Genetic Determinants of Alcohol Addiction and Metabolism: A Survey in Italy

Unraveling CYP2E1 haplotypes in alcoholics from Central Brazil: A comparative study with 1000 genomes population

We evaluated genetic variability of single nucleotide polymorphisms (SNPs) situated in the CYP2E1 gene promoter in alcoholics. We also compared 1000 Genomes Project of CYP2E1 polymorphisms with frequencies of genotypes and haplotypes. Eight variation points were exclusively found in Brazilians. The allelic distributions of the rs3813867, rs2031920 and rs2031921 polymorphisms in the CYP2E1 showed that the wild alleles (G, C, T, respectively) had higher frequencies in both groups, alcoholic (96%, 96%, 96%) and a control group (95.8%, 94.9%, 94.9%), when compared to the mutated allele (C, T, C, respectively). The variation points, rs3813867, rs2031920 and rs2031921 showed strong linkage disequilibrium (LOD ≥ 2, D ' = 1). South Asian populations presented larger LD blocks compared to the other populations. Our results showed that the allelic frequencies were markedly different among ethnicities and have contributed to the knowledge regarding the distribution among ethnic groups, being associated to alcohol consumption worldwide.

DNA damage in peripheral blood lymphocytes and association with polymorphisms in the promoter region of the CYP2E1 gene in alcoholics from Central Brazil

DNA damage caused by the accumulation of bio-products generated in the biotransformation of ethanol to acetaldehyde mediated by the CYP2E1 enzyme has been studied. To evaluate DNA damage in peripheral blood lymphocytes and the possible association with polymorphisms in the promoter region of the CYP2E1 gene, we performed a case-control study including 75 alcoholics and 59 individuals who consume alcohol socially. Alcoholics were previously diagnosed by the Psychosocial Care Center - Alcohol and Drugs (CAPS A/D) in the city of Goiania, Goias state, Central Brazil. DNA damage was evaluated by comet assay. The analysis of the rs3813867, rs2031920, and rs2031921 polymorphisms in the promoter region of CYP2E1 gene was performed by Sanger sequencing. Men older than 35 years old were the most common alcoholics. We found increased DNA damage in the case group, compared to the control group (p < 0.001). Alcoholics who were heterozygous in the rs3813867, rs2031920, and rs2031921 polymorphisms showed higher DNA damage (tail length and olive tail moment), compared to individuals with the homozygous non-mutated allele. Previous studies have shown that polymorphisms in the promoter region of the CYP2E1 gene could cause higher CYP2E1 transcriptional activity, increasing enzyme activity compared with nondrinkers, indicating that the presence of the mutated allele (heterozygous or homozygous) may be associated with higher alcohol metabolic rates and therefore show increased acetaldehyde levels after alcohol consumption, which then can exert its carcinogenic effect.

An international systematic review of smoking prevalence in addiction treatment

AIMS

Smoking prevalence is higher among people enrolled in addiction treatment compared with the general population, and very high rates of smoking are associated with opiate drug use and receipt of opiate replacement therapy (ORT). We assessed whether these findings are observed internationally.

METHODS

PubMed, PsycINFO and the Alcohol and Alcohol Problems Science Database were searched for papers reporting smoking prevalence among addiction treatment samples, published in English, from 1987 to 2013. Search terms included tobacco use, cessation and substance use disorders using and/or Boolean connectors. For 4549 papers identified, abstracts were reviewed by multiple raters; 239 abstracts met inclusion criteria and these full papers were reviewed for exclusion. Fifty-four studies, collectively comprising 37,364 participants, were included. For each paper we extracted country, author, year, sample size and gender, treatment modality, primary drug treated and smoking prevalence.

RESULTS

The random-effect pooled estimate of smoking across people in addiction treatment was 84% [confidence interval (CI) = 79, 88%], while the pooled estimate of smoking prevalence across matched population samples was 31% (CI = 29, 33%). The difference in the pooled estimates was 52% (CI = 48%, 57%, P < .0001). Smoking rates were higher in programs treating opiate use compared with alcohol use [odds ratio (OR) = 2.52, CI = 2.00, 3.17], and higher in ORT compared to out-patient programs (OR = 1.42, CI = 1.19, 1.68).

CONCLUSIONS

Smoking rates among people in addiction treatment are more than double those of people with similar demographic characteristics. Smoking rates are also higher in people being treated for opiate dependence compared with people being treated for alcohol use disorder.

