Case-control study of the D2 dopamine receptor gene and smoking status in lung cancer patients

[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.

Neuroimaging, genetics and the treatment of nicotine addiction

Advances in neuroimaging and genomics provide an unprecedented opportunity to accelerate medication development for nicotine dependence and other addictions. Neuroimaging studies have begun to elucidate the functional neuroanatomy and neurochemistry underlying effects of nicotine and nicotine abstinence. In parallel, genetic studies, including both candidate gene and genome-wide association approaches, are identifying key neurobiological targets and pathways important in addiction to nicotine. To date, only a few neuroimaging studies have explored effects of nicotine or abstinence on brain activity as a function of genotype. Most analyses of genotype are retrospective, resulting in small sample sizes for testing effects of the minor alleles for candidate genes. The purpose of this review is to provide an outline of the work in neuroimaging, genetics, and nicotine dependence, and to explore the potential for increased integration of these approaches to improve nicotine dependence treatment.

Polymorphism in environment responsive genes and association with Parkinson disease

Attempts were made in the present case-control study to investigate the association of polymorphism in the genes encoding proteins involved in toxication-detoxication and dopaminergic pathways and susceptibility to Parkinson's disease (PD). Seventy patients suffering from PD and one hundred healthy controls belonging to the same geographical location and same ethnicity were included in the study. PCR-RFLP and allele-specific PCR-based methodology were used to identify the genotypes. Multivariate logistic regression analysis revealed that heterozygous genotypes of cytochrome P4502D6*4(CYP2D6*4), CYP2E1*5B (RsaI) polymorphism and homozygous mutant genotypes of CYP2E1*6 (Dra1) were found to be overrepresented in PD cases when compared to the controls. Risk was also found to be increased in patients carrying glutathione S-transferase T1 (GSTT1) null or homozygous variant genotypes of GSTP1. Significant association was observed for monoamine oxidase-B(MAO-B) variant allele G and PD, whereas no difference in genotype and allele frequencies was observed for manganese-superoxide dismutase (MnSOD), dopamine receptor-D2(DRD2), and dopamine transporter (DAT) genes between controls and PD cases. Genotype combinations characterized by the presence of two variant genotypes on their corresponding loci revealed that four combinations of GSTT1 null and MnSOD(-9Val) or GST null and MAOB-G or CYP2E1*5B and MAO-B-AG or CYP2E1*5B and DRD2 (Taq1A-het) genotypes in the patients exhibited severalfold higher and significant association with risk to PD. Our data suggest that polymorphism in the genes involved in detoxification and dopamine regulation may modulate the susceptibility to PD and could be important risk factors in the pathogenesis of PD.

Genes implicated in serotonergic and dopaminergic functioning predict BMI categories

OBJECTIVE

This study addressed the hypothesis that variation in genes associated with dopamine function (SLC6A3, DRD2, DRD4), serotonin function (SLC6A4, and regulation of monoamine levels (MAOA) may be predictive of BMI categories (obese and overweight + obese) in young adulthood and of changes in BMI as adolescents transition into young adulthood. Interactions with gender and race/ethnicity were also examined.

METHODS AND PROCEDURES

Participants were a subsample of individuals from the National Longitudinal Study of Adolescent Health (Add Health), a nationally representative sample of adolescents followed from 1995 to 2002. The sample analyzed included a subset of 1,584 unrelated individuals with genotype data. Multiple logistic regressions were conducted to evaluate the associations between genotypes and obesity (BMI > 29.9) or overweight + obese combined (BMI > or = 25) with normal weight (BMI = 18.5-24.9) as a referent. Linear regression models were used to examine change in BMI from adolescence to young adulthood.

RESULTS

Significant associations were found between SLC6A4 5HTTLPR and categories of BMI, and between MAOA promoter variable number tandem repeat (VNTR) among men and categories of BMI. Stratified analyses revealed that the association between these two genes and excess BMI was significant for men overall and for white and Hispanic men specifically. Linear regression models indicated a significant effect of SLC6A4 5HTTLPR on change in BMI from adolescence to young adulthood.

DISCUSSION

Our findings lend further support to the involvement of genes implicated in dopamine and serotonin regulation on energy balance.

Genetics and smoking cessation improving outcomes in smokers at risk

This article reviews evidence supporting the potential utility of a pharmacogenetic approach to the treatment of nicotine dependence. There is substantial evidence that nicotine dependence and smoking persistence are heritable, and are determined by a complex interplay of polygenic and environmental influences. The most robust evidence for specific genetic influences on nicotine dependence is found in studies of genetic variation in nicotine-metabolizing enzymes. Data also support the role of genes in the dopamine and opioid pathways as predictors of dependence and smoking relapse; however, the evidence for genetic associations is not always consistent. Emerging data from pharmacogenetic trials of nicotine-dependence treatment are promising, suggesting that genetic profiles of smokers someday may be used by providers to choose the type, dose, and duration of treatment for individual smokers. However, additional trials including larger and more diverse populations are needed before such data can be translated to practice to reduce smoking prevalence and tobacco-related disease.

Racially classified social group tobacco-related health disparities: what is the role of genetics?

Certain racially classified social groups suffer disproportionately from tobacco-caused morbidity and mortality. Recent advances in genetics are leading researchers to examine variables that may account for this. However, it is critical that investigators proceed with caution and utilize transdisciplinary approaches. A number of fundamental questions might be used to stimulate consensus building in this area of science. What is race and how should its complexity be operationalized? Is it possible/likely that pharmacogenetics will allow us to match smokers with cessation strategies based on a gene-psychological profile? What are the most important conceptual and methodological issues for a research agenda in this area?

A biopsychosocial approach to examining tobacco-related health disparities among racially classified social groups

AIMS

To articulate a broader, multi-causal model that incorporates psychosocial and environmental factors that can differ systematically across racially classified social groups (RCSGs) and impact biological pathways related to the development of tobacco-related diseases.

METHODS

This paper is built upon a review of the existing scientific literature on selected biopsychosocial factors (diet/nutrition, obesity, alcoholic intake, psychosocial stress, occupational/environmental exposures and exposure to other diseases and illnesses) and tobacco use in examining the biological contributions to differences in tobacco-related health outcomes among RCSGs.

FINDINGS

Recent work has focused on RCSG genetic variations as a possible explanation for differences in tobacco-related health disparities. It is argued in this paper that, given the genetic heterogeneity 'within' RCSGs, it is unlikely that across RCSG genetic variations are likely to be the major source of differences impacting biological pathways in tobacco-related health outcomes. The evidence shows that results, even at the level of within-population genetic variations, have been limited and often inconsistent. A conceptual framework is proposed to account for biological pathways related to the development of tobacco-related diseases.

CONCLUSIONS

Determinants of tobacco-related health disparities are not understood clearly. The contribution of biological factors may be important. Current efforts to determine biological differences in tobacco use and related diseases among RCSGs have focused primarily on genetic variations. However, this approach has limitations. An alternative biopsychosocial framework that examines the potential biological mechanisms through which life experiences and behavior might affect tobacco use and health outcomes in these population groups is needed, including those of life-style (e.g. diet/nutrition, obesity, physical exercise, alcohol consumption), psychosocial (e.g. stress and coping), occupational/environmental exposures and the presence of other diseases/illnesses.

