Loci on chromosome 20 interact with rs16969968 to influence cigarettes per day in European ancestry individuals.

BACKGROUND: The understanding of the molecular genetic contributions to smoking is largely limited to the additive effects of individual single nucleotide polymorphisms (SNPs), but the underlying genetic risk is likely to also include dominance, epistatic, and gene-environment interactions. METHODS: To begin to address this complexity, we attempted to identify genetic interactions between rs16969968, the most replicated SNP associated with smoking quantity, and all SNPs and genes across the genome. RESULTS: Using the UK Biobank European subsample, we found one SNP, rs1892967, and two genes, PCNA and TMEM230, that showed a significant genome-wide interaction with rs16969968 for log10 CPD and raw CPD, respectively, in a sample of 116 442 individuals who self-reported currently or previously smoking. We extended these analyses to individuals of South Asian descent and meta-analyzed the combined sample of 117 212 individuals of European and South Asian ancestry. We replicated the gene findings in a meta-analysis of five Finnish samples (N=40 140): FinHealth, FINRISK, Finnish Twin Cohort, GeneRISK, and Health-2000-2011. CONCLUSIONS: To our knowledge, this represents the first reliable epistatic association between single nucleotide polymorphisms for smoking behaviors and provides a novel direction for possible future functional studies related to this interaction. Furthermore, this work demonstrates the feasibility of these analyses by pooling multiple datasets across various ancestries, which may be applied to other top SNPs for smoking and/or other phenotypes.

Testing Association of Previously Implicated Gene Sets and Gene-Networks in Nicotine Exposed Mouse Models with Human Smoking Phenotypes.

INTRODUCTION: Smoking behaviors are partly heritable, yet the genetic and environmental mechanisms underlying smoking phenotypes are not fully understood. Developmental nicotine exposure (DNE) is a significant risk factor for smoking and leads to gene expression changes in mouse models; however, it is unknown whether the same genes whose expression is impacted by DNE are also those underlying smoking genetic liability. We examined whether genes whose expression in D1-type striatal medium spiny neurons due to DNE in the mouse are also associated with human smoking behaviors. METHODS: Specifically, we assessed whether human orthologs of mouse-identified genes, either individually or as a set, were genetically associated with five human smoking traits using MAGMA and S-LDSC while implementing a novel expression-based gene-SNP annotation methodology. RESULTS: We found no strong evidence that these genes sets were more strongly associated with smoking behaviors than the rest of the genome, but ten of these individual genes were significantly associated with three of the five human smoking traits examined (p < 2.5e-6). Three of these genes have not been reported previously and were discovered only when implementing the expression-based annotation. CONCLUSIONS: These results suggest the genes whose expression is impacted by DNE in mice are largely distinct from those contributing to smoking genetic liability in humans. However, examining a single mouse neuronal cell type may be too fine a resolution for comparison, suggesting that experimental manipulation of nicotine consumption, reward, or withdrawal in mice may better capture genes related to the complex genetics of human tobacco use. IMPLICATIONS: Genes whose expression is impacted by DNE in mouse D1-type striatal medium spiny neurons were not found to be, as a whole, more strongly associated with human smoking behaviors than the rest of the genome, though ten individual mouse-identified genes were associated with human smoking traits. This suggests little overlap between the genetic mechanisms impacted by DNE and those influencing heritable liability to smoking phenotypes in humans. Further research is warranted to characterize how developmental nicotine exposure paradigms in mice can be translated to understand nicotine use in humans and their heritable effects on smoking.

Genetic architecture of four smoking behaviors using partitioned SNP heritability.

