Mutations in ABCA7 in a Belgian cohort of Alzheimer's disease patients: a targeted resequencing study
Mutations in ABCA7 in a Belgian cohort of Alzheimer's disease patients: a targeted resequencing study
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DOI：
10.1016/s1474-4422(15)00133-7
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发表时间：
2015-08-01
期刊：
影响因子：
48
通讯作者：
Sleegers, Kristel
中科院分区：
文献类型：
--
作者：
Cuyvers, Elise;De Roeck, Arne;Sleegers, Kristel
背景ABCA7基因在全基因组关联研究中被认为是阿尔茨海默病的危险基因。在比利时的一个队列中，它是与阿尔茨海默病风险最密切相关的基因之一。方法我们对772例阿尔茨海默病患者(发病时的平均年龄为74.6岁[SD 8.9])和757例地理匹配的社区对照(纳入时的平均年龄为73.9岁[8.0])进行了大规模的平行重测序。经生物信息学处理后，用条件Logistic回归分析常见变异体，用变异体关联工具进行稀有变异体关联分析。为了探索观察到的创始人效应，用Sanger测序法对同一队列中因生物样本不足而未被纳入大规模平行重测序的其他无关阿尔茨海默病患者(n=183，发病时平均年龄78.8岁[SD 6.0])和对照组(n=265，发病时平均年龄56.9岁[10.8])进行ABCA7移码突变Glu709fs的筛查。采用实时定量聚合酶链式反应技术，研究了阿尔茨海默病患者(n=3)和对照组(n=4)死后脑组织中ABCA7基因表达的变化；对772例阿尔茨海默病患者队列中三种功能丧失突变携带者的淋巴母细胞系进行了无义介导的mRNA降解研究。发现内含子低频突变rs78117248(58例阿尔茨海默病患者和28例对照组的次要等位基因频率分别为3.8%和1.8%)与阿尔茨海默病的发病密切相关(优势比2.07，95%可信区间1.31-3.27；P=0.0016)，并且在调节GWA顶部单核苷酸多态rs3764650、rs4147929和rs3752246(2.001.22-3.26；p=0.006)后仍然显著。我们发现，与对照组相比，患者中预测的功能丧失突变的频率增加(相对危险度4.03，95%可信区间1.75-9.29；p=0.0002)。一个移码突变(Glu709fs)在研究人群中表现出创始人效应，并在一个常染色体显性遗传的阿尔茨海默病家族中被发现与疾病分离。仅在阿尔茨海默病患者中发现的两个功能丧失突变携带者(Glu709fs和Trp1214*)的ABCA7表达低于四个非携带者对照(相对表达0.45，95%可信区间0.25-0.84；解释我们认为ABCA7基因的一个低频变异可以解释ABCA7与阿尔茨海默病之间的联系，而这个危险基因功能丧失突变的证据表明，ABCA7的部分功能丧失可能是阿尔茨海默病的一个潜在的致病机制。
Background ABCA7 was identified as a risk gene for Alzheimer's disease in genome-wide association studies (GWAS). It was one of the genes most strongly associated with risk of Alzheimer's disease in a Belgian cohort. Using targeted resequencing, we investigated ABCA7 in this cohort with the aim to directly detect rare and common variations in this gene associated with Alzheimer's disease pathogenesis.Methods We did massive parallel resequencing of ABCA7 after HaloPlex target enrichment of the exons, introns, and regulatory regions in 772 unrelated patients with Alzheimer's disease (mean age at onset 74.6 years [SD 8.9]) recruited at two memory clinics in Flanders, Belgium, and 757 geographically matched community-dwelling controls (mean age at inclusion 73.9 years [8.0]). After bioinformatic processing, common variants were analysed with conditional logistic regression and rare variant association analysis was done in Variant Association Tools. To explore an observed founder effect, additional unrelated patients with Alzheimer's disease (n=183, mean age at onset 78.8 years [SD 6.0]) and control individuals (n=265, mean age at inclusion 56.9 years [10.8]) from the same cohort who had not been included in massive parallel resequencing because of insufficient biosamples were screened for the ABCA7 frameshift mutation Glu709fs with Sanger sequencing. The effect of loss-of-function mutations on ABCA7 expression was investigated with quantitative real-time PCR in post-mortem brains of patients (n=3) and control individuals (n=4); nonsense mediated mRNA decay was investigated in lymphoblast cell lines from three predicted loss-of-function mutation carriers from the cohort of 772 patients with Alzheimer's disease.Findings An intronic low-frequency variant rs78117248 (minor allele frequency 3.8% in 58 patients with Alzheimer's disease and in controls 1.8% in 28 controls) showed strongest association with Alzheimer's disease (odds ratio 2.07, 95% CI 1.31-3.27; p=0.0016), and remained significant after conditioning for the GWAS top single nucleotide polymorphisms rs3764650, rs4147929, and rs3752246 (2.00, 1.22-3.26; p=0.006). We identified an increased frequency of predicted loss-of-function mutations in the patients compared with the controls (relative risk 4.03, 95% CI 1.75-9.29; p=0.0002). One frameshift mutation (Glu709fs) showed a founder effect in the study population, and was found to segregate with disease in a family with autosomal dominant inheritance of Alzheimer's disease. Expression of ABCA7 was reduced in the two carriers of loss-of-function mutations found only in patients with Alzheimer's disease (Glu709fs and Trp1214*) compared with four non-carrier controls (relative expression 0.45, 95% CI 0.25-0.84; p=0.002) and in lymphoblast cell lines from three carriers of Glu709fs compared with those from two non-carrier controls.Interpretation We propose that a low-frequency variant can explain the association between ABCA7 and Alzheimer's disease, and the evidence of loss-of-function mutations in this risk gene suggests that partial loss-of-function of ABCA7 could be a potential pathogenetic mechanism of Alzheimer's disease.