Prospective association of dopamine-related polymorphisms with smoking cessation in general care

A scoping review of smoking cessation pharmacogenetic studies to advance future research across racial, ethnic, and ancestral populations

Abstinence rates among smokers attempting to quit remain low despite the wide availability and accessibility of pharmacological smoking cessation treatments. In addition, the prevalence of cessation attempts and abstinence differs by individual-level social factors such as race and ethnicity. Clinical treatment of nicotine dependence also continues to be challenged by individual-level variability in effectiveness to promote abstinence. The use of tailored smoking cessation strategies that incorporate information on individual-level social and genetic factors hold promise, although additional pharmacogenomic knowledge is still needed. In particular, genetic variants associated with pharmacological responses to smoking cessation treatment have generally been conducted in populations with participants that self-identify as White race or who are determined to be of European genetic ancestry. These results may not adequately capture the variability across all smokers as a result of understudied differences in allele frequencies across genetic ancestry populations. This suggests that much of the current pharmacogenetic study results for smoking cessation may not apply to all populations. Therefore, clinical application of pharmacogenetic results may exacerbate health inequities by racial and ethnic groups. This scoping review examines the extent to which racial, ethnic, and ancestral groups that experience differences in smoking rates and smoking cessation are represented in the existing body of published pharmacogenetic studies of smoking cessation. We will summarize results by race, ethnicity, and ancestry across pharmacological treatments and study designs. We will also explore current opportunities and challenges in conducting pharmacogenomic research on smoking cessation that encourages greater participant diversity, including practical barriers to clinical utilization of pharmacological smoking cessation treatment and clinical implementation of pharmacogenetic knowledge.

Smoking Genes: A Case-Control Study of Dopamine Transporter Gene (SLC6A3) and Dopamine Receptor Genes (DRD1, DRD2 and DRD3) Polymorphisms and Smoking Behaviour in a Malay Male Cohort

Dopamine receptor and dopamine transporter genes polymorphisms have been associated with cigarette smoking behaviour in different populations. The aim of this case-control study was to evaluate polymorphisms in the dopamine transporter gene (SLC6A3 (rs27072)) and the dopamine receptor genes (DRD1 (rs686), DRD2 (rs1800497) and DRD3 (rs7653787)) and their contribution to smoking behaviour in a Malay male population. We identified 476 participants over the age of 18 years comprising 238 smokers and 238 non-smokers. Information such as age, height, weight, body mass index, systolic and diastolic blood pressures, marital status, and smoking status of close family members were taken. For the genetic study, we genotyped four genes (SLC6A3 (rs27072), DRD1 (rs686), DRD2 (rs1800497) and DRD3 (rs7653787)) using the polymerase chain reaction-restriction fragment length polymorphism method and further confirmed our findings with sequencing. Dopamine receptor genes (DRD1, DRD2 and DRD3) were found to be associated with smoking behaviour in a Malay male population. The dopamine transporter gene (SLC6A3) did not show this association. Significant differences were observed between smokers' and non-smokers' age, systolic blood pressure, marital status and family members who smoke. Smoking behaviour is significantly influenced by genetic variations of DRD1, DRD2 and DRD3 in a Malay male population.

From genes to treatments: a systematic review of the pharmacogenetics in smoking cessation

Smoking cessation treatment outcomes may be heavily influenced by genetic variations among smokers. Therefore, identifying specific variants that affect response to different pharmacotherapies is of major interest to the field. In the current study, we systematically review all studies published in or after the year 1990 which examined one or more gene-drug interactions for smoking cessation treatment. Out of 644 citations, 46 articles met the inclusion criteria for the systematic review. We summarize evidence on several genetic polymorphisms (CHRNA5-A3-B4, CYP2A6, DBH, CHRNA4, COMT, DRD2, DRD4 and CYP2B6) and their potential moderating pharamacotherarpy effects on patient cessation efficacy rates. These findings are promising and call for further research to demonstrate the effectiveness of genetic testing in personalizing treatment decision-making and improving outcome.

