一个遗传性抗凝血酶缺陷症家系的表型与基因突变分析

目的：对一例遗传性抗凝血酶（AT）缺陷症患者及其家系成员进行凝血指标和基因表型分析，初步探讨其分子发病机制。方法：在Stago仪器上检测家系各成员外周血的血浆AT活性（AT:A）、AT抗原（AT:Ag）等凝血指标；提取外周血DNA并测序，定位基因突变位点；利用生物信息学软件分析突变对蛋白功能的影响。结果：先证者及其外祖母、父亲、母亲和弟弟的AT:A均有不同程度降低，且AT:Ag同步下降，所有家系成员蛋白S活性（PS:A）和蛋白C活性（PC:A）指标均无明显异常，表现为I型AT缺陷症。基因分析显示：先证者SERPINC1 基因存在第1号外显子c.1A＞G杂合错义突变（p.Tyr2stop）以及第5号外显子c.1005G＞A杂合同义突变；其父亲携带c.1A＞G杂合错义突变，其外婆、母亲和弟弟携带c.1005G＞A杂合同义突变。保守性分析显示，Tyr2在同源物种间高度保守；MutationTaster、PolyPhen-2和LRT三个在线生物信息学软件分析均显示p.Tyr2stop突变为“致病的、有害的”；蛋白模型分析显示，p.Tyr2stop突变会引起AT基因翻译过程提前终止，产生截短蛋白。结论：该先证者及家系成员AT:A和AT:Ag不同程度降低与SERPINC1 基因上存在的c.1A＞G杂合错义突变和c.1005G＞A杂合同义突变有关。

Phenotype and gene mutation analysis of a family with hereditary antithrombin deficiency

Objective: To analyze the coagulation index and genotype of a patient with hereditary antithrombin (AT) deficiency and his family members, and to explore its molecular pathogenesis. Methods:The blood coagulation indexes such as plasma AT activity (AT:A) and AT antigen (AT:Ag) in the peripheral blood of each family member were detected on Stago instrument; the peripheral blood DNA was extracted and sequenced, and the gene mutation sites were located. The effect of mutations on protein function was analyzed by bioinformatics software. Results: The AT:A of the proband and his maternal grandmother, father, mother and younger brother all decreased to varying degrees, and AT:Ag decreased synchronously. There were no obvious abnormalities in PC:A and PS:A in all family members, showing type I AT Defects. Genetic analysis showed that the proband had a heterozygous missense mutation of c.1A>G (p.Tyr2stop) in exon 1 of SERPINC1 gene and a heterozygous synonymous mutation of c.1005G>A in exon 5; his father carried c.1A>G heterozygous missense mutation, his grandmother, mother and younger brother carry c.1005G>A heterozygous synonymous mutation.Conservation analysis showed that Tyr2 was highly conserved among homologous species. Analysis made by three online bioinformatics software, i.e., MutationTaster, PolyPhen-2 and LRT, showed that p.Tyr2stop mutation was “pathogenic and harmful”; protein model analysis showed that the p.Tyr2stop mutation could cause premature termination of AT gene translation, resulting in a truncated protein. Conclusion: The AT:A and AT:Ag reduction to different degrees in the proband and family members was related to the c.1A>G heterozygous missense mutationand the c.1005G>A heterosynonymous mutation in the SERPINC1 gene.