Abstract
目的
探讨HSPB1基因罕见变异与肌萎缩侧索硬化(ALS)发病的相关性。
方法
对166例中国ALS患者进行二代测序基因检测,筛选出HSPB1基因可能的致病性罕见变异,分别与千人计划及国内全外显子测序健康对照数据库比对分析,进行序列核关联性检验(SKAT)及优化的SKAT(SKAT-O)。
结果
本研究共筛选出3个HSPB1基因可能的致病性罕见变异:c.379C>T(p. R127W)、c.446A>C(p.D149A)及c.451A>C(p.T151P),均为错义突变。以千人计划作为对照,SKAT p=3.61×10-7,SKAT-O p= 1.62×10-6;以国内全外显子测序健康对照数据库作为对照,SKAT p=9.99×10-4,SKAT-O p=1.80×10-3。未发现该基因罕见变异携带者的特征性临床表型特点。
结论
HSPB1基因罕见变异可能与ALS发病存在相关性。
Keywords: HSPB1基因, 罕见变异, 肌萎缩侧索硬化, SKAT
Abstract
Objective
To explore the association between rare HSPB1 variants and amyotrophic lateral sclerosis (ALS).
Methods
We performed next-generation sequencing for 166 Chinese ALS patients to screen for possible pathogenic rare variants of HSPB1. The control individuals were obtained from 1000 Genome Project and an in-house whole-exome sequencing database. The Sequence Kernel Association Test (SKAT) and the SKAT-optimal test (SKAT-O) were used to identify the association between rare HSPB1 variants and ALS.
Results
We identified 3 possible pathogenic rare variants of HSPB1 (all were missenses), including c.379C>T (p.R127W), c.446A>C (p.D149A) and c.451A>C (p.T151P). Compared with 1000 Genome Project, SKAT p=3.61×10-7 and SKAT-O p=1.62×10-6; while compared with the in-house database, SKAT p=9.99×10-4, SKAT-O p= 1.80×10-3. We analyzed the phenotypes of rare HSPB1 variant carriers and found no specific clinical characteristics associated with these variants.
Conclusion
Rare variants of HSPB1 are probably associated with the pathogenesis of ALS.
Keywords: HSPB1 gene, rare variants, amyotrophic lateral sclerosis, Sequence Kernel Association Test
肌萎缩侧索硬化(ALS)是一种进行性致死性神经变性病,主要累及上、下运动神经元,患者多于发病3~5年内死于呼吸衰竭,病因尚不明确,缺乏有效治疗方法[1]。因此,ALS病因研究对于发现新的治疗靶点至关重要。现有研究显示遗传因素对ALS发病有重要作用[2],1993年超氧化物歧化酶1(SOD1)基因被报道与家族性ALS相关[3],是最早被发现的ALS致病基因,迄今已发现至少120个基因变异与ALS发病相关[2]。近年来随着大规模平行测序技术的发展,如全基因组测序及全外显子组测序,越来越多的ALS致病新基因被发现,包括TBK1、CHCHD10、TUBA4A、MATR3等[4]。但仍有许多ALS相关遗传风险变异未被发现,并且这些极有可能是罕见变异[5],推测尚有许多未被发现的致病基因罕见变异与ALS相关。