Pharmacogenetic clinical trial of sustained-release bupropion for smoking cessation

This randomized, double-blinded, placebo-controlled trial examined genetic influences on treatment response to sustained-release bupropion for smoking cessation. Smokers of European ancestry (N = 291), who were randomized to receive bupropion or placebo (12 weeks) plus counseling, were genotyped for the dopamine D2 receptor (DRD2-Taq1A), dopamine transporter (SLC6A3 3' VNTR), and cytochrome P450 2B6 (CYP2B6 1459 CT) polymorphisms. Main outcome measures were cotinine-verified point prevalence of abstinence at end of treatment and at 2-, 6-, and 12-month follow-ups post quit date. Using generalized estimating equations, we found that bupropion, compared with placebo, was associated with significantly greater odds of abstinence at all time points (all p values<.01). We found a significant DRD2 x bupropion interaction (B = 1.49, SE = 0.59, p = .012) [corrected] and a three-way DRD2 x bupropion x craving interaction on 6-month smoking cessation outcomes (B = -0.45, SE = 0.22, p = .038), such that smokers with the A2/A2 genotype demonstrated the greatest craving reduction and the highest abstinence rates with bupropion. Furthermore, there was a significant DRD2 x CYP2B6 interaction (B = 1.43, SE = 0.56, p = .01), such that individuals with the DRD2-Taq1 A2/A2 genotype demonstrated a higher odds of abstinence only if they possessed the CYP2B6 1459 T/T or C/T genotype. Because the sample size of this study was modest for pharmacogenetic investigations, the results should be interpreted with caution. Although these results require replication, the data suggest preliminarily that the DRD2-Taq1A polymorphism may influence treatment response to bupropion for smoking cessation and, further, that exploration of gene x gene and gene x craving interactions in future, larger studies may provide mechanistic insights into the complex pharmacodynamics of bupropion.

Genetic polymorphisms in dopamine-related genes and smoking cessation in women: a prospective cohort study

Background

Genes involved in dopaminergic neurotransmission have been suggested as candidates for involvement in smoking behavior. We hypothesized that alleles associated with reduced dopaminergic neurotransmission would be more common in continuing smokers than among women who quit smoking.

Methods

The study included 593 women aged 26–65 years who participated in a twelve month smoking cessation trial conducted in 1993–1994. Participants were contacted three years after the trial to obtain updated smoking history and biological specimens. Seven polymorphisms were assessed in genes involved in dopamine synthesis (tyrosine hydoxylase [TH]), receptor activation (dopamine receptors [DRD2, DRD3, DRD4]), reuptake (dopamine transporter [SLC6A3]), and metabolism (catechol-o-methyltransferase [COMT]). Smoking cessation was assessed as "short-term" quitting (abstinence for the seven days before the conclusion of the trial) and "long-term" quitting (abstinence for the six months before a subsequent interview conducted several years later).

Results

We observed no association of any polymorphism with either short- or long-term quitting. Although some relative risk estimates were consistent with weak associations, either the direction of effect was opposite of that hypothesized, or results of the short- and long-term cessation endpoints differed. However, effect modification on smoking cessation was observed between DRD2 Taq1A and SLC6A3 VNTR polymorphisms, DRD3 Ser/Gly and d,1-fenfluramine, and DRD4 VNTR and d,1-fenfluramine.

Conclusion

Although these results fail to support prior findings of independent associations of these polymorphisms with smoking status, our exploratory findings suggestive of gene-gene and gene-treatment interactions warrants further investigation.

Polymorphisms of dopamine receptor/transporter genes and risk of non-small cell lung cancer

BACKGROUND

The dopaminergic pathway may be of interest in assessing risk of non-small cell lung cancer (NSCLC). Dopamine receptors are expressed in alveolar epithelial cells and human lung tumours, and dopamine inhibits both cell proliferation in vitro and growth of lung tumour xenografts in nude mice. Moreover, dopamine selectively inhibits the vascular permeability and angiogenic activity of vascular endothelial growth factor (VPF/VEGF). The bioavailability of dopamine is regulated by dopamine receptors D2 (DRD2), D4 (DRD4) and dopamine transporter 1 (DAT1/SLC6A3) genes.

METHODS

We have analysed 10 single nucleotide polymorphisms in DRD2, DRD4 and DAT1/SLC6A3 genes in relation to lung cancer risk in a case-control study of smoking subjects. The study subjects were 413 healthy individuals from general population and 335 NSCLC cases. Both cases and controls were Caucasians of Norwegian origin.

RESULTS

We demonstrate that DRD2 polymorphisms -141Cdel, 3208G>T, TaqIB; DRD4 -521C>T and DAT1/SLC6A3 -1476T>G are associated with a two- to five-fold increased NSCLC risk. The variant alleles of DRD2 1412A>G and 960C>G had protective effects.

CONCLUSION

The dopamine receptor/transport gene polymorphisms are associated with the risk of NSCLC among smokers. The data show that the polymorphisms resulting in lower dopamine bioavailability were associated with increased risk of NSCLC.

Genetic variation and shared biological susceptibility underlying comorbidity in neuropsychiatry

Genetic factors underlying alcoholism, substance abuse, antisocial and violent behaviour, psychosis, schizophrenia and psychopathy are emerging to implicate dopaminergic and cannabinoid, but also monoaminergic and glutamatergic systems through the maze of promoter genes and polymorphisms. Candidate gene association studies suggest the involvement of a range of genes in different disorders of CNS structure and function. Indices of comorbidity both complicate the array of gene-involvement and provide a substrate of hazardous interactivity. The putative role of the serotonin transporter gene in affective-dissociative spectrum disorders presents both plausible genetic variation and complication of comorbidity The position of genetic variation is further complicated through ethnic, contextual and social factors that provide geometric progressions in the comordity already underlying diagnostic obstacles. The concept of shared biological susceptibility to two or more disorder conditions of comorbidity seems a recurring observation, e.g., bipolar disorder with alcoholism or schizophrenia with alcohol/substance abuse or diabetes with schizopsychotic disorder. Several lines of evidence seem to suggest that the factors influencing variation in one set of symptoms and those affecting one or more disorders are observed to a marked extent which ought to facilitate the search for susceptibility genes in comorbid brain disorders. Identification of regional genetic factors is awaited for a more compelling outline that ought eventually to lead to greater efficacy of symptom-disorder arrangements and an augmentation of current pharmacological treatment therapies.