A review of 5-HT transporter linked promoter region (5-HTTLPR) polymorphism and associations with alcohol use problems and sexual risk behaviors

Alcohol use and sexual risk behaviors are multidimensional phenomena involving many genetic and environmental factors. 5-HT transporter linked promoter region (5-HTTLPR) polymorphism constitutes an important factor affecting alcohol use problems and risky sexual behaviors. This paper narratively reviews studies on 5-HTTLPR polymorphism and its associations with alcohol use problems and sexual risk behaviors. We searched the electronic databases, PubMed, Ovid, and Google Scholar for articles using MeSH terms. Relevant articles were reviewed and eligible articles were selected for the study. Many studies have reported a significant but moderate association between 5-HTTLPR polymorphism and alcohol use problems. These studies have implicated the presence of at least one S allele to be associated with significant increases in alcohol use problems. Similarly, some studies associate the S allele with increased sexual risk behaviors. Effective alcohol cessation initiatives and STI/HIV prevention programs should be modified to account for 5-HTTLPR polymorphism before planning interventions; genetic effects could moderate the intervention effect.

Multi-cultural association of the serotonin transporter gene (SLC6A4) with substance use disorder

A number of studies have reported associations between the serotonin transporter gene (SLC6A4) and alcohol, heroin, cocaine, or methamphetamine abuse. Other studies have yielded contrary results. There are a number of reasons for non-replication, including inadequate statistical power, population stratification, and poor phenotype definition. This study was to test the association using a meta-analytic approach across a variety of racial and ethnic populations. Using the genotype data of 55 studies (7999 cases, 8264 controls, and 676 families or parent-offspring trios) published in the past 15 years, we have conducted comprehensive meta-analyses to examine the associations of the 5-HTTLPR and STin2 polymorphisms with substance use disorder. The meta-analyses support the associations of 5-HTTLPR with alcohol, heroin, cocaine, and methamphetamine dependence and abuse (eg, the smallest P-values were 0.0058 with odds ratio (OR)=0.54 (0.35, 0.84); 0.0024 with OR=0.77 (0.66, 0.91); 0.018 with OR=1.38 (1.06, 1.81); and 0.028 with OR=0.46 (0.23, 0.92) for alcohol, heroin, cocaine, and methamphetamine dependence/abuse, respectively). When all the phenotypes are combined, the P-value was 0.0006 with OR=0.86 (0.78, 0.94) in the combined European, Asian, and Mexican populations and P-value was 0.0028 with OR=1.41 (1.13, 1.78) in the African populations. Evidence of significant associations was also identified in other subgroup analyses regarding differently combined substance and populations. The effect sizes of 5-HTTLPR were comparable among the European, Asian, and Mexican populations, however, the risk allele was more frequent in Asians than in Europeans and Mexicans. The opposite directions of risk allele in African population might be driven by the opposite directions of risk allele in cocaine dependence. This meta-analysis supports that the association of the SLC6A4 gene with substance use disorder varies depending on substances with different risk allele frequencies in the multi-cultural populations. Further studies using larger sample size are warranted.

A large-scale meta-analysis of the association between the ANKK1/DRD2 Taq1A polymorphism and alcohol dependence

Alcohol dependence (AD) is a common neuropsychiatric disorder with high heritability. A number of studies have analyzed the association between the Taq1A polymorphism (located in the gene cluster ANKK1/DRD2) and AD. In the present study, we conducted a large-scale meta-analysis to confirm the association between the Taq1A polymorphism and the risk for AD in over 18,000 subjects included in 61 case-control studies that were published up to August 2012. Our meta-analysis demonstrated both allelic and genotypic association between the Taq1A polymorphism and AD susceptibility [allelic: P(Z) = 1.1 × 10(-5), OR = 1.19; genotypic: P(Z) = 3.2 × 10(-5), OR = 1.24]. The association remained significant after adjustment for publication bias using the trim and fill method. Sensitivity analysis showed that the effect size of the Taq1A polymorphism on AD risk was moderate and not influenced by any individual study. The pooled odds ratio from published studies decreased with the year of publication, but stabilized after the year 2001. Subgroup analysis indicated that publication bias could be influenced by racial ancestry. In summary, this large-scale meta-analysis confirmed the association between the Taq1A polymorphism and AD. Future studies are required to investigate the functional significance of the ANKK1/DRD2 Taq1A polymorphism in AD.

The investigation into CYP2E1 in relation to the level of response to alcohol through a combination of linkage and association analysis

BACKGROUND

A low level of response to alcohol during an individual's early experience with alcohol is associated with an increase risk of alcoholism. A family-based genome-wide linkage analysis using sibling pairs that underwent an alcohol challenge where the level of response to alcohol was measured with the Subjective High Assessment Scale (SHAS) implicated the 10q terminal (10qter) region. CYP2E1, a gene known for its involvement with ethanol metabolism, maps to this region.

METHODS

Variance component multipoint linkage analysis was performed on a combined map of single-nucleotide polymorphism (SNP) and microsatellite data. To account for the heterogeneity evident in the dataset, a calculation assuming locus heterogeneity was made using the Heterogeneity Log of Odds (HLOD) score. Association between SNP marker allele counts and copy number and SHAS scores were evaluated using a logistic regression model.