Pathways to precision medicine in smoking cessation treatments

Cigarette smoking is highly addictive and modern genetic research has identified robust genetic influences on nicotine dependence. An important step in translating these genetic findings to clinical practice is identifying the genetic factors affecting smoking cessation in order to enhance current smoking cessation treatments. We reviewed the significant genetic variants that predict nicotine dependence, smoking cessation, and response to cessation pharmacotherapy. These data suggest that genetic risks can predict smoking cessation outcomes and moderate the effect of pharmacological treatments. Some pharmacogenetic findings have been replicated in meta-analyses or in multiple smoking cessation trials. The variation in efficacy between smokers with different genetic markers supports the notion that personalized smoking cessation intervention based upon genotype could maximize the efficiency of such treatment while minimizing side effects, thus influencing the number needed to treat (NNT) and the number needed to harm. In summary, as precision medicine is revolutionizing healthcare, smoking cessation may be one of the first areas where genetic variants may identify individuals at increased risk. Current evidence strongly suggests that genetic variants predict cessation failure and that cessation pharmacotherapy effectiveness is modulated by biomarkers such as nicotinic cholinergic receptor α5 subunit (CHRNA5) genotypes or nicotine metabolism ratio (NMR). These findings strengthen the case for the development and rigorous testing of treatments that target patients with different biological risk profiles.

Associations between smoking behavior-related alleles and the risk of melanoma

Several studies have reported that cigarette smoking is inversely associated with the risk of melanoma. This study further tested whether incorporating genetic factors will provide another level of evaluation of mechanisms underlying the association between smoking and risk of melanoma. We investigated the association between SNPs selected from genome-wide association studies (GWAS) on smoking behaviors and risk of melanoma using 2,298 melanoma cases and 6,654 controls. Among 16 SNPs, three (rs16969968 [A], rs1051730 [A] and rs2036534 [C] in the 15q25.1 region) reached significance for association with melanoma risk in men (0.01 < = P values < = 0.02; 0.85 < = Odds Ratios (ORs) <= 1.20). There was association between the genetic scores based on the number of smoking behavior-risk alleles and melanoma risk with P-trend = 0.005 among HPFS. Further association with smoking behaviors indicating those three SNPs (rs16969968 [A], rs1051730 [A] and rs2036534 [C]) significantly associated with number of cigarettes smoked per day, CPD, with P = 0.009, 0.011 and 0.001 respectively. The SNPs rs215605 in the PDE1C gene and rs6265 in the BDNF gene significantly interacted with smoking status on melanoma risk (interaction P = 0.005 and P = 0.003 respectively). Our study suggests that smoking behavior-related SNPs are likely to play a role in melanoma development and the potential public health importance of polymorphisms in the CHRNA5-A3-B4 gene cluster. Further larger studies are warranted to validate the findings.

Association of the DBH Polymorphism rs3025343 With Smoking Cessation in a Large Population-Based Sample

Introduction

Genetic variations in DBH-gene and its surroundings have been shown to associate with smoking behavior including smoking cessation in several studies. In this study we replicate and measure the effect size for association between DBH polymorphism rs3025343 and smoking cessation in a large population-based sample while examining environmental factors that could relate to the association.

Methods

We studied 11 926 adult subjects from four surveys of the National FINRISK Study. The analysis was restricted to either current or former smokers. Logistic and linear regression analyses were conducted to investigate the relationships of the single nucleotide polymorphism (SNP), covariates, smoking cessation, and smoking severity (cotinine, CPD). Gene-environment interactions were tested by likelihood-ratio test.

Results

The association between rs3025343 and smoking cessation (prevalence odds ratio, OR = 1.12, p = .094, 95%CI = 0.98-1.30) was replicated identically with the GWAS study of The Tobacco and Genetics Consortium (OR = 1.12, 95%CI = 1.08-1.18). None of our tested phenotypes significantly influenced the association between rs3025343 and smoking cessation. Overall, marital status, education, depression, alcohol use, self-rated health, and chronic obstructive pulmonary disease (COPD) showed phenotypic associations with smoking cessation, but the association of various phenotypes with smoking cessation did not vary by genotype.

Conclusions

The current study replicates the effect size for the association between rs3025343 and smoking cessation despite lack of overall significance due to smaller sample size. We could not show environmental influences on the association of rs3025343 with smoking cessation.