HSPB1基因,位于7q11.23,编码小分子量热休克蛋白家族成员B1(HSPB1),该基因突变可导致常染色体遗传的轴索性神经病,包括腓骨肌萎缩症2F型(CMT 2F)和远端型遗传性运动神经病(dHMN)[6-9],患者的临床表现可能与ALS类似。基础研究显示HSPB1在SOD1-ALS动物模型中表达上调[10],且对SOD1致病性突变诱导的细胞死亡具有保护作用[11-12],在ALS患者脊髓组织中HSPB1表达明显增多[13],提示HSPB1基因可能与ALS发病相关。但检索Pubmed仅见一项基于意大利ALS队列的研究显示HSPB1可能参与散发性ALS致病过程[14],国内外未见其他相关临床研究,目前HSPB1基因是否与ALS发病存在关联尚未证实。
本研究通过二代测序技术对166例中国ALS患者进行了基因检测,筛选出HSPB1基因可能的致病性罕见变异,分别比对千人计划(1000 Genome)及中国国内全外显子测序健康对照数据库进行关联性检验,以明确HSPB1基因罕见变异与ALS发病的相关性。
1. 资料和方法
1.1. 研究对象
纳入2018年1月~2020年7月就诊于我院并进行二代测序基因检查的ALS患者166例。纳入标准:根据2000年修订的EI Escorial标准<sup>[<xref ref-type="bibr" rid="b15">15</xref>]</sup>诊断符合确诊、拟诊、实验室支持拟诊及可能的ALS;同意并进行了二代测序基因检查。排除标准:类ALS综合征;不同意行基因检查。收集每个研究对象的临床资料,包括性别、发病年龄、起病部位、家族史、神经系统阳性体征、肌电图结果等,并进行ALS功能评分量表-修订版(ALSFRS-R)评分。其中家族性ALS 33例,散发性ALS 133例;男性104例(62.7%),女性62例(37.3%),男女比例为1.68:1;发病年龄43.8±12.2岁;肢体起病142例(85.5%),球部起病21例(12.7%),胸段起病3例(1.8%)。以千人计划(2504个样本,<a href="http://www.internationalgenome.org/home" target="_blank">http://www.internationalgenome.org/home</a>)和国内全外显子测序健康对照数据库(1812个样本,<a href="http://www.kangso.net.cn/index.html" target="_blank">http://www.kangso.net.cn/index.html</a>)作为对照。本研究经北京大学第三医院伦理委员会批准,全部研究对象均签署了知情同意书。
1.2. 基因检测
应用二代测序技术对入组的ALS患者进行了基因检测,筛查了所有研究对象的HSPB1基因及ALS已知致病基因(包括ALS2、ANG、ANXA11、CHMP2B、DAO、DCTN1、ERBB4、FIG 4、FUS、HNRNPA1、MATR3、NEFH、NEK1、OPTN、PFN1、SETX、SIGMAR1、SOD1、SPG11、SQSTM1、TARDBP、TBK1、TUBA4A、UBLQN2、VAPB、VCP)外显子区(北京康旭医学检验所,Illumina测序),比对到人类参考基因组(hg19版),转录本NM_001540,并从全局及区间比对深度,区间覆盖情况,位点比对质量等多种指标对结果进行质量控制,并对需要验证的位点进行一代验证。
1.3. 致病性罕见变异筛选
分别对千人计划、国内全外显子测序健康对照数据库及测序得到的ALS患者的HSPB1基因单核苷酸变异(SNV)进行过滤,筛选出可能的致病性罕见变异:(1)SNV测序深度>30×;(2)导致错义突变、无义突变、插入/缺失突变等非同义突变或位于剪切位点;(3)在千人计划和国内全外显子测序健康对照数据库中的最小等位基因频率(MAF) < 1%;(4)通过联合注释相关缺失突变软件(CADD),<a href="https://cadd.gs.washington.edu" target="_blank">https://cadd.gs.washington.edu</a>,预测SNV的致病性<sup>[<xref ref-type="bibr" rid="b16">16</xref>]</sup>,筛选出“标度”的CADD分数(CADD PHRED)>20,即在所有基因组有害变异中排在前1%的变异。
1.4. 统计分析
应用SPSS 21.0软件进行描述性统计学分析,计量资料采用均数±标准差表示,计数资料用百分比表示。应用R 4.0.2软件进行HSPB1基因罕见变异的序列核关联性检验(SKAT)及优化的序列核关联性检验(SKAT-O),并对SKAT-O进行10000次随机重复取样验证,以评估HSPB1基因罕见变异在患者及对照间是否存在统计学差异,P < 0.05为差异有统计学意义。
2. 结果
2.1. HSPB1基因罕见变异筛选情况
对166例ALS患者的二代测序结果进行质控和筛选,共发现HSPB1基因3个SNV,均为错义突变,在1000 Genome及国内全外显子测序健康对照数据库中均未发现,确定为可能的致病性罕见变异(表 1)。
1.