Possible interaction between MAOA and DRD2 genes associated with antisocial alcoholism among Han Chinese men in Taiwan

Both monoamine oxidase A (MAOA) and dopamine D(2) receptor (DRD2) genes have been considered as candidate genes for antisocial personality disorder with alcoholism (Antisocial ALC) [Parsian, A., 1999. Sequence analysis of exon 8 of MAO-A gene in alcoholics with antisocial personality and normal controls. Genomics. 45, 290-295.; Samochowiec, J., Lesch, K.P., Rottmann, M., Smolka, M., Syagailo, Y.V., Okladnova, O., Rommelspacher, H., Winterer, G., Schmidt, L.G., Sander, T., 1999. Association of a regulatory polymorphism in the promoter region of the monoamine oxidase A gene with antisocial alcoholism. Psychiatry. Res. 86, 67-72.; Schmidt, L.vG., Sander, T., Kuhn, S., Smolka, M., Rommelspacher, H., Samochowiec, J., Lesch, K.P., 2000. Different allele distribution of a regulatory MAO-A gene promotor polymorphism in antisocial and anxious-depressive alcoholics. J. Neural .Transm. 107, 681-689.]. However, the association between alcoholism and MAOA or DRD2 gene has not been universally accepted [Lee, J.F., Lu, R.B., Ko, H.C., Chang, F.M., Yin, S.J., Pakstis, A.J., Kidd, K.K., 1999. No association between DRD(2) locus and alcoholism after controlling the ADH and ALDH genotypes in Chinese Han population. Alcohol. Clin. Exp. Res. 23, 592-599.; Lu, R.B., Lin, W.W., Lee, J.F., Ko, H.C., Shih, J.C., 2003. Neither antisocial personality disorder nor antisocial alcoholism association with MAOA gene among Han Chinese males in Taiwan. Alcohol. Clin. Exp. Res. 27, 889-893.]. Since dopamine is metabolized to 3,4-dihydroxyphenyl-acetaldehyde (DOPAL) via monoamine oxidase (MAO) [Westerink, B.H., de Vries, J.B., 1985. On the origin of dopamine and its metabolite in predominantly noradrenergic innervated brain areas. Brain. Res. 330, 164-166.], the interaction between MAOA and DRD2 genes might be related to Antisocial ALC. The present study aimed to determine whether Antisocial ALC might be associated with the possible interactions of DRD2 gene with MAOA gene. Of the 231 Han Chinese subjects who were recruited for the study, 73 participants were diagnosed with Antisocial ALC and 158 subjects were diagnosed with antisocial personality disorder without alcoholism (Antisocial Non-ALC). The DRD2 TaqI A and MAOA-uVNTR (variable number of tandem repeat located upstream) polymorphisms were not found to be associated with Antisocial ALC. However, an association between DRD2 TaqI A polymorphisms and Antisocial ALC was shown only after stratification for the MAOA-uVNTR 4-repeat polymorphism. Additionally, after multiple logistic regressions, we found that, under stratification of MAOA-uVNTR 4-repeat polymorphism and in comparison with the DRD2 A1/A1 genotype as a reference group, the DRD2 A1/A2 genotype has a possible protective effect against alcoholism in individuals with antisocial personality disorder (ASPD). We concluded that the possible interactions between MAOA-uVNTR polymorphism and DRD2 TaqI A polymorphism might be related to Antisocial ALC among Han Chinese men in Taiwan.

Association of specific haplotypes of neurotrophic tyrosine kinase receptor 2 gene (NTRK2) with vulnerability to nicotine dependence in African-Americans and European-Americans

BACKGROUND

The gene encoding neurotrophic tyrosine kinase receptor 2 (NTRK2) has been localized to a region on chromosome 9q22-q23 that showed a "suggestive" linkage to nicotine dependence (ND) in our previous linkage analyses. However, no association of NTRK2 with ND has been identified.

METHODS

Family-based association analyses of 2037 participants (1366 African Americans [AA], 671 European Americans [EA]) representing 602 nuclear families were performed to evaluate association of nine single nucleotide polymorphisms (SNPs) within NTRK2 with ND.

RESULTS

Individual SNP-based association analysis indicated that in the EA sample, SNPs rs1659400 and rs1187272 were significantly associated with at least one adjusted ND measure. Haplotype analysis revealed that even after Bonferroni correction, the haplotype T-T-A of rs1659400-rs1187272-rs1122530 had a highly significant positive association, with adjusted ND measures in the EA sample (max Z = 3.78; p = .0001, frequency 59.9%). We further identified a major haplotype, T-G-C-A-A (26%), formed by rs993315-rs736744-rs920776-rs4075274-rs729560, which showed a significant positive association (max Z = 2.97, p = .003) with adjusted ND measures in the AA sample.

CONCLUSIONS

These results strongly suggest that NTRK2 is a susceptibility gene for ND. These findings imply that NTRK2 plays a role in the etiology of ND and represents an important biological candidate for further investigation.

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.

The genetics of nicotine dependence: Relationship to pancreatic cancer

Smoking of tobacco products continues to be a major cause of worldwide health problems. Epidemiological studies have shown that tobacco smoking is the greatest risk factor for the development of pancreatic cancer. Smokers who are able to quit smoking can reduce their risk of pancreatic cancer by nearly 50% within two years, however, their risk of developing pancreatic cancer remains higher than that of non-smokers for 10 years. Nicotine is the major psychoactive substance in tobacco, and is responsible for tobacco dependence and addiction. Recent evidence suggests that individuals have genetically based differences in their ability to metabolize nicotine, as well as genetic differences in the psychological reward pathways that may influence individual response to smoking initiation, dependence, addiction and cessation. Numerous associations have been reported between smoking behavior and genetic polymorphisms in genes that are responsible for nicotine metabolism. In addition, polymorphisms in genes that encode neurotransmitters and transporters that function in psychological reward pathways have been implicated in differences in smoking behavior. However, there is a large degree of between-study variability that demonstrates the need for larger, well-controlled case-control studies to identify target genes and deduce mechanisms that account for the genetic basis of inter-individual differences in smoking behavior. Understanding the genetic factors that increase susceptibility to tobacco addiction may result in more effective tobacco cessation programs which will, in turn, reduce the incidence of tobacco related disease, including pancreatic cancer.

Héritabilité et gènes candidats dans le tabagisme

HERITABILITY INDICATORS: Genetic studies of tobacco use can be useful to understand the physiopathology of nicotine dependence and potentially to prevent it. Twin and adoption studies have clearly shown the role of genetic factors in tobacco use at different stages. Genetic factors account for 55% (range: 11-84%) of the smoking initiation and 61% (range: 52-71%) for persistence. Age at onset and intensity of smoking are also influenced by genetic factors. Estimation of the heritability of initiation/persistence of smoking varies by gender. It is estimated as 66%/61% for women and 49%/61% for men respectively. In adolescent twin studies, heritability estimated the liability of lifetime or current use of tobacco to be more than 80%, while the heritability for initiation being between 11% and 59%. Heavy smoking is also influenced by genetic factors, especially when patients are co-abusing alcohol or coffee. Genetics findings - Advances in molecular genetics identified different candidate genes for tobacco use mainly involving neurotransmission of neuromodulators. Because of the brain reward effects of nicotine on the mesolimbic system, the genes involved in the dopaminergic transmission receive specific attention. Genetic polymorphisms of the dopamine D1, D2, D4 and D5 receptors, dopamine transporter (DAT1) and dopamine B-hydroxylase (DBH) have been associated at least once with clinical aspects of tobacco use (initiation, dependence and intensity) and temperament traits as novelty seeking, the latter being lower in smokers and thus considered as a vulnerable marker in accordance with the reinforcement effect of nicotine. Regarding interaction between nicotine use and anxiety and depression, the gene encoding for the serotonin transporter (5-HTT) may constitute a candidate gene. Because of interindividual bioavailability of nicotine, genetic polymorphisms of metabolism enzymes have also been analysed. Some variants of the cytochrome P450 seem to be more frequent among dependent smokers than controls or ever smokers (CYP2A6) and heavier smokers (CYP2D6). Genetic research might be suitable for a therapeutic approach and identify subjects at high risk for nicotine dependence.

