Genetics of Nicotine Dependence

描述（由申请人提供）：吸烟是北美和欧洲最大的可预防的发病率和死亡率来源。双胞胎和收养研究表明，尼古丁依赖（ND）的大部分风险是遗传的。对约7500名欧洲人进行了一项全基因组关联（WGA）研究，研究了每天吸烟（CPD）的数量性状。用Affymetrix 500K芯片进行基因分型。α - 3烟碱受体亚基基因（CHRNA3）的SNP与CPD作为一个数量性状相关（p = 0.00007）。在病例-对照模式下对CPD进行分析（病例定义为吸烟超过25 CPD与对照组< 5 CPD），在第二个欧洲血统人群中进行了约6200例对照和约1740例，基因分型为约6000个snp。在第二个人群中，CHRNA3 SNP与CPD密切相关（p = 0.0000026，优势比1.30,95% CI 1.17-1.48）。这些结果与Saccone等人（2007）的ND病例对照研究相似，他们报道了几个CHRNA3 snp的相关性（0.0003< p < 0.01）。在这些snp中，所有确定的风险等位基因（N = 7）都位于一个共同的单倍型上，欧洲血统的等位基因频率约为38%。由于CHRNA3和邻近的CHRNA5基因之间存在强烈的连锁不平衡，额外的基因分型不太可能确定因果变异。本提案描述了CHRNA3和CHRNA5基因的功能研究。约200名ND患者的CHRNA3和CHRNA5重测序将用于鉴定可能易患ND的罕见功能变异。这些罕见的功能变异将在约1500名ND个体和约1500名欧洲血统的对照人群中进行连锁不平衡检查，以确定他们是否可能易患ND。CHRNA3和CHRNA5 mRNA和蛋白将在具有推定风险和保护性单倍型的人死后大脑中进行评估。CHRNA3和CHRNA5启动子序列，从风险和保护性单倍型，将在组织培养中评估转录效率。将评估CHRNA5中位于风险单倍型的错义编码SNP的结合亲和力和离子电导率的变化。这些结果将确定CHRNA3和CHRNA5基因的启动子和转录snp的功能作用。这项研究应该确定CHRNA3和/或CHRNA5基因序列增加ND风险的后果，并促进ND治疗新药的开发。

DESCRIPTION (provided by applicant): Cigarette smoking is the single largest preventable source of morbidity and mortality in North America and Europe. Twin and adoption studies indicate that a majority of risk for nicotine dependence (ND) is genetic. A genome-wide association (WGA) study of cigarettes per day (CPD), as a quantitative trait, was conducted with ~ 7500 individuals of European origin. Genotyping was done with Affymetrix 500K chips. A SNP in the alpha 3 nicotinic receptor subunit gene (CHRNA3) was associated with CPD as a quantitative trait (p = 0.00007). Analyses of CPD in a case-control mode (cases defined as smoking > 25 CPD versus controls < 5 CPD), was done in a second European-origin population of ~ 6200 controls and ~ 1740 cases, genotyped at ~ 6000 SNPs. In this second population, a CHRNA3 SNP was strongly associated with CPD (p = 0.0000026, odds ratio 1.30, 95% CI 1.17-1.48). These results are similar to a case-control study of ND by Saccone et al (2007), who reported association of several CHRNA3 SNPs (0.0003< p < 0.01). All the identified risk alleles (N = 7) at these SNPs lie on a single common haplotype, with ~ 38% allele frequency in persons of Euorpean origin. Because of strong linkage disequilibrium across the CHRNA3 and the adjacent CHRNA5 gene, additional genotyping is unlikely to identify causal variations. This proposal describes functional studies of CHRNA3 and CHRNA5 genes. Re-sequencing of CHRNA3 and CHRNA5 in ~ 200 ND persons will be employed to identify rare functional variants which might predispose to ND. These rare functional variants will be examined for linkage disequilibrium in a population of ~ 1500 ND individuals and ~ 1500 controls, all of European origin, to determine whether they might predispose to ND. CHRNA3 and CHRNA5 mRNA and protein will be assessed in post mortem human brain from individuals with the putative risk and protective haplotypes. CHRNA3 and CHRNA5 promoters sequences, from the risk and protective haplotypes, will be assessed in tissue culture for transcriptional efficiency. A mis-sense coding SNP in CHRNA5, which lies on the risk haplotype, will be assessed for change in binding affinties and ionic conductance. These results should identify the functional effects of promoter and transcribed SNPs in CHRNA3 and CHRNA5 genes. This study should identify the consequences of CHRNA3 and/or CHRNA5 gene sequences which increase risk for ND and should facilitate new drug development for treatment of ND.