Implications

Our study replicates the direction and strength of the association of DBH polymorphism rs3025343 with smoking cessation. We could not detect environmental influences on the strength of the association of rs3025343 with smoking cessation, but the limited power of our analysis needs to be taken into account.

The significant association of Taq1A genotypes in DRD2/ANKK1 with smoking cessation in a large-scale meta-analysis of Caucasian populations

Although a number of studies have analyzed the relation between the DRD2/ANKK1 gene Taq1A polymorphism and smoking cessation, the results remain controversial. The primary objective of the present study was to determine whether this variant indeed has any effect on smoking cessation. The A1-dominant model that considers A1/* (*=A1 or A2) and A2/A2 as two genotypes and compares their frequencies in current and former smokers was applied. A total of 22 studies with 11,075 subjects were included in the meta-analyses. Considering the potential influence of between-study heterogeneity, we conducted stratified meta-analyses with the Comprehensive Meta-Analysis statistical software (version 2.0). Results based on either cross-sectional or longitudinal studies consistently showed a statistically significant association between Taq1A A1/* genotypes and smoking cessation. Further, a more significant association of the variant with smoking cessation was detected when both types of studies were combined. However, there was marginal evidence of heterogeneity among studies (I(2)=33.9%; P=0.06). By excluding other ethnicities and subjects with cancer, the meta-analysis on the basis of 9487 Caucasians demonstrated that Taq1A A1/* genotypes indeed were significantly associated with smoking cessation under both the fixed- and random-effects models (pooled OR 1.22; 95% CI 1.11-1.34; P=3.9 × 10(-5) for both models). No evidence of between-study heterogeneity or publication bias was observed. Thus, we conclude that the polymorphism of Taq1A has an important role in the process of abstaining from smoking, and smokers carrying A2/A2 genotype have a higher likelihood of smoking cessation than those who carry A1/A1 or A1/A2.

A review of pharmacogenetic studies of substance-related disorders

BACKGROUND

Substance-related disorders (SRDs) are a major cause of morbidity and mortality worldwide. Family, twin, and adoption studies have demonstrated the substantial heritability of SRDs. To determine the impact of genetic variation on risk for SRD and the response to treatment, researchers have conducted a number of secondary data analyses and quasi-experimental studies that target one or more candidate gene variants.

METHODS

This review examines studies in which candidate polymorphisms were examined as mediator variables to identify pharmacogenetic effects on subjective responses to drug administration or cues or outcomes of medication trials for SRDs. Efforts to use a meta-analytic approach to quantify these effects are premature because the number of available studies using similar methods and outcomes is limited, so the present review is qualitative.

RESULTS

Findings from these studies provide preliminary evidence of clinically relevant pharmacogenetic effects. However, independent replication of these findings has been sparse.

CONCLUSIONS

Although this growing body of literature has produced conflicting results, improved statistical controls may help to clarify the findings. Additionally, the use of empirically derived sub-phenotypes (i.e., which serve to differentiate distinct groups of affected individuals) may also help to identify genetic mediators of pharmacologic response in relation to SRDs. The identification of genetic mediators can inform clinical care both by identifying risk factors for SRDs and predicting adverse events and therapeutic outcomes associated with specific pharmacotherapies.

Lack of Associations of CHRNA5-A3-B4 Genetic Variants with Smoking Cessation Treatment Outcomes in Caucasian Smokers despite Associations with Baseline Smoking

