Zhu Liqing, Zhao Misheng, Cheng Xiaoli, Yu Dandan, Li Xiaolong, Xu Fei, Wang Jinguo, Wang Mingshan
Clinical Laboratory, the First Affiliated Hospital of Wenzhou Medical University, Wenzhou, Zhejiang 325000, China.
Zhonghua Yi Xue Yi Chuan Xue Za Zhi. 2018 Apr 10;35(2):179-183. doi: 10.3760/cma.j.issn.1003-9406.2018.02.007.
To explore the genetic basis for a Chinese pedigree affected with congenital hypofibrinogenamia.
Peripheral blood samples were collected from 9 members from the pedigree. Routine coagulation tests including activated partial thromboplastin time (APTT), thrombin time (TT), the prothrombin time (PT) were carried out. The activity of fibrinogen (Fg: C) was measured using Clauss method, and fibrinogen antigen (Fg: Ag) was measured with immunoturbidimetry. All exons and exon-intron boundaries of the fibrinogen Aα, Bβ and γ chain genes were amplified using PCR, which was followed by direct sequencing. Suspected mutation was confirmed by reverse sequencing. The mutant fibrinogen was analyzed with Swiss-PdbViewer.
The proband showed prolonged APTT, PT and TT. Her functional fibrinogen (Fg: C) and antigen fibrinogen (Fg: Ag) levels were reduced to 0.69 g/L and 0.72 g/L, respectively. Her mother and grandmother also had a low levels of fibrinogen, which were 0.99 g/L and 0.83 g/L for Fg: C, 1.02 g/L and 0.87 g/L for Fg: Ag, respectively. The results of other members from the pedigree were all within the normal range. Genetic analysis reveled a heterozygous G>T mutation at nucleotide 7590 in exon 8 of γ gene in the proband, which was predicted to be a novel Ser313Ile mutation. The mutation was also found in her mother and grandmother. Model analysis showed that the Ser313Ile mutation disturbed the hydrogen bonds between Ser313, Asn319 and Asp320. Moreover, the mutation also altered the mutual electrostatic force and affected the folding and instability of the mutant fibrinogen.
The heterozygous Ser313Ile mutation probably underlies the hypofibrinogenemia in this pedigree.
探究一个患先天性低纤维蛋白原血症的中国家系的遗传基础。
采集该家系9名成员的外周血样本。进行常规凝血试验，包括活化部分凝血活酶时间（APTT）、凝血酶时间（TT）、凝血酶原时间（PT）。采用Clauss法测定纤维蛋白原活性（Fg:C），用免疫比浊法测定纤维蛋白原抗原（Fg:Ag）。用聚合酶链反应（PCR）扩增纤维蛋白原Aα、Bβ和γ链基因的所有外显子及外显子-内含子边界，随后进行直接测序。通过反向测序确认疑似突变。用Swiss-PdbViewer分析突变型纤维蛋白原。
先证者的APTT、PT和TT延长。其功能性纤维蛋白原（Fg:C）和抗原性纤维蛋白原（Fg:Ag）水平分别降至0.69g/L和0.72g/L。其母亲和祖母的纤维蛋白原水平也较低，Fg:C分别为0.99g/L和0.83g/L，Fg:Ag分别为1.02g/L和0.87g/L。该家系其他成员的检测结果均在正常范围内。基因分析显示，先证者γ基因第8外显子7590位核苷酸存在杂合G>T突变，预测为新的Ser313Ile突变。其母亲和祖母也存在该突变。模型分析表明，Ser313Ile突变破坏了Ser313、Asn319和Asp320之间的氢键。此外，该突变还改变了相互间的静电力，影响了突变型纤维蛋白原的折叠和稳定性。
杂合Ser313Ile突变可能是该家系低纤维蛋白原血症的病因。
