A functional polymorphism within the mu-opioid receptor gene and risk for abuse of alcohol and other substances

FYN Tyrosine Kinase Gene Polymorphisms in Alcohol-Dependent Korean Patients

Background

Alcohol use disorder (AUD) is a common disease with a high economic cost. The glutamate cell signaling pathway associated with alcohol has been reported to be one of the main pathologies of AUD. Previous studies have suggested that FYN, which is known to control NMDA glutamate receptor function through phosphorylation, might be associated with AUD.

Method

The present study included 354 subjects in the alcohol-dependent group and 139 subjects in the control group. The alcohol-dependent group was recruited from five university hospitals and a psychiatric hospital, and the control group was recruited from people who visited the university hospital for routine medical checkups in Korea. FYN gene single nucleotide polymorphism (SNPs) were selected based on SNP databases and previous studies of the FYN gene. Ten SNPs were genotyped using polymerase chain reaction-restriction fragment length polymorphism techniques.

Results

GG genotypes and G allele frequencies of rs1058134 in male AUD patients were significantly lower than in controls (p = 0.003). AA genotypes and A allele frequencies of rs12191154 in female AUD patients were significantly lower than in controls (p < 0.001, p = 0.003). In female AUD patients, AA genotypes and A allele frequencies of rs9387025 were significantly higher than in controls (p = 0.003).

Conclusion

These findings suggest that the FYN gene may be a candidate gene for AUD. This may help for the planning of further studies to determine the function of each SNP and the exact relationship between the FYN gene and AUD.

Candidate gene-environment interactions in substance abuse: A systematic review

BACKGROUND

The abuse of psychogenic drugs can lead to multiple health-related problems. Genetic and environmental vulnerabilities are factors in the emergence of substance use disorders. Empirical evidence regarding the gene-environment interaction in substance use is mixed. Summaries of the latest findings from a candidate gene approach will be useful for revealing the significance of particular gene contributions. Thus, we aim to identify different gene-environment interactions in patterns of substance use and investigate whether any effects trend notably across different genders and races.

METHODS

We reviewed published studies, until March 1, 2022, on substance use for candidate gene-environment interaction. Basic demographics of the included studies, target genes, environmental factors, main findings, patterns of gene-environment interaction, and other relevant information were collected and summarized.

RESULTS

Among a total of 44 studies, 38 demonstrated at least one significant interaction effect. About 61.5% of studies on the 5-HTTLPR gene, 100% on the MAOA gene, 42.9% on the DRD2 gene, 50% on the DRD4 gene, 50% on the DAT gene, 80% on the CRHR1 gene, 100% on the OPRM1 gene, 100% on the GABRA1 gene, and 50% on the CHRNA gene had a significant gene-environment interaction effect. The diathesis-stress model represents a dominant interaction pattern (89.5%) in the studies with a significant interaction effect; the remaining significant effect on substance use is found in the differential susceptibility model. The social push and swing model were not reported in the included studies.

CONCLUSION

The gene-environment interaction research on substance use behavior is methodologically multidimensional, which causes difficulty in conducting pooled analysis, or stated differently-making it hard to identify single sources of significant influence over maladaptive patterns of drug taking. In decreasing the heterogeneity and facilitating future pooled analysis, researchers must (1) replicate the existing studies with consistent study designs and measures, (2) conduct power calculations to report gene-environment correlations, (3) control for covariates, and (4) generate theory-based hypotheses with factorial based experiments when designing future studies.

Association between opioid and dopamine receptor gene polymorphisms OPRM1 rs1799971, DAT VNTR 9-10 repeat allele, DRD1 rs4532 and DRD2 rs1799732 and alcohol dependence: an ethnicity oriented meta-analysis

OBJECTIVE

We carried out a meta-analysis of four opioid and dopamine candidate gene polymorphisms having conflicting results in prior literature, namely OPRM1 rs1799971, DAT VNTR 9-10 repeat, DRD1 rs4532 and DRD2 rs1799732, to clarify their association with alcohol dependence and further stratified results by ethnicity to analyze possible ethnicity-mediated effects.

METHODS

Inclusion criteria: case-control studies assessing the association between OPRM1 rs1799971, DAT VNTR 9/10 repeat allele, DRD1 rs4532 and DRD2 rs1799732 with alcohol dependence, with sufficient data available to calculate the odds ratio (OR) within a 95% confidence interval. Exclusion criteria: studies of quantitative measures of alcohol consumption, response to medications or analyses of other markers in the candidate genes, studies without controls, animal studies and lack of genotyping data. Information sources were PubMed, Google Scholar and ScienceDirect databases, all of which were searched for articles published till 2021. Heterogeneity between studies and publication bias, subgroup analyses and sensitivity analyses were carried out.

RESULTS

A total of 41 published studies were included in the current meta-analysis. For the OPRM1 gene, there was a statistically significant association in the Asian population with a pooled OR of 1.707 (95% CI, 1.32-2.20 P  < 0.0001) and 1.618 (95% CI, 1.16-2.26 P  = 0.005) in the additive and dominant genetic models. For DAT VNTR 9/10 repeat, a statistically significant association of the risk vs. common allele was observed in AD with a pooled OR of 1.104 (95% CI, 1.00-1.21 P  = 0.046) in the allele model and the additive genetic model in the Caucasian population with pooled OR of 1.152 (95% CI, 1.01-1.31 P  = 0.034).

CONCLUSION

Results indicate that some of the effects may be ethnicity-specific.

OTHER

The meta-analysis has been registered in the CRD PROSPERO (CRD42023411576).

Association of OPRM1 with addiction: a review on drug, alcohol and smoking addiction in worldwide population

Background

Drugs are chemicals which can disrupt the nerve cell functions of the brain. The present study aims to investigate the addiction related gene (OPRM1) in three types of addiction—drugs, alcohol and smoking. Pathway for the addiction was ascertained through KEGG database, and the hotspot mutations for various populations were identified from Gnomad-exomes database. In silico analyses like SIFT, Polyphen, Hope, I-mutant and mutation taster were performed to understand the amino acid substitution, protein function, stability and pathogenicity of the variants.

Main body

Addiction-related variants were found in exons 1, 2 and 3, while the exon 4 did not exhibit any addiction related variation. Among all the variants from this gene, rs1799971 (A118G) polymorphism was the most commonly studied variation for addiction in different populations worldwide. Population-wise allele and genotype frequencies, demographic and epidemiological studies have also been performed from different populations, and the possible association of these variants with addiction was evaluated.

Conclusion

Our findings suggest that OPRM1 polymorphism impact as pharmacogenetic predictor of response to naltrexone and can also address the genetic predisposition related to addiction in human beings.

A systems omics-based approach to decode substance use disorders and neuroadaptations

Substance use disorders (SUDs) are a group of neuropsychiatric conditions manifesting due to excessive dependence on potential drugs of abuse such as psychostimulants, opioids including prescription opioids, alcohol, inhalants, etc. Experimental studies have generated enormous data in the area of SUDs, but outcomes from such data have remained largely fragmented. In this review, we attempt to coalesce these data points providing an important first step towards our understanding of the etiology of SUDs. We propose and describe a 'core addictome' pathway that behaves central to all SUDs. Besides, we also have made some notable observations paving way for several hypotheses; MECP2 behaves as a master switch during substance use; five distinct gene clusters were identified based on respective substance addiction; a central cluster of genes serves as a hub of the addiction pathway connecting all other substance addiction clusters. In addition to describing these findings, we have emphasized the importance of some candidate genes that are of substantial interest for further investigation and serve as high-value targets for translational efforts.

