Genetic association studies have demonstrated the importance of variants in the CHRNA5-CHRNA3-CHRNB4 cholinergic nicotinic receptor subunit gene cluster on chromosome 15q24-25.1 in risk for nicotine dependence, smoking, and lung cancer in populations of European descent. We have now carried out a detailed study of this region using dense genotyping in both European- and African-Americans.
We genotyped 75 known single-nucleotide-polymorphisms (SNPs) and one sequencing-discovered SNP in an African-American (AA) sample (N = 710) and European-American (EA) sample (N = 2062). Cases were nicotine-dependent and controls were non-dependent smokers.
The non-synonymous CHRNA5 SNP rs16969968 is the most significant SNP associated with nicotine dependence in the full sample of 2772 subjects (p = 4.49×10−8, OR 1.42 (1.25–1.61)) as well as in AAs only (p = 0.015, OR = 2.04 (1.15–3.62)) and EAs only (p = 4.14×10−7, OR = 1.40 (1.23–1.59)). Other SNPs that have been shown to affect mRNA levels of CHRNA5 in EAs are associated with nicotine dependence in AAs but not in EAs. The CHRNA3 SNP rs578776, which has low correlation with rs16969968, is associated with nicotine dependence in EAs but not in AAs. Less common SNPs (frequency ≤ 5%) also are associated with nicotine dependence.
In summary, multiple variants in this gene cluster contribute to nicotine dependence risk, and some are also associated with functional effects on CHRNA5. The non-synonymous SNP rs16969968, a known risk variant in European-descent populations, is also significantly associated with risk in African-Americans. Additional SNPs contribute in distinct ways to risk in these two populations.
genetic association; smoking; cholinergic nicotinic receptors; nicotinic acetylcholine receptors
Several variations in the nicotinic receptor genes have been identified to be associated with both lung cancer risk and smoking in the genome-wide association (GWA) studies. However, the relationships among these three factors (genetic variants, nicotine dependence, and lung cancer) remain unclear. In an attempt to elucidate these relationships, we applied mediation analysis to quantify the impact of nicotine dependence on the association between the nicotinic receptor genetic variants and lung adenocarcinoma risk. We evaluated 23 single nucleotide polymorphisms (SNPs) in the five nicotinic receptor related genes (CHRNB3, CHRNA6, and CHRNA5/A3/B4) previously reported to be associated with lung cancer risk and smoking behavior and 14 SNPs in the four ‘control’ genes (TERT, CLPTM1L, CYP1A1, and TP53), which were not reported in the smoking GWA studies. A total of 661 lung adenocarcinoma cases and 1,347 controls with a smoking history, obtained from the Environment and Genetics in Lung Cancer Etiology case-control study, were included in the study. Results show that nicotine dependence is a mediator of the association between lung adenocarcinoma and gene variations in the regions of CHRNA5/A3/B4 and accounts for approximately 15% of this relationship. The top two CHRNA3 SNPs associated with the risk for lung adenocarcinoma were rs1051730 and rs12914385 (p-value = 1.9×10−10 and 1.1×10−10, respectively). Also, these two SNPs had significant indirect effects on lung adenocarcinoma risk through nicotine dependence (p = 0.003 and 0.007). Gene variations rs2736100 and rs2853676 in TERT and rs401681 and rs31489 in CLPTM1L had significant direct associations on lung adenocarcinoma without indirect effects through nicotine dependence. Our findings suggest that nicotine dependence plays an important role between genetic variants in the CHRNA5/A3/B4 region, especially CHRNA3, and lung adenocarcinoma. This may provide valuable information for understanding the pathogenesis of lung adenocarcinoma and for conducting personalized smoking cessation interventions.
Previous studies revealed association of lung cancer risk with single nucleotide polymorphisms (SNPs) in chromosome 15q25 region containing CHRNA5-CHRNA3-CHRNB4 nicotinic acetylcholine receptor (nAChR) subunit gene cluster. The genetic variations in other lung nAChRs remained unknown. In this study, we perform case-control analysis of CHRNA9 and CHRNA3 genes using 340 non-small cell lung cancer cases and 435 controls.
All exons, 3’UTR, intron 1 and parts of other introns surrounding exons 2–5 of CHRNA9 gene as well as exons 2, 3 of CHRNA3 gene and parts of surrounding intronic regions were sequenced. The study was controlled for gender, age and ethnicity related differences. Each SNP in analyzed groups was assessed by allele frequency, genotype distribution and haplotype analysis.
The case-control analysis revealed that an increased risk is associated with two SNPs in CHRNA9, rs56159866 and rs6819385, and one in CHRNA3, rs8040868. The risk was reduced for three SNPs in CHRNA9, rs55998310, rs56291234, and newly discovered ss410759555, and also in carriers of the haplotype NP_060051.2 containing ancestral N442 variant of α9.
The nonsynonymous substitutions can produce receptors exhibiting unique ligand-binding and downstream signaling characteristics, synonymous as well all intronic SNPs may affect protein production at the transcriptional and/or translational levels, or just manifest association with cancer by genetic linkage to other alleles. Elucidation of the mechanisms by which individual genetic variations in α9 affect predisposition to lung cancer may lead to development of personalized approaches to cancer prevention and treatment as well as protection against tobacco consumption.
lung cancer; CHRNA3; CHRNA9; α3 and α9 nicotinic acetylcholine receptors; single nucleotide polymorphisms
Binge drinking is responsible for over half of all alcohol‐related deaths and results in significant health and economic costs to individuals and society. Knowledge of genetic aspects of this behavior, particularly as it emerges in young adulthood, could lead to improved treatment and prevention programs.