BACKGROUND AND AIMS: Although genome-wide association studies have identified many loci that influence smoking behaviors, much of the genetic variance remains unexplained. We characterized the genetic architecture of four smoking behaviors using single nucleotide polymorphism (SNP) heritability (h2SNP ). This is an estimate of narrow-sense heritability specifically estimating the proportion of phenotypic variation due to causal variants (CVs) tagged by SNPs. DESIGN: Partitioned h2SNP analysis of smoking behavior traits. SETTING: UK Biobank. PARTICIPANTS: UK Biobank participants of European ancestry. The number of participants varied depending on the trait, from 54 792 to 323 068. MEASUREMENTS: Smoking initiation, age of initiation, cigarettes per day (CPD; count, log-transformed, binned and dichotomized into heavy versus light) and smoking cessation with imputed genome-wide SNPs. FINDINGS: We estimated that, in aggregate, approximately 18% of the phenotypic variance in smoking initiation was captured by imputed SNPs [h2SNP = 0.18, standard error (SE) = 0.01] and 12% [SE = 0.02] for smoking cessation, both of which were more than twice the previously reported estimates. Estimated age of initiation (h2SNP  = 0.05, SE = 0.01) and binned CPD (h2SNP  = 0.1, SE = 0.01) were substantially below published twin-based h2 of 50%. CPD encoding influenced estimates, with dichotomized CPD h2SNP  = 0.28. There was no evidence of dominance genetic variance for any trait. CONCLUSION: A biobank study of smoking behavior traits suggested that the phenotypic variance explained by SNPs of smoking initiation, age of initiation, cigarettes per day and smoking cessation is modest overall.

Little Evidence of Modified Genetic Effect of rs16969968 on Heavy Smoking Based on Age of Onset of Smoking.

INTRODUCTION: Tobacco smoking is the leading cause of preventable death globally. Smoking quantity, measured in cigarettes per day, is influenced both by the age of onset of regular smoking (AOS) and by genetic factors, including a strong effect of the nonsynonymous single-nucleotide polymorphism rs16969968. A previous study by Hartz et al. reported an interaction between these two factors, whereby rs16969968 risk allele carriers who started smoking earlier showed increased risk for heavy smoking compared with those who started later. This finding has yet to be replicated in a large, independent sample. METHODS: We performed a preregistered, direct replication attempt of the rs16969968 × AOS interaction on smoking quantity in 128 383 unrelated individuals from the UK Biobank, meta-analyzed across ancestry groups. We fit statistical association models mirroring the original publication as well as formal interaction tests on multiple phenotypic and analytical scales. RESULTS: We replicated the main effects of rs16969968 and AOS on cigarettes per day but failed to replicate the interaction using previous methods. Nominal significance of the rs16969968 × AOS interaction term depended strongly on the scale of analysis and the particular phenotype, as did associations stratified by early/late AOS. No interaction tests passed genome-wide correction (α = 5e-8), and all estimated interaction effect sizes were much smaller in magnitude than previous estimates. CONCLUSIONS: We failed to replicate the strong rs16969968 × AOS interaction effect previously reported. If such gene-moderator interactions influence complex traits, they likely depend on scale of measurement, and current biobanks lack the power to detect significant genome-wide associations given the minute effect sizes expected. IMPLICATIONS: We failed to replicate the strong rs16969968 × AOS interaction effect on smoking quantity previously reported. If such gene-moderator interactions influence complex traits, current biobanks lack the power to detect significant genome-wide associations given the minute effect sizes expected. Furthermore, many potential interaction effects are likely to depend on the scale of measurement employed.

The Role of A Priori-Identified Addiction and Smoking Gene Sets in Smoking Behaviors.

INTRODUCTION: Smoking is a leading cause of death, and genetic variation contributes to smoking behaviors. Identifying genes and sets of genes that contribute to risk for addiction is necessary to prioritize targets for functional characterization and for personalized medicine. METHODS: We performed a gene set-based association and heritable enrichment study of two addiction-related gene sets, those on the Smokescreen Genotyping Array and the nicotinic acetylcholine receptors, using the largest available GWAS summary statistics. We assessed smoking initiation, cigarettes per day, smoking cessation, and age of smoking initiation. RESULTS: Individual genes within each gene set were significantly associated with smoking behaviors. Both sets of genes were significantly associated with cigarettes per day, smoking initiation, and smoking cessation. Age of initiation was only associated with the Smokescreen gene set. Although both sets of genes were enriched for trait heritability, each accounts for only a small proportion of the single nucleotide polymorphism-based heritability (2%-12%). CONCLUSIONS: These two gene sets are associated with smoking behaviors, but collectively account for a limited amount of the genetic and phenotypic variation of these complex traits, consistent with high polygenicity. IMPLICATIONS: We evaluated evidence for the association and heritable contribution of expert-curated and bioinformatically identified sets of genes related to smoking. Although they impact smoking behaviors, these specifically targeted genes do not account for much of the heritability in smoking and will be of limited use for predictive purposes. Advanced genome-wide approaches and integration of other 'omics data will be needed to fully account for the genetic variation in smoking phenotypes.