Differential sensitivity of human neurons carrying μ opioid receptor (MOR) N40D variants in response to ethanol

The acute and chronic effects of alcohol on the brain and behavior are linked to alterations in inhibitory synaptic transmission. Alcohol's most consistent effect at the synaptic level is probably a facilitation of γ-aminobutyric acid (GABA) release, as seen from several rodent studies. The impact of alcohol on GABAergic neurotransmission in human neurons is unknown, due to a lack of a suitable experimental model. Human neurons can also be used to model effects of genetic variants linked with alcohol use disorders (AUDs). The A118G single nucleotide polymorphism (SNP rs1799971) of the OPRM1 gene encoding the N40D (D40 minor allele) mu-opioid receptor (MOR) variant has been linked with individuals who have an AUD. However, while N40D is clearly associated with other drugs of abuse, involvement with AUDs is controversial. In this study, we employed Ascl1-and Dlx2-induced inhibitory neuronal cells (AD-iNs) generated from human iPS cell lines carrying N40D variants, and investigated the impact of ethanol acutely and chronically on GABAergic synaptic transmission. We found that N40 AD-iNs display a stronger facilitation (versus D40) of spontaneous and miniature inhibitory postsynaptic current frequency in response to acute ethanol application. Quantitative immunocytochemistry of Synapsin 1+ synaptic puncta revealed a similar synapse number between N40 and D40 iNs, suggesting an ethanol modulation of presynaptic GABA release without affecting synapse density. Interestingly, D40 iNs exposed to chronic intermittent ethanol application caused a significant increase in mIPSC frequency, with only a modest enhancement observed in N40 iNs. These data suggest that the MOR genotype may confer differential sensitivity to synaptic output, which depends on ethanol exposure time and concentration for AD-iNs and may help explain alcohol dependence in individuals who carry the MOR D40 SNPs. Furthermore, this study supports the use of human neuronal cells carrying risk-associated genetic variants linked to disease, as in vitro models to assay the synaptic actions of alcohol on human neuronal cells.

Opioid receptors: drivers to addiction?

Drug addiction is a worldwide societal problem and public health burden, and results from recreational drug use that develops into a complex brain disorder. The opioid system, one of the first discovered neuropeptide systems in the history of neuroscience, is central to addiction. Recently, opioid receptors have been propelled back on stage by the rising opioid epidemics, revolutions in G protein-coupled receptor research and fascinating developments in basic neuroscience. This Review discusses rapidly advancing research into the role of opioid receptors in addiction, and addresses the key questions of whether we can kill pain without addiction using mu-opioid-receptor-targeting opiates, how mu- and kappa-opioid receptors operate within the neurocircuitry of addiction and whether we can bridge human and animal opioid research in the field of drug abuse.

Lack of associations of the opioid receptor mu 1 (OPRM1) A118G polymorphism (rs1799971) with alcohol dependence: review and meta-analysis of retrospective controlled studies

Background

Studies have sought associations of the opioid receptor mu 1 (OPRM1) A118G polymorphism (rs1799971) with alcohol-dependence, but findings are inconsistent. We summarize the information as to associations of rs1799971 (A > G) and the alcohol-dependence.

Methods

Systematically, we reviewed related literatures using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline. Embase, PubMed, Web of Knowledge, and Chinese National Knowledge Infrastructure (CNKI) databases were searched using select medical subject heading (MeSH) terms to identify all researches focusing on the present topic up to September 2016. Odds ratios (ORs) along with the 95% confidence interval (95% CI) were estimated in allele model, homozygote model, heterozygote model, dominant model and recessive model. Ethnicity-specific subgroup-analysis, sensitivity analysis, heterogeneity description, and publication-bias assessment were also analyzed.

Results

There were 17 studies, including 9613 patients in the present meta-analysis. The ORs in the 5 genetic-models were 1.037 (95% CI: 0.890, 1.210; p = 0.64), 1.074 (95% CI: 0.831, 1.387; p = 0.586), 1.155 (95% CI: 0.935, 1.427; p = 0.181), 1.261 (95% CI: 1.008, 1.578; p = 0.042), 0.968 (95% CI: 0.758, 1.236; p = 0.793), respectively. An association is significant in the dominant model, but there is no statistical significance upon ethnicity-specific subgroup analysis.

Conclusion

The rs1799971 (A > G) is not strongly associated with alcohol-dependence. However, there are study heterogeneities and limited sample sizes.

Review: Pharmacogenetics of alcoholism treatment: Implications of ethnic diversity

BACKGROUND AND OBJECTIVES

Pharmacogenetic studies of alcohol use disorder (AUD) have suggested that the efficacy of treatments for AUD is, in part, influenced by the genetic background of an individual. Since the frequency of alleles associated with pharmacotherapy for AUD varies by ancestral background, the effectiveness of medications used to treat AUD may vary among different populations. The purpose of this review is to summarize the existing pharmacogenetic studies of treatments for AUD in individuals of European, East Asian, African, and American Indian/Alaska Native ancestry.

METHODS

Electronic databases were searched for pharmacogenetic studies of AUD treatment that included individuals of diverse ancestral backgrounds.

RESULTS

Pharmacogenetic studies of AUD reviewed here have primarily investigated genetic variation thought to play a role in the response to naltrexone, ondansetron, and topiramate. There is support that the A118G polymorphism should be further investigated in individuals of East Asian ancestry.

DISCUSSION AND CONCLUSIONS

Given the lack of pharmacogenetic research on response to AUD medication in ethnic minority populations and the mixed results, there is a critical need for future studies among individuals of different ancestries. More efforts should be devoted to standardizing procedures such that results can be more readily integrated into a body of literature that can directly inform clinical practice.

SCIENTIFIC SIGNIFICANCE

This review highlights the importance for future research to aim for inclusiveness in pharmacogenetic studies of AUD and increase diversity of clinical trials in order to provide the best treatment outcomes for individuals across different racial and ethnic groups. (Am J Addict 2017;26:516-525).

Association of the OPRM1 Variant rs1799971 (A118G) with Non-Specific Liability to Substance Dependence in a Collaborative de novo Meta-Analysis of European-Ancestry Cohorts

The mu1 opioid receptor gene, OPRM1, has long been a high-priority candidate for human genetic studies of addiction. Because of its potential functional significance, the non-synonymous variant rs1799971 (A118G, Asn40Asp) in OPRM1 has been extensively studied, yet its role in addiction has remained unclear, with conflicting association findings. To resolve the question of what effect, if any, rs1799971 has on substance dependence risk, we conducted collaborative meta-analyses of 25 datasets with over 28,000 European-ancestry subjects. We investigated non-specific risk for "general" substance dependence, comparing cases dependent on any substance to controls who were non-dependent on all assessed substances. We also examined five specific substance dependence diagnoses: DSM-IV alcohol, opioid, cannabis, and cocaine dependence, and nicotine dependence defined by the proxy of heavy/light smoking (cigarettes-per-day >20 vs. ≤ 10). The G allele showed a modest protective effect on general substance dependence (OR = 0.90, 95% C.I. [0.83-0.97], p value = 0.0095, N = 16,908). We observed similar effects for each individual substance, although these were not statistically significant, likely because of reduced sample sizes. We conclude that rs1799971 contributes to mechanisms of addiction liability that are shared across different addictive substances. This project highlights the benefits of examining addictive behaviors collectively and the power of collaborative data sharing and meta-analyses.