We have focused on the association of variation in neuronal nicotinic receptor subunit genes (CHRNs) in a cohort of 702 Hispanic and non‐Hispanic White young adults who are part of the Social and Emotional Contexts of Adolescent Smoking Patterns (SECASP) study. Fifty‐five single nucleotide polymorphisms (SNPs) covering the variation in 5 CHRNs (CHRNA4,CHRNB2,CHRNA2, CHRNB3A6, and CHRNA5A3B4) were studied.
Frequency of binge drinking and other correlated alcohol consumption measures were significantly associated with SNPs in CHRNA4 (p‐values ranged from 0.0003 to 0.02), but not with SNPs in other CHRNs. This association was independent of smoking status in our cohort.
Variants in CHRNA4 may contribute to risk of binge drinking in young adults in this cohort. Results will need to be confirmed in independent samples.
Binge Drinking; Neuronal Nicotinic Receptor Genes; Genetic Association
The contribution of common genetic variation to one or more established smoking behaviors was investigated in a joint analysis of two genome wide association studies (GWAS) performed as part of the Cancer Genetic Markers of Susceptibility (CGEMS) project in 2,329 men from the Prostate, Lung, Colon and Ovarian (PLCO) Trial, and 2,282 women from the Nurses' Health Study (NHS). We analyzed seven measures of smoking behavior, four continuous (cigarettes per day [CPD], age at initiation of smoking, duration of smoking, and pack years), and three binary (ever versus never smoking, ≤10 versus >10 cigarettes per day [CPDBI], and current versus former smoking). Association testing for each single nucleotide polymorphism (SNP) was conducted by study and adjusted for age, cohabitation/marital status, education, site, and principal components of population substructure. None of the SNPs achieved genome-wide significance (p<10−7) in any combined analysis pooling evidence for association across the two studies; we observed between two and seven SNPs with p<10−5 for each of the seven measures. In the chr15q25.1 region spanning the nicotinic receptors CHRNA3 and CHRNA5, we identified multiple SNPs associated with CPD (p<10−3), including rs1051730, which has been associated with nicotine dependence, smoking intensity and lung cancer risk. In parallel, we selected 11,199 SNPs drawn from 359 a priori candidate genes and performed individual-gene and gene-group analyses. After adjusting for multiple tests conducted within each gene, we identified between two and five genes associated with each measure of smoking behavior. Besides CHRNA3 and CHRNA5, MAOA was associated with CPDBI (gene-level p<5.4×10−5), our analysis provides independent replication of the association between the chr15q25.1 region and smoking intensity and data for multiple other loci associated with smoking behavior that merit further follow-up.
Lung cancer is a leading cause of cancer death and disease burden in many countries. Understanding of the biological pathways involved in lung cancer aetiology is required to identify key biomolecules that could be of significant clinical value, either as predictive, prognostic or diagnostic markers, or as targets for the development of novel therapies to treat this disease, in addition to smoking avoidance strategies. Genome-wide association studies (GWAS) have enabled significant progress in the past 5 years in investigating genetic susceptibility to lung cancer. Large scale, multi-cohort GWAS of mainly Caucasian, smoking, populations have identified strong associations for lung cancer mapped to chromosomal regions 15q [nicotinic acetylcholine receptor (nAChR) subunits: CHRNA3, CHRNA5], 5p (TERT-CLPTM1L locus) and 6p (BAT3-MSH5). Some studies in Asian populations of smokers have found similar risk loci, whereas GWAS in never smoking Asian females have identified associations in other chromosomal regions, e.g., 3q (TP63), that are distinct from smoking-related lung cancer risk loci. GWAS of smoking behaviour have identified risk loci for smoking quantity at 15q (similar genes to lung cancer susceptibility: CHRNA3, CHRNA5) and 19q (CYP2A6). Other genes have been mapped for smoking initiation and smoking cessation. In chronic obstructive pulmonary disease (COPD), which is a known risk factor for lung cancer, GWAS in large cohorts have also found CHRNA3 and CHRNA5 single nucleotide polymorphisms (SNPs) mapping at 15q as risk loci, as well as other regions at 4q31 (HHIP), 4q24 (FAM13A) and 5q (HTR4). The overlap in risk loci between lung cancer, smoking behaviour and COPD may be due to the effects of nicotine addiction; however, more work needs to be undertaken to explore the potential direct effects of nicotine and its metabolites in gene-environment interaction in these phenotypes. Goals of future genetic susceptibility studies of lung cancer should focus on refining the strongest risk loci in a wide range of populations with lung cancer, and integrating other clinical and biomarker information, in order to achieve the aim of personalised therapy for lung cancer.
