GWAS 报道的阿尔茨海默病易感基因在我国西南汉族人群中的验证

KIZ OpenIR > 动物模型与人类重大疾病机理重点实验室 > 疾病机理遗传学和进化医学学科组（姚永刚）

	GWAS 报道的阿尔茨海默病易感基因在我国西南汉族人群中的验证
	王慧珍
学位类型	硕士
导师	姚永刚
	2013-11
学位授予单位	中国科学院研究生院
学位授予地点	北京
学位专业	细胞生物学
关键词	阿尔茨海默病 Aβ Gwas Picalm 遗传易感性
摘要	阿尔茨海默病(Alzheimer's disease, AD)，又被称为老年痴呆症，是一种进行性发展的神经退行性疾病，是最常见的老年期痴呆类型。β淀粉样蛋白（amyloid beta protein, Aβ）在神经元外大量积累形成的胞外老年斑和微管结合蛋白（tau）高度磷酸化形成的胞内神经纤维缠结（neurofibrillary tangles, NFT）是AD 的两大主要病理特征。关于AD 的遗传学研究相当广泛，目前公认的家族性AD（familial AD, FAD）主要由Aβ前体蛋白（β-amyloid precursor protein, APP）、早老素1（presenilin 1, PSEN1）和早老素2（presenilin 2, PSEN2）编码基因的错义突变引起，其基因突变从改变酶切位点和增强分泌酶活性等方面增加Aβ的产生，导致Aβ异常分泌，从而导致早发性家族性AD（early-onset familial AD, EO-FAD）。而晚发性AD （late-onset AD, LO-AD）的发病机制仍不清楚。研究表明LO-AD 由多个基因和环境因素共同影响。载脂蛋白基因（apolipoprotein E, APOE）是目前唯一公认的 LO-AD 危险基因，APOE ε4 等位基因使AD 的发病风险增加4-15 倍，APP、PSEN1、 PSEN2 和APOE 4 个基因能解释大约50%左右的AD 的遗传力。随着全基因组关联分析（genome wide association study, GWAS）技术的发展，越来越多的研究应用该方法在全基因组范围扫描AD 的易感位点，并发现10 余个与LO-AD 易感性相关的基因，包括BIN1、CLU、ABCA7、CR1、PICALM、MS4A6A、CD33、MS4A6E、 CD2AP 和EPHA1。这些基因主要参与Aβ的产生、降解及清除，脂质代谢，先天性免疫过程及细胞信号转导等四条细胞通路。然而，这些GWAS 结果主要是在欧美人群中得到的，由于不同人群之间存在不同的遗传背景及遗传异质性，在其它人群中对这些基因的AD 易感性进行验证显得尤为重要。在本研究中，我们利用SNaPshot 基因分型平台，检测了BIN1、CLU、ABCA7、 PICALM、MS4A6A、CD33、MS4A6E 和CD2AP1 基因的15 个单核苷酸多态性位点(single nucleotide polymorphism, SNP)在我国四川LO-AD 病人（n = 333）和正常对照人群（n = 334）中的频率分布。统计结果表明，PICALM 基因的4 个SNP 位点（rs11234495，rs592297，rs676733 和rs3851179）的基因型频率在病例和对照两个群体间均有显著性差异，其中rs11234495 和rs676733 的T 等位基因都能显著增加AD 的发病风险（rs11234495，P = 0.02，OR (95% CI) = 1.31[1.05-1.62]； rs676733，P = 0.02，OR (95% CI) = 1.30[1.04-1.62]）。而GWAS 报道的阳性SNP 位点rs3851179 和另一个tag SNP 位点rs592297 的等位基因频率在病例和对照间的差异达到边缘显著水平（rs592297，P = 0.07，OR (95% CI) = 1.25[0.99-1.57]；rs3851179，P = 0.09，OR (95% CI) = 1.21[0.97-1.51]）。基于这些SNP 位点构建单倍型，发现单倍型TTT（rs11234495-rs592297-rs676733）能增加AD 的发病风险（P = 0.02，OR (95% CI) = 1.30[1.05-1.62]），此外还有一些单倍型频率在病例和对照间的频率差异达到边缘显著水平。综合分析结果提示在我国西南汉族人群中PICALM 基因与AD 的易感性相关，该结果与欧美人群的GWAS 研究结果相吻合。然而我国其它课题组对GWAS 报道的AD 易感基因的验证研究并未得到一致的结果，这提示AD 具有复杂的遗传机制，同时亦表明我们需要开展更大样本量的独立实验以及必要的功能实验来进一步证实本研究的结果。目前关于AD 的研究结果大多数支持Aβ是AD 的主要致病原因。在正常生理条件下，Aβ的产生、降解和清除过程处于一个动态的平衡中，一旦这个平衡被打破，Aβ生成、分泌过多，就会导致AD 的发生。前期的GWAS 研究发现的 AD 易感基因大多也与Aβ的生成、降解及清除过程相关，为了进一步探索Aβ生成和代谢通路相关基因在AD 疾病遗传易感中发挥的作用，我们试图通过基因分型方法探究SCARA、CD36 和LRP-1 等Aβ受体基因以及IDE、NEP 和MMP-9 等Aβ降解酶基因与AD 是否相关。结果表明CD36 基因的rs11971740 的G 等位基因（P = 0.02，OR (95% CI) = 1.30[1.03-1.64]）以及NEP 基因的rs989692 的T 等位基因和AD 易感性相关（P = 0.03，OR (95% CI) = 1.32[1.02-1.71]）。这提示 CD36 和NEP，作为Aβ转运和降解通路中较为重要的基因，可能对AD 遗传易感。该结果同样需要更大样本量进行独立验证，以及必要的功能实验来验证其在 AD 发病过程中的作用。
其他摘要	Alzheimer’s disease (AD), which mainly leads to severe memory loss in the elderly population over 65 years old, is the most prevalent neurodegenerative disease. Extracellular senile plaques (SP) and intracellular neurofibrillary tangles (NFT) are two hallmarks observed in AD brains. Besides aging, family history is the second greatest risk factor for AD, but only about 5% AD cases have family history. Rare mutations in the amyloid precursor protein (APP) and presenilin 1 and 2 (PSEN1/PSEN2) genes have been identified to be linked to these rare early-onset familial AD cases. However, the pathogenesis for the remaining 90-95% sporadic cases remains unclear, only ε4 allele of the apolipoprotein E gene (APOE) is established unequivocally as a susceptible gene for the late-onset AD. The ε4 allele carriers have a risk ratio of 4-15 to AD than non-carriers. Late onset Alzheimer’s disease (LO-AD) is influenced by