Linkage of nicotine dependence and smoking behavior on 10q, 7q and 11p in twins with homogeneous genetic background

Prepared and reactive inhibition in smokers and non-smokers

INTRODUCTION

Models of addiction have identified deficits in inhibitory control, or the ability to inhibit inappropriate or unwanted behaviors, as one factor in the development and maintenance of addictive behaviors. Current literature supports disruption of the prefrontal circuits that mediate reactive inhibitory control processes (i.e., inhibition in response to sudden, unplanned changes in environmental demands) in substance use disorders. However, the relationship between disorders of addiction, such as nicotine dependence, and planned inhibitory processes (i.e., inhibition that occurs after advance warning) is unclear. The goal of the present study was to examine the extent to which reactive and planned inhibitory processes are differentially disrupted in nicotine dependent individuals.

METHOD

We employed an internet-based novel stop signal task wherein participants were instructed to stop a continuous movement at either a predictable or unpredictable time. This task explicitly separated planned and reactive inhibitory processes and assessed group differences in task performance between smokers (N = 281) and non-smokers (N = 164). The smoker group was defined as any participant that identified as a smoker and reported an average daily nicotine consumption of at least 2 mg. The non-smoker group was defined as any participant that identified as a non-smoker and had not been a former smoker that quit within the last year. The smoker group also completed a questionnaire regarding smoking behaviors which included the Fägerstrom Test of Nicotine Dependence (FTND). We used these data to assess the continuous relation between planned stopping, unplanned stopping, and smoking behaviors.

RESULTS

We found significant differences in stop times for both reactive and planned stopping between groups as well as within the smoker group. Additionally, in the smoker group, dependence as measured by the FTND was associated with longer stop times on planned stop trials. Surprisingly, greater daily average consumption of nicotine was related to faster stopping for both trial types.

CONCLUSION

These results indicate the relevance of measuring both reactive and planned inhibitory processes for elucidating the relationship between nicotine addiction and mechanisms of inhibitory control.

Identification of slit3 as a locus affecting nicotine preference in zebrafish and human smoking behaviour

To facilitate smoking genetics research we determined whether a screen of mutagenized zebrafish for nicotine preference could predict loci affecting smoking behaviour. From 30 screened F3 sibling groups, where each was derived from an individual ethyl-nitrosurea mutagenized F0 fish, two showed increased or decreased nicotine preference. Out of 25 inactivating mutations carried by the F3 fish, one in the slit3 gene segregated with increased nicotine preference in heterozygous individuals. Focussed SNP analysis of the human SLIT3 locus in cohorts from UK (n=863) and Finland (n=1715) identified two variants associated with cigarette consumption and likelihood of cessation. Characterisation of slit3 mutant larvae and adult fish revealed decreased sensitivity to the dopaminergic and serotonergic antagonist amisulpride, known to affect startle reflex that is correlated with addiction in humans, and increased htr1aa mRNA expression in mutant larvae. No effect on neuronal pathfinding was detected. These findings reveal a role for SLIT3 in development of pathways affecting responses to nicotine in zebrafish and smoking in humans.

Associations between polygenic risk for tobacco and alcohol use and liability to tobacco and alcohol use, and psychiatric disorders in an independent sample of 13,999 Australian adults

BACKGROUND

Substance use, substance use disorders (SUDs), and psychiatric disorders commonly co-occur. Genetic risk common to these complex traits is an important explanation; however, little is known about how polygenic risk for tobacco or alcohol use overlaps the genetic risk for the comorbid SUDs and psychiatric disorders.

METHODS

We constructed polygenic risk scores (PRSs) using GWAS meta-analysis summary statistics from a large discovery sample, GWAS & Sequencing Consortium of Alcohol and Nicotine use (GSCAN), for smoking initiation (SI; N = 631,564), age of initiating regular smoking (AI; N = 258,251), cigarettes per day (CPD; N = 258,999), smoking cessation (SC; N = 312,273), and drinks per week (DPW; N = 527,402). We then estimated the fixed effect of these PRSs on the liability to 15 phenotypes related to tobacco and alcohol use, substance use disorders, and psychiatric disorders in an independent target sample of Australian adults.

RESULTS

After adjusting for multiple testing, 10 of 75 combinations of discovery and target phenotypes remained significant. PRS-SI (R² range: 1.98%-5.09 %) was positively associated with SI, DPW, and with DSM-IV and FTND nicotine dependence, and conduct disorder. PRS-AI (R²: 3.91 %) negatively associated with DPW. PRS-CPD (R²: 1.56 %-1.77 %) positively associated with DSM-IV nicotine dependence and conduct disorder. PRS-DPW (R²: 3.39 %-6.26 %) positively associated with only DPW. The variation of DPW was significantly influenced by sex*PRS-SI, sex*PRS-AI and sex*PRS-DPW. Such interaction effect was not detected in the other 14 phenotypes.

CONCLUSIONS

Polygenic risks associated with tobacco use are also associated with liability to alcohol consumption, nicotine dependence, and conduct disorder.

Molecular Mechanisms Associated with Nicotine Pharmacology and Dependence

Tobacco dependence is a leading cause of preventable disease and death worldwide. Nicotine, the main psychoactive component in tobacco cigarettes, has also been garnering increased popularity in its vaporized form, as derived from e-cigarette devices. Thus, an understanding of the molecular mechanisms underlying nicotine pharmacology and dependence is required to ascertain novel approaches to treat drug dependence. In this chapter, we review the field's current understanding of nicotine's actions in the brain, the neurocircuitry underlying drug dependence, factors that modulate the function of nicotinic acetylcholine receptors, and the role of specific genes in mitigating the vulnerability to develop nicotine dependence. In addition to nicotine's direct actions in the brain, other constituents in nicotine and tobacco products have also been found to alter drug use, and thus, evidence is provided to highlight this issue. Finally, currently available pharmacotherapeutic strategies are discussed, along with an outlook for future therapeutic directions to achieve to the goal of long-term nicotine cessation.