Lung cancer; genetics; pulmonary disease; chronic obstructive; genome-wide association study (GWAS)
Several previous genome-wide and targeted association studies revealed that variants in the CHRNA5-CHRNA3-CHRNB4 (CHRNA5/A3/B4) gene cluster on chromosome 15 that encode the α5, α3 and β4 subunits of the nicotinic acetylcholine receptor (nAChRs) are associated with nicotine dependence (ND) in European Americans (EAs) or others of European origin. Considering the distinct linkage disequilibrium patterns in European and other ethnic populations such as African Americans (AAs), it would be interesting to determine whether such associations exist in other ethnic populations. We performed a comprehensive association and interaction analysis of the CHRNA5/A3/B4 cluster in two ethnic samples to investigate the role of variants in the risk for ND, which was assessed by Smoking Quantity, Heaviness Smoking Index, and Fagerström test for ND. Using a family-based association test, we found a nominal association of single nucleotide polymorphisms (SNPs) rs1317286 and rs8040868 in CHRNA3 with ND in the AA and combined AA and EA samples. Furthermore, we found that several haplotypes in CHRNA5 and CHRNA3 are nominally associated with ND in AA, EA, and pooled samples. However, none of these associations remained significant after correction for multiple testing. In addition, we performed interaction analysis of SNPs within the CHRNA5/A3/B4 cluster using the pedigree-based generalized multifactor dimensionality reduction method and found significant interactions within CHRNA3 and among the three subunit genes in the AA and pooled samples. Together, these results indicate that variants within CHRNA3 and among CHRNA5, CHRNA3, and CHRNB4 contribute significantly to the etiology of ND through gene-gene interactions, although the association of each subunit gene with ND is weak in both the AA and EA samples.
Association analysis; CHRNA5; CHRNA3; CHRNB4; Interaction analysis; Nicotine dependence; Smoking
Several single nucleotide polymorphisms (SNPs) in an α-neuronal nicotinic acetylcholine receptor subunit (CHRNA3/5) were identified to be associated with chronic obstructive pulmonary disease (COPD) in a study based on a Norwegian population. However, results from subsequent studies have been controversial, particularly in studies recruiting Asians. In the present study, we conducted a comprehensive search and meta-analyses to identify susceptibility SNPs for COPD in the CHRNA3/5 locus.
A comprehensive literature search was conducted to find studies that have reported an association between SNPs in the CHRNA3/5 locus and COPD risk. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) for each SNP were calculated with the major allele or genotype as the reference group. The influence of individual studies on pooled measures was assessed, in addition to publication bias.
A total of 12 articles with 14 eligible studies were included in this analysis. Association between 4 SNPs in the CHRNA3/5 locus and COPD was evaluated and included rs1051730, rs8034191, rs6495309, and rs16969968. Significant associations between the 4 SNPs and COPD were identified under allele (rs1051730: OR = 1.14, 95%CI = 1.10–1.18; rs8034191: OR = 1.29, 95%CI = 1.18–1.41; rs6495309: OR = 1.26, 95%CI = 1.09–1.45; rs16969968: OR = 1.27, 95%CI = 1.17–1.39) and genotype models. Subgroup analysis conducted for rs1051730 showed a significant association between this SNP and COPD risk in non-Asians (OR = 1.14, 95%CI = 1.10–1.18), but not Asians (OR = 1.23, 95%CI = 0.91–1.67). Rs1051730 and rs6495309 were also significantly associated with COPD after adjusting for multiple variables, including age and smoking status.
Our results indicate that 4 SNPs in the CHRNA3/5 locus are associated with COPD risk. Rs1051730 was particularly associated with COPD in non-Asians, but its role in Asians still needs to be verified. Additional studies will be necessary to assess the effect of rs6495309 on COPD. Although rs1051730 and rs6495309 were shown to be independent risk factors for COPD, validation studies should be performed.
Background and aims
Gene variants in CHRNA5-A3-B4, which encode for the α5, α3 and β4 nicotinic receptor subunits, are associated with altered smoking behaviors in European-Americans. Little is known about CHRNA5-A3-B4 and its association with smoking behaviors and weight in Alaska-Native people, which is a population with high prevalence but low levels of tobacco consumption, extensive smokeless tobacco use, and high rates of obesity. We investigated CHRNA5-A3-B4 haplotype structure and its association with nicotine intake and obesity in Alaska-Native people.
Design, Setting, Participants
A cross sectional study of 400 Alaska-Native individuals including 290 tobacco users.
CHRNA5-A3-B4 genotype, body weight, and tobacco consumption biomarkers such as plasma cotinine and urinary total nicotine equivalents (TNE).
Alaska-Native people have a distinct CHRNA5-A3-B4 haplotype structure compared with European/African-Americans. In 290 Alaska-Native tobacco users, the ‘G’ allele of rs578776, which tagged a 30kb haplotype in CHRNA5-A3-B4, was prevalent (16%) and significantly associated with nicotine intake (20% higher plasma cotinine, P<0.001, 16% higher TNE, P=0.076), while rs16969968 was not associated with nicotine intake. Rs578776 acted in combination with CYP2A6, the main nicotine-metabolizing enzyme, to increase nicotine intake by 1.8 fold compared with the low risk group (P<0.001). Furthermore rs2869950, a single nucleotide polymorphism 5′ to CHRNB4, was significantly associated with increased body mass index (P<0.01) in the tobacco users even after controlling for differences in nicotine intake (P<0.01).
Genetic variants in CHRNA5-A3-B4 alter nicotine intake and body mass index in a population of Alaska-Native people, who have a distinct haplotype structure, smoking behaviors and prevalence of obesity.