Common and Rare Variants Genetic Association Analysis of Cigarettes per Day Among Ever-Smokers in Chronic Obstructive Pulmonary Disease Cases and Controls.

INTRODUCTION: Cigarette smoking is a major environmental risk factor for many diseases, including chronic obstructive pulmonary disease (COPD). There are shared genetic influences on cigarette smoking and COPD. Genetic risk factors for cigarette smoking in cohorts enriched for COPD are largely unknown. METHODS: We performed genome-wide association analyses for average cigarettes per day (CPD) across the Genetic Epidemiology of COPD (COPDGene) non-Hispanic white (NHW) (n = 6659) and African American (AA) (n = 3260), GenKOLS (the Genetics of Chronic Obstructive Lung Disease) (n = 1671), and ECLIPSE (the Evaluation of COPD Longitudinally to Identify Predictive Surrogate Endpoints) (n = 1942) cohorts. In addition, we performed exome array association analyses across the COPDGene NHW and AA cohorts. We considered analyses across the entire cohort and stratified by COPD case-control status. RESULTS: We identified genome-wide significant associations for CPD on chromosome 15q25 across all cohorts (lowest p = 1.78 × 10-15), except in the COPDGene AA cohort alone. Previously reported associations on chromosome 19 had suggestive and directionally consistent associations (RAB4, p = 1.95 × 10-6; CYP2A7, p = 7.50 × 10-5; CYP2B6, p = 4.04 × 10-4). When we stratified by COPD case-control status, single nucleotide polymorphisms on chromosome 15q25 were nominally associated with both NHW COPD cases (ß = 0.11, p = 5.58 × 10-4) and controls (ß = 0.12, p = 3.86 × 10-5) For the gene-based exome array association analysis of rare variants, there were no exome-wide significant associations. For these previously replicated associations, the most significant results were among COPDGene NHW subjects for CYP2A7 (p = 5.2 × 10-4). CONCLUSIONS: In a large genome-wide association study of both common variants and a gene-based association of rare coding variants in ever-smokers, we found genome-wide significant associations on chromosome 15q25 with CPD for common variants, but not for rare coding variants. These results were directionally consistent among COPD cases and controls. IMPLICATIONS: We examined both common and rare coding variants associated with CPD in a large population of heavy smokers with and without COPD of NHW and AA descent. We replicated genome-wide significant associations on chromosome 15q25 with CPD for common variants among NHW subjects, but not for rare variants. We demonstrated for the first time that common variants on chromosome 15q25 associated with CPD are similar among COPD cases and controls. Previously reported associations on chromosome 19 showed suggestive and directionally consistent associations among common variants (RAB4, CYP2A7, and CYP2B6) and for rare variants (CYP2A7) among COPDGene NHW subjects. Although the genetic effect sizes for these single nucleotide polymorphisms on chromosome 15q25 are modest, we show that this creates a substantial smoking burden over the lifetime of a smoker.

Examination of the Involvement of Cholinergic-Associated Genes in Nicotine Behaviors in European and African Americans.