Cholinergic nicotinic receptor genes implicated in a nicotine dependence association study targeting 348 candidate genes with 3713 SNPs

Nicotine dependence is one of the world's leading causes of preventable death. To discover genetic variants that influence risk for nicotine dependence, we targeted over 300 candidate genes and analyzed 3713 single nucleotide polymorphisms (SNPs) in 1050 cases and 879 controls. The Fagerström test for nicotine dependence (FTND) was used to assess dependence, in which cases were required to have an FTND of 4 or more. The control criterion was strict: control subjects must have smoked at least 100 cigarettes in their lifetimes and had an FTND of 0 during the heaviest period of smoking. After correcting for multiple testing by controlling the false discovery rate, several cholinergic nicotinic receptor genes dominated the top signals. The strongest association was from an SNP representing CHRNB3, the beta3 nicotinic receptor subunit gene (P = 9.4 x 10(-5)). Biologically, the most compelling evidence for a risk variant came from a non-synonymous SNP in the alpha5 nicotinic receptor subunit gene CHRNA5 (P = 6.4 x 10(-4)). This SNP exhibited evidence of a recessive mode of inheritance, resulting in individuals having a 2-fold increase in risk of developing nicotine dependence once exposed to cigarette smoking. Other genes among the top signals were KCNJ6 and GABRA4. This study represents one of the most powerful and extensive studies of nicotine dependence to date and has found novel risk loci that require confirmation by replication studies.

Dopamine D2 receptor polymorphisms in inflammatory bowel disease and the refractory response to treatment

Dopamine and its receptors may be involved in inflammatory reaction. The availability of this molecule depends on its receptors. The DRD2 gene, which codifies for the D2 dopamine receptor, has several polymorphisms. In this study, the DRD2 TaqIA polymorphism, which confers a decreased receptor density, was evaluated in 313 individuals including 220 inflammatory bowel disease patients (143 patients with Crohn's disease and 77 with ulcerative colitis) and in 93 healthy blood donors. The analysis was carried out by PCR-RFLP techniques. The frequencies of A (1) A (1) and A (2) A (2) genotypes were similar among Crohn's disease, ulcerative colitis patients, and health controls. Also, the genotype frequency was similar in different groups of disease localization, behavior, and age of disease onset. However, the Crohn's disease patients carriers of A (2) A (2) genotype showed a lower risk for development refractory Crohn's disease (37 out 65) than A (1) A (1) and A (1) A (2) carriers (28 out of 65) [(OR=0.4, 95% CI 0.21-0.87; p=0.02)]. Our results support an involvement of the dopamine receptor in inflammatory bowel disease and suggest a new potential target for therapy in refractory Crohn's disease patients.

Pharmacogenetics and nicotine addiction treatment

This review focuses on the current status of, and future directions for, pharmacogenetic research on nicotine dependence and smoking cessation treatment. Pharmacological treatment involving nicotine replacement therapy and bupropion for nicotine addiction and smoking cessation has been shown to be efficacious when provided in combination with behavioral support. Cessation rates remain somewhat modest, however, and one possibility is that success rates may be enhanced by offering treatments tailored to an individual's genotype. Nonetheless, research on this issue remains in its infancy, and although the scope for individualized treatment tailored to genotype is promising, there are substantial practical, ethical and social considerations that must be addressed before such research is translated into clinical practice.

Association between the DRD2 A1 allele and response to methadone and buprenorphine maintenance treatments

The TaqI A polymorphism (A(1)) of the dopamine D(2) receptor gene (DRD2), although not a specific predictor of opioid dependence, has been strongly associated with high levels of prior heroin use and poor treatment outcomes among methadone maintenance patients. The aims of this study were to confirm these findings via a retrospective analysis of A(1) allele frequency in methadone (n = 46) and buprenorphine (n = 25) patients, and non-opioid-dependent controls (n = 95). Subjects were genotyped at the DRD2 TaqI A locus using PCR amplification followed by TaqI restriction enzyme digestion and gel electrophoresis. For methadone and buprenorphine subjects, heroin use (prior to treatment), treatment outcomes, and withdrawal occurrence were determined from comprehensive case notes. No significant differences in A(1) allele frequency (%) were observed between: methadone (19.6%), buprenorphine (18.0%), and control (17.9%) groups (P > 0.7); successful and poor treatment outcome groups, methadone: 20.0% and 19.2%, respectively (P = 1.0); buprenorphine: 18.4% and 20.0%, respectively (P = 1.0). Also, there were no significant relationships between TaqI A genotype and prior heroin use (P = 0.47). However, among the successful methadone subjects, significantly fewer A(1) allele carriers experienced withdrawal than non-A(1) carriers (P = 0.04). In conclusion, the DRD2 genotype effects did not affect opioid maintenance treatment outcomes. This suggests the need for a further prospective investigation into the role of the DRD2 A(1) allele in heroin use and response to maintenance pharmacotherapies for opioid dependence.

Association between glutathione S-transferase pi polymorphisms and survival in patients with advanced nonsmall cell lung carcinoma

BACKGROUND

Glutathione S-transferase (GST) pi (GSTP1) is a detoxification enzyme with substrate specificity for both exogenous carcinogens and chemotherapy agents. Genetic polymorphisms of GSTP1 exon 5 (Ile105Val) and exon 6 (Ala114Val) appear to reduce this enzyme's activity. Previously, the authors reported that the exon 6 variant was associated with an increased risk of lung carcinoma, particularly among men, younger patients, and ever smokers. In this study, the authors hypothesized that variant GSTP1 genotype would result in reduced inactivation of chemotherapy agents and improved survival in patients with advanced-stage nonsmall cell lung carcinoma (NSCLC), a population that is likely to receive platinum-based chemotherapy.

METHODS

Patients with Stage III and IV NSCLC who were enrolled in a molecular epidemiology study were identified, and a polymerase chain reaction-restriction fragment length polymorphism assay was used to genotype GSTP1 exons 5 and 6 in 424 patients and 425 patients, respectively.