Alaska-Native People; Smoking; CHRNA5-A3-B4; Obesity
Genetic effects contribute to individual differences in smoking behavior. Persistence to smoke despite known harmful health effects is mostly driven by nicotine addiction. As the physiological effects of nicotine are mediated by nicotinic acetylcholine receptors (nAChRs), we aimed at examining whether single nucleotide polymorphisms (SNPs) residing in nAChR subunit (CHRN) genes, other than CHRNA3/CHRNA5/CHRNB4 gene cluster previously showing association in our sample, are associated with smoking quantity or serum cotinine levels.
The study sample consisted of 485 Finnish adult daily smokers (age 30–75 years, 59% men) assessed for the number of cigarettes smoked per day (CPD) and serum cotinine level. We first studied SNPs residing on selected nAChR subunit genes (CHRNA2, CHRNA4, CHRNA6/CHRNB3, CHRNA7, CHRNA9, CHRNA10, CHRNB2, CHRNG/CHRND) genotyped within a genome-wide association study for single SNP and multiple SNP associations by ordinal regression. Next, we explored individual haplotype associations using sliding window technique.
At one of the 8 loci studied, CHRNG/CHRND (chr2), single SNP (rs1190452), multiple SNP, and 2-SNP haplotype analyses (SNPs rs4973539–rs1190452) all showed statistically significant association with cotinine level. The median cotinine levels varied between the 2-SNP haplotypes from 220 ng/ml (AA haplotype) to 249 ng/ml (AG haplotype). We did not observe significant associations with CPD.
These results provide further evidence that the γ−δ nAChR subunit gene region is associated with cotinine levels but not with the number of CPD, illustrating the usefulness of biomarkers in genetic analyses.
Cholinergic nicotinic receptor (CHRN) gene family has been known to mediate the highly additive effects of nicotine in the body, and implicated nicotine dependence (ND) and related phenotypes. Previous studies have found that CHRNA6-CHRNB3 cluster polymorphisms were significantly associated with the risk of ND and various tobacco behaviors. The aim of study was to evaluate the genetic association of CHRNB3 and CHRNA6 polymorphisms with the risk of ND based on the Fagerstrom Test for Nicotine Dependence (FTND) score and five subscales of nicotine dependence syndrome scale (NDSS) in Korean population.
Six SNPs in CHRNA6-CHRNB3 cluster were analyzed in 576 Korean subjects. Association analysis using logistic models and regression analysis with NDSS were performed.
There was no association in the case-control analysis, whereas all six SNPs were significantly associated with drive factor among NDSS in subgroup based on the FTND score. CHRNB3 rs4954 and CHRNA6 rs16891604 showed significant associations with NDSSF1 (drive) in dominant models among moderate to severe ND among smokers after correction (pcorr=0.02 and 0.001, respectively), whereas other four SNPs showed significant associations among mild ND after correction (pcorr=0.03-0.02 in dominant model).
This study showed that the genetic influence of CHRNB3-CHRNA6 cluster polymorphisms are found in a ND endophenotype (drive) using NDSS subscales, rather than the risk of ND in Korean population. Our findings might be the first report for the association of CHRNB3-CHRNA6 cluster with ND-related phenotypes in Korean and might offer an approach to elucidating the molecular mechanisms of ND and ND-related phenotypes.
CHRNB3; CHRNA6; SNP; Nicotine dependence; NDSS
Studies in European and East Asian populations have identified lung cancer susceptibility loci in nicotinic acetylcholine receptor (nAChR) genes on chromosome 15q25.1 which also appear to influence smoking behaviors. We sought to determine if genetic variation in nAChR genes influences lung cancer susceptibly in African-Americans, and evaluated the association of these cancer susceptibility loci with smoking behavior. A total of 1308 African-Americans with lung cancer and 1241 African-American controls from three centers were genotyped for 378 single nucleotide polymorphisms (SNPs) spanning the sixteen human nAChR genes. Associations between SNPs and the risk of lung cancer were estimated using logistic regression, adjusted for relevant covariates. Seven SNPs in three nAChR genes were significantly associated with lung cancer at a strict Bonferroni-corrected level, including a novel association on chromosome 2 near the promoter of CHRNA1 (rs3755486: OR = 1.40, 95% CI = 1.18-1.67, P = 1.0 × 10−4). Association analysis of an additional 305 imputed SNPs on 2q31.1 supported this association. Publicly available expression data demonstrated that the rs3755486 risk allele correlates with increased CHRNA1 gene expression. Additional SNP associations were observed on 15q25.1 in genes previously associated with lung cancer, including a missense variant in CHRNA5 (rs16969968: OR = 1.60, 95% CI = 1.27-2.01, P = 5.9 × 10−5). Risk alleles on 15q25.1 also correlated with an increased number of cigarettes smoked per day among the controls. These findings identify a novel lung cancer risk locus on 2q31.1 which correlates with CHRNA1 expression and replicate previous associations on 15q25.1 in African-Americans.