Association of A118G polymorphism in the μ-opioid receptor gene with smoking behaviors: a meta-analysis

Many studies have investigated the association between the A118G polymorphism in the μ-opioid receptor gene and smoking behaviors, but the results remain controversial. This meta-analysis aimed to derive a more reliable estimate of the effect of the A118G polymorphism on smoking behaviors. We systematically searched the PubMed/Medline, Embase and Web of Science databases for eligible articles published up to October 23, 2014. A total of six studies were selected. Odds ratios (ORs) as well as their corresponding 95% confidence intervals (CIs) were used to estimate the association between A118G polymorphism and smoking behaviors in four genetic models. Heterogeneity analysis and publication bias were also performed. Subgroup analysis was conducted according to different ethnicities. The meta-analysis was performed using either a fixed- or random-effects model as deemed appropriate. In the result of the meta-analysis, a significant association was detected in the dominant model in the Caucasian subgroup (OR = 3.26, 95% CI = 2.65-4.05). This result indicated that Caucasians carrying the G allele (AG + GG) of the A118G polymorphism in the μ-opioid receptor gene were more likely to be addicted to smoking compared with those with the AA homozygote. However, no significant association was found in other genetic models.

Co-development of early adolescent alcohol use and depressive feelings: The role of the mu-opioid receptor A118G polymorphism

Alcohol use and depressive feelings are often related among early adolescents. However, the nature and underlying mechanisms of this association are not yet clear. The aim of this study was to investigate the co-development of alcohol use and depressive feelings over time and to examine the effects of the mu-opioid receptor (OPRM1) A118G genotype on such co-development. Data from a five-wave longitudinal, genetically informed survey study, with intervals of 4 months among a group of 739 normative early adolescents (12-13 years of age at baseline), were analyzed using a dual latent growth curve approach. OPRM1 status was evaluated from saliva-derived DNA samples. The results indicated a positive association between alcohol use and depressive feelings both at the initial levels and over time, indicating co-development in early adolescence. Compared to OPRM1 118G carriers, homozygous 118A carriers showed a greater increase in frequency of alcohol use and higher levels of depressive feelings over time. Evidence for co-development was only found within the group of homozygous 118A carriers, whereas in OPRM1 118G carriers the development of alcohol use and depressive feelings over time were not significantly associated. These results highlight the potential of OPRM1 as a common etiological factor for the development of alcohol use and depressive feelings in early adolescence.

Association between the A107V substitution in the δ-opioid receptors and ethanol drinking in mice selected for high and low analgesia

Experimental evidence suggests that endogenous opioids play an important role in the development of ethanol addiction. In this study, we employed two mouse lines divergently bred for opioid-mediated stress-induced analgesia. In comparison with HA (high analgesia line) mice, LA (low analgesia line) mice, having lower opioid receptor system activity, manifest enhanced basal as well as stress-induced ethanol drinking. Here, we found that recently discovered C320T transition in exon 2 of the δ-opioid receptor gene (EU446125.1), which results in an A107V substitution (ACA23171.1), leads to higher ethanol preference in CT mice compared with CC homozygotes. This genetic association is particularly evident under chronic mild stress (CMS) conditions. The interaction between stress and ethanol intake was significantly stronger in HA than in LA mice. Ethanol almost completely attenuated the pro-depressive effect of CMS (assessed with the tail suspension test) in both the CC and CT genotypes in the HA line. In the LA mice, a lack of response to ethanol was observed in the CC genotype, whereas ethanol consumption strengthened depressive-like behaviours in CT individuals. Our results suggest that constitutively active A107V substitution in δ-opioid receptors may be involved in stress-enhanced vulnerability to ethanol abuse and in the risk of ethanol dependence.

Dual growth of adolescent smoking and drinking: evidence for an interaction between the mu-opioid receptor (OPRM1) A118G polymorphism and sex

Smoking and alcohol use often co-occur during adolescence, but little is known about the codevelopment of these substances. In the search for etiological factors that help to explain the development of adolescent substance use patterns, studies have revealed substantial heritability for both alcohol use and smoking. In this regard, the µ-opioid receptor gene (OPRM1, chromosome 6q24-q25) has been linked to both substances. This study examined the predictive relationships between initial level and growth of smoking and drinking in 311 early adolescents (13-15 years old) over a 4-year period. In addition, the effects of the A118G polymorphism of the OPRM1 gene on the initial values and the development over time of alcohol use and smoking were assessed. Finally, as prevalence and heritability estimates for both alcohol- and smoking-related behaviors differ between males and females, OPRM1 by sex interactions were tested. We found that high initial levels of early adolescent alcohol consumption were related to a stronger increase in smoking levels over time. In contrast, high initial levels of smoking were not related to growth of alcohol use. No main OPRM1 effects were found, but sex-specificity of the gene was found for smoking development. Male A-allele carriers showed a faster development in smoking behavior, whereas in females, the G-allele led to a faster development in smoking. Thus, in addition to high levels of alcohol as a risk factor for the development of smoking behavior, sex-specific effects exist for OPRM1, which may additionally have consequences for the development of adolescent smoking.

RGS17: an emerging therapeutic target for lung and prostate cancers

Ligands for G-protein-coupled receptors (GPCRs) represent approximately 50% of currently marketed drugs. RGS proteins modulate heterotrimeric G proteins and, thus, GPCR signaling, by accelerating the intrinsic GTPase activity of the Gα subunit. Given the prevalence of GPCR targeted therapeutics and the role RGS proteins play in G protein signaling, some RGS proteins are emerging as targets in their own right. One such RGS protein is RGS17. Increased RGS17 expression in some prostate and lung cancers has been demonstrated to support cancer progression, while reduced expression of RGS17 can lead to development of chemotherapeutic resistance in ovarian cancer. High-throughput screening is a powerful tool for lead compound identification, and utilization of high-throughput technologies has led to the discovery of several RGS inhibitors, thus far. As screening technologies advance, the identification of novel lead compounds the subsequent development of targeted therapeutics appears promising.

μ-Opioid receptor gene (OPRM1) polymorphism A118G: lack of association in Finnish populations with alcohol dependence or alcohol consumption

Aims: The molecular epidemiological studies on the association of the opioid receptor µ-1 (OPRM1) polymorphism A118G (Asn40Asp, rs1799971) and alcohol use disorders have given conflicting results. The aim of this study was to test the possible association of A118G polymorphism and alcohol use disorders and alcohol consumption in three large cohort-based study samples. Methods: The association between the OPRM1 A118G (Asn40Asp, rs1799971) polymorphism and alcohol use disorders and alcohol consumption was analyzed using three different population-based samples: (a) a Finnish cohort study, Health 2000, with 503 participants having a DSM-IV diagnosis for alcohol dependence and/or alcohol abuse and 506 age- and sex-matched controls; (b) a Finnish cohort study, FINRISK (n = 2360) and (c) the Helsinki Birth Cohort Study (n = 1384). The latter two populations lacked diagnosis-based phenotypes, but included detailed information on alcohol consumption. Results: We found no statistically significant differences in genotypic or allelic distribution between controls and subjects with alcohol dependence or abuse diagnoses. Likewise no significant effects were observed between the A118G genotype and alcohol consumption. Conclusion: These results suggest that A118G (Asn40Asp) polymorphism may not have a major effect on the development of alcohol use disorders at least in the Finnish population.

