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Sichuan Da Xue Xue Bao Yi Xue Ban. 2022 Jan 20; 53(1): 171–174.
PMCID: PMC10408859

Language: Chinese | English

1例遗传性异常纤维蛋白原血症的家系分析和诊断报告

Pedigree Analysis and Diagnosis of Congenital Dysfibrinogenemia: A Case Report

娟 骆

四川大学华西第二医院 新生儿科 出生缺陷与相关妇儿疾病教育部重点实验室 (成都 610041), Department of Neonatology, West China Second University Hospital, Key Laboratory of Birth Defects and Related Disease of Women and Children of the Ministry of Education, Sichuan University, Chengdu 610041, China

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苏容 段

四川大学华西第二医院 新生儿科 出生缺陷与相关妇儿疾病教育部重点实验室 (成都 610041), Department of Neonatology, West China Second University Hospital, Key Laboratory of Birth Defects and Related Disease of Women and Children of the Ministry of Education, Sichuan University, Chengdu 610041, China

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华 王

四川大学华西第二医院 新生儿科 出生缺陷与相关妇儿疾病教育部重点实验室 (成都 610041), Department of Neonatology, West China Second University Hospital, Key Laboratory of Birth Defects and Related Disease of Women and Children of the Ministry of Education, Sichuan University, Chengdu 610041, China 四川大学华西第二医院 新生儿科 出生缺陷与相关妇儿疾病教育部重点实验室 (成都 610041), Department of Neonatology, West China Second University Hospital, Key Laboratory of Birth Defects and Related Disease of Women and Children of the Ministry of Education, Sichuan University, Chengdu 610041, China 滨州医学院第一临床医学系 (滨州 264003), First School of Clinical Medicine, Bingzhou Medical University, Binzhou 264003, China

结论

CD主要依据基因检测进行确诊,其治疗特点为精准个体化原则,对于没有临床表现的患者无需特殊治疗,但对备孕的女性患者充分做好产前诊断及随访十分重要,避免流产及产后凝血功能异常所致的并发症出现。

Keywords: 纤维蛋白原, 遗传性异常纤维蛋白原血症, 家系, 基因突变, 产前诊断, 遗传咨询

Abstract

Objective

To improve the understanding and diagnosis and treatment of congenital dysfibrinogenemia (CD) through analyzing the clinical data of a pediatric patient and his pedigree.

Methods

The clinical manifestations, laboratory findings and treatment of a case of CD diagnosed at West China Second University Hospital, Sichuan University and those of its pedigree members were analyzed, and genetic tracing and follow-up were conducted on the patient and its pedigree.

Results

The child has no clinical manifestations at the time of admission. Coagulation function examination showed normal prothrombin time (PT), normal activated partial thrombin time (APTT), significantly prolonged thrombin time (TT), fibrinogen activity (Fg: C<0.5 g/L) measured with the Clauss method, and fibrinogen antigen (Fg: Ag) measured at 2.8 g/L with PT algorithm. Gene sequencing results showed that heterozygous missense mutation c.901C>T (p.Arg301Cys) in exon 8 of FGG gene. Combined with the family history, the child was diagnosed with CD. During the follow-up of 4 + months, the patient did not present bleeding, abnormal coagulation or thrombosis, and the coagulation function did not show significant changes compared with the findings obtained on admission.

Conclusion

The diagnosis of CD is confirmed mainly based on genetic testing and the treatment is characterized by the principle of precise individualized treatment. No special treatment is needed for patients presenting no clinical manifestations. However, it is important to provide thorough prenatal diagnosis and follow-up services for female patients planning for pregnancy so as to prevent miscarriage and complications caused by postpartum coagulation dysfunction.

Keywords: Fibrinogen, Congenital dysfibrinogenemia, Pedigree, Genetic mutation, Prenatal diagnosis, Genetic counseling

遗传性异常纤维蛋白原血症(congenital dysfibrinogenemia, CD)是一种因基因突变而导致纤维蛋白原(fibrinogen, Fg)分子结构和功能异常的遗传性疾病,大多数为常染色体显性遗传,小部分为隐性遗传。其临床表现具有高度异质性,患者中约55%无症状、25%有出血症状、20%有血栓形成,其中部分患者可同时或先后有出血和血栓形成 [ 1 ] ,部分患者表现为伤口愈合不良,合并妊娠的女性CD患者可出现反复流产及胎盘早剥并可致产后出血及血栓形成的风险升高 [ 2 ] 。本文收集了1例CD患儿及其家系资料,报道如下。

