Department of Genetics, Yale University School of Medicine, New Haven, Connecticut, USA.
Biol Psychiatry. 2011 Sep 15;70(6):528-36. doi: 10.1016/j.biopsych.2011.04.017. Epub 2011 Jun 17.
Several studies report association of alpha-4 nicotinic acetylcholine receptors (encoded by CHRNA4) with nicotine dependence (ND). A meta-analysis of genomewide linkage studies for ND implicated a single chromosomal region, which includes CHRNA4, as genome-wide significant.
After establishing that common variants are unlikely to completely account for this linkage, we investigated the distribution of CHRNA4 rare variants by sequencing the coding exons and flanking intronic regions of CHRNA4 in 209 European American (EA) ND cases and 183 EA control subjects. Because most of the rare variants that we detected (and all nonsynonymous changes) were in Exon 5, we sequenced Exon 5 in an additional 1000 ND cases and 1000 non-ND comparison subjects, both of which included equal numbers of EAs and African Americans.
Comparison subjects had a higher frequency of rare nonsynonymous variants in the Exon 5 region (encoding the large intercellular loop of the α4 subunit; Fisher's Exact Test p = .009; association test p = .009, odds ratio = .43; weighted-sum method p = .014), indicating a protective effect against ND. Considering data from the two stages combined and only nonsynonymous variants predicted to alter protein function, the association was stronger (Fisher's Exact Test p = .005; association test p = .008, odds ratio = .29; weighted-sum method p = .005). Single-photon emission computed tomography imaging results were consistent with functionality.
CHRNA4 functional rare variants may reduce ND risk. This is the first demonstration that rare functional variants at a candidate locus protect against substance dependence to our knowledge, suggesting a novel mechanism of substance dependence heritability that is potentially of general importance.
几项研究报告表明，α-4 型烟碱型乙酰胆碱受体（由 CHRNA4 编码）与尼古丁依赖（ND）有关。对 ND 的全基因组连锁研究的荟萃分析提示，一个包括 CHRNA4 的单一染色体区域与全基因组显著相关。
在确定常见变体不太可能完全解释这种连锁之后，我们通过对 209 例欧洲裔美国 ND 病例和 183 例欧洲裔美国对照个体的 CHRNA4 编码外显子和侧翼内含子区域进行测序，研究了 CHRNA4 稀有变体的分布。因为我们检测到的大多数稀有变体（以及所有非同义变化）都在外显子 5 中，所以我们在另外 1000 例 ND 病例和 1000 例非 ND 对照个体中对 Exon 5 进行了测序，这两个群体都包括相等数量的欧洲裔美国人和非洲裔美国人。
对照个体在 Exon 5 区域（编码 α4 亚基的大细胞间环）中具有更高频率的稀有非同义变体（Fisher 精确检验 p =.009；关联检验 p =.009，优势比 =.43；加权总和法 p =.014），表明对 ND 具有保护作用。考虑到两个阶段的数据以及仅预测会改变蛋白功能的非同义变体，相关性更强（Fisher 精确检验 p =.005；关联检验 p =.008，优势比 =.29；加权总和法 p =.005）。单光子发射计算机断层扫描成像结果与功能一致。
CHRNA4 功能性稀有变体可能降低 ND 风险。这是我们所知的首个在候选基因座中证明稀有功能变体可预防物质依赖的研究，提示了一种潜在具有普遍重要性的物质依赖遗传的新机制。