Direct-to-consumer genetic testing for addiction susceptibility: a premature commercialisation of doubtful validity and value

Genetic research on addiction liability and pharmacogenetic research on treatments for addiction have identified some genetic variants associated with disease risk and treatment. Genetic testing for addiction liability and treatment response has not been used widely in clinical practice because most of the genes identified only modestly predict addiction risk or treatment response. However, many of these genetic tests have been commercialized prematurely and are available direct to the consumer (DTC). The easy availability of DTC tests for addiction liability and lack of regulation over their use raises a number of ethical concerns. Of paramount concern is the limited predictive power and clinical utility of these tests. Many DTC testing companies do not provide the consumer with the necessary genetic counselling to assist them in interpreting and acting on their test results. They may also engage in misleading marketing to entice consumers to purchase their products. Consumers' genetic information may be vulnerable to misuse by third parties, as there are limited standards to protect the privacy of the genetic information. Non-consensual testing and inappropriate testing of minors may also occur. The United States Food and Drug Administration plans to regulate DTC genetic tests. Based on the ethical concerns we discuss below, we believe there is a strong case for regulation of DTC genetic tests for addiction liability and treatment response. We argue that until this occurs, these tests have more potential to cause harm than to contribute to improved prevention and treatment of addiction.

Ethnic-specific meta-analyses of association between the OPRM1 A118G polymorphism and alcohol dependence among Asians and Caucasians

BACKGROUND

Many studies have investigated the association between the OPRM1 A118G polymorphism (rs1799971) and alcohol dependence, but the results were inconsistent. To better understand this relationship, ethnicity-specific meta-analyses were conducted.

METHODS

We retrieved all eligible studies published up to April 12, 2011 from the PubMed/MEDLINE, EMBASE, and ISI Web of Science databases. Ethnicity-specific meta-analyses were performed using either fixed- or random-effect models as appropriate.

RESULTS

Twelve independent studies with 1900 cases and 2382 controls were included. Five studies were conducted in Asians and seven in Caucasians. Ethnicity-specific meta-analyses revealed that the A118G polymorphism was significantly associated with alcohol dependence risk in Asians (GA vs. AA: odds ratio [OR], 1.73; 95% confidence interval [CI], 1.33-2.25; GA+GG vs. AA: OR, 1.57; 95% CI, 1.22-2.02), but not in Caucasians (GA vs. AA: OR, 1.05; 95% CI, 0.75-1.49; GA+GG vs. AA: OR, 1.11; 95% CI, 0.79-1.55).

CONCLUSIONS

The OPRM1 A118G polymorphism may contribute to the susceptibility of alcohol dependence in Asians but not in Caucasians.

The genetics of the opioid system and specific drug addictions

Addiction to drugs is a chronic, relapsing brain disease that has major medical, social, and economic complications. It has been established that genetic factors contribute to the vulnerability to develop drug addiction and to the effectiveness of its treatment. Identification of these factors may increase our understanding of the disorders, help in the development of new treatments and advance personalized medicine. In this review, we will describe the genetics of the major genes of the opioid system (opioid receptors and their endogenous ligands) in connection to addiction to opioids, cocaine, alcohol and methamphetamines. Particular emphasis is given to association and functional studies of specific variants. We will provide information on the sample populations and the size of each study, as well as a list of the variants implicated in association with addiction-related phenotypes, and with the effectiveness of pharmacotherapy for addiction.

Variation in regulator of G-protein signaling 17 gene (RGS17) is associated with multiple substance dependence diagnoses

Background

RGS17 and RGS20 encode two members of the regulator of G-protein signaling RGS-Rz subfamily. Variation in these genes may alter their transcription and thereby influence the function of G protein-coupled receptors, including opioid receptors, and modify risk for substance dependence.

Methods

The association of 13 RGS17 and eight RGS20 tag single nucleotide polymorphisms (SNPs) was examined with four substance dependence diagnoses (alcohol (AD), cocaine (CD), opioid (OD) or marijuana (MjD)] in 1,905 African Americans (AAs: 1,562 cases and 343 controls) and 1,332 European Americans (EAs: 981 cases and 351 controls). Analyses were performed using both χ² tests and logistic regression analyses that covaried sex, age, and ancestry proportion. Correlation of genotypes and mRNA expression levels was assessed by linear regression analyses.

Results

Seven RGS17 SNPs showed a significant association with at least one of the four dependence traits after a permutation-based correction for multiple testing (0.003≤P_empirical≤0.037). The G allele of SNP rs596359, in the RGS17 promoter region, was associated with AD, CD, OD, or MjD in both populations (0.005≤P_empirical≤0.019). This allele was also associated with significantly lower mRNA expression levels of RGS17 in YRI subjects (P = 0.002) and non-significantly lower mRNA expression levels of RGS17 in CEU subjects (P = 0.185). No RGS20 SNPs were associated with any of the four dependence traits in either population.

Conclusions

This study demonstrated that variation in RGS17 was associated with risk for substance dependence diagnoses in both AA and EA populations.

Pilot study examining the frequency of several gene polymorphisms involved in morphine pharmacodynamics and pharmacokinetics in a morbidly obese population

Morbidly obese patients are at significantly elevated risk of postsurgery complications and merit closer monitoring by health care professionals after bariatric surgery. It is now recognized that genetic factors influence individual patient's response to drug used in anesthesia and analgesia. Among the many drug administered by anesthetists, we focused in this pilot study on morphine, since morphine patient-controlled anesthesia in obese patients undergoing gastric bypass surgery is frequently prescribed. We examined the allelic frequency of three polymorphisms involved in morphine pharmacodynamics and pharmacokinetics in patients with body mass index (BMI) >40. One hundred and nine morbidly obese patients (BMI = 49.1 ± 7.7 kg/m²) were genotyped for three polymorphisms c.A118G of mu opioid receptor (OPRM1), c.C3435T of the P-glycoprotein gene (ABCB1), and p.Val158Met of catechol-O-methyltransferase gene (COMT). Allelic frequencies were 118G-0.22, C3435-0.55, and 158Met-0.5 in our whole population and 0.23, 0.5, and 0.47 in Caucasian population. Allelic frequencies did not differ according to gender. Mean BMI did no differ according to the allelic variant. OPRM1118G allele was more frequent in our population than in most previously described European populations. Since the concept of "personalized medicine" promises to individualize therapeutics and optimize medical treatment in term of efficacy and safety, especially when prescribing drugs with a narrow therapeutic index such as morphine, further clinical studies examining the clinical consequences of the OPRM1 c.A118G polymorphism in patients undergoing gastric bypass surgery are needed.

The role of the Asn40Asp polymorphism of the mu opioid receptor gene (OPRM1) on alcoholism etiology and treatment: a critical review

The endogenous opioid system has been implicated in the pathophysiology of alcoholism as it modulates the neurobehavioral effects of alcohol. A variant in the mu opioid receptor gene (OPRM1), the Asn40Asp polymorphism, has received attention as a functional variant that may influence a host of behavioral phenotypes for alcoholism as well as clinical response to opioid antagonists. This paper will review converging lines of evidence on the effect of the Asn40Asp SNP on alcoholism phenotypes, including: (i) genetic association studies; (ii) behavioral studies of alcoholism; (iii) neuroimaging studies; (iv) pharmacogenetic studies and clinical trials; and (v) preclinical animal studies. Together, these lines of research seek to elucidate the effects of this functional polymorphism on alcoholism etiology and treatment response.

Possible association between OPRM1 genetic variance at the 118 locus and alcohol dependence in a large treatment sample: relationship to alcohol dependence symptoms

BACKGROUND

Several lines of evidence from previous research indicate that opioid receptors play an important role in ethanol reinforcement and alcohol dependence (AD) risk. Conflicting results were reported on the role of the mu-opioid receptor (OPRM1) polymorphism A118G (Asn40Asp, rs1799971) in the development of alcoholism.