Position | c.DNA | Amino acid | 1000 Genome | In-house database | CADD PHRED |
Chr7:75933133 | c.379C > T | p.R127W | not report | not report | 24.7 |
Chr7:75933318 | c.446A > C | p.D149A | not report | not report | 28.4 |
Chr7:75933323 | c.451A > C | p.T151P | not report | not report | 22.5 |
2.2. 罕见变异关联性检验
分别以千人计划和国内全外显子测序健康对照数据库作为对照进行了SKAT、SKAT-O及SKAT-O随机重复取样验证,结果显示,两组间HSPB1基因罕见变异分布差异存在统计学意义(P < 0.05,表 2)。
2.
Control | SKAT p-value | SKAT-O p-value | Resampling p-value |
*P < 0.05 vs 1000 Genome or in-house database. | |||
1000 Genome | 3.61×10-7* | 1.62×10-6* | 3.90×10-3* |
In-house database | 9.99×10-4* | 1.80×10-3* | 4.30×10-3* |
2.3. HSPB1基因罕见变异携带者临床表型特点
共筛选出的3个HSPB1基因可能的致病性罕见变异由3名散发性ALS患者携带,均为杂合突变,其中1名患者携带两种SNV,这些患者未发现其他ALS已知致病基因变异。患者1为男性,携带c.379C>T SNV,36岁发病,以下肢无力起病,逐渐进展,症状局限在下肢超过8年,后逐渐出现左上肢无力,我院就诊时病程已10年,查体示颈段及腰段上、下运动单位损害表现,肌电图示颈、胸及腰三段神经源性损害表现,诊断为拟诊的ALS。患者2为女性,携带c.446A>C,62岁发病,以下肢无力起病,逐渐加重,发病1年半出现上肢力弱、言语不清,我院就诊时病程21月,查体示球、颈、腰三段上运动单位及颈、腰段下运动单位损害表现,合并面具脸、下肢铅管样肌张力增高等可疑锥体外系损害体征,肌电图示颈、腰段神经源性损害表现,诊断为拟诊的ALS。患者3为男性,携带c.446A>C及c.451A>C两个SNV,34岁发病,以言语不清起病,发病半年出现颈肌无力、呼吸困难,3年半出现四肢近端力弱,我院就诊时病程53月,查体示颈、胸、腰三段上运动单位损害表现,四段上运动单位损害表现,肌电图示四段神经源性损害表现,诊断为确诊的ALS。3名患者均无认知功能损害表现(表 3)。
3.
Patient number | Variant c.DNA | Gender | Onset age (years) | Onset region | Diagnostic category at presentation | ALSFRS-R score at presentation |
1 | c.379C > T | Male | 36 | lower limb | Probable ALS | 46 |
2 | c.446A > C | Female | 62 | lower limb | Probable ALS | 23 |
3 | c.446A > C c.451A > C |
Male | 34 | bulbar | Definite ALS | 31 |
3. 讨论
HSPB1基因位于7号染色体,总长度为1739 bp,包含3个外显子,编码小分子量热休克蛋白(sHSP)家族的重要成员HSPB1,因其相对分子质量为27 000,也被称为热休克蛋白27(HSP27)。sHSP属于分子伴侣蛋白,其典型功能是维持细胞蛋白质稳态,该家族由10个成员组成(HSPB1-10),它们具有共同的α-晶体蛋白结构域(ACD),该结构域高度保守[7],参与二聚体的形成和稳定,是后续形成寡聚复合物与目标蛋白底物结合的基础[17]。HSPB1普遍表达于多种组织细胞中,能够减少错误折叠蛋白的聚集[6],对维持细胞蛋白质稳态至关重要,参与细胞自噬、凋亡、氧化还原平衡以及细胞骨架动力学的调节等多种功能[7, 18]。HSPB1基因突变可导致常染色体遗传的轴索性神经病[7-9],遗传方式主要为常染色体显性遗传,少量病例为常染色体隐性遗传,迄今已发现超过30种该基因与CMT2F及dHMN相关的致病突变,多位于ACD结构域[9]。近期的基础研究显示HSPB1对维持运动神经元的健康和稳定起着重要作用[12],可通过与SQSTM1结合影响自噬通路功能[6]。HSPB1在ALS动物模型及患者的脊髓组织中均表达上调[10, 13],散发性ALS患者携带的HSPB1基因突变导致其丧失分子伴侣功能[14],推测HSPB1可能与ALS发病相关,但也有研究显示ALS患者脊髓腹角的HSPB1表达减少[19]。目前HSPB1基因与ALS发病是否存在关联仍不明确。
