosis (AUDC-ve, N = 107) were assessed. FibroScan/sonographic evidence was used to rule out fibrosis in the AUDC-ve group. Genomic DNA was used for genotyping at the ALDH2 (rs2238151) locus. A subset of 89 samples was used for DNA methylation (AUDC+ve, N = 44; and AUDC-ve, N = 45) analysis at long interspersed nucleotide element 1 (LINE-1) and ALDH2 cytosine-phosphate-guanine (CpG) loci by pyrosequencing. ALDH2 DNA methylation was significantly lower in the AUDC+ve group compared with the AUDC-ve group (p < 0.001). Lower methylation was associated with a risk allele (T) of the ALDH2 locus (rs2238151) (p = 0.01). Global (LINE-1) DNA methylation levels were also significantly lower in the AUDC+ve group compared with the AUDC-ve group (p = 0.01). Compromised global methylation (LINE-1) and hypomethylation at the ALDH2 gene was observed in patients with cirrhosis compared with those without cirrhosis. DNA methylation could be explored as a biomarker for cirrhosis and liver complications.

Biochemical Mechanisms Associating Alcohol Use Disorders with Cancers

Simple Summary

Of all yearly deaths attributable to alcohol consumption globally, approximately 12% are due to cancers, representing approximately 0.4 million deceased individuals. Ethanol metabolism disturbs cell biochemistry by targeting the structure and function of essential biomolecules (proteins, nucleic acids, and lipids) and by provoking alterations in cell programming that lead to cancer development and cancer malignancy. A better understanding of the metabolic and cell signaling realm affected by ethanol is paramount to designing effective treatments and preventive actions tailored to specific neoplasias.

Abstract

The World Health Organization identifies alcohol as a cause of several neoplasias of the oropharynx cavity, esophagus, gastrointestinal tract, larynx, liver, or female breast. We review ethanol’s nonoxidative and oxidative metabolism and one-carbon metabolism that encompasses both redox and transfer reactions that influence crucial cell proliferation machinery. Ethanol favors the uncontrolled production and action of free radicals, which interfere with the maintenance of essential cellular functions. We focus on the generation of protein, DNA, and lipid adducts that interfere with the cellular processes related to growth and differentiation. Ethanol’s effects on stem cells, which are responsible for building and repairing tissues, are reviewed. Cancer stem cells (CSCs) of different origins suffer disturbances related to the expression of cell surface markers, enzymes, and transcription factors after ethanol exposure with the consequent dysregulation of mechanisms related to cancer metastasis or resistance to treatments. Our analysis aims to underline and discuss potential targets that show more sensitivity to ethanol’s action and identify specific metabolic routes and metabolic realms that may be corrected to recover metabolic homeostasis after pharmacological intervention. Specifically, research should pay attention to re-establishing metabolic fluxes by fine-tuning the functioning of specific pathways related to one-carbon metabolism and antioxidant processes.

Association of alcohol dehydrogenase and aldehyde dehydrogenase Polymorphism with Spontaneous Deep Intracerebral Haemorrhage in the Taiwan population

Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) encode essential alcohol-metabolizing enzymes. While alcohol use is associated with spontaneously deep intracerebral haemorrhage (SDICH), particularly in males, the activities and genetic variants of ADH and ALDH may affect SDICH development. This case-control study was conducted to identify the interaction of alcohol use and SDICH with five single-nucleotide polymorphisms (SNPs): ADH1B rs1229984, ADH1C rs2241894, ALDH2 rs671, ALDH2 rs886205, and ALDH2 rs4648328. We enrolled 208 patients with SDICH and 244 healthy controls in a Taiwanese population. ALDH2 rs671 was significantly associated with SDICH in the dominant (P < 0.001) and additive models (P = 0.007). ALDH2 rs4648328 was borderline significantly associated with SDICH in the recessive (P = 0.024) or additive models (P = 0.030). In alcohol-using patients, the ALDH2 rs671 GG genotype was associated with SDICH risk compared to the GA+AA genotype (P = 0.010). ADH1B rs1229984, ADH1C rs2241894, and ALDH2 rs886205 did not demonstrate association with SDICH. Thus, the ALDH2 rs671 GG genotype is a risk factor for SDICH. Because the genetic distributions of ALDH2 rs671 exhibited strong ethnic heterogeneity, further studies in different populations are needed to validate these findings.