METHODS

We investigated a total number of 1,845 alcohol-dependent subjects recruited from inpatient facilities in Germany and 1,863 controls for the mu-opioid receptor (OPRM1) polymorphism using chi-square statistics.

RESULTS

An association between the OPRM variant and AD was detected (p = 0.022), in recessive (AA vs. GA/GG) and co-dominant (AA vs. GA) models of inheritance. An association between the OPRM variant and the DSM-IV criterion "efforts to cut down or could not" (p = 0.047) was found, but this did not remain significant after the correction for multiple testing.

CONCLUSIONS

The results indicate that this functional OPRM variant is associated with risk of AD and these findings apply to more severe AD, although the association is only nominally significant.

Molecular mechanisms of opioid receptor-dependent signaling and behavior

Opioid receptors have been targeted for the treatment of pain and related disorders for thousands of years and remain the most widely used analgesics in the clinic. Mu (μ), kappa (κ), and delta (δ) opioid receptors represent the originally classified receptor subtypes, with opioid receptor like-1 (ORL1) being the least characterized. All four receptors are G-protein coupled and activate inhibitory G proteins. These receptors form homo- and heterodimeric complexes and signal to kinase cascades and scaffold a variety of proteins.The authors discuss classic mechanisms and developments in understanding opioid tolerance and opioid receptor signaling and highlight advances in opioid molecular pharmacology, behavioral pharmacology, and human genetics. The authors put into context how opioid receptor signaling leads to the modulation of behavior with the potential for therapeutic intervention. Finally, the authors conclude there is a continued need for more translational work on opioid receptors in vivo.

Pharmacogenetics of naltrexone in asian americans: a randomized placebo-controlled laboratory study

Recent clinical and laboratory studies have shown that the effects of naltrexone for alcoholism may be moderated by the Asn40Asp single-nucleotide polymorphism (SNP) of the μ-opioid receptor gene (OPRM1). Allele frequencies for this polymorphism, however, have been shown to vary substantially as a function of ethnic background, such that individuals of Asian descent are more likely to carry the minor (Asp40) allele. The objective of this study is to test the naltrexone pharmacogenetic effects of the Asn40Asp SNP in a sample of Asian Americans. This study consists of a double-blinded, randomized, placebo-controlled laboratory trial of naltrexone. Participants (n=35, 10 females; 13 Asn40Asn and 22 Asp40 carriers) were non-treatment-seeking heavy drinkers recruited from the community. After taking naltrexone or placebo, participants completed an intravenous alcohol administration session. The primary outcome measures were subjective intoxication and alcohol craving. Results suggested that Asp40 carriers experienced greater alcohol-induced sedation, subjective intoxication, and lower alcohol craving on naltrexone, as compared to placebo, and to Asn40 homozygotes. There results were maintained when controlling for ALDH2 (rs671) and ADH1B (rs1229984) markers and when examining the three levels of OPRM1 genotype, thereby supporting an OPRM1 gene dose response. These findings provide a much-needed extension of previous studies of naltrexone pharmacogenetics to individuals of Asian descent, an ethnic group more likely to express the minor allele putatively associated with improved biobehavioral and clinical response to this medication. These findings help further delineate the biobehavioral mechanisms of naltrexone and its pharmacogenetics.

Pharmacogenomics of the human µ-opioid receptor

The µ-opioid receptor is a primary target for clinically important opioid analgesics, including morphine, fentanyl and methadone. Many genetic variations have been identified in the human µ-opioid receptor MOP gene (OPRM1), and their implications have been reported in the effects of opioid drugs and susceptibility to drug dependence. Interestingly, agonistic and antagonistic opioid effects are inversely associated with the A118G polymorphism genotype. The A118G polymorphism may also be associated with substance dependence and susceptibility to other disorders, including epilepsy and schizophrenia. The IVS1+A21573G, IVS1-T17286C, and TAA+A5359G polymorphisms in the OPRM1 gene may be associated with alcohol, opioid and tobacco dependence, respectively. However, some studies have failed to confirm the correlations between the polymorphisms and opioid effects and substance dependence. Further studies are needed to elucidate the molecular mechanisms underlying the effects of OPRM1 polymorphisms.

OPRM1 gene variants modulate amphetamine-induced euphoria in humans

The μ-opioid receptor is involved in the rewarding effects of not only opioids like morphine but also psychostimulants like amphetamine. This study aimed to investigate associations between subjective response to amphetamine and genetic polymorphisms and haplotypes in the μ-opioid receptor including the exonic variant rs1799971 (Asp40Asn). One hundred and sixty-two Caucasian volunteers participated in three sessions receiving either placebo or d-amphetamine (10 and 20 mg). Associations between levels of self-reported Euphoria, Energy and Stimulation [Addiction Research Center Inventory 49-item questionnaire (ARCI-49)] after d-amphetamine ingestion and polymorphisms in OPRM1 were investigated. The intronic single nucleotide polymorphisms (SNPs) rs510769 and rs2281617 were associated with significantly higher ratings of Euphoria, Energy and Stimulation after 10 mg amphetamine. Feelings of Euphoria, Energy and Stimulation were also found to be associated with a two-SNP haplotype formed with rs1799971 and rs510769 and a three-SNP haplotype formed with rs1918760, rs2281617 and rs1998220. These results support the hypothesis that genetic variability in the μ-opioid receptor gene influences the subjective effects of amphetamine and may suggest new strategies for prevention and treatment of psychostimulant abuse.

Subjective responses to alcohol consumption as endophenotypes: advancing behavioral genetics in etiological and treatment models of alcoholism

Individual differences in subjective responses to alcohol consumption represent genetically mediated biobehavioral mechanisms of alcoholism risk (i.e., endophenotype). The objective of this review is three-fold: (1) to provide a critical review the literature on subjective response to alcohol and to discuss the rationale for its conceptualization as an endophenotype for alcoholism; (2) to examine the literature on the neurobiological substrates and associated genetic factors subserving individual differences in subjective response to alcohol; and (3) to discuss the treatment implications of this approach and to propose a framework for conceptualizing, and systematically integrating, endophenotypes into alcoholism treatment.

OPRM1 SNP (A118G): involvement in disease development, treatment response, and animal models

Endogenous opioids acting at mu-opioid receptors mediate many biological functions. Pharmacological intervention at these receptors has greatly aided in the treatment of acute and chronic pain, in addition to other uses. However, the development of tolerance and dependence has made it difficult to adequately prescribe these therapeutics. A common single nucleotide polymorphism (SNP), A118G, in the mu-opioid receptor gene can affect opioid function and, consequently, has been suggested to contribute to individual variability in pain management and drug addiction. Investigation into the role of A118G in human disease and treatment response has generated a large number of association studies across various disease states as well as physiological responses. However, characterizing the functional consequences of this SNP and establishing if it causes or contributes to disease phenotypes have been significant challenges. In this manuscript, we will review a number of association studies as well as investigations of the functional impact of this gene variant. In addition, we will describe a novel mouse model that was generated to recapitulate this SNP in mice. Evaluation of models that incorporate known human genetic variants into a tractable system, like the mouse, will facilitate the understanding of discrete contributions of SNPs to human disease.

Genetics of drug dependence

Drug-dependence disorders (we focus here on cocaine, opioid, and nicotine dependence) are genetically influenced. Risk genes have been located based primarily on genetic linkage studies, and identified primarily based on genetic association studies. In this article we review salient results from linkage, association, and genome-wide association study methodologies, and discuss future prospects for risk allele identification based on these, and on newer, methodologies. Although considerable progress has been made, it is likely that the application of more extensive sequencing than has previously been practical will be required to identify a fuller range of risk variants.