Lung cancer; nicotine dependence; African-Americans; genetic association; smoking
There is considerable variability in the susceptibility of smokers to develop chronic obstructive pulmonary disease (COPD). The only known genetic risk factor is severe deficiency of α1-antitrypsin, which is present in 1–2% of individuals with COPD. We conducted a genome-wide association study (GWAS) in a homogenous case-control cohort from Bergen, Norway (823 COPD cases and 810 smoking controls) and evaluated the top 100 single nucleotide polymorphisms (SNPs) in the family-based International COPD Genetics Network (ICGN; 1891 Caucasian individuals from 606 pedigrees) study. The polymorphisms that showed replication were further evaluated in 389 subjects from the US National Emphysema Treatment Trial (NETT) and 472 controls from the Normative Aging Study (NAS) and then in a fourth cohort of 949 individuals from 127 extended pedigrees from the Boston Early-Onset COPD population. Logistic regression models with adjustments of covariates were used to analyze the case-control populations. Family-based association analyses were conducted for a diagnosis of COPD and lung function in the family populations. Two SNPs at the α-nicotinic acetylcholine receptor (CHRNA 3/5) locus were identified in the genome-wide association study. They showed unambiguous replication in the ICGN family-based analysis and in the NETT case-control analysis with combined p-values of 1.48×10−10, (rs8034191) and 5.74×10−10 (rs1051730). Furthermore, these SNPs were significantly associated with lung function in both the ICGN and Boston Early-Onset COPD populations. The C allele of the rs8034191 SNP was estimated to have a population attributable risk for COPD of 12.2%. The association of hedgehog interacting protein (HHIP) locus on chromosome 4 was also consistently replicated, but did not reach genome-wide significance levels. Genome-wide significant association of the HHIP locus with lung function was identified in the Framingham Heart study (Wilk et al., companion article in this issue of PLoS Genetics; doi:10.1371/journal.pgen.1000429). The CHRNA 3/5 and the HHIP loci make a significant contribution to the risk of COPD. CHRNA3/5 is the same locus that has been implicated in the risk of lung cancer.
There is considerable variability in the susceptibility of smokers to develop chronic obstructive pulmonary disease (COPD), which is a heritable multi-factorial trait. Identifying the genetic determinants of COPD risk will have tremendous public health importance. This study describes the first genome-wide association study (GWAS) in COPD. We conducted a GWAS in a homogenous case-control cohort from Norway and evaluated the top 100 single nucleotide polymorphisms in the family-based International COPD Genetics Network. The polymorphisms that showed replication were further evaluated in subjects from the US National Emphysema Treatment Trial and controls from the Normative Aging Study and then in a fourth cohort of extended pedigrees from the Boston Early-Onset COPD population. Two polymorphisms in the α-nicotinic acetylcholine receptor 3/5 locus on chromosome 15 showed unambiguous evidence of association with COPD. This locus has previously been implicated in both smoking behavior and risk of lung cancer, suggesting the possibility of multiple functional polymorphisms in the region or a single polymorphism with wide phenotypic consequences. The hedgehog interacting protein (HHIP) locus on chromosome 4, which is associated with COPD, is also a significant risk locus for COPD.
Neuronal nicotinic acetylcholine receptors are activated by both endogenous acetylcholine and exogenous nicotine, making sequence variations in these receptors likely candidates for association with tobacco phenotypes. Previous studies have found evidence for significant association between SNPs in the genomic region containing the CHRNA6 and CHRNB3 genes and tobacco behaviors (Bierut et al, 2007; Greenbaum et al, 2006; Saccone et al, 2007; Zeiger et al, 2008). In this study, we provide support for an association between these genes and tobacco dependence in the National Youth Survey Family Study wave 10, a nationally representative sample of households. Eight single nucleotide polymorphisms (SNPs) in the CHRNA6 and CHRNB3 genomic region were genotyped in 1051 subjects, approximately half of whom are members of sibling pairs. Genetic association with DSM-IV dependence was assessed using a family-based approach as implemented in the statistical package PBAT. Individual SNPs were tested for association with quit attempts and overall dependence. Variation in CHRNA6 was found to be associated with tobacco dependence (p=0.007 in Caucasians). SNPs in CHRNB3 were found to be associated with the number of quit attempts (p=0.0024). Together these results further implicate the region downstream of CHRNA6 and the region upstream of CHRNB3 in risk of nicotine dependence.
Nicotinic receptors; SNP; Genetic association; Tobacco use; Nicotine Dependence
Tobacco smoking continues to be a leading cause of preventable death. Recent research has underscored the important role of specific cholinergic nicotinic receptor subunit (CHRN) genes in risk for nicotine dependence and smoking. To detect and characterize the influence of genetic variation on vulnerability to nicotine dependence, we analyzed 226 SNPs covering the complete family of 16 CHRN genes, which encode the nicotinic acetylcholine receptor (nAChR) subunits, in a sample of 1050 nicotine-dependent cases and 879 non-dependent controls of European descent. This expanded SNP coverage has extended and refined the findings of our previous large scale genome-wide association and candidate gene study. After correcting for the multiple tests across this gene family, we found significant association for two distinct loci in the CHRNA5-CHRNA3-CHRNB4 gene cluster, one locus in the CHRNB3-CHRNA6 gene cluster, and a fourth, novel locus in the CHRND-CHRNG gene cluster. The two distinct loci in CHRNA5-CHRNA3-CHRNB4 are represented by the non-synonymous SNP rs16969968 in CHRNA5 and by rs578776 in CHRNA3, respectively, and joint analyses show that the associations at these two SNPs are statistically independent. Nominally significant single-SNP association was detected in CHRNA4 and CHRNB1. In summary, this is the most comprehensive study of the CHRN genes for involvement with nicotine dependence to date. Our analysis reveals significant evidence for at least four distinct loci in the nicotinic receptor subunit genes that each influence the transition from smoking to nicotine dependence and may inform the development of improved smoking cessation treatments and prevention initiatives.
cholinergic nicotinic receptors; nicotinic acetylcholine receptors; smoking; genetic association
Genetic variants that contribute to the risk of psychiatric disorders may also affect normal variation in psychological function. Indeed, the behavioral effects of many genetic variants may be better understood as process-specific rather than disease-specific. A functional valine-to-methionine (Val158Met) polymorphism in the catechol-O-methyltransferase (COMT) gene has been associated with cognitive function and brain metabolic activity accompanying such tasks. Not all studies are consistent, and less is known about the effect of this polymorphism during development. The authors tested the hypothesis that a more informative COMT haplotype predicts normal cognitive development in a large population-based cohort of children enrolled in the Avon Longitudinal Study of Parents and children.