Neuregulin signaling pathway in smoking behavior

Understanding molecular processes that link comorbid traits such as addictions and mental disorders can provide novel therapeutic targets. Neuregulin signaling pathway (NSP) has previously been implicated in schizophrenia, a neurodevelopmental disorder with high comorbidity to smoking. Using a Finnish twin family sample, we have previously detected association between nicotine dependence and ERBB4 (a neuregulin receptor), and linkage for smoking initiation at the ERBB4 locus on 2q33. Further, Neuregulin3 has recently been shown to associate with nicotine withdrawal in a behavioral mouse model. In this study, we scrutinized association and linkage between 15 036 common, low frequency and rare genetic variants in 10 NSP genes and phenotypes encompassing smoking and alcohol use. Using the Finnish twin family sample (N=1998 from 740 families), we detected 66 variants (representing 23 LD blocks) significantly associated (false discovery rate P<0.05) with smoking initiation, nicotine dependence and nicotine withdrawal. We comprehensively annotated the associated variants using expression (eQTL) and methylation quantitative trait loci (meQTL) analyses in a Finnish population sample. Among the 66 variants, we identified 25 eQTLs (in NRG1 and ERBB4), 22 meQTLs (in NRG3, ERBB4 and PSENEN), a missense variant in NRG1 (rs113317778) and a splicing disruption variant in ERBB4 (rs13385826). Majority of the QTLs in blood were replicated in silico using publicly available databases, with additional QTLs observed in brain. In conclusion, our results support the involvement of NSP in smoking behavior but not in alcohol use and abuse, and disclose functional potential for 56 of the 66 associated single-nucleotide polymorphism.

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

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

Reframing video gaming and internet use addiction: empirical cross-national comparison of heavy use over time and addiction scales among young users

BACKGROUND AND AIMS

Evidence-based and reliable measures of addictive disorders are needed in general population-based assessments. One study suggested that heavy use over time (UOT) should be used instead of self-reported addiction scales (AS). This study compared UOT and AS regarding video gaming and internet use empirically, using associations with comorbid factors.

DESIGN

Cross-sectional data from the 2011 French Survey on Health and Consumption on Call-up and Preparation for Defence-Day (ESCAPAD), cross-sectional data from the 2012 Swiss ado@internet.ch study and two waves of longitudinal data (2010-13) of the Swiss Longitudinal Cohort Study on Substance Use Risk Factors (C-SURF).

SETTING

Three representative samples from the general population of French and Swiss adolescents and young Swiss men, aged approximately 17, 14 and 20 years, respectively.

PARTICIPANTS

ESCAPAD: n =22 945 (47.4% men); ado@internet.ch: n =3049 (50% men); C-SURF: n =4813 (baseline + follow-up, 100% men).

MEASUREMENTS

We assessed video gaming/internet UOT ESCAPAD and ado@internet.ch: number of hours spent online per week, C-SURF: latent score of time spent gaming/using internet] and AS (ESCAPAD: Problematic Internet Use Questionnaire, ado@internet.ch: Internet Addiction Test, C-SURF: Gaming AS). Comorbidities were assessed with health outcomes (ESCAPAD: physical health evaluation with a single item, suicidal thoughts, and appointment with a psychiatrist; ado@internet.ch: WHO-5 and somatic health problems; C-SURF: Short Form 12 (SF-12 Health Survey) and Major Depression Inventory (MDI).

FINDINGS

UOT and AS were correlated moderately (ESCAPAD: r = 0.40, ado@internet.ch: r = 0.53 and C-SURF: r = 0.51). Associations of AS with comorbidity factors were higher than those of UOT in cross-sectional (AS: .005 ≤ |b| ≤ 2.500, UOT: 0.001 ≤ |b| ≤ 1.000) and longitudinal analyses (AS: 0.093 ≤ |b| ≤ 1.079, UOT: 0.020 ≤ |b| ≤ 0.329). The results were similar across gender in ESCAPAD and ado@internet.ch (men: AS: 0.006 ≤ |b| ≤ 0.211, UOT: 0.001 ≤ |b| ≤ 0.061; women: AS: 0.004 ≤ |b| ≤ 0.155, UOT: 0.001 ≤ |b| ≤ 0.094).

CONCLUSIONS

The measurement of heavy use over time captures part of addictive video gaming/internet use without overlapping to a large extent with the results of measuring by self-reported addiction scales (AS). Measuring addictive video gaming/internet use via self-reported addiction scales relates more strongly to comorbidity factors than heavy use over time.

Role of the Neuregulin Signaling Pathway in Nicotine Dependence and Co-morbid Disorders

Smoking is currently the leading cause of preventable death in the United States and is responsible for over four million deaths annually worldwide. Therefore, there is a vast clinical unmet need with regards to therapeutics targeting smoking cessation. This is even more apparent when examining smokers co-morbid with psychiatric illness, as rates of smoking in this population are ~4× higher than in the general population. Examining common genetic and molecular signaling pathways impinging upon both smoking behavior and psychiatric illness will lead to a better understanding of co-morbid disorders and potential development of novel therapeutics. Studies have implicated the Neuregulin Signaling Pathway in the pathophysiology of a number of psychiatric illnesses. Additionally, recent studies have also shown an association between the Neuregulin Signaling Pathway and smoking behaviors. This review outlines basic mechanisms of the Neuregulin Signaling Pathway and how it may be exploited for precision medicine approaches in treating nicotine dependence and mental illness.

Organic cation transporter variation and response to smoking cessation therapies

INTRODUCTION

We evaluated chr6q25.3 organic cation transporter gene (SLC22A1, SLC22A2, SLC22A3) variation and response to smoking cessation therapies. The corresponding proteins are low-affinity transporters of choline, acetylcholine and monoamines, and smoking cessation pharmacotherapies expressed in multiple tissues.

METHODS

We selected 7 common polymorphisms for mega-regression analysis. We assessed additive model association of polymorphisms with 7-day point prevalence abstinence overall and by assigned pharmacotherapy at end of treatment and at 6 months among European-ancestry participants of 7 randomized controlled trials adjusted for demographic, population genetic, and trial covariates.

RESULTS

Initial results were obtained in 6 trials with 1,839 participants. Nominally statistically significant associations of 2 SLC22A2 polymorphisms were observed: (1) with rs316019 at 6 months, overall ([c.808T>G; p.Ser270Ala], OR = 1.306, 95% CI = 1.034-1.649, p = .025), and among those randomized to nicotine replacement therapy (NRT) (OR = 1.784, 95% CI = 1.072-2.970, p = .026); and (2) with rs316006 (c.1502-529A>T) among those randomized to varenicline (OR = 1.420, 95% CI = 1.038-1.944, p = .028, OR = 1.362, 95% CI = 1.001-1.853, p = .04) at end of treatment and 6 months. Individuals randomized to NRT from a seventh trial were genotyped for rs316019; rs316019 was associated with a nominally statistically significant effect on abstinence overall at 6 months among 2,233 participants (OR = 1.249, 95% CI = 1.007-1.550, p = .043).

CONCLUSIONS

The functional OCT2 Ser270Ala polymorphism is nominally statistically significantly associated with abstinence among European-ancestry treatment-seeking smokers after adjustments for pharmacotherapy, demographics, population genetics, and without adjustment for multiple testing of 7 SNPs. Replication of these preliminary findings in additional randomized controlled trials of smoking cessation therapies and from multiple continental populations would describe another pharmacogenetic role for SLC22A2/OCT2.