Meta-analysis of 15 genome-wide linkage scans of smoking behavior

BACKGROUND

A genetic contribution to smoking behavior is well-established. To identify loci that increase the risk for smoking behavior, many genome-wide linkage scans have been performed with various smoking behavior assessments. Numerous putative susceptibility loci have been identified, but only a few of these were replicated in independent studies.

METHODS

We used genome search meta-analysis (GSMA) to identify risk loci by pooling all available independent genome scan results on smoking behavior. Additionally, to minimize locus heterogeneity, subgroup analyses of the smoking behavior assessed by the Fagerstrom Test for Nicotine Dependence (FTND) and maximum number of cigarettes smoked in a 24-hour period (MaxCigs24) were carried out. Samples of European ancestry were also analyzed separately.

RESULTS

A total number of 15 genome scan results were available for analysis, including 3404 families with 10,253 subjects. Overall, the primary GSMA across all smoking behavior identified a genome-wide suggestive linkage in chromosome 17q24.3-q25.3 (p(SR) = .001). A secondary analysis of FTND in European-ancestry samples (625 families with 1878 subjects) detected a genome-wide suggestive linkage in 5q33.1-5q35.2 (p(SR) = .0076). Subgroup analysis of MaxCigs24 (966 families with 3273 subjects) identified a genome-wide significant linkage in 20q13.12-q13.32 (p(SR) = .00041, p(OR) = .048), where a strongly supported nicotine dependence candidate gene, CHRNA4, is located.

CONCLUSIONS

The regions identified in the current study deserve close attention and will be helpful for candidate gene identification or target re-sequencing studies in the future.

Single-nucleotide polymorphism (A118G) in exon 1 of OPRM1 gene causes alteration in downstream signaling by mu-opioid receptor and may contribute to the genetic risk for addiction

The opioid receptor mu1 (OPRM1) mediates the action of morphine. Although genetic background plays an important role in the susceptibility toward abuse of drugs as evident from familial, adoption and twin studies, association of specific single-nucleotide polymorphisms of OPRM1 gene with narcotic addiction is to be established. Here, we demonstrate the involvement of A118G polymorphism of exon1 of human OPRM1 gene (hOPRM1), with heroin and alcohol addiction, in a population in eastern India. Statistical analysis exhibited a significant association of G allele with both heroin and alcohol addiction with a risk factor of P(trend) < 0.05. The functional significance of G allele in A118G single-nucleotide polymorphisms was evaluated by studying the regulation of protein kinase A (PKA), pCREB, and pERK1/2 by morphine in Neuro 2A cells, stably transfected with either wild type or A118G mutant hOPRM1. Unlike acute morphine treatment, both chronic morphine exposure and withdrawal precipitated by naloxone were differentially regulated by A118 and G118 receptor isoforms when both PKA and pERK1/2 activities were compared. Results suggest that the association of A118G polymorphism to heroin and alcohol addiction may be because of the altered regulation of PKA and pERK1/2 during opioid and alcohol exposures.

The interaction of reward genes with environmental factors in contribution to alcoholism in mexican americans

BACKGROUND

Alcoholism is a polygenic disorder resulting from reward deficiency; polymorphisms in reward genes including serotonin transporter (5-HTT)-linked polymorphic region (5-HTTLPR), A118G in opioid receptor mu1 (OPRM1), and -141C Insertion/Deletion (Ins/Del) in dopamine receptor D2 (DRD2) as well as environmental factors (education and marital status) might affect the risk of alcoholism. Objective of the current study was to examine the main and interacting effect of these 3 polymorphisms and 2 environmental factors in contribution to alcoholism in Mexican Americans.

METHODS

Genotyping of 5-HTTLPR, OPRM1 A118G, and DRD2-141C Ins/Del was performed in 365 alcoholics and 338 nonalcoholic controls of Mexican Americans who were gender- and age-matched. Alcoholics were stratified according to tertiles of MAXDRINKS, which denotes the largest number of drinks consumed in one 24-hour period. Data analysis was done in the entire data set and in each alcoholic stratum. Multinomial logistic regression was conducted to explore the main effect of 3 polymorphisms and 2 environmental factors (education and marital status); classification tree, generalized multifactor dimensionality reduction (GMDR) analysis, and polymorphism interaction analysis version 2.0 (PIA 2) program were used to study factor interaction.

RESULTS

Main effect of education, OPRM1, and DRD2 was detected in alcoholic stratum of moderate and/or largest MAXDRINKS with education < or =12 years, OPRM1 118 A/A, and DRD2 -141C Ins/Ins being risk factors. Classification tree analysis, GMDR analysis, and PIA 2 program all supported education*OPRM1 interaction in alcoholics of largest MAXDRINKS with education < or =12 years coupled with OPRM1 A/A being a high risk factor; dendrogram showed synergistic interaction between these 2 factors; dosage-effect response was also observed for education*OPRM1 interaction. No definite effect of marital status and 5-HTTLPR in pathogenesis of alcoholism was observed.

CONCLUSIONS

Our results suggest main effect of education background, OPRM1 A118G, and DRD2 -141C Ins/Del as well as education*OPRM1 interaction in contribution to moderate and/or severe alcoholism in Mexican Americans. Functional relevance of these findings still needs to be explored.

The opioid peptides enkephalin and beta-endorphin in alcohol dependence

BACKGROUND

Experimental evidence indicates that the endogenous opioid system influences stress responses as well as reinforces effects of addictive drugs. Because stress is an important factor contributing to drug dependence and relapse, we have now studied ethanol preference in enkephalin- and beta-endorphin-deficient mice under baseline conditions and after stress exposure.

METHODS

In the present study we used a two-bottle choice paradigm to study ethanol consumption and stress-induced ethanol preference. To examine alcohol withdrawal symptoms the forced drinking procedure was employed. We performed an association analysis in two case-control samples of alcohol addicts to determine whether these opioid peptides also contribute to ethanol dependence in humans.

RESULTS

Ethanol consumption was significantly reduced in the absence of beta-endorphins, particularly in female knockout animals. Stress exposure results in an increased ethanol consumption in wild-type mice but did not influence ethanol-drinking in beta-endorphin knockouts. Enkephalin-deficient mice showed no difference from wild-type mice in baseline ethanol preference but also showed no stress-induced elevation of ethanol consumption. Interestingly, we found a two-marker haplotype in the POMC gene that was associated with alcohol dependence in females in both cohorts.

CONCLUSIONS

Together these results indicate a contribution of beta-endorphin to ethanol consumption and dependence.

The role of 5-HT3 receptors in drug abuse and as a target for pharmacotherapy

Alcohol and drug abuse continue to be a major public health problem in the United States and other industrialized nations. Extensive preclinical research indicates the mesolimbic dopamine (DA) pathway and associated regions mediate the rewarding and reinforcing effects of drugs of abuse and natural rewards, such as food and sex. The serotonergic (5-HT) system, in concert with others neurotransmitter systems, plays a key role in modulating neuronal systems within the mesolimbic pathway. A substantial portion of this modulation is mediated by activity at the 5-HT3 receptor. The 5-HT3 receptor is unique among the 5-HT receptors in that it directly gates an ion channel inducing rapid depolarization that, in turn, causes the release of neurotransmitters and/or peptides. Preclinical findings indicate that antagonism of the 5-HT3 receptor in the ventral tegmental area, nucleus accumbens or amygdala reduces alcohol self-administration and/or alcohol-associated effects. Less is known about the effects of 5-HT3 receptor activity on the self-administration of other drugs of abuse or their associated effects. Clinical findings parallel the preclinical findings such that antagonism of the 5-HT3 receptor reduces alcohol consumption and some of its subjective effects. This review provides an overview of the structure, function, and pharmacology of 5-HT3 receptors, the role of these receptors in regulating DA neurotransmission in mesolimbic brain areas, and discusses data from animal and human studies implicating 5-HT3 receptors as targets for the development of new pharmacological agents to treat addictions.