RESULTS

Linkage analysis detected significant linkage to CYP2E1, which was diminished because of apparent locus heterogeneity traced to a single family with extreme phenotypes. In retrospect, circumstances recorded during testing for this family suggest that their phenotype data are likely to be unreliable. Significant allelic associations were detected for several CYP2E1 polymorphisms and the SHAS score. DNA sequencing from families that contributed the greatest evidence for linkage did not detect any changes directly affecting the primary amino acid sequence. With the removal of a single family, combined evidence from microsatellites and SNPs offers significant linkage between the level of response to alcohol and the region on the end of chromosome 10.

CONCLUSION

Combined linkage and association indicate that sequence changes in or near CYP2E1 affect the level of response to alcohol providing a predictor of risk of alcoholism. The absence of coding sequence changes indicates that regulatory sequences are responsible. Implicating CYP2E1 in the level of response to alcohol allows inferences to be made about how the brain perceives alcohol.

Interaction among genes influencing ethanol metabolism and sex is association with alcohol use disorders in a Tibet population

Associations between alcohol use disorders and polymorphisms of genes influencing ethanol metabolism have been widely reported, but gene-gene and gene-sex interaction studies have rarely been examined. Using a set of samples collected during an epidemiological study of alcohol use disorders AUDs in a Tibetan population in China, we performed a case-control study to investigate the relationship between the functional polymorphisms of genes influencing ethanol metabolism and AUDs. The sample included 383 individuals with an AUDIT score >or=10 and 350 control subjects with the AUDIT score <or=5. All participants were genotyped for ALDH2*1/*2, ADH1B*1/*2, and CYP2E1*c1/c2*. Data were analyzed employing an integrated strategy using MDR, SPSS, and UNPHASED software. The MDR analysis showed that the four-factor model including ADH1B*1/*2, ALDH2*1/*2, and CYP2E1*c1/*c2 polymorphisms, and sex was the most accurate model associated with AUDs with the highest OR 3.299. It also revealed that CYP2E1 *c1/*c2 polymorphism interacted significantly with sex. Independent analysis confirmed that both ADH2*2 and ALDH2*2 allele were significantly associated with AUDs (OR: 0.441 for ADH2*2 and 0.137 for ALDH2*2). CYP2E1*c2 was positively associated with AUDs only in males homozygotic for ALDH2*1 and ADH1B*1 (OR: 2.585). Cumulative association analysis showed the number of protective alleles and genotypes were negatively associated with AUDs. In conclusion, ALDH2*2 and ADH1B*2 alleles were not only independently associated with AUDs but also demonstrated cumulative dosage effects. However the positive association between CYP2E1*c2 allele and AUDs might only exist in males homozygotic for ALDH2*1 and ADH1B*1.

Genetic polymorphism analysis of cytochrome P4502E1 (CYP2E1) in Chinese Han populations from four different geographic areas of Mainland China

CYP2E1 is one of a superfamily of enzymes that play a central role in activating and detoxifying many xenobiotics and endogenous compounds thought to be involved in the development of several human diseases. Among other factors, individual susceptibility to developing these pathologies relies on genetic polymorphisms, which are related to ethnic differences, since the frequency of mutant genotypes varies in different populations. The aim of this study was to investigate the genetic basis of CYP2E1 polymorphisms in the populations of four different geographical locations of China. Twenty-two different CYP2E1 polymorphisms, including six novel variants in promoter regions and a novel nonsense mutation, were identified. The frequencies of some polymorphisms and genotypes demonstrated significant differences among the four populations. Linkage disequilibrium analysis and tag SNP selection were performed. Haplotypes were analyzed within the selected tag SNPs. Tag SNP selection and haplotype distributions showed differences across the four populations.

Association of metabolic gene polymorphisms with alcohol consumption in controls

The objectives were to study the association between metabolic genes involved in alcohol metabolism (CYP2E1 RsaI, CYP2E1 DraI, ADH1C, NQO1) and alcohol consumption in a large sample of healthy controls. Healthy subjects were selected from the International Collaborative Study on Genetic Susceptibility to Environmental Carcinogens (GSEC). Subjects with information on both alcohol consumption and at least one of the studied polymorphisms were included in the analysis (n=2224). Information on the amount of alcohol consumption was available for a subset of subjects (n=844). None of the studied genes was significantly associated with drinking habits. A significant heterogeneity with age was observed when studying the association between CYP2E1 RsaI and alcohol drinking. CYP2E1 RsaI polymorphism was significantly associated with being a never drinker at older ages (odds ratio [OR] 2.4, 95% confidence interval [CI] 1.2-4.8; at ages above 68 years), while the association was reversed at ages below 47 years (OR 0.5, 95% CI 0.2-1.4). For subjects with detailed information on alcohol intake, no association between alcohol quantity and polymorphisms in metabolic genes was observed; subjects carrying the NQO1 polymorphism tended to drink more than subjects carrying the wild-type alleles. Therefore, no significant association between CYP2E1 RsaI, CYP2E1 DraI, ADH1C, NQO1 polymorphisms and alcohol consumption was observed in healthy controls.