Role of nicotine dependence in the association between the dopamine receptor gene DRD3 and major depressive disorder

Background

The aims of this study were to analyze associations of dopamine receptor genes (DRD1-5) with Major Depressive Disorder (MDD) and nicotine dependence (ND), and to investigate whether ND moderates genetic influences on MDD.

Methods

The sample was ascertained from the Finnish Twin Cohort. Twin pairs concordant for smoking history were recruited along with their family members, as part of the multisite Nicotine Addiction Genetics consortium. Genetic association analyses were based on 1428 adults. Total of 70 tagging single nucleotide polymorphisms within the dopamine receptor genes were genotyped and analyzed for association with MDD, ND, and MD-ND co-morbidity. Individual level logistic regression analyses were based on 1296 adults with data on ND and MDD diagnoses, as well as on dopamine receptor genotypes adjusted for sex, age, and alcohol use. Four independent samples, such as population-based and case-control samples, were used for replication.

Results

Rs2399496, located 1.5 kb downstream of DRD3, showed suggestive association for MDD (p = 0.00076) and significant association for MDD-ND co-morbidity (p = 0.000079). Suggestive gene-(rs2399496) by-ND-interaction justified analyses by genetic risk variant and ND status. Individuals with ND and two minor alleles (AA) of rs2399496 had almost six-fold risk for MDD (OR 5.74, 95%CI 3.12–10.5, p = 9.010e-09) compared to individuals without ND and with two major alleles (TT).

Conclusions

Significant association between a variant downstream of DRD3 and a co-morbid MDD-ND phenotype was detected. Our results further suggest that nicotine dependence may potentiate the influence of the DRD3 genetic variant on MDD.

Genome-wide association study on detailed profiles of smoking behavior and nicotine dependence in a twin sample

Smoking is a major risk factor for several somatic diseases and is also emerging as a causal factor for neuropsychiatric disorders. Genome-wide association (GWA) and candidate gene studies for smoking behavior and nicotine dependence (ND) have disclosed too few predisposing variants to account for the high estimated heritability. Previous large-scale GWA studies have had very limited phenotypic definitions of relevance to smoking-related behavior, which has likely impeded the discovery of genetic effects. We performed GWA analyses on 1114 adult twins ascertained for ever smoking from the population-based Finnish Twin Cohort study. The availability of 17 smoking-related phenotypes allowed us to comprehensively portray the dimensions of smoking behavior, clustered into the domains of smoking initiation, amount smoked and ND. Our results highlight a locus on 16p12.3, with several single-nucleotide polymorphisms (SNPs) in the vicinity of CLEC19A showing association (P<1 × 10(-6)) with smoking quantity. Interestingly, CLEC19A is located close to a previously reported attention-deficit hyperactivity disorder (ADHD) linkage locus and an evident link between ADHD and smoking has been established. Intriguing preliminary association (P<1 × 10(-5)) was detected between DSM-IV (Diagnostic and Statistical Manual of Mental Disorders, 4th edition) ND diagnosis and several SNPs in ERBB4, coding for a Neuregulin receptor, on 2q33. The association between ERBB4 and DSM-IV ND diagnosis was replicated in an independent Australian sample. Recently, a significant increase in ErbB4 and Neuregulin 3 (Nrg3) expression was revealed following chronic nicotine exposure and withdrawal in mice and an association between NRG3 SNPs and smoking cessation success was detected in a clinical trial. ERBB4 has previously been associated with schizophrenia; further, it is located within an established schizophrenia linkage locus and within a linkage locus for a smoker phenotype identified in this sample. In conclusion, we disclose novel tentative evidence for the involvement of ERBB4 in ND, suggesting the involvement of the Neuregulin/ErbB signalling pathway in addictions and providing a plausible link between the high co-morbidity of schizophrenia and ND.

Introduction to deep sequencing and its application to drug addiction research with a focus on rare variants

Through linkage analysis, candidate gene approach, and genome-wide association studies (GWAS), many genetic susceptibility factors for substance dependence have been discovered such as the alcohol dehydrogenase gene (ALDH2) for alcohol dependence (AD) and nicotinic acetylcholine receptor (nAChR) subunit variants on chromosomes 8 and 15 for nicotine dependence (ND). However, these confirmed genetic factors contribute only a small portion of the heritability responsible for each addiction. Among many potential factors, rare variants in those identified and unidentified susceptibility genes are supposed to contribute greatly to the missing heritability. Several studies focusing on rare variants have been conducted by taking advantage of next-generation sequencing technologies, which revealed that some rare variants of nAChR subunits are associated with ND in both genetic and functional studies. However, these studies investigated variants for only a small number of genes and need to be expanded to broad regions/genes in a larger population. This review presents an update on recently developed methods for rare-variant identification and association analysis and on studies focused on rare-variant discovery and function related to addictions.

A genome-wide association study of monozygotic twin-pairs suggests a locus related to variability of serum high-density lipoprotein cholesterol

Genome-wide association analysis on monozygotic twin-pairs offers a route to discovery of gene environment interactions through testing for variability loci associated with sensitivity to individual environment/lifestyle. We present a genome-wide scan of loci associated with intra-pair differences in serum lipid and apolipoprotein levels. We report data for 1,720 monozygotic female twin-pairs from GenomEUtwin project with 2.5 million SNPs, imputed or genotyped, and measured serum lipid fractions for both twins. We found one locus associated with intra-pair differences in high-density lipoprotein cholesterol, rs2483058 in an intron of SRGAP2, where twins carrying the C allele are more sensitive to environmental factors(P=3.98 x 10-8). We followed up the association in further genotyped monozygotic twins (N= 1,261),which showed a moderate association for the variant (P= 0.200, same direction of an effect). In addition,we report a new association on the level of apolipoprotein A-ll (P= 4.03 x 1 o-8).

Sex-specific influence of DRD2 on ADHD-type temperament in a large population-based birth cohort

Attention-deficit/hyperactivity disorder (ADHD) is a childhood-onset neurodevelopmental disorder with a significant public-health impact. Previously, we described a candidate gene study in a population-based birth cohort that demonstrated an association with ADHD-affected males and the dopamine receptor D2 (DRD2). The current study evaluates potential associations of dopamine receptor genes and Cloninger temperament traits within this same sample. Participants with stringent lifetime ADHD diagnoses were ascertained systematically from the genetically isolated Northern Finland 1986 Birth Cohort (n=9432), resulting in 178 cases and 157 controls. Markers in all known dopamine receptor genes were genotyped. We report an association of DRD2 with low Persistence in females (rs1079727 P=0.02, rs1124491 P=0.02, rs1800497 P=0.03). The associated DRD2 minor allelic haplotype (CAA, P=0.03) is the same haplotype we previously associated with ADHD in males in this birth cohort. The current study further supports previous results on the role of DRD2 in individuals with ADHD. Investigations suggest that DRD2 may have an impact on both males and females, but the particular outcome appears sex-specific, manifesting as ADHD in males and low Persistence in females. Furthermore, these findings suggest that the putative role of low Persistence as an endophenotype for ADHD deserves further investigation.