Genetic polymorphisms of ALDH2 are associated with lumbar disc herniation in a Chinese Han population

Aldehyde dehydrogenase (ALDH) is a key enzyme for the catalytic oxidation of acetaldehyde to acetic acid. Genetic polymorphisms of ALDH2 have been associated with a wide range of diseases and cancers. However, little information is found about the association between ALDH2 polymorphisms and lumbar disc herniation (LDH) in Chinese Han population. We investigated the association between single nucleotide polymorphisms (SNPs) in ALDH2 and LDH risk in a case–control study that included 380 LDH cases and 692 healthy controls. Eight SNPs were selected and genotyped using the Sequenom MassARRAY platform. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using unconditional logistic regression after adjusting for gender and age. In the allele model analysis, we found the frequency of the “A” allele of rs671 was significantly higher in LDH cases than in controls (OR = 1.414, 95%CI: 1.109–1.803, P = 0.005). In the genetic model analysis, we found the minor allele “A” of rs671 was associated with increased risk of LDH under log-additive model (OR = 1.42, 95%CI: 1.11–1.82, P = 0.0062); and the minor allele “C” of rs7296651 was associated with decreased risk of LDH under over-dominant model (OR = 0.72, 95%CI: 0.53–0.97, P = 0.031). Additionally, the haplotype “GGCTCACG” constructed by rs886205, rs2238152, rs4648328, rs441, rs4646778, rs671, rs11066028, and rs7296651 was associated with increased risk of LDH (OR = 1.45; 95% CI = 1.11–1.90; P = 0.0071). Our data shed new light on the association between genetic polymorphisms of ALDH2 and LDH susceptibility in a Chinese Han population.

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.

Free will in addictive behaviors: A matter of definition

Certain people are at risk for using alcohol or other drugs excessively and for developing problems with their use. Their susceptibility might arise from a variety of factors, including their genetic make-up, brain chemistry, family background, personality and other psychological variables, and environmental and sociocultural variables. Moreover, after substance use has become established, there are additional cognitive-motivational variables (e.g., substance-related attentional bias) that contribute to enacting behaviors consistent with the person's motivation to acquire and use the substance. People who are at such risk are likely to choose to use addictive substances even though doing so entails negative consequences. In the sense of complete freedom from being determined by causal factors, we believe that there is no such thing as free will, but defined as ability to make choices from among multiple options, even though the choices are ultimately governed by natural processes, addicted individuals are free to choose. Although they might appear unable to exercise this kind of free will in decisions about their substance use, addictive behaviors are ultimately always goal-directed and voluntary. Such goal pursuits manifest considerable flexibility. Even some severely addicted individuals can cease their use when the value of continuing the use abruptly declines or when the subjective cost of continuing the use is too great with respect to the incentives in other areas of their lives. Formal treatment strategies (e.g., contingency management, Systematic Motivational Counseling, cognitive training) can also be used to facilitate this reversal.

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.

Alcohol Consumption, Aldehyde Dehydrogenase 2 Gene Polymorphisms, and Cardiovascular Health in Korea

Alcohol consumption is a serious health issue in Korea in terms of the amount consumed and the behavior related to its consumption. Aldehyde dehydrogenase 2 (ALDH2) is a key enzyme in alcohol metabolism that degrades acetaldehyde to nontoxic acetic acid. The enzyme is coded by the ALDH2 gene, which is commonly polymorphic in East Asian populations. A point mutation in the ALDH2 gene (the rs671 allele) yields an inactive form of ALDH2 that causes acetaldehyde accumulation in the body after alcohol consumption, thereby inhibiting normal alcohol metabolism. Individuals who are homozygous for polymorphism in ALDH2 tend to refrain from drinking alcohol, decreasing their chances of developing alcoholism and exposure to the associated risks. Mendelian randomization (MR) studies have demonstrated that alcohol consumption predicted by ALDH2 genotype is causally related to cardiovascular risks. Moreover, recent MR studies suggest that the ALDH2 variant has mechanistic effects on some disease outcomes or mortality through increased blood levels of acetaldehyde, showing differences therein between heterozygotes (ALDH2*2*2) and homozygotes (ALDH2*1*2) in those who consume alcohol. Accordingly, consideration of ALDH2 genotype in alcohol prevention programs is warranted. In conclusion, strategies that incorporate genetic information and provide an evidential basis from which to help people make informed decisions on alcohol consumption are urgently required.