RESULTS

Patients who had the exon 6 variant genotype (Ala/Val or Val/Val) had significantly better survival compared with patients who had the wild type genotype (Ala/Ala; P = 0.037), with median survival of 16.1 months and 11.4 months, respectively. Multivariate analysis revealed a reduced adjusted hazard ratio (HR) of death associated with the exon 6 variant genotype of 0.75 (95% confidence interval [95% CI], 0.54-1.05). This protective association was observed in younger patients (younger than age 62 yrs; HR, 0.59; 95% CI, 0.57-0.97) and in males (HR, 0.64; 95% CI, 0.41-0.99). GSTP1 exon 5 genotype was not associated with survival.

CONCLUSIONS

GSTP1 exon 6 variant genotypes may be associated with improved survival among patients with Stage III and IV NSCLC.

Interaction between variation in the D2 dopamine receptor (DRD2) and the neuronal calcium sensor-1 (FREQ) genes in predicting response to nicotine replacement therapy for tobacco dependence

We have previously demonstrated that a functional dopamine D2 receptor promoter variant (DRD2 -141 Ins/Del) predicts response to nicotine replacement therapy (NRT). The present study extends this finding in the same population of 363 NRT-treated subjects, by examining variation in the gene encoding the neuronal calcium sensor-1 protein (FREQ), which functions to regulate D2 receptor desensitization. The results indicate a statistically significant interaction effect of DRD2-141 and FREQ genotypes on abstinence at the end of the NRT treatment phase; 62% of the smokers with at least one copy of the DRD2 -141 Del allele and two copies of the FREQ rs1054879 A allele were abstinent from smoking, compared to 29-38% abstinence rates for other smokers in the trial. This result suggests that the interaction between variation in the DRD2 and FREQ genes, which both encode components of the D2 dopamine receptor signal transduction pathway, impacts the efficacy of NRT.

Role of functional genetic variation in the dopamine D2 receptor (DRD2) in response to bupropion and nicotine replacement therapy for tobacco dependence: results of two randomized clinical trials

Although bupropion and nicotine replacement therapy (NRT) are efficacious tobacco dependence treatments, there is substantial interindividual variability in therapeutic response and most smokers relapse. Pharmacogenetics research may improve treatment outcomes by identifying genetic variants predictive of therapeutic response. We investigated the roles of two functional genetic variants in the dopamine D2 receptor (DRD2) gene in response to pharmacotherapy for tobacco dependence among participants in two randomized clinical trials with a 6-month follow-up period: a double-blind placebo-controlled trial of bupropion (n=414) and an open label trial of transdermal nicotine vs nicotine nasal spray (n=368). At the end of the treatment phase, a statistically significant (p=0.01) interaction between the DRD2 - 141C Ins/Del genotype and treatment indicated a more favorable response to bupropion among smokers homozygous for the Ins C allele compared to those carrying a Del C allele. By contrast, smokers carrying the Del C allele had statistically significantly (p=0.006) higher quit rates on NRT compared to those homozygous for the Ins C allele, independent of NRT type. The C957T variant was also associated (p=0.03) with abstinence following NRT. These results suggest that bupropion may be the preferred pharmacologic treatment for smokers homozygous for the DRD2 - 141 Ins C allele, while NRT may be more beneficial for those who carry the Del C allele. Study findings require confirmation in additional larger samples before they are applied in practice.

Genetic Influences on Smoking

Smoking is a complex behavior influenced by environ-mental and genetic factors. A number of twin studies demonstrate genetic influences on multiple aspects of smoking including initiation, dependence, continuation, amount consumed, and cessation. It is likely that this genetic risk involves a complex interaction between multiple genes in different biologic pathways. These may include genes involved in the general aspect of dependence (eg, genes within the dopaminergic system) and those more specific to nicotine dependence (eg, genes encoding nicotinic acetylcholine receptors and nicotine-metabolizing enzymes). Genome-wide linkage analyses and gene association studies provide approaches for identifying these genes. This review provides a brief highlight of data from some of the candidate gene association studies and discusses some of the discrepancies found in the literature. In addition, the authors have reviewed some recent studies examining how genetic variations in drug-metabolizing enzymes and drug targets can influence the response to treatment with drugs such as bupropion and nicotine.These latter studies provide the potential for maximizing treatment efficacy by individualizing the type, dosage, and duration of the treatment based on an individual's genotype/phenotype. Significant advances have been made in understanding the genetic contribution to smoking behaviors. These and future studies will provide potential directions for novel prevention and treatment strategies.

The association between the DRD2 TaqI A polymorphism and smoking cessation in response to acupuncture in Koreans

OBJECTIVES

The response to acupuncture is presumed to differ with the individual; this variation might be due to genetic differences. Therefore, we examined whether the DRD2 TaqI A polymorphism is associated with the response to acupuncture in the treatment of smoking cessation in a Korean population.

SUBJECTS

A total of 231 healthy Korean male smokers participated in this study.

INTERVENTIONS

The subjects underwent three manual auricular acupuncture treatments in one week.

DESIGN AND OUTCOME MEASURES

After 1 week, high and low responders to the acupuncture treatment were selected according to their cigarette consumption and the desire to smoke. A DRD2 TaqI A restriction enzyme fragment length polymorphism (RFLP) study examined genomic DNA extracted from blood samples.

RESULTS

The proportions of high, intermediate, and low responders were 28.6, 55.4, and 16.0%, respectively. The RFLP study showed that the distribution of the DRD2*A genotype and allele frequencies differed significantly between the high and low responders (chi(2) test, p = 0.031 and 0.016, respectively), and that high responders had a higher DRD2*A2 allele frequency than low responders.

CONCLUSIONS

Our findings suggest that DRD2 TaqI A polymorphism is related to acupuncture response in smoking cessation treatment.

Genotype combinations for monoamine oxidase-B intron 13 polymorphism and dopamine D2 receptor TaqIB polymorphism are associated with ever-smoking status among men

Tobacco smoke inhibits monoamine oxidase-B (MAO-B) activity in vitro and in vivo, suggesting that MAO-B inhibition is a possible contributing factor to tobacco smoke addiction. Thus, MAO-B is a possible candidate gene for predisposition to smoking. The TaqIB polymorphism for the Dopamine D2 Receptor gene (DRD2) has been previously associated with smoking status, although with some contradictory results. We investigated whether genetic variants of MAO-B intron 13 and DRD2 TaqIB polymorphism could be associated with smoking status among control subjects. There was no association of the intron 13 polymorphism itself with smoking status in either men or women. Similarly, no association with smoking status was observed for the TaqIB polymorphism of DRD2 itself. However, among men, there was an interaction between MAO-B intron 13 polymorphism and the DRD2 TaqIB polymorphisms, in which subjects carrying MAO-B allele A and genotype B12 of DRD2 were 2.50 times (95% CI=1.05-5.95) more likely to be ever-smokers than the pool of men carrying all other genotype combinations. These results demonstrate that particular combinations of genotypes for MAO-B and DRD2 genes are associated with significantly higher risk for smoking behavior in men, but not in women.