Genetics of dopamine receptors and drug addiction: a comprehensive review

Drug dependence is a chronic, relapsing disorder in which compulsive drug-seeking and drug-taking behaviours persist despite serious negative consequences. Addictive substances, such as opioids, ethanol, psychostimulants and nicotine, induce pleasant states or relieve distress, effects that contribute to their recreational use. Dopamine is critically involved in drug addiction processes. However, the role of the various dopaminergic receptor subtypes has been difficult to delineate. Here, we will review the information collected implicating the receptors of the D1 family (DRD1 and DRD5) and of the D2 family (DRD2, DRD3 and DRD4) in drug addiction. We will summarize the distribution of these receptors in the brain, the preclinical experiments carried out with pharmacological and transgenic approaches and the genetic studies carried out linking genetic variants of these receptors to drug addiction phenotypes. A meta-analysis of the studies carried out evaluating DRD2 and alcohol dependence is also provided, which indicates a significant association. Overall, this review indicates that different aspects of the addiction phenotype are critically influenced by dopaminergic receptors and that variants of those genes seem to influence some addiction phenotypes in humans.

[Genetic factors of alcohol-dependence]

INTRODUCTION

Alcohol dependence is a complex and multifactorial disease resulting both from neurobiological mechanisms and environmental factors. It is frequently associated with comorbid psychiatric disorders or with specific personality or behavioral features. Although action can be taken on the environment in order to decrease the risk of the illness, current methods used to prevent or to treat this pathology show moderate efficacy: problematic consumption of ethanol in the general population as well as relapse rates under treatment in dependent patients remain indeed very high.

LITERATURE FINDINGS

It is therefore of major importance to broaden our knowledge of alcohol dependence and its comorbidities so as to improve both their prevention and treatment. In this perspective, recent progress in the field of neurosciences may contribute to achieve this goal. Precisely, genetics is a promising way benefiting from many advances in genetic epidemiology, cellular and molecular biology, neuroimaging and pharmacology. In parallel with a better understanding of the neurobiology of addictions and associated behaviors, these techniques led to the identification of brain mechanisms in which a genetic variation may influence the individual vulnerability towards alcohol dependence. Moreover, there is growing evidence that alcoholism results from the interaction of genetic and environmental factors influencing both its expression and its course. Given the fact that alcohol-dependence seems highly heritable (50 to 60% of the variance in both men and women), this review assesses the role of some of the genomic regions linked with the disease, as well as the principal variants of candidate genes identified as specifically involved in the predisposition. Polymorphisms of genes influencing alcohol metabolism, GABAergic, dopaminergic and serotonergic neurotransmission seem, indeed, at stake in the development of alcohol-dependence and its related features such as personality, behavior, impulse control or craving. In the future, a better characterization of the links between genotypes and phenotypes will probably increase our ability to treat alcoholic patients.

A haplotype analysis of CYP2E1 polymorphisms in relation to alcoholic phenotypes in Mexican Americans

BACKGROUND

Studies regarding the association between the 4 polymorphisms of CYP2E1 (CYP2E1*1D, *5B, *6, and *1B) and alcoholism are inconsistent and inconclusive. The purpose of the present study was to clarify previously discordant studies by haplotype analysis in the Mexican American population.

METHODS

The 4 polymorphisms of CYP2E1 were studied in 334 alcoholics and 365 controls. Genotype, allele, and haplotype frequency comparisons between alcoholics and controls were assessed. Patterns of linkage disequilibrium (LD) at CYP2E1 were determined. Reconstructed haplotypes were tested for associations with clinical phenotypes (age onset of drinking, Maxdrinks, and smoking status).

RESULTS

No significant associations between the 4 polymorphisms of CYP2E1 and alcoholism were revealed by single allele tests. High LD was found between the CYP2E1 c2 and C alleles in Mexican Americans. Eleven haplotypes were present in the 699 participants. The 6 main haplotypes with frequencies higher than 1% made up 97% of the total halpotypes. The frequency of subjects carrying H6 (1C-c2-C-A2) was significantly higher in alcoholics than in controls (p = 0.0001). In contrast, the frequencies of H7 (1C-c2-C-A1) and H10 (1C-c2-D-A1) were significantly lower in alcoholics than in controls (p = 0.0072 for H7 and p = 0.0407 for H10). The frequency of H6 was significantly higher in alcoholics who had late onset of drinking than in nonalcoholic controls. Furthermore, the frequencies of H6 haplotype were also consistently higher in groups who had high number of maximum drinks (9 to 32 drinks) than in controls. When smokers are excluded, the frequencies of H6, H7, and H9 (1C-c2-D-A2) showed statistically significant differences between alcoholics and controls (p < 0.05). Moreover, the association between H6 and alcoholism become more robust when smokers are excluded. Furthermore, the frequency of H1 (1C-c1-D-A2) in alcoholic-smokers was much higher than in alcoholic-nonsmokers (p = 0.0028). In contrast, alcoholic-smokers carried less H2 (1C-c1-D-A1) in comparison with alcoholic-nonsmokers (p = 0.0417). The H3 (1D-c2-C-A2) frequency in alcoholic-smokers was much lower than in alcoholic-nonsmokers (p = 0.0042) and control-smokers (p = 0.0363).