CHRNA5-A3-B4 variants, rs16969968, rs588765 and rs578776, are consistently associated with tobacco consumption among smokers, but the association with smoking cessation is less consistent. Among the studies that reported significant associations with cessation, the effects were observed in smokers treated with placebo treatment in some studies and conversely in those receiving active pharmacological therapy (bupropion and nicotine replacement therapies) in others. Thus, it remains unclear whether CHRNA5-A3-B4 is a useful marker for optimizing smoking cessation. Using data from 654 Caucasian smokers treated with placebo, nicotine patch or varenicline, we investigated whether CHRNA5-A3-B4 variants were associated with smoking cessation outcomes, and whether there were significant genotype-by-treatment or haplotype-by-treatment interactions. We observed no significant associations between CHRNA5-A3-B4 variants and smoking cessation, despite replicating previous associations with baseline tobacco consumption. At end of treatment the effect size on smoking cessation in the placebo, patch and varenicline groups for rs16969968 [GG vs. GA+AA] was OR = 0.66 (P = 0.23), OR = 1.01 (P = 0.99), and OR = 1.30 (P = 0.36) respectively, of rs588765 [CC vs. CT+TT] was OR = 0.96 (P = 0.90), OR = 0.84 (P = 0.58), and OR = 0.74 (P = 0.29) respectively, and for rs578776 [GG vs. GA+AA] on smoking cessation was OR = 1.02 (P = 0.95), OR = 0.75 (P = 0.35), and OR = 1.20 (P = 0.51) respectively. Furthermore, we observed no associations with cessation using the CHRNA5-A3-B4 haplotype (constructed using rs16969968 and rs588765), nor did we observe any significant genotype-by-treatment interactions, with or without adjusting for the rate of nicotine metabolism (all P>0.05). We also observed no significant genetic associations with 6 month or 12 month smoking abstinence. In conclusion, we found no association between CHRNA5-A3-B4 variants and smoking cessation rates in this clinical trial; however, as expected, significant associations with baseline tobacco consumption were replicated. Our data suggest that CHRNA5-A3-B4 gene variants do not exhibit a robust association with smoking cessation and are unlikely to be useful for clinically optimizing smoking cessation pharmacotherapy for Caucasian smokers.

CHRNA5 risk variant predicts delayed smoking cessation and earlier lung cancer diagnosis--a meta-analysis

BACKGROUND

Recent meta-analyses show strong evidence of associations among genetic variants in CHRNA5 on chromosome 15q25, smoking quantity, and lung cancer. This meta-analysis tests whether the CHRNA5 variant rs16969968 predicts age of smoking cessation and age of lung cancer diagnosis.

METHODS

Meta-analyses examined associations between rs16969968, age of quitting smoking, and age of lung cancer diagnosis in 24 studies of European ancestry (n = 29 072). In each dataset, we used Cox regression models to evaluate the association between rs16969968 and the two primary phenotypes (age of smoking cessation among ever smokers and age of lung cancer diagnosis among lung cancer case patients) and the secondary phenotype of smoking duration. Heterogeneity across studies was assessed with the Cochran Q test. All statistical tests were two-sided.

RESULTS

The rs16969968 allele (A) was associated with a lower likelihood of smoking cessation (hazard ratio [HR] = 0.95, 95% confidence interval [CI] = 0.91 to 0.98, P = .0042), and the AA genotype was associated with a four-year delay in median age of quitting compared with the GG genotype. Among smokers with lung cancer diagnoses, the rs16969968 genotype (AA) was associated with a four-year earlier median age of diagnosis compared with the low-risk genotype (GG) (HR = 1.08, 95% CI = 1.04 to 1.12, P = 1.1*10(-5)).

CONCLUSION

These data support the clinical significance of the CHRNA5 variant rs16969968. It predicts delayed smoking cessation and an earlier age of lung cancer diagnosis in this meta-analysis. Given the existing evidence that this CHRNA5 variant predicts favorable response to cessation pharmacotherapy, these findings underscore the potential clinical and public health importance of rs16969968 in CHRNA5 in relation to smoking cessation success and lung cancer risk.

Contribution of Variants in CHRNA5/A3/B4 Gene Cluster on Chromosome 15 to Tobacco Smoking: From Genetic Association to Mechanism