Significant association of interleukin 8 -251T/A polymorphism with smoking behavior in a Japanese population

Accumulating evidence indicates that the genotype may impact on smoking behavior and a deeper understanding of the molecular basis could lead to more effective strategies for preventing initiation of the habit and to help smokers to quit. Since individual variation in airway responsiveness to cigarette smoke might have an important influence, we have focused on associations between smoking behavior and polymorphisms affecting the inflammatory cytokine, IL-8. In the present study, 453 Japanese non-cancer outpatients (191 males and 262 females) who visited Aichi Cancer Center Hospital were genotyped for the IL8 -251T/A polymorphism, and age- and sex-adjusted odds ratios (aORs) for smoking were estimated using a logistic regression model. The aORs for IL8 251-TA and AA combined, genotypes associated with high production of IL-8, were 0.52 (95% CI 0.33-0.82, P=0.004) for ever having smoked and 0.55 (0.33-0.92, P=0.023) for being a current smoker. Our results suggest that the inflammatory-prone genotype of IL8 may act to deter initiation or characteristics of the smoking habit.

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.

Dopamine receptor DRD2 genotype and smoking cessation outcome following treatment with bupropion SR

The A1 allele of the dopamine D2 receptor gene (DRD2) is associated with a reduced number of dopamine binding sites in the brain and with the increased likelihood of substance abuse and addictive behavior. In a study of smokers enrolled in an open-label, randomized effectiveness trial, we investigated whether variants in the DRD2 receptor gene are associated with smoking cessation outcomes following treatment with a combination of bupropion SR and behavioral counseling. Adherence to treatment and point-prevalent smoking status were assessed at 3 and 12 months, respectively, following a target quit date. Compared to women who carry both A2 alleles, women with at least one A1 allele were more likely to report having stopped taking bupropion due to medication side effects (odds ratio (OR)=1.91, 95% confidence interval (CI)=1.01-3.60; P<0.04) and at 12 months were somewhat more likely to report smoking (OR=0.76, 95% CI=0.56-1.03; P<0.076). Significant associations or trends were not observed in men. In women, individual variability in responsiveness to bupropion-based treatment may be partially due to differences in genetic variants influencing dopamine receptor function.

Dopamine receptor (DRD2) genotype‐dependent effects of nicotine on attention and distraction during rapid visual information processing

The effects of nicotine, distractor type, and dopamine type-2 receptor (DRD2) genotype on rapid visual information processing (RVIP) task performance were assessed in habitual smokers. Four RVIP tasks differed in terms of distractor location (central vs. peripheral) and distractor type (numeric vs. emotional). Each participant performed each of the tasks on two different days, once while wearing an active nicotine patch and once while wearing a placebo patch. Overall, the nicotine patch produced more accurate detection of and faster reaction times to target sequences; however, these effects varied with distractor type and genotype. Nicotine speeded reaction time more with left-visual-field (LVF) than right-visual-field (RVF) emotional distractors but speeded reaction time more with RVF than LVF numeric distractors, especially when the distractor digit matched the target sequence in terms of numeric oddness or evenness. Nicotine tended to facilitate performance more in individuals with at least one A1 allele than in homozygous A2A2 individuals, especially with numeric distractors presented to the left hemisphere. Nicotine tended to reduce distraction by negative stimuli more than other types of stimuli. Few gender differences were observed. The overall pattern of results was consistent with the view that nicotine modulates selective attention or subsequent information processing in a manner that depends partly on the emotional versus numeric nature of task distractors, DRD2 genotype, and the brain hemisphere that initially processes the distractors (visual field of distractor).

Effects of dopamine D2 receptor (DRD2) and transporter (SLC6A3) polymorphisms on smoking cue-induced cigarette craving among African-American smokers

Cue-induced craving for addictive substances has long been known to contribute to the problem of persistent addiction in humans. Research in animals over the past decade has solidly established the central role of dopamine in cue-induced craving for addictive substances, including nicotine. Analogous studies in humans, however, are lacking, especially among African-American smokers, who have lower quit rates than Caucasian smokers. Based on the animal literature, the study's objective was to test the hypothesis that smokers carrying specific variants in dopamine-related genes previously associated with risk for addictive behaviors would exhibit heightened levels of cigarette craving following laboratory exposure to cues. To this end, cigarette craving was induced in healthy African-American smokers (n=88) through laboratory exposure to smoking cues. Smokers carrying either the DRD2 (D2 dopamine receptor gene) TaqI A1 RFLP or the SLC6A3 (dopamine transporter gene) 9-repeat VNTR polymorphisms had stronger cue-induced cravings than noncarriers (Ps <0.05 and 0.01, respectively). Consistent with the separate biological pathways involved (receptor, transporter), carriers of both polymorphisms had markedly higher craving responses compared to those with neither (P<0.0006), reflecting additive effects. Findings provide support for the role of dopamine in cue-induced craving in humans, and suggest a possible genetic risk factor for persistent smoking behavior in African-American smokers.

Nicotine addiction through a neurogenomic prism: ethics, public health, and smoking

Studies are under way to examine the neurogenetic factors contributing to smoking behaviors. The combined approaches of genomics, molecular biology, neuroscience, and pharmacology are expected to fuel developments in pharmacogenetics, to create new genetic tests, and ultimately to provide the basis for innovative strategies for smoking cessation and prevention. The emergence of a neurogenomic understanding of nicotine addiction is likely to induce fundamental changes in popular, clinical, and public health views of smoking, which could significantly shape existing practices and policies to reduce tobacco use. Still a nascent area of research, nicotine addiction provides an excellent case study through which to anticipate key ethical and policy issues in both behavioral genetics and the neurogenomics of addictive behaviors.

Validity of retrospective assessments of nicotine dependence: a preliminary report

Information about levels of nicotine dependence in ex-smokers when they smoked, or in current smokers at an earlier date, is useful for clinical and research purposes. To estimate the accuracy of retrospective reports of dependence, 28 individuals who completed either the Fagerström Tolerance Questionnaire (FTQ) or Fagerström Test for Nicotine Dependence (FTND) in smoking cessation trials conducted 5 to 12 years earlier were asked to respond again to the same questions, thinking back to their smoking behavior just prior to their on-study quit attempt. Concordance and Kappa values for the items ranged from 50.0% to 95.0% and 0.00 to 0.92, respectively. The mean difference between the baseline and follow-up total scale scores was 0.05 for the FTQ and 0.38 for the FTND, and the correlation between these assessments was 0.62 for the FTQ (p<0.005) and 0.72 for the FTND (p<0.05). These preliminary results suggest that retrospectively assessed FTQ/FTND scale scores have acceptable reliability.

The dopamine D2 receptor C32806T polymorphism (DRD2 Taq1A RFLP) exhibits no association with smoking behaviour in a healthy UK population

A single nucleotide polymorphism (SNP) in the Taq1A site near the DRD2 gene has been associated in several studies with smoking behaviour. We genotyped 732 current smokers (241 low, one to nine cigarettes a day, 250 mid, 10-19 cigarettes, 241 high, 20+cigarettes) and 243 never-smokers at this site (C32806T), to test for effects on smoking initiation and amount of tobacco consumed. No significant association between minor allele frequency and smoking status was detected. Multiple regression analysis including DRD2 genotype, sex, age and alcohol consumption as predictors showed that level of cigarette consumption was associated with sex (p=0.003) and age (p=0.002) but not with alcohol consumption (p=0.25) or DRD2 genotype (p=0.76).