INTRODUCTION: Cigarette smoking is a physiologically harmful habit. Nicotinic acetylcholine receptors (nAChRs) are bound by nicotine and upregulated in response to chronic exposure to nicotine. It is known that upregulation of these receptors is not due to a change in mRNA of these genes, however, more precise details on the process are still uncertain, with several plausible hypotheses describing how nAChRs are upregulated. We have manually curated a set of genes believed to play a role in nicotine-induced nAChR upregulation. Here, we test the hypothesis that these genes are associated with and contribute risk for nicotine dependence (ND) and the number of cigarettes smoked per day (CPD). METHODS: Studies with genotypic data on European and African Americans (EAs and AAs, respectively) were collected and a gene-based test was run to test for an association between each gene and ND and CPD. RESULTS: Although several novel genes were associated with CPD and ND at P < 0.05 in EAs and AAs, these associations did not survive correction for multiple testing. Previous associations between CHRNA3, CHRNA5, CHRNB4 and CPD in EAs were replicated. CONCLUSIONS: Our hypothesis-driven approach avoided many of the limitations inherent in pathway analyses and provided nominal evidence for association between cholinergic-related genes and nicotine behaviors. IMPLICATIONS: We evaluated the evidence for association between a manually curated set of genes and nicotine behaviors in European and African Americans. Although no genes were associated after multiple testing correction, this study has several strengths: by manually curating a set of genes we circumvented the limitations inherent in many pathway analyses and tested several genes that had not yet been examined in a human genetic study; gene-based tests are a useful way to test for association with a set of genes; and these genes were collected based on literature review and conversations with experts, highlighting the importance of scientific collaboration.

The ß3 subunit of the nicotinic acetylcholine receptor: Modulation of gene expression and nicotine consumption.

Genetic factors explain approximately half of the variance in smoking behaviors, but the molecular mechanism by which genetic variation influences behavior is poorly understood. SNPs in the putative promoter region of CHRNB3, the gene that encodes the ß3 subunit of the nicotinic acetylcholine receptor (nAChR), have been repeatedly associated with nicotine behaviors. In this work we sought to identify putative function of three SNPs in the promoter region of CHRNB3 on in vitro gene expression. Additionally, we used ß3 null mutant mice as a model of reduced gene expression to assess the effects on nicotine behaviors. The effect of rs13277254, rs6474413, and rs4950 on reporter gene expression was examined using a luciferase reporter assay. A major and minor parent haplotype served as the background on which alleles at the three SNPs were flipped onto different backgrounds (e.g. minor allele on major haplotype background). Constructs were tested in three human cell lines: BE(2)-C, SH-SY5Y and HEK293T. In all cell types the major haplotype led to greater reporter gene expression compared to the minor haplotype, and results indicate that this effect is driven by rs6474413. Moreover, mice lacking the ß3 subunit showed reduced voluntary nicotine consumption compared that of wildtype animals. These data provide evidence that the protective genetic variant at rs6474413 identified in human genetic studies reduces gene expression and that decreased ß3 gene expression in mice reduces nicotine intake. This work contributes to our understanding of the molecular mechanisms that contribute to the human genetic associations of tobacco behaviors.

The interactive effect of neighborhood peer cigarette use and 5HTTLPR genotype on individual cigarette use.

BACKGROUND: Previous cross-sectional research has shown that adolescents' cigarette use is interactively associated with that of their school peers and their 5HTTLPR genotype, such that the cigarette use of persons with more copies of the 5HTTLPR*S' allele is more dependent on school peers' cigarette use behaviors than their counterparts. This analysis seeks to extend this novel finding by examining whether the same conclusion can be reached when substituting neighborhood peers for school peers and examining the timing of the initiation of any and regular smoking in adolescence. METHODS: This analysis employs an independent sample with longitudinal measures of cigarette use among 6th through 8th graders clustered in 82 neighborhoods, of whom 1098 contributed genetic data. The proportion of respondents who had ever smoked cigarettes by the first wave was calculated for each census block group in the study. 5HTTLPR genotype was assayed using the method of Whisman et al. (2011). The timing of any or regular smoking initiation and over four years were modeled as dependent variables using Cox proportional hazard models. RESULTS: The interaction of neighborhood peer smoking behavior in the first wave and 5HTTLPR genotype statistically significantly predicted any smoking initiation (hazard ratio: 3.532; p-value=0.002) and regular smoking initiation (hazard ratio: 5.686; p-value=0.000), net of controls for sex, race/ethnicity, grade in the first wave of data, and parental educational attainment. These findings reach the same conclusions as previous cross-sectional research. CONCLUSIONS: These results differ in the model of gene-environment interaction that they support. The findings for any smoking initiation are consistent with the diathesis-stress model of gene-environment interaction; the findings for regular smoking initiation are consistent with the differential susceptibility model.