Genetic polymorphisms in ALDH2 are associated with drug addiction in a Chinese Han population

We investigated the association between single nucleotide polymorphisms (SNPs) in ALDH2, which has been associated with alcohol dependence and several types of diseases, and the risk of drug addiction in a Chinese Han population. In a case-control study that included 692 cases and 700 healthy controls, eight SNPs in ALDH2 were selected and genotyped using the Sequenom MassARRAY platform. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using unconditional logistic regression after adjusting for age and gender. We determined that rs671 is significantly associated with a 1.551-fold increased drug addiction risk (95% CI = 1.263-1.903; p < 0.001). In the genetic model analysis, we found that rs671 is associated with an increased risk of drug addiction under additive, dominant and recessive models (p < 0.001), while rs886205, rs441 and rs4646778 displayed a decreased drug addiction risk under additive and recessive model, respectively (p < 0.05). SNP rs671 remained significant after Bonferroni correction (p<0.00125). Additionally, we observed that haplotype "GTCAC" was associated with increased drug addiction risk (OR = 1.668; 95% CI, 1.328-2.094, p < 0.001); in contrast, "ATCGC" was a protective haplotype for drug addiction risk (OR = 0.444; 95% CI, 0.281-0.704, p < 0.001). Our findings showed that ALDH2 polymorphisms are significantly associated with the risk of drug addiction in the Chinese Han population.

Neuroscience of attentional processes for addiction medicine: from brain mechanisms to practical considerations

The present chapter first argues how having a goal for procuring alcohol or other substances leads to the development of a time-binding, dynamic, and goal oriented motivational state termed current concern, as the origin of substance-related attentional bias. Next, it discusses the importance of attentional bias in the development, continuation of, and relapsing to substance abuse. It further proceeds with a review of selective evidence from cognitive psychology that helps account for making decisions about using an addictive substance or refraining from using it. A discussion on the various brain loci that are involved in attentional bias and other kinds of cue reactivity is followed by presenting findings from neurocognitive research. Finally, from an interdisciplinary perspective, the chapter presents new trends and ideas that can be applied to addiction-related cognitive measurement and training.

The motivational basis of cognitive determinants of addictive behaviors

If a person expects that (a) drinking alcohol or using another addictive substance will enhance positive affect or reduce negative affect, and (b) there is a strong likelihood that these desirable consequences will occur if the substance is used, that person is likely to form a goal of using the substance. The theoretical framework presented here predicts that when that happens, the person will have a current concern for using the substance, with the person thereby sensitized to environmental stimuli related to procuring and using the substance. One indication of the sensitization is selective attention to substance-related stimuli, which is correlated with urges to use and actual use of the substance. Accordingly, interventions have been developed for helping substance users to overcome substance-related attentional bias. The results are promising for reducing both the attentional bias and the substance use. Finally, we discuss other cognitive-modification and motivational techniques that have been evaluated with promising results.

A personalized medicine approach for Asian Americans with the aldehyde dehydrogenase 2*2 variant

Asian Americans are one of the fastest-growing populations in the United States. A relatively large subset of this population carries a unique loss-of-function point mutation in aldehyde dehydrogenase 2 (ALDH2), ALDH2*2. Found in approximately 560 million people of East Asian descent, ALDH2*2 reduces enzymatic activity by approximately 60% to 80% in heterozygotes. Furthermore, this variant is associated with a higher risk for several diseases affecting many organ systems, including a particularly high incidence relative to the general population of esophageal cancer, myocardial infarction, and osteoporosis. In this review, we discuss the pathophysiology associated with the ALDH2*2 variant, describe why this variant needs to be considered when selecting drug treatments, and suggest a personalized medicine approach for Asian American carriers of this variant. We also discuss future clinical and translational perspectives regarding ALDH2*2 research.