Effects on verbal and performance IQ as well as verbal inhibition were assessed at age 8, and effects onworking memory were assessed at age 10. From the five COMT single nucleotide polymorphisms (SNPs) genotyped, the effect of a functional three-SNP haplotype consisting of Val158Met and two synonymous SNPs (rs6269 and rs4818), which together exert a major influence on the level of COMT expression and enzyme activity, was evaluated.
This three-SNP haplotype predicted both verbal inhibition and working memory, and there was a genotype-by-sex interaction on verbal IQ. The effect of COMT genotype (diplotype) on cognition was curvilinear, which is consistent with the “inverted U” model of dopamine effect on frontal cortical efficiency. In addition, the SNP rs2075507 (previously rs2097603) was independently associatedwith verbal inhibition, while rs165599 showed no main cognitive effects. However, rs165599 showed a genotype-by-sex interaction with working memory.
Genetic variation at several loci in the COMT gene affects normal cognitive function in children.
Heterogeneous phenotypes of complex disorders pose a great challenge for genetic association studies and for the development of personalized treatment strategies. Cluster analysis of phenotypic data has been recently proposed as a reliable auxiliary method for such studies. A cohort of 236 treatment-seeking smokers was investigated after overnight nicotine abstinence. Alpha4 nicotinic acetylcholine receptor (nAChR) subunit-related phenotypes were assessed by the Fagerström Test for Nicotine Dependence (FTND), exhaled carbon monoxide (CO) measurements, the Minnesota Nicotine Withdrawal Scale (MNWS) and the Zung Self-Rating Depression Scale (ZSDS). Seven tag SNPs (single-nucleotide polymorphisms) across CHRNA4 (the gene encoding alpha4 subunit of the nicotinic acetylcholine receptor) were genotyped and two-step cluster analysis was used for phenotypic cluster characterization. Haplotype estimation was determined by HapStat module of R 2.0 software. Three different phenotypic clusters were identified and the C3 cluster was characterized by the highest ZSDS and MNWS scores compared to others. Furthermore, lifetime prevalence of major depression was significantly higher in the C3 cluster (p = 0.019). In genetic association tests, this cluster was also significantly associated with rs3787138 genotypes (p = 0.004) while haplotype analyses of three SNPs (rs3787138, rs1044396, rs3787140) revealed that the risk for C3 phenotype was almost three times higher in GCC haplotype carriers compared to others (pperm = 0.013). This is the first report on a significant association between CHRNA4 variants and a subgroup of smokers characterized by massive withdrawal symptoms and affective vulnerability. Identification of such a phenotypic cluster can be a pivotal step for further pharmacogenetic studies on ligands of the alpha4 nAChR subunit. Our results suggest that performing cluster analysis in genetic association studies can be proposed for complex disorders.
Owing to the clinical relationship between bipolar disorder and nicotine dependence, we investigated two research questions: (i) are genetic associations with nicotine dependence different in individuals with bipolar disorder as compared with individuals without bipolar disorder, and (ii) do loci earlier associated with nicotine dependence have pleiotropic effects on these two diseases.
Our study consisted of 916 cases with bipolar disorder and 1028 controls. On the basis of known associations with nicotine dependence, we genotyped eight single-nucleotide polymorphisms (SNPs) on chromosome 8 (three bins) in the regions of CHRNB3 and CHRNA6, and six SNPs on chromosome 15 (three bins) in the regions of CHRNA5 and CHRNA3.
To determine whether the genetic associations with nicotine dependence are different in bipolar disorder than in the general population, we compared allele frequencies of candidate SNPs between individuals with nicotine dependence only and individuals with both nicotine dependence and bipolar disorder. There were no statistical differences between these frequencies, indicating that genetic association with nicotine dependence is similar in individuals with bipolar disorder as in the general population. In the investigation of pleiotropic effects of these SNPs on bipolar disorder, two highly correlated synonymous SNPs in CHRNB3, rs4952 and rs4953, were significantly associated with bipolar disorder (odds ratio 1.7, 95% confidence interval: 1.2–2.4, P = 0.001). This association remained significant both after adjusting for a smoking covariate and analyzing the association in nonsmokers only.