Cigarette smoking is the major cause of preventable death and morbidity throughout the world. Many compounds are present in tobacco, but nicotine is the primary addictive one. Nicotine exerts its physiological and pharmacological roles in the brain through neuronal nicotinic acetylcholine receptors (nAChRs), which are ligand-gated ion channels consisting of five membrane-spanning subunits that can modulate the release of neurotransmitters, such as dopamine, glutamate, and GABA and mediate fast signal transmission at synapses. Considering that there are 12 nAChR subunits, it is highly likely that subunits other than α4 and β2, which have been intensively investigated, also are involved in nicotine addiction. Consistent with this hypothesis, a number of genome-wide association studies (GWAS) and subsequent candidate gene-based associated studies investigating the genetic variants associated with nicotine dependence (ND) and smoking-related phenotypes have shed light on the CHRNA5/A3/B4 gene cluster on chromosome 15, which encodes the α5, α3, and β4 nAChR subunits, respectively. These studies demonstrate two groups of risk variants in this region. The first one is marked by single nucleotide polymorphism (SNP) rs16969968 in exon 5 of CHRNA5, which changes an aspartic acid residue into asparagine at position 398 (D398N) of the α5 subunit protein sequence, and it is tightly linked SNP rs1051730 in CHRNA3. The second one is SNP rs578776 in the 3'-untranslated region (UTR) of CHRNA3, which has a low correlation with rs16969968. Although the detailed molecular mechanisms underlying these associations remain to be further elucidated, recent findings have shown that α5* (where "*" indicates the presence of additional subunits) nAChRs located in the medial habenulo-interpeduncular nucleus (mHb-IPN) are involved in the control of nicotine self-administration in rodents. Disruption of α5* nAChR signaling diminishes the aversive effects of nicotine on the mHb-IPN pathway and thereby permits more nicotine consumption. To gain a better understanding of the function of the highly significant genetic variants identified in this region in controlling smoking-related behaviors, in this communication, we provide an up-to-date review of the progress of studies focusing on the CHRNA5/A3/B4 gene cluster and its role in ND.

Interplay of genetic risk (CHRNA5) and environmental risk (partner smoking) on cigarette smoking reduction

BACKGROUND

This study tests whether the genetic predictor (CHRNA5 nicotine receptor gene variants) and an environmental risk factor (partner smoking) interact in the prediction of smoking reduction.

METHODS

Subjects were from a community-based, longitudinal study of women (n=1856) who smoked before pregnancy, and a randomized comparative effectiveness smoking cessation trial (n=1065). Smoking reduction was defined as the trajectory of self-reported smoking quantities over time in the observational study, and as the trajectory of alveolar CO levels in the cessation trial.

RESULTS

In the pregnancy study, rs16969968 genotype and partner smoking status interacted such that the smoking reduction was lowest for expectant mothers with high genetic risk and partner smoking, and highest for those with high genetic risk but not partner smoking (interaction of genotype×partner smoking on smoking quantity trajectory slope β=0.071, 95%CI=0.013, 0.13, p=0.017). In the clinical trial, a similar interaction was found (interaction β=0.20, 95%CI=0.049, 0.36, p=0.010). Furthermore, these associations were moderated by pharmacotherapy such that the interactive relation of genetic and environmental factors occurred in the placebo group, but not in the active pharmacotherapy group (interaction of genotype×partner smoking×pharmacotherapy on CO trajectory slope β=-0.25, 95%CI=-0.42, -0.091, p=0.0023).

CONCLUSIONS

The CHRNA5 genetic risk synergized the effect of partner smoking, producing an especially low likelihood of successful smoking reduction in two complementary studies. This suggests that the genetic vulnerability may be mitigated by altering environmental factors. In addition, cessation pharmacotherapy neutralizes the increase in cessation failure associated with combined genetic and environmental risks, which has possible relevance to treatment algorithms.

CHRNA5 variant predicts smoking cessation in patients with acute myocardial infarction

INTRODUCTION

While smoking is a major modifiable risk factor for secondary prevention of myocardial infarction (MI), active smoking is common among patients hospitalized with acute MI. Recent studies suggest that nicotinic receptor variants, and specifically the high-risk CHRNA5 rs16969968 A allele, are associated with cessation failure among noncardiac patients. This study investigates the association between CHRNA5 rs16969968 and smoking cessation in patients hospitalized with acute MI.

METHODS

Using data from the TRIUMPH study, we ascertained smoking status at the time of index hospitalization for acute MI and 1 year after hospitalization. After adjusting for age and sex, we used logistic regression to model the association between smoking cessation and CHRNA5 rs16969968.