Stress-response pathways are altered in the hippocampus of chronic alcoholics.

The chronic high-level alcohol consumption seen in alcoholism leads to dramatic effects on the hippocampus, including decreased white matter, loss of oligodendrocytes and other glial cells, and inhibition of neurogenesis. Examining gene expression in post mortem hippocampal tissue from 20 alcoholics and 19 controls allowed us to detect differentially expressed genes that may play a role in the risk for alcoholism or whose expression is modified by chronic consumption of alcohol. We identified 639 named genes whose expression significantly differed between alcoholics and controls at a False Discovery Rate (FDR) ≤ 0.20; 52% of these genes differed by at least 1.2-fold. Differentially expressed genes included the glucocorticoid receptor and the related gene FK506 binding protein 5 (FKBP5), UDP glycosyltransferase 8 (UGT8), urea transporter (SLC14A1), zinc transporter (SLC39A10), Interleukin 1 receptor type 1 (IL1R1), thioredoxin interacting protein (TXNIP), and many metallothioneins. Pathways related to inflammation, hypoxia, and stress showed activation, and pathways that play roles in neurogenesis and myelination showed decreases. The cortisol pathway dysregulation and increased inflammation identified here are seen in other stress-related conditions such as depression and post-traumatic stress disorder and most likely play a role in addiction. Many of the detrimental effects on the hippocampus appear to be mediated through NF-κB signaling. Twenty-four of the differentially regulated genes were previously identified by genome-wide association studies of alcohol use disorders; this raises the potential interest of genes not normally associated with alcoholism, such as suppression of tumorigenicity 18 (ST18), BCL2-associated athanogene 3 (BAG3), and von Willebrand factor (VWF).

Functional characterization of SNPs in CHRNA3/B4 intergenic region associated with drug behaviors.

The cluster of human neuronal nicotinic receptor genes (CHRNA5/A3/B4) (15q25.1) has been associated with a variety of smoking and drug-related behaviors, as well as risk for lung cancer. CHRNA3/B4 intergenic single nucleotide polymorphisms (SNPs) rs1948 and rs8023462 have been associated with early initiation of alcohol and tobacco use, and rs6495309 has been associated with nicotine dependence and risk for lung cancer. An in vitro luciferase expression assay was used to determine whether these SNPs and surrounding sequences contribute to differences in gene expression using cell lines either expressing proteins characteristic of neuronal tissue or derived from lung cancers. Electrophoretic mobility shift assays (EMSAs) were performed to investigate whether nuclear proteins from these cell lines bind SNP alleles differentially. Results from expression assays were dependent on cell culture type and haplotype. EMSAs indicated that rs8023462 and rs6495309 bind nuclear proteins in an allele-specific way. Additionally, GATA transcription factors appeared to bind rs8023462 only when the minor/risk allele was present. Much work has been done to describe the rat Chrnb4/a3 intergenic region, but few studies have examined the human intergenic region effects on expression; therefore, these studies greatly aid human genetic research as it relates to observed nicotine phenotypes, lung cancer risk and potential underlying genetic mechanisms. Data from these experiments support the hypothesis that SNPs associated with human addiction-related phenotypes and lung cancer risk can affect gene expression, and are potential therapeutic targets. Additionally, this is the first evidence that rs8023462 interacts with GATA transcription factors to influence gene expression.

Alternative CHRNB4 3'-UTRs mediate the allelic effects of SNP rs1948 on gene expression.

Common genetic factors strongly contribute to both nicotine, the main addictive component of tobacco, and alcohol use. Several lines of evidence suggest nicotinic acetylcholine receptors as common sites of action for nicotine and alcohol. Specifically, rs1948, a single-nucleotide polymorphism (SNP) located in the CHRNB4 3'-untranslated region (UTR), has been associated to early age of initiation for both alcohol and tobacco use. To determine the allelic effects of rs1948 on gene expression, two rs1948-containing sequences of different lengths corresponding to the CHRNB4 3'-UTR were cloned into pGL3-promoter luciferase reporter vectors. Data obtained showed that the allelic effects of SNP rs1948 on luciferase expression are mediated by the length and species of transcripts generated. In addition, it was found that miR-3157 increased the overall luciferase expression while miR-138, a microRNA known to play a role in neuroadaptation to drug abuse, decreased luciferase expression when compared to basal conditions. These findings demonstrate the importance of SNP rs1948 on the regulation of CHRNB4 expression and provide the first evidence of CHRNB4 down-regulation by miR-138.