CYP2C9 variants increase risk of colorectal adenoma recurrence and modify associations with smoking but not aspirin treatment

PURPOSE

The cytochrome P450 2C9 enzyme (CYP2C9) is involved in metabolism of endogenous compounds, drugs, and procarcinogens. Two common nonsynonymous polymorphisms in CYP2C9 are associated with reduced enzyme activity: CYP2C9*2 (rs1799853, R144C) and CYP2C9*3 (rs1057910, I359L).

METHODS

We investigated whether CYP2C9 genotype was associated with risk of colorectal adenoma and/or modified associations with aspirin treatment or cigarette smoking in a cohort of 928 participants in a randomized trial of aspirin chemoprevention. Generalized linear regression was used to compute relative risks (RRs) and 95 % confidence intervals (95 % CIs). Multiplicative interactions terms were used to assess effect modification.

RESULTS

CYP2C9 genotype was associated with increased risks for adenoma recurrence of 29 % (RR = 1.29, 95 % CI 1.09-1.51) for ≥1 variant allele (CYP2C9*2 or *3) and 47 % (RR = 1.47, 95 % CI 1.19-1.83) for ≥1 CYP2C9*3 allele. The risk for advanced lesions or multiple (≥3) adenomas was increased by 64 % (RR = 1.64, 95 % CI 1.18-2.28) for ≥1 variant allele (CYP2C9*2 or *3) and 79 % (RR = 1.79, 95 % CI 1.16-2.75) for ≥1 CYP2C9*3 allele. Genotype modified associations with smoking, but not aspirin treatment. The adenoma risk was increased by 26 % (RR = 1.26, 95 % CI 0.99-1.58) for former smokers and 60 % (RR = 1.60, 95 % CI 1.19-2.15) for current smokers among wild-type individuals, but there was no increased risk among individuals with ≥1 variant allele (CYP2C9*2 or *3) (p (interaction) = 0.04).

CONCLUSIONS

Carriers of CYP2C9 variants with lower enzyme activity have increased overall risk of colorectal adenoma but reduced adenoma risk associated with cigarette smoking. These results may be due to effects on the synthesis of endogenous eicosanoids and/or reduced activation of procarcinogens in smoke by CYP2C9 variants.

Prevalence of myocardial infarction polymorphisms in Afyonkarahisar, Western Turkey

The aim of the study was to investigate relationship between polymorphisms in genes that are clinical and environmental features and the risk of myocardial infarction (MI) in Afyonkarahisar subjects living in Turkey. Prevalence of the several genes polymorphisms, ≤45 (42.04 ± 3.3) and ≥46 (57.19 ± 7.5) years were studied in individuals with MI and without MI (40.30 ± 9.01) individuals were studied. We tested 140 with MI individuals for factor V (FV) Leiden, FV H1299R, Prothrombin G20210A, factor XIII (FXIII) V34L, β-fibrinogen b-455G/A, plasminogen activator inhibitor-1 (PAI-1)-675 4G/5G, human platelet antigens 1 (HPA-1) a/b, apolipoprotein B (ApoB) R3500Q, apolipoprotein E (ApoE), E2, E3, and E4, angiotensin-converting enzyme (ACE) D/I, 5,10 methylenetetrahydrofolate reductase (MTHFR) 677C/T, and MTHFR 1298A/C polymorphisms using a ViennaLab CVD strip assay. This study results were compared without MI control groups. According to the our results, prothrombin, factor XIII and MTHFRC677T deletions were the most frequent genetic variants in risk groups of hyperlipidemic patients (value of odds ratio sequentially [OR] = 4.5, p = 0.05, [OR] = 2.16, p = 0.04 and [OR] = 2.8, p = 0.09). MTHFRA1298C and PAI-1 deletions were most frequent genetic variants in risk groups for MI in patients with diabetes mellitus (value of odds ratio sequentially [OR] = 3.79, p = 0.06 and [OR] = 5 × 10(8), p = 0.000). ACE deletions were positively associated with family history of cardiovascular events (OR = 3.62, p = 0.03). We found a strong relationship between genetic variants and risk factors. Significant associations between genetic variants predicting cardiovascular events and common risk factors (hyperlipidemia, smoking, diabetes mellitus and family history) patients were found.

Chromosome 20 shows linkage with DSM-IV nicotine dependence in Finnish adult smokers

INTRODUCTION

Chromosome 20 has previously been associated with nicotine dependence (ND) and smoking cessation. Our aim was to replicate and extend these findings.

METHODS

First, a total of 759 subjects belonging to 206 Finnish families were genotyped with 18 microsatellite markers residing on chromosome 20, in order to replicate previous linkage findings. Then, the replication data were combined to an existing whole-genome linkage data resulting in a total of 1,302 genotyped subjects from 357 families. ND diagnosed by DSM-IV criteria, the Fagerström Test for Nicotine Dependence (FTND) score, and the lifetime maximum number of cigarettes smoked within a 24-hr period (MaxCigs24) were used as phenotypes in the nonparametric linkage analyses.

RESULTS

We replicated previously reported linkage to DSM-IV ND, with a maximum logarithm of odd (LOD) score of 3.8 on 20p11, with females contributing more (maximum LOD [MLOD] score 3.4 on 20q11) than males (MLOD score 2.6 on 20p11). With the combined sample, a suggestive LOD score of 2.3 was observed for DSM-IV ND on 20p11. Sex-specific analyses revealed that the signal was driven by females with a maximum LOD score of 3.3 (on 20q11) versus LOD score of 1.3 in males (on 20q13) in the combined sample. No significant linkage signals were obtained for FTND or MaxCigs24.

CONCLUSIONS

Our results provide further evidence that chromosome 20 harbors genetic variants influencing ND in adult smokers.

Analysis of detailed phenotype profiles reveals CHRNA5-CHRNA3-CHRNB4 gene cluster association with several nicotine dependence traits

INTRODUCTION

The role of the nicotinic acetylcholine receptor gene cluster on chromosome 15q24-25 in the etiology of nicotine dependence (ND) is still being defined. In this study, we included all 15 tagging single nucleotide polymorphisms (SNPs) within the CHRNA5-CHRNA3-CHRNB4 cluster and tested associations with 30 smoking-related phenotypes.