complicated interactions between genetic components and environmental risk factors. Genome-wide association studies (GWAS), which aimed to identifying disease risk gene/loci, had been conducted and identified 10 novel AD risk genes (BIN1, CLU, ABCA7, CR1, PICALM, MS4A6A, CD33, MS4A6E, CD2AP and EPHA1). Collectively, these genes can explain around 50% heritability of LO-AD and can be divided into pathways of production, degradation, and clearance of Aβ, cholesterol metabolism, immunity, and cellular signaling. However, these GWAS were conducted in American and European populations, while no GWAS data in Chinese population have been reported. A total of 667 Han Chinese populations, including 333 LO-AD patients and 334 cognitively healthy controls, were collected from Sichuan Province, Southwest China in this study. Patients were diagnosed independently by two psychiatrists according to the criteria of DSM-IV and NINCDS-ADRDA. In order to measure the influence of these GWAS reported genes/single nucleotide polymorphisms (SNPs) in Han Chinese population, we genotyped a SNP cohort comprising 8 GWAS reported SNPs: rs744373 (BIN1), rs1136000 (CLU), rs3764650 (ABCA7), rs38551179 (PICALM), rs610932 (MS4A6A), rs3865444 (CD33), rs670139 (MS4A6E), rs9349407 (CD2AP) and 7 tag SNPs which were selected according to the linkage disequilibrium pattern of these genes. Allele, genotype and haplotype analyses were conducted for these 15 SNPs. Our data showed that only SNPs in PICALM gene were significantly associated with LO-AD in Han Chinese, while no signicant association was observed for the remaining 7 genes. The four SNPs in PICALM gene were significantly different in genotype frequency distribution between case and control populations, and two of them (rs11234495 and rs676733) were also showed difference in allelic level. Window slide analysis indicated that haplotype TTT (composed of rs11234495-rs592297-rs676733) in the PICALM gene was significantly associated with LO-AD, and several haplotypes were marginally related to LO-AD.The result of the current study in Han Chinese population validated the association of PICALM with LO-AD. Further study with a large sample size should be carried out to solidify our conclusion. Aβ is the primary cause for Alzheimer's disease. There were some studies indicated that if the equilibrium betwen processing of APP to generate Aβ and the degrading/clearance of Aβ was disrupted by factors such as mutations in the APP, PSEN1 and PSEN2 genes, then abnormal secretion of Aβ and acceleration of SP formation would happen. Genes encoding Aβ receptors and Aβ degrading enzymes, including SCARA, CD36, LRP-1, IDE, NEP and MMP-9, play very important role in clearance and degrading Aβ. We tested whether these genes confer susceptibility to AD in our samples and found that there was no positive association between these genes and AD, except for rs11971740 (P = 0.04) in CD36 and rs989692 (P = 0.03) in NEP, which were marginally significant in allelic comparison. This result indicated that CD36 and NEP may play limited role in progression of AD, but this also need to be solidified by independent validation studies and essential function assay.
语种	中文
文献类型	学位论文
条目标识符	http://ir.kiz.ac.cn/handle/152453/7791
专题	动物模型与人类重大疾病机理重点实验室_疾病机理遗传学和进化医学学科组（姚永刚）
推荐引用方式 GB/T 7714	王慧珍. GWAS 报道的阿尔茨海默病易感基因在我国西南汉族人群中的验证[D]. 北京. 中国科学院研究生院,2013.

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