Our results suggest that (i) bipolar disorder does not modify the association between nicotine dependence and nicotinic receptor subunit genes, and (ii) variants in CHRNB3/CHRNA6 are independently associated with bipolar disorder. Psychiatr Genet 00:000–000.
analyses; CHRNA3; CHRNA5; CHRNA6; genetic association; nicotine; tobacco use disorder
People who begin daily smoking at an early age are at greater risk of long-term nicotine addiction. We tested the hypothesis that associations between nicotinic acetylcholine receptor (nAChR) genetic variants and nicotine dependence assessed in adulthood will be stronger among smokers who began daily nicotine exposure during adolescence. We compared nicotine addiction—measured by the Fagerstrom Test of Nicotine Dependence—in three cohorts of long-term smokers recruited in Utah, Wisconsin, and by the NHLBI Lung Health Study, using a candidate-gene approach with the neuronal nAChR subunit genes. This SNP panel included common coding variants and haplotypes detected in eight α and three β nAChR subunit genes found in European American populations. In the 2,827 long-term smokers examined, common susceptibility and protective haplotypes at the CHRNA5-A3-B4 locus were associated with nicotine dependence severity (p = 2.0×10−5; odds ratio = 1.82; 95% confidence interval 1.39–2.39) in subjects who began daily smoking at or before the age of 16, an exposure period that results in a more severe form of adult nicotine dependence. A substantial shift in susceptibility versus protective diplotype frequency (AA versus BC = 17%, AA versus CC = 27%) was observed in the group that began smoking by age 16. This genetic effect was not observed in subjects who began daily nicotine use after the age of 16. These results establish a strong mechanistic link among early nicotine exposure, common CHRNA5-A3-B4 haplotypes, and adult nicotine addiction in three independent populations of European origins. The identification of an age-dependent susceptibility haplotype reinforces the importance of preventing early exposure to tobacco through public health policies.
Tobacco use is a global health care problem, and persistent smoking takes an enormous toll on individual health. The onset of daily smoking in adolescence is related to chronic use and severe nicotine dependence in adulthood. Since nicotine is the key addictive chemical in tobacco, we tested the hypothesis that genetic variants within nicotinic acetylcholine receptors will influence the severity of addiction measured in adulthood. Using genomic resequencing to define the patterns of variation found in these candidate genes, we observed that common haplotypes in the CHRNA5-A3-B4 gene cluster are associated with adult nicotine addiction, specifically among those who began daily smoking before age 17. We show that in populations of European origins, one haplotype is a risk factor for dependence, one is protective, and one is neutral. These observations suggest that genetic determinants expressed during human adolescence contribute to the risk of lifetime addiction severity produced from early onset of cigarette use. Because disease risk from the adverse health effects of tobacco smoke is related to lifetime tobacco exposure, the finding that an age-dependent effect of these haplotypes has a strong influence on lifetime smoking behavior reinforces the public health significance of delaying smoking onset.
Smokers have a lower risk of Parkinson's disease (PD). Recent genome-wide association studies (GWAS) have consistently linked several single nucleotide polymorphisms (SNPs) in the CHRNA3-CHRNA5-CHRNB4 cluster on chromosome 15.q25 to smoking behaviors and nicotine dependence. Investigations into these SNPs may help explain the nature and mechanisms of the smoking-PD relationship. Objective: To examine whether the genetic variations that were consistently associated with smoking or nicotine dependence in recent GWAS also predict the risk of PD.
This is a population-based case-control study of 788 physician-diagnosed PD patients and 911 controls, all non-Hispanic Whites. Seven SNPs were selected based on findings from recent GWAS on smoking and nicotine dependence, all from the nicotinic acetylcholine receptor subunits (CHRN) A3-A5-B4. Odds ratios (ORs) and 95% confidence intervals were derived from logistic regression models under the assumption of logit-additive allelic effects.
Four SNPs in linkage disequilibrium from the CHRNA3-CHRNA5-CHRNB4 cluster were associated with smoking duration (OR >1.3, p < 0.05). However, none of the SNPs from this cluster was associated with PD risk in the overall analysis or after stratifying on smoking status.
This preliminary analysis does not support a relationship between these smoking-related GWAS SNPs and PD.
Parkinson's disease; Smoking; CHRNA3-CHRNA5-CHRNB4 cluster; Nicotine dependence
Several genome-wide association studies identified the chr15q25.1 region, which includes three nicotinic cholinergic receptor genes (CHRNA5-B4) and the cell proliferation gene (PSMA4), for its association with lung cancer risk in Caucasians. A haplotype and its tagging single nucleotide polymorphisms (SNPs) encompassing six genes from IREB2 to CHRNB4 were most strongly associated with lung cancer risk (OR = 1.3; P < 10−20). In order to narrow the region of association and identify potential causal variations, we performed a fine-mapping study using 77 SNPs in a 194 kb segment of the 15q25.1 region in a sample of 448 African-American lung cancer cases and 611 controls. Four regions, two SNPs and two distinct haplotypes from sliding window analyses, were associated with lung cancer. CHRNA5 rs17486278 G had OR = 1.28, 95% CI 1.07–1.54 and P = 0.008, whereas CHRNB4 rs7178270 G had OR = 0.78, 95% CI 0.66–0.94 and P = 0.008 for lung cancer risk. Lung cancer associations remained significant after pack-year adjustment. Rs7178270 decreased lung cancer risk in women but not in men; gender interaction P = 0.009. For two SNPs (rs7168796 A/G and rs7164594 A/G) upstream of PSMA4, lung cancer risks for people with haplotypes GG and AA were reduced compared with those with AG (OR = 0.56, 95% CI 0.38–0.82; P = 0.003 and OR = 0.73, 95% CI 0.59–0.90, P = 0.004, respectively). A four-SNP haplotype spanning CHRNA5 (rs11637635 C, rs17408276 T, rs16969968 G) and CHRNA3 (rs578776 G) was associated with increased lung cancer risk (P = 0.002). The identified regions contain SNPs predicted to affect gene regulation. There are multiple lung cancer risk loci in the 15q25.1 region in African-Americans.