METHODS

The study sample was ascertained from the Finnish Twin Cohort study. Twin pairs born 1938-1957 and concordant for a history of cigarette smoking were recruited along with their family members (mainly siblings), as part of the Nicotine Addiction Genetics consortium. The study sample consisted of 1,428 individuals (59% males) from 735 families, with mean age 55.6 years.

RESULTS

We detected multiple novel associations for ND. DSM-IV ND symptoms associated significantly with the proxy SNP Locus 1 (rs2036527, p = .000009) and Locus 2 (rs578776, p = .0001) and tolerance factor of the Nicotine Dependence Syndrome Scale (NDSS) showed suggestive association to rs11636753 (p = .0059), rs11634351 (p = .0069), and rs1948 (p = .0071) in CHRNB4. Furthermore, we report significant association with DSM-IV ND diagnosis (rs2036527, p = .0003) for the first time in a Caucasian population. Several SNPs indicated suggestive association for traits related to ages at smoking initiation. Also, rs11636753 in CHRNB4 showed suggestive association with regular drinking (p = .0029) and the comorbidity of depression and ND (p = .0034).

CONCLUSIONS

We demonstrate novel associations of DSM-IV ND symptoms and the NDSS tolerance subscale. Our results confirm and extend association findings for other ND measures. We show pleiotropic effects of this gene cluster on multiple measures of ND and also regular drinking and the comorbidity of ND and depression.

A 3p26-3p25 genetic linkage finding for DSM-IV major depression in heavy smoking families

OBJECTIVE

The authors tested for genetic linkage of DSM-IV-diagnosed major depressive disorder in families that were ascertained for cigarette smoking.

METHOD

Within a study that targeted families characterized by a history of smoking, analyses derived a subset of 91 Australian families with two or more offspring with a history of DSM-IV major depressive disorder (affected sibling pairs, N=187) and 25 Finnish families (affected sibling pairs, N=33). Within this affected sibling pairs design, the authors conducted nonparametric linkage analysis.

RESULTS

In the Australian heavy smoking families, the authors found a genome-wide significant multipoint LOD score of 4.14 for major depressive disorder on chromosome 3 at 24.9 cM (3p26-3p25).

CONCLUSIONS

Genome-wide significant linkage was detected for major depressive disorder on chromosome 3p in a sample ascertained for smoking. A linkage peak at this location was also observed in an independent study of major depressive disorder.

Linkage scan of nicotine dependence in the University of California, San Francisco (UCSF) Family Alcoholism Study

BACKGROUND

Nicotine dependence has been shown to represent a heritable condition, and several research groups have performed linkage analysis to identify genomic regions influencing this disorder though only a limited number of the findings have been replicated.

METHOD

In the present study, a genome-wide linkage scan for nicotine dependence was conducted in a community sample of 950 probands and 1204 relatives recruited through the University of California, San Francisco (UCSF) Family Alcoholism Study. A modified version of the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA) with additional questions that probe nicotine use was used to derive DSM-IV nicotine dependence diagnoses.

RESULTS

A locus on chromosome 2q31.1 at 184 centiMorgans nearest to marker D2S2188 yielded a logarithm (base 10) of odds (LOD) score of 3.54 (point-wise empirical p=0.000012). Additional peaks of interest were identified on chromosomes 2q13, 4p15.33-31, 11q25 and 12p11.23-21. Follow-up analyses were conducted examining the contributions of individual nicotine dependence symptoms to the chromosome 2q31.1 linkage peak as well as examining the relationship of this chromosomal region to alcohol dependence.

CONCLUSIONS

The present report suggests that chromosome 2q31.1 confers risk to the development of nicotine dependence and that this region influences a broad range of nicotine dependence symptoms rather than a specific facet of the disorder. Further, the results show that this region is not linked to alcohol dependence in this population, and thus may influence nicotine dependence specifically.

Evening types are more often current smokers and nicotine-dependent-a study of Finnish adult twins

AIMS

To examine the association between diurnal type and smoking status and nicotine dependence (ND).

DESIGN

A cohort study using random-effects model regressions for repeated longitudinal panel data was used to analyse smoking status by diurnal type. Regression analyses examined the association between diurnal type and ND.

PARTICIPANTS

A total of 23, 289 same-sex adult twin individuals from Finnish Twin Cohort. Nicotine dependence was studied in a subsample of 676 twin individuals.

MEASUREMENTS

Subjects were classified by self-report into four categories: morning type, somewhat morning type, somewhat evening type, evening type (in 1981). Smoking status was defined as current and ever smoking (in 1975, 1981 and 1990). ND was measured by DSM-IV and Fagerström Test for Nicotine Dependence (FTND) (during 2001-05). Findings  Evening types of both genders were much more likely to be current (OR = 2.91, 95% CI 2.50, 3.38) and life-time smokers (OR = 2.67, 95% CI 2.96, 4.07) compared to morning types. Evening types were less likely to stop smoking. The risk of nicotine dependence assessed by DSM-IV criteria was higher among evening types (OR = 2.78, 95% CI 1.64, 4.72). Evening types scored 0.59 (95% CI 0.01, 1.17) points higher than morning types on the FTND. Adjustment for potential confounders did not change these associations.

CONCLUSIONS

Being an evening type is associated independently with a higher risk of being a current smoker, being more highly dependent upon cigarettes and a lower likelihood of stopping smoking. Understanding the cause of these associations could elucidate the causes of tobacco addiction.

Genome-wide scan for self-rating of the effects of alcohol in American Indians

OBJECTIVE

This study's aims were to map loci linked to self-rating of the effects of alcohol and to determine if there was overlap with loci mapped earlier for other substance dependence phenotypes in an American Indian community at high risk for substance dependence.

METHODS

Each participant gave a blood sample and completed a structured diagnostic interview using the Semi Structured Assessment for the Genetics of Alcoholism. Retrospective report of responses to alcohol during the FIRST FIVE TIMES they had ever drank alcohol was estimated from the Self-Rating of the Effects of Alcohol (SRE) questionnaire for each participant. Genotypes were determined for a panel of 791 micro-satellite polymorphisms in 381 members of multiplex families using SOLAR.

RESULTS

Analyses of multipoint variance component Log of Odds (LOD) scores, for the FIRST FIVE TIMES phenotype, revealed two loci that had a LOD score greater than 3.0 on chromosomes 6 and 9. In addition, three locations were identified with LOD scores above 2.0 on chromosomes 10, 12, 17.

CONCLUSION

These results corroborate the importance of regions on chromosome 6 and 9 highlighted in earlier segregation studies in this and other populations for substance dependence-related phenotypes, as well as an area on chromosome 10 earlier identified for the FIRST FIVE TIMES phenotype in the collaborative study on the genetics of alcoholism. These studies additionally lend further support the construct that the SRE may represent an important endophenotype associated with alcohol and other substance dependence.