Alcohol consumption and lifetime change in cognitive ability: a gene × environment interaction study

Studies of the effect of alcohol consumption on cognitive ability are often confounded. One approach to avoid confounding is the Mendelian randomization design. Here, we used such a design to test the hypothesis that a genetic score for alcohol processing capacity moderates the association between alcohol consumption and lifetime change in cognitive ability. Members of the Lothian Birth Cohort 1936 completed the same test of intelligence at age 11 and 70 years. They were assessed for recent alcohol consumption in later life and genotyped for a set of four single-nucleotide polymorphisms in three alcohol dehydrogenase genes. These variants were unrelated to late-life cognition or to socioeconomic status. We found a significant gene × alcohol consumption interaction on lifetime cognitive change (p = 0.007). Individuals with higher genetic ability to process alcohol showed relative improvements in cognitive ability with more consumption, whereas those with low processing capacity showed a negative relationship between cognitive change and alcohol consumption with more consumption. The effect of alcohol consumption on cognitive change may thus depend on genetic differences in the ability to metabolize alcohol.

The genetics of alcohol dependence

Alcohol consumption dates back to the Neolithic period, and alcohol dependence contributes substantially to the current global burden of disease. Despite this, optimal therapies and preventive strategies are lacking. Formal genetic studies of alcohol dependence have shown that genetic factors play as large a role in disease etiology as environmental factors. Molecular genetic studies may identify causal factors and facilitate the development of novel preventive and therapeutic approaches. Whereas earlier studies involved the use of linkage- and candidate-gene approaches, recent years have witnessed the introduction of genome-wide association studies (GWAS). The present review provides a brief overview of the findings of formal genetic studies, summarizes the results of earlier molecular-genetic investigations, and presents a detailed overview of all published GWAS in the field of alcohol dependence research. To date, few genome-wide significant findings have been reported. However, through the polygenic approach, GWAS have both confirmed the existence of a multitude of novel risk genes and indicated interesting new candidates.

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.

Recent advances in the genetic epidemiology and molecular genetics of substance use disorders

This article reviews current advances in the genetics of substance use disorders (SUDs). Both genetic and environmental sources of risk are required to develop a complete picture of SUD etiology. Genetic sources of risk for SUDs are not highly substance specific in their effects. Genetic and environmental risks for SUDs typically do not only add together but also interact with each other over development. Risk gene identification for SUDs has been difficult, with one recent success in identifying nicotinic receptor variants that affect risk for nicotine dependence. The impact of genetic variants on SUD risk will individually be small. Although genetic epidemiologic methods are giving us an increasingly accurate map of broad causal pathways to SUDs, gene discovery will be needed to identify the specific biological systems. Identifying these risk genes and understanding their action will require large clinical samples, and interaction between these studies and work in model organisms.

ALDH2 in alcoholic heart diseases: molecular mechanism and clinical implications

Alcoholic cardiomyopathy is manifested as cardiac hypertrophy, disrupted contractile function and myofibrillary architecture. An ample amount of clinical and experimental evidence has depicted a pivotal role for alcohol metabolism especially the main alcohol metabolic product acetaldehyde, in the pathogenesis of this myopathic state. Findings from our group and others have revealed that the mitochondrial isoform of aldehyde dehydrogenase (ALDH2), which metabolizes acetaldehyde, governs the detoxification of acetaldehyde formed following alcohol consumption and the ultimate elimination of alcohol from the body. The ALDH2 enzymatic cascade may evolve as a unique detoxification mechanism for environmental alcohols and aldehydes to alleviate the undesired cardiac anomalies in ischemia-reperfusion and alcoholism. Polymorphic variants of the ALDH2 gene encode enzymes with altered pharmacokinetic properties and a significantly higher prevalence of cardiovascular diseases associated with alcoholism. The pathophysiological effects of ALDH2 polymorphism may be mediated by accumulation of acetaldehyde and other reactive aldehydes. Inheritance of the inactive ALDH2*2 gene product is associated with a decreased risk of alcoholism but an increased risk of alcoholic complications. This association is influenced by gene-environment interactions such as those associated with religion and national origin. The purpose of this review is to recapitulate the pathogenesis of alcoholic cardiomyopathy with a special focus on ALDH2 enzymatic metabolism. It will be important to dissect the links between ALDH2 polymorphism and prevalence of alcoholic cardiomyopathy, in order to determine the mechanisms underlying such associations. The therapeutic value of ALDH2 as both target and tool in the management of alcoholic tissue damage will be discussed.