RESULTS

At index admission, 752 Caucasian subjects were active smokers and 699 were former smokers. Among these ever-smokers, the A allele was associated with significantly decreased abstinence (45.0% abstinence for A allele carriers vs. 51.7% for GG homozygotes; odds ratio [OR] = 0.70, 95% confidence interval [CI] = 0.56-0.88, p = .0027). The A allele was also significantly associated with decreased abstinence at 1 year (69.1% abstinence for A allele carriers vs. 76.0% for GG homozygotes; OR = 0.70, 95% CI = 0.53-0.94, p = .0185).

CONCLUSIONS

Among patients who have smoked and who are hospitalized with acute MI, the high-risk CHRNA5 allele was associated with lower likelihood of quitting before hospitalization and significantly less abstinence 1 year after hospitalization with MI. The CHRNA5 rs16969968 genotype may therefore identify patients who would benefit from aggressive, personalized smoking cessation intervention.

Genomics and personalized medicine: CHRNA5-CHRNA3-CHRNB4 and smoking cessation treatment

Cigarette smoking is highly addictive, and modern genetic research has identified robust genetic influences on nicotine dependence. An important step in translating these genetic findings is to identify the genetic factors affecting smoking cessation in order to enhance current smoking cessation treatments. We review the significance of variants in the nicotinic receptor gene cluster (CHRNA5-CHRNA3-CHRNB4) in the prediction of smoking quantity, smoking cessation, and response to cessation medication in multiple studies of smoking cessation. Three common haplotypes (low-risk, intermediate-risk, and high-risk) in the CHRNA5-CHRNA3-CHRNB4 region are defined by rs16969968 and rs680244. The genetic variants in the CHRNA5-CHRNA3-CHRNB4 region that predict nicotine dependence also predict a later age of smoking cessation in a community-based sample. In a smoking cessation trial, these variants predict abstinence at end of treatment in individuals receiving placebo medication, but not amongst individuals receiving active medication. Pharmacological treatments moderate the genetic risk in affecting cessation success. These pharmacogenetic interactions have been reproduced by a recent meta-analysis of smoking cessation trials. The number needed to treat (NNT) is 4 for smokers with the high-risk haplotype, 7 for smokers with the intermediate-risk haplotype, and >1000 for smokers with the low-risk haplotype. The wide variation in NNT between smokers with different haplotypes supports the notion that personalized smoking cessation intervention based upon genotype could meaningfully increase the efficiency of such treatment. In summary, variants in the CHRNA5-CHRNA3-CHRNB4 region identify individuals at increased risk of cessation failure, and this increased risk can be ameliorated by cessation pharmacotherapy.

Physician advice for smoking cessation

BACKGROUND

Healthcare professionals frequently advise people to improve their health by stopping smoking. Such advice may be brief, or part of more intensive interventions.

OBJECTIVES

The aims of this review were to assess the effectiveness of advice from physicians in promoting smoking cessation; to compare minimal interventions by physicians with more intensive interventions; to assess the effectiveness of various aids to advice in promoting smoking cessation, and to determine the effect of anti-smoking advice on disease-specific and all-cause mortality.

SEARCH METHODS

We searched the Cochrane Tobacco Addiction Group trials register in January 2013 for trials of interventions involving physicians. We also searched Latin American databases through BVS (Virtual Library in Health) in February 2013.

SELECTION CRITERIA

Randomised trials of smoking cessation advice from a medical practitioner in which abstinence was assessed at least six months after advice was first provided.

DATA COLLECTION AND ANALYSIS

We extracted data in duplicate on the setting in which advice was given, type of advice given (minimal or intensive), and whether aids to advice were used, the outcome measures, method of randomisation and completeness of follow-up.The main outcome measure was abstinence from smoking after at least six months follow-up. We also considered the effect of advice on mortality where long-term follow-up data were available. We used the most rigorous definition of abstinence in each trial, and biochemically validated rates where available. People lost to follow-up were counted as smokers. Effects were expressed as relative risks. Where possible, we performed meta-analysis using a Mantel-Haenszel fixed-effect model.