Barriers to translating emerging genetic research on smoking into clinical practice. Perspectives of primary care physicians

OBJECTIVE

Smoking remains the leading cause of preventable death nationally. Emerging research may lead to improved smoking cessation treatment options, including tailoring treatment by genotype. Our objective was to assess primary care physicians' attitudes toward new genetic-based approaches to smoking treatment.

DESIGN AND SETTING

A 2002 national survey of primary care physicians. Respondents were randomly assigned a survey including 1 of 2 scenarios: a scenario in which a new test to tailor smoking treatment was described as a "genetic" test or one in which the new test was described as a "serum protein" test.

PARTICIPANTS

The study sample was randomly drawn from all U.S. primary care physicians in the American Medical Association Masterfile (e.g., those with a primary specialty of internal medicine, family practice, or general practice). Of 2,000 sampled physicians, 1,120 responded, yielding a response rate of 62.3%.

MEASUREMENTS AND MAIN RESULTS

Controlling for physician and practice characteristics, describing a new test as "genetic" resulted in a regression-adjusted mean adoption score of 73.5, compared to a score of 82.5 for a nongenetic test, reflecting an 11% reduction in physicians' likelihood of offering such a test to their patients.

CONCLUSIONS

Merely describing a new test to tailor smoking treatment as "genetic" poses a significant barrier to physician adoption. Considering national estimates of those who smoke on a daily basis, this 11% reduction in adoption scores would translate into 3.9 million smokers who would not be offered a new genetic-based treatment for smoking. While emerging genetic research may lead to improved smoking treatment, the potential of novel interventions will likely go unrealized unless barriers to clinical integration are addressed.

Treating Tobacco Dependence: State of the Science and New Directions

Despite almost two decades of intensive tobacco control efforts, nearly one quarter of Americans continue to smoke. The two United States Food and Drug Administration–approved medications used to treat tobacco dependence, bupropion and nicotine replacement therapy, are effective for only a fraction of smokers. Investigations of medications approved for affective disorders and other forms of substance abuse, such as fluoxetine and naltrexone, have yielded mixed results as tobacco dependence treatments. A particular challenge in tobacco dependence treatment is the development of effective approaches for smokers with unique needs, such as cancer patients and pregnant women. Despite new developments in these areas, significant gaps in knowledge and practice remain. Basic research in the neurobiologic and genetic basis of nicotine dependence offers promise for the development of novel and more effective treatment approaches. For example, emerging research in pharmacogenetics explores how genetic variation in drug-metabolizing enzymes and drug targets modifies response to pharmacotherapy. These discoveries could someday help practitioners to individualize the type, dosage, and duration of tobacco dependence treatment based on genotype, and maximize the efficacy.

The use of race variables in genetic studies of complex traits and the goal of reducing health disparities: A transdisciplinary perspective

The use of racial variables in genetic studies has become a matter of intense public debate, with implications for research design and translation into practice. Using research on smoking as a springboard, the authors examine the history of racial categories, current research practices, and arguments for and against using race variables in genetic analyses. The authors argue that the sociopolitical constructs appropriate for monitoring health disparities are not appropriate for use in genetic studies investigating the etiology of complex diseases. More powerful methods for addressing population structure exist, and race variables are unacceptable as gross proxies for numerous social/environmental factors that disproportionately affect minority populations. The authors conclude with recommendations for genetic researchers and policymakers, aimed at facilitating better science and producing new knowledge useful for reducing health disparities.

Chemoprevention of lung cancer

Lung cancer remains a major cause of mortality worldwide, despite advances in surgery, radiotherapy and chemotherapy. Most patients present with advanced disease, and early detection approaches are still experimental. Chemoprevention strategies are therefore essential. Chemoprevention can be defined as the use of specific natural or synthetic chemical agents to reverse, suppress or prevent progression to invasive cancer. The present review will provide an update on lung cancer clinical chemoprevention trials as well as the molecular basis of lung carcinogenesis. A better knowledge of lung carcinogenesis is obviously fundamental to improve chemoprevention strategies. Identification of molecular defects involved in premalignant lesions and/or invasive cancer could lead to clinical studies with new molecular-targeted agents (mainly tyrosine kinase inhibitors, farnesyl-transferase inhibitors and/or antiangiogenic molecules) and the development of surrogate biomarkers. Such biomarkers would be essential to detect high-risk patients, select adequate chemoprevention strategies and monitor drug efficacy. New chemoprevention trials are planned with collaborative efforts of researchers involved in fundamental or clinical studies.

Criteria to rationalize population screening to control oral cancer

Screening populations for the early detection of asymptomatic malignancies and potential malignancies are intuitively attractive strategies to control or reduce the burden of oral cancer on society. Subsequent preventive and/or therapeutic measures must, however, be substantiated by prospective randomized controlled trials (RCT) to markedly improve patient outcomes to reconcile such usages of 'scarce' healthcare resources. This strategic objective is more likely to be achieved by adopting the precedent established by cardiology, where prevention is emphasized over the treatment of occult lesions. For example, the screening identification of individuals at high oral carcinogenic risk will offer potential educational opportunities to change their behaviors, and/or optimize the implementation of contemporary preventive and therapeutic measures for non-compliant individuals. The imperative to substantiate the effectiveness of the screening assays (tests) by prospective RCT also cannot be ignored to safeguard the public against potential false-negative or false-positive diagnoses.

Stress-induced cigarette craving: effects of the DRD2 TaqI RFLP and SLC6A3 VNTR polymorphisms

Animal models have long implicated dopamine in stress-induced craving for a variety of addictive substances. However, translational studies of dopamine, stress and craving in humans are lacking. Based on the animal literature, this study's objective was to test the hypothesis that cigarette smokers carrying specific variants in dopamine-related genes would have heightened levels of cigarette craving following exposure to a laboratory stressor. Cigarette craving induced by controlled exposure to a laboratory stressor was assessed in healthy adult smokers (n=108) recruited by advertisement. Significantly stronger stress-induced cigarette craving was found for individuals carrying either the DRD2 (D2 dopamine receptor gene) A1, or the SLC6A3 (dopamine transporter gene) nine-repeat allelic variants. Stress-induced craving was markedly higher for those carrying both alleles, compared to those with neither, consistent with the separate biological pathways involved (receptor, transporter). Findings provide strong support for the possibility that dopamine involvement in stress-induced craving well established in animal models also applies to humans, and suggest a potential genetic risk factor for persistent smoking behavior.

Cigarette smoking and nicotine dependence

Tobacco use is the single most preventable cause of death, disability, and disease in the United States and is projected to be the leading cause of death and disability across all developed countries by the year 2020. Understanding nicotine dependence, its causes, consequences, and effective treatments is critical to the nation's public health agenda. This article presents a brief overview of nicotine dependence with particular emphasis placed on understanding what nicotine dependence is, why it occurs, how it is measured, and how it can be managed through effective treatments.