Pharmacogenetic treatments for drug addiction: alcohol and opiates

AIMS

Psychiatric pharmacogenetics involves the use of genetic tests that can predict the effectiveness of treatments for individual patients with mental illness such as drug dependence. This review aims to cover these developments in the pharmacotherapy of alcohol and opiates, two addictive drugs for which we have the majority of our FDA approved pharmacotherapies.

METHODS

We conducted a literature review using Medline searching terms related to these two drugs and their pharmacotherapies crossed with related genetic studies.

RESULTS

Alcohol's physiological and subjective effects are associated with enhanced beta-endorphin release. Naltrexone increases baseline beta-endorphin release blocking further release by alcohol. Naltrexone's action as an alcohol pharmacotherapy is facilitated by a putative functional single nucleotide polymorphism (SNP) in the opioid mu receptor gene (Al18G) which alters receptor function. Patients with this SNP have significantly lower relapse rates to alcoholism when treated with naltrexone. Caucasians with various forms of the CYP2D6 enzyme results in a 'poor metabolizer' phenotype and appear to be protected from developing opioid dependence. Others with a "ultra-rapid metabolizer" phenotype do poorly on methadone maintenance and have frequent withdrawal symptoms. These patients can do well using buprenorphine because it is not significantly metabolized by CYP2D6.

CONCLUSIONS

Pharmacogenetics has great potential for improving treatment outcome as we identify gene variants that affect pharmacodynamic and pharmacokinetic factors. These mutations guide pharmacotherapeutic agent choice for optimum treatment of alcohol and opiate abuse and subsequent relapse.

The OPRD1 and OPRK1 loci in alcohol or drug dependence: OPRD1 variation modulates substance dependence risk

Eleven single-nucleotide polymorphisms (SNPs) spanning OPRD1 were examined in 1063 European Americans (EAs) (620 cases with substance dependence (SD), including 557 with alcohol dependence (AD), 225 with cocaine dependence (CD) and 111 with opioid dependence (OD), and 443 controls). Nominally significant associations (P<0.05) of five SNPs with SD were observed; only the association of the non-synonymous variant G80T with OD remained significant after correction for multiple testing using SNPSpD. Haplotype analyses with six tag SNPs indicated that a specific haplotype GCAACT, which harbors G80T G-allele and C921T C-allele, was significantly associated with AD (chi(2)=14.82, degrees of freedom (d.f.)=1, P<0.001), CD (chi(2)=9.19, d.f.=1, P=0.002) and OD (chi(2)=20.68, d.f.=1, P<0.001). Logistic regression analyses, with sex and age being considered, demonstrated that this haplotype had a risk effect on AD (P=0.03, beta=1.86, odds ratio (OR)=6.43) and especially on OD (P<0.001, beta=3.92, OR=50.57). Moreover, seven SNPs covering OPRK1 were examined in the majority of the above subjects (390 cases, including 327 AD, 177 CD and 97 OD subjects, and 358 controls). Although no significant differences in allele, genotype or haplotype frequency distributions were seen between cases and controls, a specific OPRK1 haplotype, GGCTTCT, was significantly associated with AD (chi(2)=8.12, d.f.=1, P=0.004). Logistic regression analyses also revealed its risk effect on AD (P=0.009, beta=1.06, OR=2.90). Population stratification artifact was not observed in the sample. Taken together, our findings supported a positive association between OPRD1 variants and SD, and a positive haplotypic association between OPRK1 and AD in EAs.

A118g polymorphism in mu opioid receptor gene (oprm1): association with opiate addiction in subjects of Indian origin

The opioidergic hypothesis suggests an association between genetic variations at the opioid receptor mu 1 (OPRM1) gene locus and opiate addiction. The OPRM1 gene, which encodes for mu opioid receptor, contains several single nucleotide polymorphisms (SNPs) in exon I. Two of these, C17T and A118G, have been reported to be associated with substance abuse. The present study aims to delineate the frequency of these variants in the subjects of Indian origin and study their association with the phenotype of opioid dependence. A118G (rs 1799971) and C17T (rs 1799972) were genotyped using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. For 118G allele, the control subjects (n = 156) showed a frequency of 0.12 while the opioid dependents (n = 126) had an approximately 2.5-fold higher frequency of 0.31 (Odds Ratio 3.501; CI(95%) 2.212-5.555; p < 0.0001). For C17T polymorphism, the controls (n = 57) showed a frequency of 0.89 for C allele versus 0.83 seen in dependents (n = 123; odds ratio of 0.555; CI(95%) 0.264-1.147; p = 0.121). A significant association was observed between the 118G allele and no association was seen with C17T polymorphism and opioid dependence.

Cigarette smoking and the lifetime alcohol involvement continuum

Greater understanding of how alcohol use relates to the initiation, progression, and persistence of cigarette smoking is of great significance for efforts to prevent and treat smoking and excessive drinking and their substantial combined iatrogenic effects on health. Studies investigating the relationship between levels of alcohol involvement and smoking have typically been limited by analytic approaches that treat drinking behavior and alcohol use disorder diagnoses as separate phenomena rather than as indicators of a single latent alcohol involvement dimension. The purposes of the present study were (a) to create a lifetime index of alcohol involvement that integrates information about alcohol consumption and alcohol problems into a single measure and (b) to relate this index to initiation of smoking, progression from initiation to daily smoking, progression from initiation to dependence, and persistence of smoking. Rasch model analyses of data from 1508 middle-aged (34-44 years) adults showed that creating an additive index of lifetime alcohol involvement was psychometrically supported. Significant quadratic effects of alcohol involvement on initiation, progression, and persistence of smoking demonstrated that there were specific regions of the alcohol involvement continuum that were particularly strongly related to increased smoking. These results provide the most comprehensive depiction to date of the nature of the relationship between lifetime alcohol involvement and lifetime cigarette smoking and suggest potential avenues for research on the etiology and maintenance of smoking and tobacco dependence.

Genetics of nicotine dependence and pharmacotherapy

Nicotine dependence is substantially heritable. Several regions across the genome have been implicated in containing genes that confer liability to nicotine dependence and variation in individual genes has been associated with nicotine dependence. Smoking cessation measures are also heritable, and measured genetic variation is associated with nicotine dependence treatment efficacy. Despite significant strides in the understanding of the relative contribution of genetic and environmental factors to nicotine dependence and treatment, emergent challenges necessitate interdisciplinary coordinated effort for effective problem solving. These challenges include refinement of the nicotine dependence phenotype, better understanding of the dynamic interplay between genes and environment in nicotine dependence etiology, application and development of molecular and statistical methodology that can adequately address vast amounts of data, and continuous translational cross-talk.