Bruxism is associated with nicotine dependence: a nationwide Finnish twin cohort study

OBJECTIVES

To investigate the association of smoking with bruxism while controlling for genetic and environmental factors using a co-twin-control design. Especially, the role of nicotine dependence was studied in this context.

METHODS

The material derives from the Finnish Twin Cohort consisting of 12,502 twin individuals who responded to a questionnaire in 1990 (response rate of 77%). All were born in 1930-1957, the mean age being 44 years. The questionnaire covered 103 multiple choice questions, 7 dealing with tobacco use and 22 with sleep and vigilance matters, including perceived bruxism. In addition, a subsample derived from the Nicotine Addiction Genetics Finland Study containing 445 twin individuals was studied.

RESULTS

In age- and gender-controlled multinomial logistic regression, both monthly and rarely reported bruxism associated with both current cigarette smoking (odds ratio [OR] = 1.74 and 1.64) and former cigarette smoking (OR = 1.64 and 1.47). Weekly bruxism associated with current smoking (OR = 2.85). Current smokers smoking 20 or more cigarettes a day reported weekly bruxism more likely (OR = 1.61-1.97) than those smoking less. Among twin pairs (N = 142) in which one twin was a weekly bruxer and the cotwin a never bruxer, there were 13 monozygotic pairs in which one twin was a current smoker and the other twin was not. In all cases, the bruxer was the smoker (p = .0003). Nicotine dependence associated significantly with bruxism.

CONCLUSIONS

Our twin study provides novel evidence for a possible causal link between tobacco use and bruxism among middle-aged adults. Nicotine dependence may be a significant predisposing factor for bruxism.

Multiple independent loci at chromosome 15q25.1 affect smoking quantity: a meta-analysis and comparison with lung cancer and COPD

Recently, genetic association findings for nicotine dependence, smoking behavior, and smoking-related diseases converged to implicate the chromosome 15q25.1 region, which includes the CHRNA5-CHRNA3-CHRNB4 cholinergic nicotinic receptor subunit genes. In particular, association with the nonsynonymous CHRNA5 SNP rs16969968 and correlates has been replicated in several independent studies. Extensive genotyping of this region has suggested additional statistically distinct signals for nicotine dependence, tagged by rs578776 and rs588765. One goal of the Consortium for the Genetic Analysis of Smoking Phenotypes (CGASP) is to elucidate the associations among these markers and dichotomous smoking quantity (heavy versus light smoking), lung cancer, and chronic obstructive pulmonary disease (COPD). We performed a meta-analysis across 34 datasets of European-ancestry subjects, including 38,617 smokers who were assessed for cigarettes-per-day, 7,700 lung cancer cases and 5,914 lung-cancer-free controls (all smokers), and 2,614 COPD cases and 3,568 COPD-free controls (all smokers). We demonstrate statistically independent associations of rs16969968 and rs588765 with smoking (mutually adjusted p-values<10(-35) and <10(-8) respectively). Because the risk alleles at these loci are negatively correlated, their association with smoking is stronger in the joint model than when each SNP is analyzed alone. Rs578776 also demonstrates association with smoking after adjustment for rs16969968 (p<10(-6)). In models adjusting for cigarettes-per-day, we confirm the association between rs16969968 and lung cancer (p<10(-20)) and observe a nominally significant association with COPD (p = 0.01); the other loci are not significantly associated with either lung cancer or COPD after adjusting for rs16969968. This study provides strong evidence that multiple statistically distinct loci in this region affect smoking behavior. This study is also the first report of association between rs588765 (and correlates) and smoking that achieves genome-wide significance; these SNPs have previously been associated with mRNA levels of CHRNA5 in brain and lung tissue.

A genomewide association study of nicotine and alcohol dependence in Australian and Dutch populations

Persistent tobacco use and excessive alcohol consumption are major public health concerns worldwide. Both alcohol and nicotine dependence (AD, ND) are genetically influenced complex disorders that exhibit a high degree of comorbidity. To identify gene variants contributing to one or both of these addictions, we first conducted a pooling-based genomewide association study (GWAS) in an Australian population, using Illumina Infinium 1M arrays. Allele frequency differences were compared between pooled DNA from case and control groups for: (1) AD, 1224 cases and 1162 controls; (2) ND, 1273 cases and 1113 controls; and (3) comorbid AD and ND, 599 cases and 488 controls. Secondly, we carried out a GWAS in independent samples from the Netherlands for AD and for ND. Thirdly, we performed a meta-analysis of the 10,000 most significant AD- and ND-related SNPs from the Australian and Dutch samples. In the Australian GWAS, one SNP achieved genomewide significance (p < 5 x 10(-8)) for ND (rs964170 in ARHGAP10 on chromosome 4, p = 4.43 x 10(-8)) and three others for comorbid AD/ND (rs7530302 near MARK1 on chromosome 1 (p = 1.90 x 10(-9)), rs1784300 near DDX6 on chromosome 11 (p = 2.60 x 10(-9)) and rs12882384 in KIAA1409 on chromosome 14 (p = 4.86 x 10(-8))). None of the SNPs achieved genomewide significance in the Australian/Dutch meta-analysis, but a gene network diagram based on the top-results revealed overrepresentation of genes coding for ion-channels and cell adhesion molecules. Further studies will be required before the detailed causes of comorbidity between AD and ND are understood.

Confirmation and generalization of an alcohol-dependence locus on chromosome 10q

Several genome scans on alcohol dependence (AD) and AD-related traits have been published. In this article, we present the results of a genome-wide linkage scan on AD and several related traits in 322 European-American (EA) families, and results of additional analysis in 335 African-American (AA) families that were the subject of a previous report. All families were initially ascertained for cocaine and/or opioid dependence. Non-parametric linkage analysis in the EA sample revealed suggestive linkages on chromosomes 7 (LOD=2.1 at 82.8 cM, p=0.0009) and 10 (LOD=3.0 at 137.7 cM, p=0.0001). The chromosome 10 linkage peak is 20 cM distal from a genome-wide significant linkage peak we observed previously in the AA sample. Parametric linkage analysis on chromosome 10 (assuming a recessive model, 80% penetrance, disease allele frequency=0.3) resulted in LOD scores of 2.7 at 136.7 cM and 1.9 at 121.7 cM in the EA and AA samples, respectively, with a combined sample genome-wide significant LOD score of 4.1 at 131.7 cM. To reduce heterogeneity of the AD phenotype, we also assessed linkage of chromosome 10 markers with the presence of alcohol withdrawal symptoms, one of the seven components of the DSM-IV diagnosis of AD. Suggestive evidence for linkage was observed in both populations with only 5 cM separating the location of the peak LOD scores despite a loss of power due to a smaller number of families informative for this trait. Results of our study confirm a chromosome 10 risk locus for AD in two genetically distinct populations and suggest that this locus may correspond more precisely to a specific component of the disorder.