Subjective effects for alcohol, tobacco, and marijuana association with cross-drug outcomes.

METHODS: The cross-drug relationship of subjective experiences between alcohol, tobacco, and marijuana and problem drug use behaviors were examined. Data were drawn from 3853 individuals between the ages of 11 and 30 years of age participating in the Colorado Center on Antisocial Drug Dependence [CADD]. Subjective experiences were assessed using a 13-item questionnaire that included positive and negative responses for alcohol, tobacco, and marijuana. Lifetime abuse and dependence on these three drugs was assessed using the Composite International Diagnostic Interview, Substance Abuse Module [CIDI-SAM]. RESULTS: Positive and negative subjective experience scales were similar for alcohol, tobacco, and marijuana, although the hierarchical ordering of items differed by drug. Subjective experience scales for each of the three drugs examined correlated significantly, with the strongest relationship being for alcohol and marijuana experiences. Significant associations were identified between how a person experienced a drug and abuse and dependence status for the same or different drug. CONCLUSION: Cross-drug relationships provide evidence for a common liability or sensitivity towards responding in a similar manner to drugs of abuse within and across different pharmacological classes.

The CHRNA5/A3/B4 gene cluster and tobacco, alcohol, cannabis, inhalants and other substance use initiation: replication and new findings using mixture analyses.

Multiple studies have provided evidence for genetic associations between single nucleotide polymorphisms (SNPs) located on the CHRNA5/A3/B4 gene cluster and various phenotypes related to Nicotine Dependence (Greenbaum et al. 2009). Only a few studies have investigated other substances of abuse. The current study has two aims, (1) to extend previous findings by focusing on associations between the CHRNA5/A3/B4 gene cluster and age of initiation of several different substances, and (2) to investigate heterogeneity in age of initiation across the different substances. All analyses were conducted with a subset of the Add Health study with available genetic data. The first aim was met by modeling onset of tobacco, alcohol, cannabis, inhalants, and other substance use using survival mixture analysis (SMA). Ten SNPs in CHRNA5/A3/B4 were used to predict phenotypic differences in the risk of onset, and differences between users and non-users. The survival models aim at investigating differences in the risk of initiation across the 5-18 age range for each phenotype separately. Significant or marginally significant genetic effects were found for all phenotypes. The genetic effects were mainly related to the risk of initiation and to a lesser extent to discriminating between users and non-users. To address the second goal, the survival analyses were complemented by a latent class analysis that modeled all phenotypes jointly. One of the ten SNPs was found to predict differences between the early and late onset classes. Taken together, our study provides evidence for a general role of the CHRNA5/A3/B4 gene cluster in substance use initiation that is not limited to nicotine and alcohol.

Externalizing behaviors are associated with SNPs in the CHRNA5/CHRNA3/CHRNB4 gene cluster.

There is strong evidence for shared genetic factors contributing to childhood externalizing disorders and substance abuse. Externalizing disorders often precede early substance experimentation, leading to the idea that individuals inherit a genetic vulnerability to generalized disinhibitory psychopathology. Genetic variation in the CHRNA5/CHRNA3/CHRNB4 gene cluster has been associated with early substance experimentation, nicotine dependence, and other drug behaviors. This study examines whether the CHRNA5/CHRNA3/CHRNB4 locus is correlated also with externalizing behaviors in three independent longitudinally assessed adolescent samples. We developed a common externalizing behavior phenotype from the available measures in the three samples, and tested for association with 10 SNPs in the gene cluster. Significant results were detected in two of the samples, including rs8040868, which remained significant after controlling for smoking quantity. These results expand on previous work focused mainly on drug behaviors, and support the hypothesis that variation in the CHRNA5/CHRNA3/CHRNB4 locus is associated with early externalizing behaviors.