Genome-wide association studies identify genetic loci related to alcohol consumption in Korean men

BACKGROUND

Genome-wide association (GWA) studies regarding the quantitative trait of alcohol consumption are limited.

OBJECTIVE

The objective of the study was to explore genetic loci associated with the amount of alcohol consumed.

DESIGN

We conducted a GWA study with discovery data on single nucleotide polymorphisms (SNPs) for 1721 Korean male drinkers aged 40-69 y who were included in an urban population-based cohort. Another sample that comprised 1113 male drinkers who were from an independent cohort enrolled in a rural area served as a resource for replication. At baseline (18 June 2001 through 29 January 2003), members of both cohorts provided information on average daily alcohol consumptions, and their DNA samples were collected for genotyping.

RESULTS

We tested 315,914 SNPs of discovery data by using multivariate linear regression analysis adjusted for age and smoking, and 12 SNPs on chromosome 12q24 had genome-wide significant associations with alcohol consumption; adjusted P values by using Bonferroni correction were 1.6 × 10(-5) through 5.8 × 10(-46). We observed most SNPs in intronic regions and showed that the genes that harbor SNPs were C12orf51, CCDC63, MYL2, OAS3, CUX2, and RPH3A. In particular, signals in or near C12orf51, CCDC63, and MYL2 were successfully replicated in the test for 317,951 SNPs; rs2074356 in C12orf51 was in high linkage disequilibrium with SNPs in ALDH2, but other SNPs were not.

CONCLUSIONS

In a GWA study, we identified loci and alleles highly associated with alcohol consumption. The findings suggest the need for further investigations on the genetic propensity for drinking excessive amounts of alcohol.

A genome-wide association study of upper aerodigestive tract cancers conducted within the INHANCE consortium

Genome-wide association studies (GWAS) have been successful in identifying common genetic variation involved in susceptibility to etiologically complex disease. We conducted a GWAS to identify common genetic variation involved in susceptibility to upper aero-digestive tract (UADT) cancers. Genome-wide genotyping was carried out using the Illumina HumanHap300 beadchips in 2,091 UADT cancer cases and 3,513 controls from two large European multi-centre UADT cancer studies, as well as 4,821 generic controls. The 19 top-ranked variants were investigated further in an additional 6,514 UADT cancer cases and 7,892 controls of European descent from an additional 13 UADT cancer studies participating in the INHANCE consortium. Five common variants presented evidence for significant association in the combined analysis (p ≤ 5 × 10⁻⁷). Two novel variants were identified, a 4q21 variant (rs1494961, p = 1×10⁻⁸) located near DNA repair related genes HEL308 and FAM175A (or Abraxas) and a 12q24 variant (rs4767364, p =2 × 10⁻⁸) located in an extended linkage disequilibrium region that contains multiple genes including the aldehyde dehydrogenase 2 (ALDH2) gene. Three remaining variants are located in the ADH gene cluster and were identified previously in a candidate gene study involving some of these samples. The association between these three variants and UADT cancers was independently replicated in 5,092 UADT cancer cases and 6,794 controls non-overlapping samples presented here (rs1573496-ADH7, p = 5 × 10⁻⁸); rs1229984-ADH1B, p = 7 × 10⁻⁹; and rs698-ADH1C, p = 0.02). These results implicate two variants at 4q21 and 12q24 and further highlight three ADH variants in UADT cancer susceptibility.

Alcohol-use disorders

Alcohol dependence and alcohol abuse or harmful use cause substantial morbidity and mortality. Alcohol-use disorders are associated with depressive episodes, severe anxiety, insomnia, suicide, and abuse of other drugs. Continued heavy alcohol use also shortens the onset of heart disease, stroke, cancers, and liver cirrhosis, by affecting the cardiovascular, gastrointestinal, and immune systems. Heavy drinking can also cause mild anterograde amnesias, temporary cognitive deficits, sleep problems, and peripheral neuropathy; cause gastrointestinal problems; decrease bone density and production of blood cells; and cause fetal alcohol syndrome. Alcohol-use disorders complicate assessment and treatment of other medical and psychiatric problems. Standard criteria for alcohol dependence-the more severe disorder-can be used to reliably identify people for whom drinking causes major physiological consequences and persistent impairment of quality of life and ability to function. Clinicians should routinely screen for alcohol disorders, using clinical interviews, questionnaires, blood tests, or a combination of these methods. Causes include environmental factors and specific genes that affect the risk of alcohol-use disorders, including genes for enzymes that metabolise alcohol, such as alcohol dehydrogenase and aldehyde dehydrogenase; those associated with disinhibition; and those that confer a low sensitivity to alcohol. Treatment can include motivational interviewing to help people to evaluate their situations, brief interventions to facilitate more healthy behaviours, detoxification to address withdrawal symptoms, cognitive-behavioural therapies to avoid relapses, and judicious use of drugs to diminish cravings or discourage relapses.