近期的大型全基因组关联研究显示ALS可能为寡基因罕见变异致病[1, 5]。SKAT是一种用于罕见变异与性状关联性分析的检验方法,可用于检验一个基因中多个罕见变异的联合效应,SKAT-O是考虑到变异间相关性后对SKAT的优化算法[20]。已有多项应用SKAT分析罕见变异与疾病关联性的研究[21-23],但该法应用于ALS的研究较少,国内未见报道。为明确HSPB1基因与ALS发病的相关性,我们应用SKAT对ALS患者HSPB1基因可能的致病性罕见变异与不同种族背景的对照进行了关联性检验。本研究共纳入166例ALS患者,其男女比例、发病部位情况与以往中国ALS流行病学数据无明显差异,但平均发病年龄较轻[24-25],更利于研究遗传因素对ALS的作用。本研究共筛选出HSPB1基因的3个可能的致病性罕见变异,分别与千人计划和国内全外显子测序健康对照数据库比对进行关联性检验,结果提示HSPB1基因罕见变异与ALS发病存在相关性。
携带HSPB1致病突变的患者通常表现为进行性下肢无力,以双足下垂为首发症状,发病年龄通常在30岁左右,患者也可能出现轻微的感觉受累[7-8, 26-28]。既往文献报告3例ALS患者携带HSPB1基因突变[9, 14],患者均于50岁后发病,无ALS家族史,均有球部受累,查体存在上运动单位损害体征。1例患者携带c.570G>C突变,58岁发病,球部起病,合并认知功能损害,于发病2年死亡[14];1例患者携带c.610dupG突变,73岁发病,合并锥体外系损害,77岁出现球部受累,病程超过9年尚存活[12];1例患者携带c.80G>T突变,58岁发病,上肢及球部起病,病程进展迅速,于发病18月死亡[9]。本研究共筛选出HSPB1基因的3个可能的致病性罕见变异,c.379C>T、c.446A>C及c.451A>C,均位于ACD结构域,其中c.379C>T为dHMN已知致病突变[8-9];c.451A>C与既往dHMN已知致病突变c.452C>T(p.T151I)影响同一氨基酸[8-9],Mutation Taster预测为致病性变异、SIFT预测为耐受、PolyPhen2预测为可能致病;c.446A>C致病性既往未见报道,Mutation Taster预测为致病性变异、SIFT预测为有害、PolyPhen2预测为可能致病。3名携带HSPB1基因致病性罕见变异的ALS患者,均为散发性病例,无认知功能损害表现,未发现共同的临床表型特点。患者1携带已知致病突变,下肢起病,病程较长。患者2合并可疑锥体外系损害体征,与既往携带c.610dupG突变患者一致[12],但发病更早,病情进展更快。患者3携带c.446A>C及c.451A>C两个位置接近的SNV,发病年龄早,球部起病,就诊时病程较长,为确诊的ALS。
本研究应用SKAT对HSPB1基因罕见变异与ALS的关联性进行了检验,结果显示该基因可能与ALS发病存在相关性,为国内外首次报道,但研究样本量相对较小,考虑可能存在选择偏倚,可进一步扩大样本量以验证研究结果。对携带HSPB1基因致病性罕见变异的ALS患者进行临床表型分析,未发现特征性临床表型特点,尚需对筛选出的SNV进行功能验证及患者随访,以进一步明确该基因与ALS发病及患者临床表型的关系。
Biography
陈君逸,博士,E-mail: cjy@bjmu.edu.cn
Funding Statement
国家自然科学基金(81873784)
Supported by National Natural Science Foundation of China (81873784)
Contributor Information
陈 君逸 (Junyi CHEN), Email: cjy@bjmu.edu.cn.
樊 东升 (Dongsheng FAN), Email: dsfan@sina.com.
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