MAIN RESULTS

We identified 42 trials, conducted between 1972 and 2012, including over 31,000 smokers. In some trials, participants were at risk of specified diseases (chest disease, diabetes, ischaemic heart disease), but most were from unselected populations. The most common setting for delivery of advice was primary care. Other settings included hospital wards and outpatient clinics, and industrial clinics.Pooled data from 17 trials of brief advice versus no advice (or usual care) detected a significant increase in the rate of quitting (relative risk (RR) 1.66, 95% confidence interval (CI) 1.42 to 1.94). Amongst 11 trials where the intervention was judged to be more intensive the estimated effect was higher (RR 1.84, 95% CI 1.60 to 2.13) but there was no statistical difference between the intensive and minimal subgroups. Direct comparison of intensive versus minimal advice showed a small advantage of intensive advice (RR 1.37, 95% CI 1.20 to 1.56). Direct comparison also suggested a small benefit of follow-up visits. Only one study determined the effect of smoking advice on mortality. This study found no statistically significant differences in death rates at 20 years follow-up.

AUTHORS' CONCLUSIONS

Simple advice has a small effect on cessation rates. Assuming an unassisted quit rate of 2 to 3%, a brief advice intervention can increase quitting by a further 1 to 3%. Additional components appear to have only a small effect, though there is a small additional benefit of more intensive interventions compared to very brief interventions.

Physician advice for smoking cessation

BACKGROUND

Healthcare professionals frequently advise people to improve their health by stopping smoking. Such advice may be brief, or part of more intensive interventions.

OBJECTIVES

The aims of this review were to assess the effectiveness of advice from physicians in promoting smoking cessation; to compare minimal interventions by physicians with more intensive interventions; to assess the effectiveness of various aids to advice in promoting smoking cessation, and to determine the effect of anti-smoking advice on disease-specific and all-cause mortality.

SEARCH METHODS

We searched the Cochrane Tobacco Addiction Group trials register in January 2013 for trials of interventions involving physicians. We also searched Latin American databases through BVS (Virtual Library in Health) in February 2013.

SELECTION CRITERIA

Randomised trials of smoking cessation advice from a medical practitioner in which abstinence was assessed at least six months after advice was first provided.

DATA COLLECTION AND ANALYSIS

We extracted data in duplicate on the setting in which advice was given, type of advice given (minimal or intensive), and whether aids to advice were used, the outcome measures, method of randomisation and completeness of follow-up.The main outcome measure was abstinence from smoking after at least six months follow-up. We also considered the effect of advice on mortality where long-term follow-up data were available. We used the most rigorous definition of abstinence in each trial, and biochemically validated rates where available. People lost to follow-up were counted as smokers. Effects were expressed as relative risks. Where possible, we performed meta-analysis using a Mantel-Haenszel fixed-effect model.

MAIN RESULTS

We identified 42 trials, conducted between 1972 and 2012, including over 31,000 smokers. In some trials, participants were at risk of specified diseases (chest disease, diabetes, ischaemic heart disease), but most were from unselected populations. The most common setting for delivery of advice was primary care. Other settings included hospital wards and outpatient clinics, and industrial clinics.Pooled data from 17 trials of brief advice versus no advice (or usual care) detected a significant increase in the rate of quitting (relative risk (RR) 1.66, 95% confidence interval (CI) 1.42 to 1.94). Amongst 11 trials where the intervention was judged to be more intensive the estimated effect was higher (RR 1.84, 95% CI 1.60 to 2.13) but there was no statistical difference between the intensive and minimal subgroups. Direct comparison of intensive versus minimal advice showed a small advantage of intensive advice (RR 1.37, 95% CI 1.20 to 1.56). Direct comparison also suggested a small benefit of follow-up visits. Only one study determined the effect of smoking advice on mortality. This study found no statistically significant differences in death rates at 20 years follow-up.

AUTHORS' CONCLUSIONS

Simple advice has a small effect on cessation rates. Assuming an unassisted quit rate of 2 to 3%, a brief advice intervention can increase quitting by a further 1 to 3%. Additional components appear to have only a small effect, though there is a small additional benefit of more intensive interventions compared to very brief interventions.

Interplay of genetic risk factors (CHRNA5-CHRNA3-CHRNB4) and cessation treatments in smoking cessation success

OBJECTIVE

Smoking is highly intractable, and the genetic influences on cessation are unclear. Identifying the genetic factors affecting smoking cessation could elucidate the nature of tobacco dependence, enhance risk assessment, and support development of treatment algorithms. This study tested whether variants in the nicotinic receptor gene cluster CHRNA5-CHRNA3-CHRNB4 predict age at smoking cessation and relapse after an attempt to quit smoking.