A Genomewide Association Study of Nicotine and Alcohol Dependence in Australian and Dutch Populations

Persistent tobacco use and excessive alcohol consumption are major public health concerns worldwide. Both alcohol and nicotine dependence (AD, ND) are genetically influenced complex disorders that exhibit a high degree of comorbidity. To identify gene variants contributing to one or both of these addictions, we first conducted a pooling-based genomewide association study (GWAS) in an Australian population, using Illumina Infinium 1M arrays. Allele frequency differences were compared between pooled DNA from case and control groups for: (1) AD, 1224 cases and 1162 controls; (2) ND, 1273 cases and 1113 controls; and (3) comorbid AD and ND, 599 cases and 488 controls. Secondly, we carried out a GWAS in independent samples from the Netherlands for AD and for ND. Thirdly, we performed a meta-analysis of the 10, 000 most significant AD- and ND-related SNPs from the Australian and Dutch samples. In the Australian GWAS, one SNP achieved genomewide significance (p < 5 x 10-8) for ND (rs964170 in ARHGAPlOon chromosome 4, p = 4.43 x 10”8) and three others for comorbid AD/ND (rs7530302 near MARK1 on chromosome 1 (p = 1.90 x 10-9), rs1784300 near DDX6 on chromosome 11 (p = 2.60 x 10-9) and rs12882384 in KIAA1409 on chromosome 14 (p = 4.86 x 10-8)). None of the SNPs achieved genomewide significance in the Australian/Dutch meta-analysis, but a gene network diagram based on the top-results revealed overrepre-sentation of genes coding for ion-channels and cell adhesion molecules. Further studies will be requirec before the detailed causes of comorbidity between AC and ND are understood.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Genetic linkage findings for DSM-IV nicotine withdrawal in two populations

Nicotine withdrawal (NW) is both an important contributor to difficulty quitting cigarettes and because of mood-related withdrawal symptoms a problem of particular relevance to psychiatry. Twin-studies suggest that genetic factors influence NW (heritability = 45%). Only one previous linkage study has published findings on NW [Swan et al. (2006); Am J Med Genet Part B 141B:354-360; LOD = 2.7; Chr. 6 at 159 cM]. As part of an international consortium, genome-wide scans (using over 360 autosomal microsatellite markers) and telephone diagnostic interviews were conducted on 289 Australian (AUS) and 161 Finnish (FIN, combined (COMB) N = 450 families) families ascertained from twin registries through index-cases with a lifetime history of cigarette smoking. The statistical approach used an affected-sib-pair design (at least two adult full siblings reported a history of DSM-IV NW) and conducted the linkage analyses using MERLIN. Linkage signals with LOD scores >1.5 were found on two chromosomes: 6 (FIN: LOD = 1.93 at 75 cM) and 11 at two different locations (FIN: LOD = 3.55 at 17 cM, and AUS: LOD = 1.68 with a COMB: LOD = 2.30 at 123 cM). The multipoint LOD score of 3.55 on chromosome 11p15 in FIN met genomewide significance (P = 0.013 with 1,000 simulations). At least four strong candidate genes lie within or near this peak on chromosome 11: DRD4, TPH, TH, and CHRNA10. Other studies have reported that chromosome 11 may harbor genes associated with various aspects of smoking behavior. This study adds to that literature by highlighting evidence for NW.

Differential contribution of genetic variation in multiple brain nicotinic cholinergic receptors to nicotine dependence: recent progress and emerging open questions

Nicotine dependence (ND), a major public health challenge, is a complex, multifactorial behavior, in which both genetic and environmental factors have a role. Brain nicotinic acetylcholine receptor (nAChR)-encoding genes are among the most prominent candidate genes studied in the context of ND, because of their biological relevance as binding sites for nicotine. Until recently, most research on the role of nAChRs in ND has focused on two of these genes (encoding the alpha4- and beta2-subunits) and not much attention has been paid to the possible contribution of the other nine brain nAChR subunit genes (alpha2-alpha3, alpha5-alpha7, alpha9-alpha10, beta3-beta4) to the pathophysiology and genetics of ND. This situation has changed dramatically in the last 2 years during which intensive research had addressed the issue, mainly from the genetics perspective, and has shown the importance of the CHRNA5-CHRNA3-CHRNB4 and CHRNA6-CHRNB3 loci in ND-related phenotypes. In this review, we highlight recent findings regarding the contribution of non-alpha4/beta2-subunit containing nAChRs to ND, based on several lines of evidence: (1) human genetics studies (including linkage analysis, candidate-gene association studies and whole-genome association studies) of several ND-related phenotypes; (2) differential pharmacological and biochemical properties of receptors containing these subunits; (3) evidence from genetically manipulated mice; and (4) the contribution of nAChR genes to ND-related personality traits and neurocognitive profiles. Combining neurobiological genetic and behavioral perspectives, we suggest that genetic susceptibility to ND is not linked to one or two specific nAChR subtype genes but to several. In particular, the alpha3, alpha5-6 and beta3-4 nAChR subunit-encoding genes may play a much more pivotal role in the neurobiology and genetics of ND than was appreciated earlier. At the functional level, variants in these subunit genes (most likely regulatory) may have independent as well as interactive contributions to the ND phenotype spectrum. We address methodological challenges in the field, highlight open questions and suggest possible pathways for future research.

Impact of the dopamine receptor gene family on temperament traits in a population-based birth cohort

Although the genetic determinants of personality have been intensively investigated especially since Cloninger proposed his psychobiological model of temperament and character, findings to date remain inconclusive and very few studies have addressed the topic in large population cohorts. In the current study we investigated one gene family in its entirety by addressing the role of all known dopamine receptor genes, DRD1-DRD5, on Cloninger's temperament traits in a Finnish population-based birth cohort. The study sample (n = 1,434) was ascertained from the Northern Finland Birth Cohort 1966 with over 5,000 study individuals tested at the age of 31 years. We utilized the genetic homogeneity and genealogical structure of this population to uncover putative effects of these genes on temperament traits at the population level. Our strategy utilizing a large birth cohort and its well established genealogical structure represents an optimal design for studying normally distributed traits. We also wished to provide a comprehensive view to one biologically relevant gene family instead of testing single candidate genes. We report evidence of association of several SNPs at the 5' end of dopamine receptor D2 (DRD2) with Novelty seeking (low) and Harm avoidance (high), and at the 3' end of DRD2 with Persistence. The strongest evidence of association emerged from females. Our study supports the involvement of the dopamine pathway in temperament traits, in particular underlining the role of DRD2 in Novelty seeking, Harm avoidance and Persistence.