CONCLUSIONS

Our data demonstrate that carrying haplotype H6 might enhance susceptibility to developing alcoholism, but possessing the H7 or H10 haplotype appears to decrease this susceptibility. The H6, H7, and H9 haplotypes may play certain roles in different clinical phenotypes in Mexican American alcoholics. In addition, our data suggest that the H1, H2, and H3 haplotypes are associated with alcohol drinking and smoking. These results support that haplotype analysis is much more informative than single allele analysis. Our findings clearly indicate the importance of H6 haplotype in alcohol drinking in Mexican Americans.

Meta-analysis of the association of the Taq1A polymorphism with the risk of alcohol dependency: a HuGE gene-disease association review

The human dopamine 2 receptor Taq1A allele has been implicated as a vulnerability factor for alcohol dependence in a number of studies and reviews. To determine whether this allele is associated with alcoholism, the authors conducted a Human Genome Epidemiology review and meta-analysis. Forty-four studies with 9,382 participants were included. An odds ratio of 1.38 (95% confidence interval: 1.20, 1.58; heterogeneity, 50.5%) was found for the A1A1 + A1A2 versus the A2A2 genotype. Sensitivity analyses suggested lack of ethnic matching as a possible source of heterogeneity; a small, significant association was detected in studies with ethnic-matched controls (odds ratio = 1.26, 95% confidence interval: 1.02, 1.56; heterogeneity, 37%). Significant associations were also found in analyses restricted to studies reporting use of blinding and those with adequate screening of controls for alcohol dependency. For the A1A1 versus the A1A2 + A2A2 genotype, the odds ratio was 1.22 (95% confidence interval: 1.05, 1.43; heterogeneity, 0%). Sensitivity analyses on groups of studies reporting use of ethnic-matched controls and those that screened controls for alcohol dependency still showed significant associations. The relatively small effect for the association of the A1 allele, or another genetic variant linked to it, with alcohol dependence indicates a multigene causality for this complex disorder.

Heavy nicotine and alcohol use in alcohol dependence is associated with D2 dopamine receptor (DRD2) polymorphism

Cigarette smoking in those who are alcohol dependent is associated with higher morbidity and mortality. The A1 allele of the D2 dopamine receptor (DRD2) gene has been independently associated with alcohol and nicotine dependence. Whether this polymorphism is associated with nicotine dependence in those who are also alcohol dependent has not been investigated. Subjects were 84 (61 males; 23 females) Caucasian DSM IV diagnosed nicotine- and alcohol-dependent subjects sampled from consecutive admissions to a hospital alcohol detoxification ward. Data were obtained through standardised measures of nicotine and alcohol consumption and dependence severity. A1+ allelic (A1/A1 or A1/A2 genotype) compared to A1- allelic (A2/A2 genotype only) patients were characterised by higher levels of alcohol and cigarette consumption. A1+ allelic patients reported greater alcohol dependence severity, but not nicotine dependence severity. When the combined nicotine and alcohol dose was examined, A1+ allelic patients consumed significantly more of these drugs than their A1- allelic counterparts.

Genetic background of the multifactorial liver and bile duct diseases

The majority of liver diseases, are complex. They are the results of interactions between several genes and environmental factors. Familial aggregation and higher concordance rate of monozygotic twins compared to those of dizygotic twins provide evidence for the importance of genetic factors in the pathogenesis. There are only limited data in connection with the genetic background of multifactorial liver diseases. In the future, the genetic background may permit prevention, early, accurate diagnosis, prediction of disease course, complications, prognosis, as well as treatment response.

The DRD2 TaqI-B polymorphism and its relationship to smoking abstinence and withdrawal symptoms

The dopamine receptor D2 (DRD2) gene has polymorphisms that have been linked to regulation of the dopamine system and to an increased prevalence of smoking. The present study examined the relationship of the DRD2 TaqI-A and -B polymorphisms with short-term clinical outcome (abstinence and withdrawal symptoms), collected from daily (14 pre-quit and 42 post-quit) diary data among smokers (n=116) treated with the nicotine patch plus either venlafaxine or placebo. The results showed that B1/B1 or B1/B2 smokers were slightly less likely to be abstinent on a given day than those homozygous for the TaqI-B2 allele. Significant DRD2 TaqI-B x time interactions were found for several of the withdrawal scales, indicating that those smokers with the B1/B1 or B1/B2 genotypes tended to report more symptoms over time compared to those with the B2/B2 genotype. No interactions or main effects were found for the DRD2 TaqI-A polymorphism. The findings demonstrate that smokers homozygous for the TaqI-B2 allele experience progressive improvement in self-reported withdrawal symptoms while smokers with the TaqI-B1 allele showing little change.