METHOD

In a community-based, crosssectional study (N=5,216) and a randomized comparative effectiveness smoking cessation trial (N=1,073), the authors used Cox proportional hazard models and logistic regression to model the relationships of smoking cessation (self-reported quit age in the community study and point-prevalence abstinence at the end of treatment in the clinical trial) to three common haplotypes in the CHRNA5-CHRNA3-CHRNB4 region defined by rs16969968 and rs680244.

RESULTS

The genetic variants in the CHRNA5-CHRNA3-CHRNB4 region that predict nicotine dependence also predicted a later age at smoking cessation in the community sample. In the smoking cessation trial, haplotype predicted abstinence at end of treatment in individuals receiving placebo but not among individuals receiving active medication. Haplotype interacted with treatment in affecting cessation success.

CONCLUSIONS

Smokers with the high-risk haplotype were three times as likely to respond to pharmacologic cessation treatments as were smokers with the low-risk haplotype. The high-risk haplotype increased the risk of cessation failure, and this increased risk was ameliorated by cessation pharmacotherapy. By identifying a high-risk genetic group with heightened response to smoking cessation pharmacotherapy, this work may support the development of personalized cessation treatments.

Genetics of dopamine receptors and drug addiction

Dopamine plays a key role in reward behavior, yet the association of drug dependence as a chronic, relapsing disorder with the genes encoding the various dopaminergic receptor subtypes remains difficult to delineate. In the context of subsequent genome-wide association (GWAS) research and post-GWAS investigations, we summarize the novel data that link genes encoding molecules involved in the dopaminergic system (dopamine receptors, transporter and enzymes in charge of its metabolism) to drug addiction. Recent reports indicate that the heritability of drug addiction should be high enough to allow a significant role for a specific set of genes, and the available genetic studies, which might not be already conclusive because of the heterogeneity of designs, methods and recruited samples, should support the idea of a significant role of at least one gene related to dopaminergic system. Evolutionary changes in primates and non-primate animals of genes coding for molecules involved in dopaminergic system highlight why addictive disorders are mainly limited to humans. Restricting the analyses to more specific intermediate phenotypes (or endophenotypes) such as attention allocation, stress reactivity, novelty seeking, behavioral disinhibition and impulsivity, instead of the broad addictive disorder concept can be instrumental to identify novel genes associated with these traits in the context of genome-wide studies.

Dopamine-related genes and spontaneous smoking cessation in ever-heavy smokers

Several studies have provided evidence for associations of polymorphisms located in and near dopamine-related genes and nicotine dependence and other smoking-related phenotypes, including pharmacogenetic interactions.

AIM

The purpose of the present work was to examine the association of SNPs in the DOPA decarboxylase (DDC), dopamine receptor D2 (DRD2) and dopamine transporter (SLC6A3) genes with smoking cessation in a large retrospective study featuring approximately 900 cessation events.

MATERIALS & METHODS

Data originated from the enrollment questionnaire of the epidemiological ESTHER study of community-dwelling adults aged 50-74 years, conducted in the German state of Saarland between July 2000 and December 2002. Restricting the analyses to subjects who reported to have regularly smoked > 20 cigarettes per day at some point in their life, we used survival analysis methods to model the time from initiation of regular smoking to cessation (defined as quitting with abstinence lasting until enrollment) and its relation with eight polymorphisms in the aforementioned genes (five in DDC, two in DRD2 and one in SLC6A3) in 1446 participants.

RESULTS

Neither individual variants nor DDC haplotypes were associated with the probability of overcoming nicotine dependence in this cohort.

CONCLUSION

The repeated suggestion of associations between the variants examined and nicotine dependence in previous reports seems to contrast the negative results in the present study. This would appear consistent with the hypothesis that the establishment of regular heavy smoking might abolish associations between genetic determinants of nicotine dependence and nicotine dependence-related phenotypes, in particular the probability of successful smoking cessation.