遗传性异常纤维蛋白原血症一家系的发病机制分析

Pathogenesis study of inherited dysfibrinogenemia

目的对1个遗传性异常纤维蛋白原血症家系进行表型和基因型分析及相关功能结构研究，探讨其发病机制。方法采集2012年11月浙江大学医学院附属第二医院诊断的遗传性异常纤维蛋白原血症1家系4代共19人外周静脉血，检测凝血指标，用免疫比浊法检测纤维蛋白原抗原含量。通过血栓弹力图检测血小板功能和纤维蛋白原功能；用PCR方法对纤维蛋白原基因FGA、FGB和FGG所有外显子及其侧翼序列进行基因扩增，通过正反向测序明确突变位点；用还原性十二烷基硫酸钠-聚丙烯酰胺凝胶电泳（SDS-PAGE）免疫印迹法检测纤维蛋白原突变体；采用分子结构模拟图分析预测突变氨基酸对纤维蛋白原的结构和功能的影响。结果先证者（Ⅱ-1）及其母亲（I-2）、妹妹（Ⅱ-2）、弟弟（Ⅱ-3）、女儿（II-1）纤维蛋白原活性明显下降，凝血酶时间（1tr）明显延长，但纤维蛋白原抗原含量、活化部分凝血酶原时间（APYF）和D-二聚体（D—dimer）均在正常范围内。血栓弹力图显示I-2、Ⅱ-2、111．1血小板功能正常，纤维蛋白原功能减低，而先证者及Ⅱ-3纤维蛋白原功能严重降低。基因检测结果显示先证者及Ⅱ-3存在纤维蛋白原FGGC．1001A〉C纯合突变，导致叫链第308位天冬酰胺（Asn）突变为苏氨酸（Thr）（P．Asn308Thr），而I-2、Ⅱ-2及IL-1存在纤维蛋白原FGGC．1001A〉c（P．Asn308Thr）杂合突变，家系其他成员均未检测到此突变位点。还原性SDS—PAGE免疫印迹未检测到纤维蛋白原突变体。分子结构模拟图显示突变位点Asn308位于纤维蛋白原二聚体结合的接触面，此位置氨基酸突变会对纤维蛋白的正常形成及功能产生影响。结论该家系成员异常纤维蛋白原血症系显性遗传，纤维蛋白原FGGC．1001A〉C突变是引起该家系异常纤维蛋白原血症的发病原因。

Objective To explore the pathogenesis of a family with inherited dysfibrinogenemia. Methods Coagulation parameters of peripheral venous blood of a family with inherited dysfibrinogenemia from November 2012 were measured. And platelet and fibrinogen functions were examined by thromboelastogram. The antigen concentration of fibrinogen was detected by immune nephelometry. All exons and exon-intron boundaries of FGA, FGB and FGG were amplified and subjected to mutation screening by direct/reverse sequencing. And the influences of mutant fibrinogen structure and function were analyzed and predicated by a molecular structure model. Results The values of activated partial thromboplastin time （ AprlT）, D-dimer and fibrinogen antigen of the propositus and his mother（ I -2）, younger brother （ II -3 ）, younger sister （II-2） and daughter （ III-1 ） were all in normal reference value ranges. However thrombin time （TI＂） was significantly prolonged and the activity of fibrinogen was much lower compared to its antigenicity. Thromboelastogram indicated normal function of platelet and impaired function of fibrinogen of I-2, II-2 and IliA. However the fibrinogen functions of proband and II-3 became much more impaired. Mutation screening demonstrated the homozygous mutation of proband and II-3 while I -2, II-2 and III-1 showed heterozygous mutation of FGG c. 1001 A 〉 C （ p. Asn308Thr）. No mutation was detected among other family members and reducing SDS-PAGE immunoblot showed no variants. Asn308, located at the interface of fibrinogen dimmer, participated in the fibrous structure assembling from the structure model. And nmtation at this position will affect the stability of fiber structure. Conclusion FGG c. 1001 A 〉 C mutation may account for dominant genetic dysfibrinogenemia in these family members.