Interleukin-1 alpha and beta, TNF-alpha and HTTLPR gene variants study on alcohol toxicity and detoxification outcome

Genetic factors may influence the liability to treatment outcome and medical complications in alcoholism. In the present study we investigated the IL-1A rs1800587, IL-1B rs3087258, TNF-alpha rs1799724 and the HTTLPR variants in a sample of 64 alcohol dependents and 47 relatives versus a set of clinical parameters and outcome measures. Alcohol dependents had a less favorable clinical profile compared to relatives (higher cholesterol, triglycerides, glucose, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, gamma-glutamyltransferase). After detoxification, all clinical indexes improved and hepatic enzyme levels were similar in alcohol dependents and relatives, except for the GGT that remained significantly higher in alcohol dependents. Alcoholic depressive and anxiety scores were significantly reduced after detoxification. IL-1A, IL-1B, TNF-alpha and HTTLPR variants were not associated with any baseline clinical index or change after detoxification. In our sample IL-1A, IL-1B, TNF-alpha and HTTLPR do not appear as liability factors for alcohol toxicity or detoxification outcome, however the small sample size may influence the observed results.

Global pharmacogenetics: giving the genome to the masses

With pharmacogenetics comes the promise of individualized therapy selection for many common diseases where multiple treatment options are available. Recent advances including the Human Genome Project, the International HapMap project, advances in throughput and reduction in cost of genetic testing, and the inclusion of genotype-related dosing recommendations into package inserts all point to the integration of pharmacogenetics into clinical practice. However, many countries will not have access to pharmacogenetics resources in the near future. Generation of global genotype profiles will provide a useful, but not perfect resource for incorporating pharmacogenetics into national drug formularies in the form of prioritization or surveillance where individual genotype data would not be attainable. The PharmacoGenetics for Every Nation Initiative is a first step to making pharmacogenetics applicable on a global level.

The role of genetic polymorphisms in alcoholic liver disease

Chronic alcohol consumption is a major cause of liver cirrhosis which, however, develops in only a minority of heavy drinkers. Evidence from twin studies indicates that genetic factors account for at least 50% of individual susceptibility. The contribution of genetic factors to the development of diseases may be investigated either by means of animal experiments, through linkage studies in families of affected patients, or population based case-control studies. With regard to the latter, single nucleotide polymorphisms of genes involved in the degradation of alcohol, antioxidant defense, necroinflammation, and formation and degradation of extracellular matrix are attractive candidates for studying genotype-phenotype associations. However, many associations in early studies were found to be spurious and could not be confirmed in stringently designed investigations. Therefore, future genotype-phenotype studies in alcoholic liver disease should meet certain requirements in order to avoid pure chance observations due to a lack of power, false functional interpretation, and insufficient statistical evaluation.

Do alcohol-metabolizing enzyme gene polymorphisms increase the risk of alcoholism and alcoholic liver disease?

Case-control studies that have investigated the association between alcoholism and alcohol-induced liver damage and the ADH2, ADH3, CYP2E1, and ADLH2 polymorphisms have reported controversial or inconclusive results. Thus, we conducted a meta-analysis of 50 association studies of the above polymorphisms. We explored potential sources of heterogeneity and bias, performed subgroup analyses by racial background and sex, performed sensitivity analyses for studies not in Hardy-Weinberg equilibrium, and performed a subgroup analysis for cases that met strict criteria for alcoholism. The present meta-analysis underscores significant associations of ADH2*1, ADH3*2, and ALDH2*1 alleles and the risk of alcoholism (OR = 1.89 [95% CI 1.56-2.28], 1.32 [95% CI 1.12-1.57], and 4.35 [95% CI 3.04-6.23], respectively). The subsequent subgroup analyses showed association for ADH2*1 and ADH3*2 only in East Asians (OR = 2.23 [95% CI 1.81-2.74] and 1.91 [95% CI 1.45-2.53], respectively) and East Asian males (OR = 2.21 [95% CI 1.57-3.10], 1.69 [95% CI 1.10-2.59], respectively). In East Asian males, the OR for ALDH2*1 was 3.66 (95% CI 1.68-7.96). In Caucasians, sensitivity analysis revealed an association for ADH2*1 in alcoholism (OR = 1.62 [95% CI 1.22-1.89]). When strict criteria were imposed, the pattern of results remained unaltered. For liver disease, there were no significant associations for ADH2*1, ADH3*2, or ALDH2*1 in all subpopulations. The CYP2E1 polymorphism showed no association whatsoever. There is evidence that alleles are mainly dominant. In conclusion, there was heterogeneity between studies in alcoholism for ADH2, ADH3, and ALDH2, and lack of bias in all polymorphisms. The above findings reinforce the need for more rigorous studies, and for regular synthesis of studies' results.

