早发家族性阿尔茨海默病新致病基因的鉴定和分析

Alzheimer’s disease (AD) is a common neurodegenerative disorder, which causes devastating cognitive impairment and mainly affects individuals over 65 years of age. Early-onset familial Alzheimer’s disease (EOFAD) is characterized by dementia onset before 65 years of age and positive family history for dementia. Although genome-wide association studies (GWASs) in European populations or populations of European origin have identified several risk SNPs for AD, these common variants only had small effects on AD risk and generally do not had obvious functional effects. Up to 5% of all cases of AD are Early-onset Alzheimer’s disease (EOAD). EOAD provides unique opportunities to gain special insights into the pathogenesis and phenotypes of AD. So far, genetic analyses for AD in Han Chinese are very insufficient. We launched a project for genetic screening for known AD pathogenic mutations in Han Chinese families with early-onset familial Alzheimer’s disease from Yunnan Province, and we identified two novel mutations of the PSEN1 gene in 2 families, whereas the other studied families had no known AD pathogenic mutations, indicating that additional genes may contribute to EOAD and EOFAD risk. In order to identify new pathogenic genes / mutations, we are planning to carry out genetic screening in the PSEN1, PSEN2 and APP genes in 50 EOAD cases, and we will select 5 EOFAD cases to perform whole-exome sequencing to identify disease-causing mutations. Next we will examine whether these mutations are associated with increased risk for AD in 200 patients with early-onset Alzheimer’s disease from Yunnan Province. Considering the heterogeneities of the EOAD and EOFAD clinical spectra, detailed clinical assessments, neuropsychological assessments and MRI image data will be carried out to assess the association between the identified mutations and AD risk. Meanwhile, we will also characterize the pathogenicity of the mutations at the cellular level. Our study will identify novel pathogenic genes / mutations in Chinese patients with EOAD and / or EOFAD. This information will be helpful for genetic counseling, prevention and intervention in EOAD, EOFAD patients and their relatives.

阿尔茨海默病（Alzheimer’s disease, AD）是一种常见神经退行性疾病。大规模遗传分析已在欧洲人群中鉴定出若干致病基因与遗传易感基因/位点，系统地AD遗传研究在我国人群中亟待开展。前期我们对4个早发AD家系进行了分析，检测到两个PSEN1基因的致病突变，但在其他家系中没有检测出已知的致病突变，提示存在新的致病变异。本项目拟在此基础上，对云南省具有高遗传风险的早发AD（EOAD）及早发家族性AD（EOFAD）家系开展已知致病基因突变的遗传筛查，精选出5个不含有已知致病突变的EOFAD家系开展全外显子测序，并于200例早发病例中验证检测出的致病变异，开展细胞水平的功能验证。同时，结合AD患者详细的临床表型、认知功能及MRI影像数据，分析新突变或变异与临床表型的关联。本研究将有助于我们发现EOAD和EOFAD高风险人群的新的致病基因或突变，并为患者的诊治提供遗传咨询等信息。

阿尔茨海默病是最为常见的痴呆类型，早发型及早发家族性AD虽然发病率低，但是对AD的病理机制的研究很重要。此外，AD与其它类型的痴呆的临床表现会有交叉、重叠，导致鉴别诊断困难，尤其是不典型的早发AD的确诊困难，通过遗传学检测来分析和探索病理机制很重要，还可协助痴呆类型的精确诊断，鉴别AD。近年来，通过二代测序，不断有新AD致病或重要风险基因被筛查出。我们假设：新的风险基因还将被鉴定出；不同类型的痴呆可能有重叠的分子机制和遗传基础。我们采用全外显子组测序和热点突变区Sanger测序方法，对收集自云南地区及其他地区的的早发AD及早发家族性AD样本，对180多例中国汉族家族性早发性AD患者的痴呆病因基因突变模式进行了分析。结果：检测出位于三个AD致病基因（APP, PSEN1, PSEN2）的9个突变和位于非AD致病基因上的7个突变，包括额颞叶痴呆致病基因GRN，TBK1和血管性痴呆的致病基因NOTCH3。额颞叶痴呆致病基因VCP中一个常见的剪接变异位点rs514492与AD风险呈正相关。路易体痴呆致病基因LRRK2中罕见错义变异rs33949390对AD风险有保护作用。VCP rs514492 与 LRRK2 p.R1398H是中国南方AD常见风险变异，而在北方VCP rs514492 与 COL4A1 p.Q1334H 是常见AD风险变异位点。散发性AD风险基因APOEε4等位基因显示出与早发与家族性AD风险的密切相关(P=1.12×10−11, OR=3.513)。发现了一个与中国汉族阿尔茨海默病风险相关的新的稀有突变位点 C7 rs3792646。研究结果表明：不同类型痴呆的致病基因中存在不同突变和风险变异；AD患者需要筛查痴呆致病基因的突变，以避免误诊，尤其是早发AD或家族性AD。提示AD和其他痴呆之间有重叠的病理机制，解释临床表现交叉的现象。本项目资助发表SCI期刊论文4篇，培养研究生多名，项目按照预期目标顺利完成。