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).

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.

The association of ADH and ALDH gene variants with alcohol drinking habits and cardiovascular disease risk factors

BACKGROUND

Genetic variation in ethanol metabolism may have an influence on both alcohol drinking habits and the susceptibility to health effects of alcohol drinking. Such influences are likely to bias exposure-disease associations in epidemiologic studies of health effects of alcohol drinking. In a Caucasian population, we examined the association of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) genetic variants with alcohol drinking habits, biomarkers of alcohol exposure, and risk factors for cardiovascular disease.

METHODS

The study population consisted of 1,216 Danish men and women aged 15-77 years participating in a health examination in 1998. The health examination included a self-administered questionnaire (alcohol drinking habits), a physical examination (blood pressure), and various blood tests [alanine aminotransferase (ALAT), erythrocyte mean corpuscular volume (E-MCV), and lipids]. ADH and ALDH gene variants were determined by standard techniques. Data were analyzed by regression analyses adjusted for relevant confounders.

RESULTS

Self-reported alcohol drinking was significantly associated with increasing levels of ALAT, E-MCV, high-density lipoprotein cholesterol, and blood pressure. The ALDH1b ala69val variant was associated with nondrinking and total alcohol intake. The ALDH2 promoter variant was associated with binge-drinking, and the ALDH1b1 ala69val polymorphism was associated with diastolic blood pressure. We did not find any statistically significant interactions between any of the gene variants and alcohol consumption in relation to the various outcomes.

CONCLUSIONS

In this Caucasian population sample, we found evidence to support that genetic variation in ethanol metabolism may influence drinking habits, but no statistically significant gene-environment interactions. More large-scale epidemiologic studies are needed to confirm theses results and to further investigate genetic susceptibility to the effects of alcohol drinking.

Genetic polymorphisms in alcohol metabolism, alcohol intake and the risk of stomach cancer in Warsaw, Poland

Genetic variations increasing blood levels of acetaldehyde, the first metabolite of alcohol, refrain their carriers from drinking alcohol but may also put them at increased risk of cancer because of the mutagenic and carcinogenic effect of acetaldehyde. In a population-based study of 305 cases and 428 controls in Warsaw, Poland, we evaluated the effect of polymorphisms in alcohol metabolizing genes, including ADH1B (Ex9+5C>T, Ex3+23A>G, Ex3+58A>T and Ex9+77A>G), ADH1C (Ex8-56A>G and Ex6-14G>A) and ALDH2 (Ex1+82A>G), on levels of alcohol drinking and susceptibility of stomach cancer. We found that among control subjects frequency of alcohol drinking varied by alcohol metabolizing genotype. In particular, the weekly consumption of individuals carrying the AA, GA and GG genotypes of ALDH2 Ex1+82A>G polymorphism were 3.75, 2.26 and 1.53 drinks, respectively (p=0.04). However, none of the assessed polymorphisms in these 3 genes had a measurable effect on stomach cancer risk. When stratified by ALDH2 Ex1+82A>G polymorphism, alcohol-related increases in stomach cancer risk were restricted to individuals with the AG/GG genotypes, with a more than 2-fold risk among daily drinkers (OR=2.63, 95% CI=1.00-6.88) and 3-fold risk (OR=3.66, 95% CI=1.19-11.24) among those with 40 or more drink-years. In summary, our results suggested that the ALDH2 Ex1+82 G allele may be functionally deficient in eliminating acetaldehyde and discourage alcohol drinking. Furthermore, heavy drinkers of alcohol who were genetically prone to accumulate acetaldehyde may face an increased risk of stomach cancer.

Alcohol: effects on neurobehavioral functions and the brain

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