Dizziness and the genetic influences on subjective experiences to initial cigarette use.

AIM: To examine individual differences in positive and negative subjective experiences to initial cigarette use. DESIGN: Retrospective self-reports of initial subjective experiences were examined to estimate the genetic and environmental influences and the extent of their covariation across different effects. PARTICIPANTS: Data was drawn from 2482 young adult same-and opposite sex twins- and siblings participating in the National Longitudinal Study of Adolescent Health. MEASUREMENT: Subjective experiences were retrospectively collected using the Early Smoking Experience (ESE) questionnaire. FINDINGS: Positive experiences evidenced moderate heritable contributions (40%, 95% CI: 0.22 to 0.56), as did an overall hedonic measure (34%, 95% CI: 0.22 to 0.46) and dizziness (34%, 95% CI: 0.15 to 0.52). Negative experiences evidenced small heritable contributions (13%, 95% CI: 0.00 to 0.36). Individual specific environmental influences were strong and accounted for the remaining proportion of observed variation in these experiences. Multivariate genetic modeling identified a moderately heritable underlying factor (37%, 95% CI: 0.22 to 0.52) that influenced the covariation of diverse subjective experiences and loaded most heavily on dizziness. Positive experiences also evidence residual genetic influences that were uncorrelated with other subjective experiences. CONCLUSIONS: How a person experiences their initial few cigarettes is due to both heritable contributions and environmental experiences unique to the person. The covariation of diverse subjective experiences appears to be due to a heritable latent sensitivity to the chemicals contained in an average cigarette and is best indexed by dizziness.

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.

Subjective effects to marijuana associated with marijuana use in community and clinical subjects.

INTRODUCTION: Marijuana is the most commonly used illicit drug among adolescents. Marijuana use induces both psychological and physiological responses, which can be interpreted by an individual in a variety of ways (i.e. subjective effects). We have examined subjective effects in adolescent, young adult community, and clinical populations to determine how patterns of use may be predicted by an individual's subjective experiences with the drug. METHOD: Participants were community and clinical sample subjects drawn from the Colorado Center of Antisocial Drug Dependence (CADD) and a sample of adjudicated youth from the Denver metropolitan area (aged 11-30). They were evaluated with the Composite International Diagnostic Interview-Substance Abuse Module (CIDI-SAM) and the Lyons battery for subjective effects. Scales for subjective effects were created using Mokken scale analysis. Multivariate linear and logistic regression was used to examine associations between the subjective scales and marijuana outcomes. RESULTS: Mokken scaling revealed two subjective effects scales, positive and negative. Both scales were significantly positively associated with marijuana abuse or dependence in both the community and clinical sample and regular use in the community sample. The negative scale was negatively associated with past six-month use in the community sample (p<0.05) and clinical sample, after controlling for age and gender effects. CONCLUSIONS: These findings suggest that diverse subjective experiences with marijuana can be ordered hierarchically and that the resulting short scales can be used in either clinical or community settings. Further, they suggest that the potential for marijuana use problems is related to the type of subjective experience from marijuana exposure.

Association of CHRN genes with "dizziness" to tobacco.

The neuronal nicotinic receptor genes (CHRN) have been implicated in a variety of smoking-related behaviors. Here we tested for association between an early subjective response phenotype, "dizziness," and 226 single nucleotide polymorphisms (SNPs) in CHRN genes. The sample included 789 nicotine-dependent cases and 811 controls, where early "dizziness" reports were significantly associated with case/control status (P < 0.0001). Multiple SNPs in the putative promoter region of the CHRNB3 gene were nominally associated with "dizziness" experience from the first few cigarettes (P < 0.01). Cell culture studies were conducted to examine the ability of different haplotypes in the CHRNB3 promoter to drive luciferase expression. Data from these experiments support the hypothesis that different alleles in the CHRNB3 upstream promoter region may lead to different levels of RNA expression. In addition, a novel finding of association between SNPs in the CHRNA10 gene reached experiment-wide empirical significance (P = 0.048), which implicates another CHRN gene as being involved in early subjective response to tobacco.