The opioid system in alcohol and drug dependence: family-based association study

Opioid receptors and their endogenous peptide ligands play important roles in neurotransmission and neuromodulation in response to addictive drugs such as heroin, cocaine, and alcohol. In an earlier study, we reported that variation in the genes encoding the kappa-opioid receptor (OPRK1) and its peptide ligand (PDYN) were associated with the risk for alcoholism. We continued our investigation of the role of the opioid system in alcohol dependence by analyzing the genes encoding the micro- and delta-opioid receptors and their peptide ligands. We analyzed 18 OPRM1 SNPs, 18 OPRD1 SNPs, 7 PENK SNPs, and 7 POMC SNPs in a sample of 1923 European Americans from 219 multiplex alcohol dependent families. Employing a family-based test of association, we found no evidence that these four genes were significantly associated with alcohol dependence. We also did not find association between these genes and illicit drug dependence. Secondary analyses employing the narrower phenotype of opioid dependence (83 affected individuals) demonstrated association with SNPs in PENK and POMC, but not in OPRM1 or OPRD1. Haplotype analyses provided further support for the association of PENK and POMC with opioid dependence. Therefore, our data provide no support for the idea that variations in OPRM1, OPRD1, PENK and POMC are associated with alcohol dependence or general illicit drug dependence, but variations in PENK and POMC appear to be associated with the narrower phenotype of opioid dependence in these families.

Genetics and smoking behavior

Accumulating data support the role of genetic factors in smoking initiation, progression to tobacco dependence, and smoking persistence. This review summarizes current research on the heritability of tobacco use phenotypes and genetic association studies of smoking-related behaviors. Although progress has been made in genetics research on smoking behavior, many studies have methodological limitations, including insufficient samples for detecting gene-gene and gene-environment interactions and use of less refined phenotypes. Pharmacogenetic investigations also are identifying variants in drug-metabolizing enzymes, receptors, and transporters that modify therapeutic response to smoking cessation medications; however, the field is relatively new, and most findings in this area have yet to be replicated. As this research advances, it will be important to study and address practical, economic, ethical, and social barriers to the translation of genetics research on tobacco use to clinical practice.

Polymorphisms in the µ-opioid receptor gene (OPRM1) and the implications for alcohol dependence in humans

Twin and adoption studies have shown that alcohol dependence contains a substantial genetic component. In attempts to identify the genetic factors involved, association studies have linked the opioid system to alcohol dependence, with a main focus on the OPRM1 gene encoding the μ-opioid receptor. Our aim was to conduct a systematic review of the literature on the associations between polymorphisms in OPRM1 and alcohol dependence. We addressed findings of 12 studies that met our inclusion criteria. All studies employed a case–control design and included alcohol dependence as a dependent outcome measure. Our review showed that clinical studies do not unequivocally support an association between polymorphisms in OPRM1 and alcohol dependence. Factors that complicate genetic research on alcohol dependence, such as gene–environment interaction, and genetic and clinical heterogeneity, are discussed.

The influence of genetics on nicotine dependence and the role of pharmacogenetics in treating the smoking habit

Despite the considerable efforts made in the fight against smoking in the last decades, there are still substantial numbers of people who, in full knowledge of the health hazards, begin smoking or continue smoking. Recent studies have focused on the genetic bases of the nicotine addiction. Various genetic polymorphisms have been associated with smoking. However, environmental factors have also been shown to play a role. In this review, we present some of the principal data collected in genetic studies of smoking behavior. The results obtained through this line of research will eventually aid clinicians in individualizing the type, dosage and duration of treatment for patients with nicotine dependence in accordance with the genotype of each smoker, thereby maximizing the efficacy of the proposed treatment regimen.

Multiple ADH genes modulate risk for drug dependence in both African- and European-Americans

Drug dependence (DD) is commonly co-morbid with alcohol dependence (AD). Many studies have also shown common genetic risk factors for these disorders. We previously reported associations of AD with seven alcohol dehydrogenase (ADH) genes. The present study examines the relationship between these genes and DD. We genotyped 16 markers within the ADH gene cluster and 38 unlinked ancestry-informative markers in a case-control sample of 718 individuals. All markers were consistent with Hardy-Weinberg equilibrium in controls, but some markers showed Hardy-Weinberg disequilibrium in cases (minimal P = 0.002). Genotypes of many markers were associated with DD, both before and after controlling for admixture effects (minimal P < 1.0 x 10(-6)). Diplotype trend regression analysis showed that ADH5 and ADH6 genotypes, and diplotypes at ADH1A, ADH1B, ADH1C and ADH7 (minimal P = 0.002), were associated with DD in European-Americans and/or African-Americans. This first report of an allelic association of these loci with DD provides new insight into the mechanism of genetic risk for DD. These findings, obtained using a series of powerful and reliable analytic methods, may also help to explain the high rate of co-morbidity between AD and DD.

Association of mu-opioid receptor gene polymorphism A118G with alcohol dependence in a Japanese population

Ethanol is considered to activate the brain reward system by increasing the release of an endogenous opioid receptor ligand, beta-endorphin. The polymorphism A118G in the mu-opioid receptor gene (OPRM1) causes the amino acid change Asn40Asp and has been reported to affect the affinity of the ligand for the receptor. The association of this polymorphism with the vulnerability to alcohol dependence has been studied in many populations, but not yet in Japanese people. In the present study, we compared the frequencies of the polymorphism OPRM1 A118G between patients with alcohol dependence and healthy control subjects living in a Japanese provincial prefecture. We also genotyped a polymorphism, G1510A, in the acetaldehyde dehydrogenase 2 gene (ALDH2), in which the A allele causes poor metabolism of acetaldehyde, a major metabolite of alcohol. Both OPRM1 118G and ALDH2 1510G were significantly associated with alcohol dependence. These results suggest that OPRM1 118G in addition to ALDH2 1510G might be one of the risk factors for alcohol dependence in Japanese people.

Targeting treatments for alcohol dependence: the pharmacogenetics of naltrexone

Alcohol dependence is one of the leading causes of morbidity worldwide, yet only a minority of those afflicted engages in treatment. While increasing access to treatment is an important public health approach, increasing the success of treatment is also likely to lead to greater engagement. However, alcohol dependence is a complex disorder likely to consist of several biological subtypes. Recent evidence from a number of different studies has suggested that genetic variation in the mu-opioid receptor has a significant influence on clinical presentation of alcohol problems and response to treatment with an opioid antagonist. Most notably, the A118G polymorphism of the mu-receptor gene has been demonstrated to predict clinical response to naltrexone in alcohol-dependent individuals. This article reviews the biological correlates and outlines a scientific agenda for better understanding the role of opioid neurotransmission in the etiology, maintenance and treatment of alcohol dependence.

The mu-opioid receptor gene and smoking initiation and nicotine dependence

The gene encoding the mu-opioid receptor (OPRM1) is reported to be associated with a range of substance dependence. Experiments in knockout mice indicate that the mu-opioid receptor may mediate reinforcing effects of nicotine. In humans, opioid antagonist naltrexone may reduce the reinforcing effects of tobacco smoking. Additionally, the OPRM1 gene is located in a region showing linkage to nicotine dependence. The OPRM1 is thus a plausible candidate gene for smoking behavior. To investigate whether OPRM1 contributes to the susceptibility of smoking initiation and nicotine dependence, we genotyped 11 SNPs in the gene for 688 Caucasian subjects of lifetime smokers and nonsmokers. Three SNPs showed nominal significance for smoking initiation and one reached significance for nicotine dependence. The global test for three-marker (rs9479757-rs2075572-rs10485057) haplotypes was significant for smoking initiation (p = 0.0022). The same three-marker haplotype test was marginal (p = 0.0514) for nicotine dependence. These results suggest that OPRM1 may be involved in smoking initiation and nicotine dependence.