Genetic variation in dopaminergic pathways and short-term effectiveness of the nicotine patch

Polymorphisms in the dopamine D2 receptor (DRD2 C/T and DRD2 A/G) and in dopamine beta hydroxylase (DBH A/G) have been implicated in modulation of smoking and other reward-seeking behaviours. We hypothesized that these alleles would predict the outcome of nicotine patch therapy for smoking cessation. In 1991-93, we performed a randomized controlled trial of the nicotine patch on 1686 heavy smokers (> or = 15 cigarettes/day). In 1999-2000, we contacted 1532 of the 1612 subjects still available; 767 (50%) completed a questionnaire and gave a blood sample. In the 755 cases in which DNA was successfully genotyped, we examined associations between the polymorphisms in DRD2 and DBH, and smoking cessation. At 1 week, the patch was more effective for smokers with DRD2 CT/TT genotype [patch/placebo odds ratio (OR) 2.8, 95% confidence interval (CI) 1.7-4.6] than with CC (OR 1.4, 0.9-2.1; P for difference in ORs 0.04). Smokers with both DRD2 CT/TT and DBH GA/AA genotypes had an OR of 3.6 (2.0-6.5) compared to 1.4 (1.0-2.1) for others (P = 0.01). At 12 weeks, the ORs for these genotypic groups were 3.6 (1.7-7.8) and 1.4 (0.9-2.3), respectively (P = 0.04). There was no association between patch effectiveness and DRD2 exon 8. Short-term effectiveness of the nicotine patch may be related to dopamine beta-hydroxylase and dopamine D2 receptor genotype. Our results support the need for further investigation into personalized therapies for smoking cessation based on individual genotype.

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.

Progress in searching for susceptibility loci and genes for smoking-related behaviour

Smoking behaviour is influenced by both genetic and environmental factors. Many years of twin and adoption studies have demonstrated that heritability is at least 50% responsible for both smoking initiation and smoking persistence. Furthermore, the extent, to which genetic and environmental factors contribute to smoking behaviour, is significantly different in men and women. Linkage analyses from several independent studies provide evidences for suggested linkage of smoking behaviour to chromosomes 1, 2, 4, 5, 6, 9, 10, 11, 14, 17, 18 and 21. However, almost none of these loci have been replicated yet. Furthermore, numerous population-based association studies have been performed to examine the effects of a number of candidate genes, such as cytochrome P450, dopamine receptor (DR) and transporter, serotonin transporter and nicotinic acetylcholine receptor, on smoking behaviour. However, many of these reports have not yet received independent confirmation. Of these candidate genes, the D2 dopamine receptor (DRD2) gene has been extensively studied. Meta-analysis of 12 reported studies showed a significantly higher prevalence of the DRD2 TaqI A1 allele in smokers than that in non-smokers (p < 0.0001; pooled OR = 1.50; 95% CI = 1.33-1.70). For other candidate genes, insufficient published studies are available to allow a meta-analysis to be performed, or meta-analysis showed no significant difference between smokers and non-smokers. More studies are necessary to determine whether these genes play a significant role in smoking behaviour.

Alcohol-related expectancies are associated with the D2 dopamine receptor and GABAA receptor beta3 subunit genes

Molecular genetic research has identified promising markers of alcohol dependence, including alleles of the D2 dopamine receptor (DRD2) and the GABAA receptor beta3 subunit (GABRB3) genes. Whether such genetic risk manifests itself in stronger alcohol-related outcome expectancies, or in difficulty resisting alcohol, is unknown. In the present study, A1+ (A1A1 and A1A2 genotypes) and A1- (A2A2 genotype) alleles of the DRD2 and G1+ (G1G1 and G1 non-G1 genotypes) and G1- (non-G1 non-G1 genotype) alleles of the GABRB3 gene were determined in a group of 56 medically ill patients diagnosed with alcohol dependence. Mood-related alcohol expectancy (AE) and drinking refusal self-efficacy (DRSE) were assessed using the Drinking Expectancy Profile (Manual for the Drinking Expectancy Profile, Behaviour Research and Therapy Centre, Brisbane, 1996). Patients with the DRD2 A1+ allele, compared with those with the DRD2 A1- allele, reported significantly lower DRSE in situations of social pressure. Similarly, lower DRSE was reported under social pressure by patients with the GABRB3 G1+ allele when compared to those with the GABRB3 G1- alleles. Patients with the GABRB3 G1+ allele also revealed reduced DRSE in situations characterized by negative affect than those with the GABRB3 G1- alleles. Patients carrying the GABRB3 G1+ allele showed stronger AE relating to negative affective change (for example, increased depression) than their GABRB3 G1- counterparts. Biological influence in the development of some classes of cognitions is hypothesized. The clinical implications, particularly with regard to patient-treatment matching and the development of an integrated psychological and pharmacogenetic approach, are discussed.

A genomic scan for habitual smoking in families of alcoholics: common and specific genetic factors in substance dependence

Smoking is a highly heritable, addictive disorder that commonly co-occurs with alcohol dependence. The purpose of this study is to perform a genomic screen for habitual smoking and comorbid habitual smoking and alcohol dependence in families from the Collaborative Study on the Genetics of Alcoholism (COGA). Subjects were assessed using the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA) to evaluate alcohol dependence and habitual smoking (smoking one pack per day or more for at least 6 months). Sixty seven multi-generational families with 154 independent sibling pairs affected with habitual smoking were genotyped in a screening sample. Analyses on 79 multi-generational families with 173 independent sibling pairs were repeated in a replication sample. Sibpair analyses were performed using ASPEX. Four chromosomal regions in the screening sample had increased allele sharing among sibling pairs for habitual smoking with a LOD score greater than 1 (chromosomes 5, 9, 11, and 21). The highest LOD score was on chromosome 9 (LOD = 2.02; allele sharing 58.9%). Four chromosomal regions also had modest evidence for linkage to the comorbid phenotype habitual smoking and alcohol dependence (chromosomes 1, 2, 11, 15); and the strongest finding was on chromosome 2 (LOD = 3.30; allele sharing 69.1%). Previously identified areas (chromosomes 1 and 7) implicated in the development of alcohol dependence in this same data set did not provide evidence for linkage to habitual smoking in the screening sample. In the replication data set, there continued to be increased allele sharing near peaks identified in the screening sample on chromosomes 2 and 9, but the results were modest. An area on chromosome 7, approximately 60 cM from a location previously identified in linkage analysis with alcohol dependence, had increased allele sharing for the comorbid habitual smoking and alcohol dependence. These data provide evidence of specific genetic regions involved in the development of habitual smoking and not alcohol dependence. Conversely, genetic regions that influence the development of alcohol dependence do not appear to contribute to the development of habitual smoking. Finally, there is also evidence of an area on chromosome 2 that may reflect a common genetic vulnerability locus to both habitual smoking and alcohol dependence.