1. 病例资料

患儿,男,系G 12 P 3 、胎龄37 +1 周足月新生儿,因胎膜早破剖宫产娩出,否认宫内窘迫史及生后抢救史,体格检查无异常。凝血功能:凝血酶原时间(PT)16.3 s,活化的部分凝血活酶时间(APTT)38.4 s,凝血酶时间(TT)38.1 s,Clauss法检测纤维蛋白原活性(fibrinogen activity, Fg: C)<0.5 g/L,PT演算法测定纤维蛋白原抗原(fibrinogen antigen, Fg: Ag)2.8 g/L,Fg: Ag/Fg: C>5.6。因患儿母亲已确诊为CD患者,故提取患儿外周血DNA对纤维蛋白原编码基因 FGA FGB FGG 的所有外显子及侧翼序列和启动子区进行PCR扩增后( FGG- exon8引物F: 5′-GAAGCATCCTACGAAAGAGGG-3′; R: 5′-ACTGTGGGTTGTGGGATCTC-3′)采用Sanger法测序分析,结果为 FGG 基因第8号外显子杂合性错义变异c.901C>T(p.Arg301Cys)( 图1 )。诊断为CD,因无出血及血栓形成等表现,未予特殊治疗,嘱密切观察病情变化,出院后血液科长期随访。

Gene sequencing variation of the patient

患儿基因测序变异图

家族史:患儿母亲曾因反复流产伴双下肢静脉血栓,在四川大学华西医院就诊,凝血功能PT 13.1 s,APTT 30.2 s,TT 139.6 s,Fg:C<0.5 g/L,Fg:Ag 4.3 g/L,Fg:Ag/Fg:C>8.6,提取外周血DNA进行二代测序,通过对近700个血液系统遗传性疾病和免疫缺陷病相关基因目标区域捕获和深度测序(平均测序深度500~1 000 X),对所发现突变基因应用SIFT、PolyPhen2、LRT、MutationTaster等方法进行分析,检测出 FGG 基因第8号外显子杂合性改变c.901C>T(p.Arg301Cys)为致病基因,诊断为CD,因生产本例患儿在我院妇产科就诊。确诊为CD后,患儿母亲曾先后予“那屈肝素钙”及“华法林”抗凝治疗,复查超声提示双下肢血栓部分再通;此次剖宫产术前3日查Fg:C<0.5 g/L,予输注纤维蛋白原浓缩剂后复查Fg:C为1.52 g/L,剖宫产术中输注新鲜冰冻血浆,产后继续予低分子肝素钠预防血栓,后改为口服抗凝药治疗,术中、术后未发生大出血及血栓形成。患儿致病基因检测结果与母亲相同,其家系资料见 表1 表2 图2

表 1

Pregnancy history of the patient’s mother and its second aunt

患儿母亲及患儿二姨母孕产史

Family member Pregnancy number Delivery number Abortion number Stillbirth number Induced labor number Death number Survival number
Mother 12 3 9 0 1 1 1
Second aunt 7 4 3 1 0 0 3

表 2

Laboratory test findings of the pedigree members

家系成员的实验室检测结果

Family member PT APTT
/(g/L)
Fg:Ag
/(g/L)
Fg:Ag/Fg:C Liver function Platelet count Gene test
The child Normal Normal Prolong <0.5 2.8 >5.6 Normal Normal Mutation
Mother Normal Normal Prolong <0.5 4.3 >8.6 Normal Normal Mutation
Second aunt Normal Normal Prolong 0.58 3.1 5.3 Normal Normal Unchecked
Grandfather Normal Normal Prolong 0.62 3.2 5.2 Normal Normal Unchecked
Grandmother Normal Normal Normal 2.6 2.7 1.0 Normal Normal Unchecked

Pedigree chart of the case

此病例家系图谱

通过对本病例中患儿及其母亲疾病的诊断、治疗及其家系资料的采集,我们了解到患儿祖父及二姨母可能为CD患者,建议完善相关基因检测。由于患儿祖父有下肢疼痛、肿胀病史,建议其完善相关血管影像学检查,警惕静脉血栓形成;同时建议二姨母的孩子行CD基因检测,警惕出血及血栓形成风险。如果该患儿母亲仍有再次怀孕的计划,建议其做好孕期、产前及产后管理,避免再次发生流产、出血、血栓形成,如果再次分娩为女婴,可能会对女婴成年后的孕产健康有较大影响,需要对其进行严密的产前诊断及监测。

2. 讨论

检索人类纤维蛋白原变异数据库( http://site.geht.org/base-de-donnees-fibrinogene/ ),目前已有超过450个Fg突变基因被注册 [ 3 ] ,截止到2020年6月1日,国际上已报道的Fg分子缺陷病例共有1 215例,包括Aα链突变(626例)、Bβ链突变(154例)和γ链突变(435例)。遗传性纤维蛋白原缺陷症是一种Fg的编码基因缺陷导致的遗传性凝血功能异常疾病,其发病率约为1/10 6 ,可分为2种类型 [ 4 ] 。I型是Fg数量缺乏,包括低纤维蛋白原血症和无纤维蛋白原血症;Ⅱ型则是Fg分子结构或功能异常,包括异常纤维蛋白原血症和低异常纤维蛋白原血症。CD属于Ⅱ型纤维蛋白原缺陷症。