DRD2 genotypes and substance use in adolescent children of alcoholics

Research has identified children of alcoholics (COAs) as a population at increased risk for developing substance use problems. Genetic studies support the Al allele of the D2 dopamine receptor gene (DRD2) as a risk marker for alcoholism and substance use disorders. In this study, substance use was assessed in 48 adolescent boys of alcoholics with the DRDR A1(+) allele (A1A1/A1A2 genotypes) or the A1(-) allele (A2A2 genotype). The results revealed that boys with the A1(+) allele tried (p=0.0001) and got intoxicated on alcohol more often (p=0.009) than boys with the A1(-) allele. Boys with the A1(+) allele tried more (p=0.004) and used more substances overall (p=0.008) than boys with the A1(-) allele. Boys with the A1(+) allele developed a tobacco habit more often (p=0.03) and experienced marijuana high at an earlier age (p=0.001) than boys with the A1(-) allele. The best predictors of substance use severity in boys with the A1(+) allele were Psychoticism (p=0.01) and Negative Affect (p=0.04). The results provide support for the DRD2 A1 allele as a marker identifying a subgroup of COAs at high risk for developing substance use problems.

Association of the serotonin transporter gene polymorphism with Korean male alcoholics

This study investigated the association between the serotonin transporter polymorphism (5-HTTLPR) and alcoholism in the Korean population. In addition, in order to reduce the clinical heterogeneity, sub-analysis was carried out according to some clinical variables such as a family history of alcoholism, aggressive/violent behavior and the age of onset of alcoholism. One hundred and forty-five patients meeting the DSM-VI criteria for alcohol dependence and 201 healthy controls were examined. Genotyping was performed using a polymerase chain reaction (PCR)-based method. The frequency of the L-allele of 5-HTTLPR was significantly higher in the alcohol dependent patients than in the normal controls (chi(2)=19.11, df=1, p<0.001). Furthermore, there was a significant difference in the allelic distribution between the subgroups defined by a family history of alcoholism (chi(2)=4.005, df=1, p=0.045). This study suggests a putative role of the 5-HTTLPR for alcoholism in the Korean population. However, a replication study with larger different ethnic samples and a refinement of the subtype of alcoholism is needed.

Polymorphismes géniques de marqueurs sérotoninergiques et alcoolodépendance

Genetic factors have a non-specific but significant impact on the risk of alcohol-dependence. Molecular genetic analyses are now less devoted to the genes involved in the metabolism of ethanol, focusing on core concepts of addiction, such as arousal, pleasure, reward, craving, and impulsivity. Indeed, the neuro-cognitive functions, temperament traits and psycho-behavioral specificities of patients with alcohol abuse or dependence led to select new sets of candidate genes. One of them are related to serotonin transmission, as serotonin modulates dopaminergic pathways, and is also stimulated by many addictive susbtances. The genetic analyses of serotonin in alcohol-dependence are mainly focused on the serotonin transporter gene (5-HTT), as one polymorphism within the promoter has a functional impact. From the 16 case-control association studies yet performed, many are positive, and one family-based study showed a large excess of transmission of the short allele. We performed a meta-analysis of the case-control studies showing that the S allele could be a risk factor for a phenotype related to alcohol-dependence (OR=1.31), with still unknown boundaries. Other genes coding for serotonin receptors were analysed with mainly negative results, for example the 5-HT2A, 5-HT2C, 5-HT5A and 5-HT7 receptors. The 5-HT1B could be more interesting as being located in a locus linked to alcohol preference in rodents, and associated with antisocial alcoholism in two human studies. Genetics may thus provide new insights about the different mechanisms which explain why some subjects are more at risk for the development of alcohol abuse or dependence. Genes involved in the transmission, reuptake and metabolism of serotonin constitute a set of candidate genes that could be involved in core aspects of alcoholism, such as the tendency to prefer immediate reward, despite negative consequences.

Genetic polymorphisms of ADH2, ADH3, CYP4502E1 Dra-I and Pst-I, and ALDH2 in Spanish men: lack of association with alcoholism and alcoholic liver disease

BACKGROUND/AIMS

The relationship between polymorphisms at the alcohol dehydrogenase 2 (ADH(2)), ADH(3), CYP(450)2E1 and aldehyde dehydrogenase 2 (ALDH(2)) loci and the individual predisposition to alcoholism and alcoholic liver disease in Caucasians is controversial.