Impulsiveness and cigarette smoking

OBJECTIVE

Varying aspects of impulsive personality have been associated with tobacco use in cross-sectional and prospective studies, including novelty seeking and (low) constraint but most studies have not examined more than one tobacco use phenotype (e.g., any tobacco use versus dependence) or considered more than one variety of impulsiveness simultaneously.

METHODS

The current study was conducted to evaluate the association of impulsive personality features with multiple tobacco use phenotypes including smoking status, lifetime tobacco consumption, and dependence in a sample of 1284 adults between the ages of 30 and 54. Participants completed multiple self-report measures of impulsive personality and were interviewed regarding lifetime tobacco use.

RESULTS

Results revealed that reward seeking and disinhibitory traits were both associated with smoking status but only disinhibition was associated with tobacco dependence, after controlling for reward seeking.

CONCLUSIONS

The results reported here may aid investigations aimed at identifying neurobiological, including genetic, correlates of tobacco use and dependence by providing potential behavioral correlates of the diversity of tobacco use phenotypes. Moreover, successful efforts to prevent tobacco-related disease through prevention or cessation programs will be facilitated by the identification of factors that are differentially associated with different smoking phenotypes.

Genetic variation in the dopamine pathway and smoking cessation

Twin and family studies have established that genetic factors account for much of the variation in tobacco dependence. Therefore, identification of genetic variants predictive of successful smoking cessation has implications for the future prospect of personalized smoking cessation therapies. Converging data implicate the dopamine pathway as an important neural substrate for tobacco dependence. Several candidate genes within the dopamine pathway (e.g., DRD2 and COMT) have been reported to be associated with the efficacy of bupropion and nicotine replacement therapy, and others (e.g., SLC6A3 and DRD4) have been reported to be associated with smoking cessation independent of pharmacotherapy. However, few of these candidate genes are present within regions of suggestive or significant linkage or overlap with genome-wide linkage or association studies of tobacco dependence or smoking cessation. Future studies should seek to replicate genome-wide association analyses with individual-level genotyping, and use better-defined smoking cessation phenotypes. Once robust evidence for association is established, which may take several more years, further research into the likely cost-effectiveness, feasibility and acceptability of personalized medicine for smoking cessation will be necessary before it can be translated into practice.

Genetic variability in nicotinic acetylcholine receptors and nicotine addiction: converging evidence from human and animal research

Tobacco smoking is a leading preventable cause of death in the United States and produces a major health and economic burden. Although the majority of smokers want to quit, few are successful. These data highlight the need for additional research into the neurobiology of tobacco dependence. Addiction to nicotine, the main psychoactive component of tobacco, is influenced by multiple factors that include individual differences in genetic makeup. Twin studies have demonstrated that genetic factors can influence vulnerability to nicotine addiction, and subsequent research has identified genes that may alter sensitivity to nicotine. In humans, genome-wide and candidate gene association studies have demonstrated that genes encoding nicotinic acetylcholine receptor (nAChR) proteins are associated with multiple smoking phenotypes. Similarly, research in mice has provided evidence that naturally occurring variability in nAChR genes is associated with changes in nicotine sensitivity. Furthermore, the use of genetic knockout mice has allowed researchers to determine the nAChR genes that mediate the effects of nicotine, whereas research with knockin mice has demonstrated that changes to nAChR genes can dramatically alter nicotine sensitivity. This review will examine the genetic factors that alter susceptibility to nicotine addiction, with an emphasis on the genes that encode nAChR proteins.

Substance dependence low-density whole genome association study in two distinct American populations

Cocaine and opioid dependence are common, complex disorders with high heritability that commonly co-occur with other substance dependence disorders. Improved insight into the genetic basis of substance dependence would help elucidate its etiology and could inform its prevention and treatment. To generate new hypotheses about the genetics of substance dependence, we genotyped 5633 tagging single nucleotide polymorphism (SNP) markers in 1699 subjects from 339 African American (AA) families and 334 European American (EA) families ascertained through a sib pair meeting DSM-IV criteria for either cocaine or opioid dependence. The associations between genetic markers and five substance dependence traits (cocaine dependence, opioid dependence, cocaine-induced paranoia, alcohol dependence, and nicotine dependence) were assessed by family based association tests (FBAT). Results were ranked according to several criteria including statistical significance, concordance of results across population samples, and potential biological relevance of the implicated gene. The top-ranked result was an association of SNP rs1133503 in the MANEA gene with cocaine-induced paranoia (CIP). Our study provides an initial substance dependence trait-specific blueprint of associated regions for future candidate gene studies.

Differences in smoking habits of MZ and DZ twins: a commentary on Tishler and Carey

Tishler and Carey (this issue, 2007) have analyzed the difference in ever smoking prevalence between monozygotic (MZ) and dizygotic (DZ) twins in 8 published twin studies. They conclude that the lower prevalence in MZ twins might invalidate conclusions from classic twin models. I critique the conducted meta-analysis and suggest additional analyses to be conducted. A reanalysis of the Finnish Twin Cohort 1975 questionnaire data (included in Tisher and Carey) indicates that when intrapair correlations are correctly taken into account, the MZ-DZ difference in that study is no longer statistically significant. Even if the Tisher/Carey finding holds up in further analyses, it pertains only to the observed trait, the effect is small in size, and the mechanism underlying it needs to be explored.

Identifying susceptibility loci for nicotine dependence: 2008 update based on recent genome-wide linkage analyses

Tobacco smoking is a severe health hazard worldwide, as nearly one-third of the global adult population smokes tobacco products. This high prevalence highlights the importance of studying the genetic determinants of nicotine dependence (ND). To identify such genetic factors, more than 20 genome-wide linkage studies have been conducted across different populations using a variety of ND assessment approaches, including smoking quantity (SQ), Heaviness of Smoking Index (HSI), Fagerström Test for Nicotine Dependence (FTND), ever-smoking, habitual smoking, or maximum number of cigarettes smoked in a 24-h period. This review provides a critical update on the progress during the years since our last review, published in 2004, in identifying susceptibility loci for ND. Although a significant number of reported genomic regions did not reach the level of "suggestive" or "significant" linkage and failed to be replicated in other independent studies, thirteen regions, located on chromosomes 3-7, 9-11, 17, 20, and 22, have been found to be suggestive or significant in at least two independent samples. Among them, the regions on chromosomes 9 (91.9-136.5 cM), 10, 11, and 17 have received the strongest support. A summary of eight regions that have been nominated for "significant" linkage to ND is provided.