Fg是由多肽链 Aα、Bβ、γ构成的二聚体,编码基因位于 4 号染色体长臂,其中 FGA 编码 Aα 链, FGB 编码 Bβ 链, FGG 编码 γ 链。任何一条编码基因突变均可导致Fg结构和/或功能异常,其中大多数是由杂合错义突变引起的,约85%的基因突变发生在 FGA 的第2号外显子或 FGG 的第8号外显子中 [ 5 - 6 ] 。Fg作为血浆中含量最高的凝血因子,在纤维蛋白凝块形成、血小板活化及纤溶调节中发挥重要作用 [ 7 ] 。在妊娠期间,Fg通过促进滋养细胞增殖,起到稳定胚胎植入、维持胎盘完整、满足胎儿血氧供应的作用 [ 8 ] 。故CD患者容易发生出血、血栓形成等临床表现以及妊娠期胎儿宫内发育迟缓甚至胎停 [ 9 ] 。IWAKI等 [ 10 ] 的实验显示,敲除Fg的编码基因的小鼠受孕后,不能维持至足月妊娠。CD的临床表型与基因型有一定的相关性 [ 4 7 11 ] ,除血液系统外,肾脏泌尿系统也会有所影响,但由于发生出血、血栓等具有多因素性,目前仍有较多CD的临床表型与基因型关系不明确。虽然国内外已有不少关于CD的文献报道,但对于本病例 FGG- exon8杂合错义突变c.901C>T(p.Arg301Cys)的报道极少。

CD常常由于发现凝血功能异常(TT 延长;Fg:C显著降低,Fg:Ag正常或增高;Fg:Ag/Fg:C>1.43;PT、APTT多为正常),结合临床表现及家族史考虑临床诊断,辅助基因检测以确诊 [ 11 ] 。目前尚无CD 的发生与地域、季节、种族、年龄相关性的报道。虽有资料显示,女性发病率高于男性,但这可能与女性多由于妊娠、产科手术等需要进行常规术前检查,继而发现凝血功能异常而就诊密切相关。据统计 [ 12 ] CD 患者平均每年每1 000人中有5.58人发生深静脉血栓,而正常人平均每年每1 000人中仅有1.5人发病。女性月经量过多及经期延长,不明原因的各种静脉血栓形成、肾功能损伤等均要注意对CD进行鉴别诊断。其治疗方案的制定应根据临床表现、个人史、家族史、Fg水平等实验室检查及基因突变类型等综合考虑,以个体化原则为其特点,无症状患者无需特殊治疗。对于出血,主要采用止血和Fg替代治疗 [ 13 ] 。对于血栓,在抗凝的基础上警惕出血,必要时同时补充Fg [ 14 ] 。对于妊娠期CD患者,整个孕期及产后均需密切监测凝血功能及Fg:C水平。专家共识建议 [ 15 ] ,在孕早/中期血浆Fg:C水平应维持在0.5~1.0 g/L,孕晚期及围生期保持在1~2 g/L;在分娩过程中需维持在1.5 g/L以上。孕期使用高水平Fg替代治疗的CD 患者,可同时进行抗凝治疗预防血栓形成。

本文报道的患儿及其母亲均存在4号染色体长臂 FGG 第8号外显子c.901C>T的杂合错义突变,引起Fgγ链第301位精氨酸突变为半胱氨酸(Arg301Cys)。蛋白同源性分析发现Fgγ链Arg301位点在脊椎动物中高度保守,其结构改变极易造成功能异常。蛋白质建模显示,由带正电荷的Arg变为不带电荷的Cys,导致了纤维分支及氢键数目减少 [ 16 ] ,可能是其致病的分子学基础之一。有研究表明 [ 17 ] ,Fg中Arg变为Cys可使患者发生血栓形成的易感性增加。文献报道 [ 18 ] ,血栓相关性Fg突变的女性,妊娠期发生流产及产后出现血栓栓塞的风险增高。患儿母亲先后9次自然流产,且病程中确诊患有“双下肢静脉血栓”,与上述文献报道相符。患儿目前4 + 月,虽然现身体健康,无出血、凝血异常及血栓形成表现,但据统计,34岁是CD 患者发生静脉血栓的中位年龄,49岁是发生动脉血栓的中位年龄 [ 12 ] ,而大出血主要发生在20岁至40岁之间 [ 19 ] ,故仍需警惕该男性患儿血栓形成及出血风险,需要长期进行血液科随访。

通过分析本病例及其家系基因,复习相关文献后我们总结出CD基因型及表型有一定相关性,在表型不明确的分子缺陷患者中,采用蛋白质建模分析突变位点对Fg结构的影响,应用血栓弹力图、纤维蛋白聚集曲线、扫描电镜观察纤维蛋白凝块等方法研究Fg功能,有助于临床医生识别发病机制、制定治疗计划并预测临床结局。今后还需要对CD基因突变机制进行深入研究,以便在诊治时对患者及家系提供更精准的建议,尤其需要重视对于女性患者的产前咨询及长期随访。

*    *    *

利益冲突 所有作者均声明不存在利益冲突

Funding Statement

四川省科技厅应用基础研究项目(No. 2021YJ0171)资助

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