METHODS

We determined the genotypes of ADH(2), ADH(3), CYP(450)2E1 (Pst-I and Dra-I) and ALDH(2) in 519 male Spaniards: 264 alcoholic subjects (47 without liver disease, 118 with non-cirrhotic liver disease and 99 with cirrhosis) and 255 non-alcoholic subjects (64 healthy controls, 110 with non-cirrhotic non-alcoholic liver disease and 81 with cirrhosis unrelated to alcohol). Genotyping was performed using PCR-RFLP methods on white cell DNA.

RESULTS

The distribution of the allelic variants (allele *1 and allele *2) in the whole subjects analyzed was: ADH(2) 93.1% and 6.9%; ADH(3) 55.7 and 44.3%; CYP(450)2E1 Dra-I 11.2 and 88.8%; CYP(450)2E1 Pst-I 96.2 and 3.8% and ALDH2 100 and 0%, respectively. No differences were observed in the allelic distributions of the alcoholic and non-alcoholic subjects for the loci examined. Allele distribution in alcoholics with no liver disease, with alcoholic steatosis or hepatitis, and with cirrhosis was also similar.

CONCLUSIONS

ADH(2), ADH(3), and CYP(450)2E1 Pst-I and Dra-I genetic variations are not related to alcoholism or susceptibility to alcoholic liver disease in our male population. ALDH(2) locus is monomorphic.

Advances in molecular genetics and the prevention and treatment of substance misuse: Implications of association studies of the A1 allele of the D2 dopamine receptor gene

Substance misuse is influenced by multiple genetic and environmental factors. Recent research has identified a number of potential genetic markers of risk and those associated with drug reward substrates show particular promise. The current study reexamines the extant published data of the association between the D2 dopamine receptor (DRD2) gene minor Taq 1A (A1) allele and substance misuse risk. A series of meta-analyses was performed on 64 studies examining DRD2 A1+ allelic status and substance misuse. In addition, personality was examined as a possible endophenotype. Significant association was found between the A1 allele and severe substance dependence in both Caucasian and non-Caucasian groups. The data did not support a significant association between the A1 allele and personality features. While the specific mechanism underlying these associations requires further elucidation, this genetic marker shows promise as a marker of brain reinforcement processes. Possible ways of utilising the A1 allele to inform prevention and treatment initiatives are discussed.

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.

D2 dopamine receptor gene in psychiatric and neurologic disorders and its phenotypes

The D2 dopamine receptor (DRD2) has been one of the most extensively investigated gene in neuropsychiatric disorders. After the first association of the TaqI A DRD2 minor (A1) allele with severe alcoholism in 1990, a large number of international studies have followed. A meta-analysis of these studies of Caucasians showed a significantly higher DRD2 A1 allelic frequency and prevalence in alcoholics when compared to controls. Variants of the DRD2 gene have also been associated with other addictive disorders including cocaine, nicotine and opioid dependence and obesity. It is hypothesized that the DRD2 is a reinforcement or reward gene. The DRD2 gene has also been implicated in schizophrenia, posttraumatic stress disorder, movement disorders and migraine. Phenotypic differences have been associated with DRD2 variants. These include reduced D2 dopamine receptor numbers and diminished glucose metabolism in brains of subjects who carry the DRD2 A1 allele. In addition, pleiotropic effects of DRD2 variants have been observed in neurophysiologic, neuropsychologic, stress response, personality and treatment outcome characteristics. The involvement of the DRD2 gene in certain neuropsychiatric disorders opens up the potential of a targeted pharmacogenomic approach to the treatment of these disorders.

Male limited association of the dopamine receptor D2 gene TaqI a polymorphism and alcohol dependence

Association studies of the TaqI A allele of the dopamine receptor D2 (DRD2) gene with alcohol dependence have produced conflicting findings. Although a wide series of clinical features have been considered in the different association studies performed, very few studies specifically analyzed the role of gender. We compared the TaqI A polymorphisms of the DRD2 gene in 120 French Caucasian alcohol-dependent inpatients (62 males and 58 females) and 107 healthy ethnically matched controls (66 males and 41 females). We observed that 55% of alcohol-dependent males have at least one A1 allele, a prevalence that is significantly above that observed in the control males (38%). On the contrary, no differences were found in females between the alcohol-dependent inpatients and controls for the A1 allele prevalence. In our sample, this male-specific association was not explained by gender specificities of alcohol dependence, such as age at onset and severity measures (mean numbers of social, somatic, and withdrawal complications). On the other hand, alcohol-dependent women with the A1 allele reported more frequently a major depressive disorder (70% vs. 40%, P = 0.03). We thus replicated the allelic association of the A1 allele of the DRD2 gene with alcohol dependence, but showed a male-limited effect of this "vulnerability allele." Recent evidence for gender difference in dopamine D2-like receptor levels and affinity may explain this discrepancy.