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.
luciferase; nicotinic receptor; EMSA; rs1948; rs6495309; rs8023462
There is shared genetic risk for dependence on multiple substances, and the nicotinic receptor gene cluster on chromosome 15 harbors multiple polymorphisms that associate to this risk. Here, we report the results of an association study with 21 SNPs genotyped across the CHRNA5, CHRNA3, and CHRNB4 loci on chromosome 15q25.1. The sample consists of a discovery set (N=1858) of European-American and African-American (AA) families, ascertained on the basis of a sibling pair with cocaine and/or opioid dependence, and a case–control replication sample (N=3388) collected for association studies of alcohol, cocaine, and opioid dependence. We tested the SNPs for association with lifetime cocaine, opioid, nicotine, and alcohol dependence. We replicated several previous findings, including associations between rs16969968 and nicotine dependence (P=0.002) and cocaine dependence (P=0.02), with opposite risk alleles for each substance. We observed these associations in AAs, which is a novel finding. The strongest association signal in either sample was between rs684513 in CHRNA5 and cocaine dependence (OR=1.43, P=0.0004) in the AA replication set. We also observed two SNPs associated with alcohol dependence, that is, rs615470 in CHRNA5 (OR=0.77, P=0.0006) and rs578776 (OR=0.78, P=0.001). The associations between CD and rs684513, AD and rs615470, and AD and rs578776 remained significant after a permutation-based correction for multiple testing. These data reinforce the importance of variation in the chromosome 15 nicotinic receptor subunit gene cluster for risk of dependence on multiple substances, although the direction of the effects may vary across substances.
genetic association; substance dependence; nicotinic acetylcholine receptors; Acetylcholine; Addiction & Substance Abuse; Neurogenetics; Epidemiology; Genetic Association
Cigarette smoking is a major risk factor for COPD and COPD severity. Previous genome-wide association studies (GWAS) have identified numerous single nucleotide polymorphisms (SNPs) associated with the number of cigarettes smoked per day (CPD) and a Dopamine Beta-Hydroxylase (DBH) locus associated with smoking cessation in multiple populations.
To identify SNPs associated with lifetime average and current CPD, age at smoking initiation, and smoking cessation in COPD subjects.
GWAS were conducted in 4 independent cohorts encompassing 3,441 ever-smoking COPD subjects (GOLD stage II or higher). Untyped SNPs were imputed using HapMap (phase II) panel. Results from all cohorts were meta-analyzed.
Several SNPs near the HLA region on chromosome 6p21 and in an intergenic region on chromosome 2q21 showed associations with age at smoking initiation, both with the lowest p=2×10−7. No SNPs were associated with lifetime average CPD, current CPD or smoking cessation with p<10−6. Nominally significant associations with candidate SNPs within alpha-nicotinic acetylcholine receptors 3/5 (CHRNA3/CHRNA5; e.g. p=0.00011 for SNP rs1051730) and Cytochrome P450 2A6 (CYP2A6; e.g. p=2.78×10−5 for a nonsynonymous SNP rs1801272) regions were observed for lifetime average CPD, however only CYP2A6 showed evidence of significant association with current CPD. A candidate SNP (rs3025343) in the DBH was significantly (p=0.015) associated with smoking cessation.
We identified two candidate regions associated with age at smoking initiation in COPD subjects. Associations of CHRNA3/CHRNA5 and CYP2A6 loci with CPD and DBH with smoking cessation are also likely of importance in the smoking behaviors of COPD patients.
Chronic Obstructive Pulmonary Disease (COPD); Genome Wide Association study (GWAS); smoking behaviors; Single Nucleotide Polymorphism (SNP)
Three genome-wide association studies identified a region on chromosome 15q25.1 associated with lung cancer and measures of nicotine addiction. This region includes nicotinic acetylcholine receptor subunit genes CHRNA3 and CHRNA5. These studies were conducted in European or European American populations and do not provide risk estimates for African Americans. The goal of this study was to determine whether recently identified genetic variation in 3 SNPs (rs1051730, rs931794, rs8034191) on chromosome 15q25.1 contributes to risk of lung cancer in African Americans.
Data were derived from three case-control studies. Participants included 1058 population-based non-small cell lung cancer cases selected from the Detroit area SEER registry and 1314 controls matched within study by age, race, and sex. Thirty-nine percent of participants were African American.
Risk associated with rs1051730 (odds ratio 1.59; 95% confidence interval 1.16–2.19) and rs931794 (odds ratio 1.39; 95% confidence interval 1.09–1.78) increased in ever smoking African Americans adjusting for cigarettes smoked per day. Among white cases, the number of cigarettes smoked varied by genotype at all three SNPs, and when smoking quantity was included in the models, risk was not significantly associated with any of the three SNPs.
These findings suggest that SNPs in the CHRNA3 and CHRNA5 region contribute to lung cancer risk, and while variant alleles are less frequent in African Americans, risk in this group may be greater than in whites and less likely to reflect an indirect effect on lung cancer risk through nicotine dependence.
Non-small cell lung cancer; Smoking; SNPs