一个遗传性抗凝血酶缺陷症家系的表型与基因突变分析

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

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。

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 mutation and the c.1005G>A heterosynonymous mutation in the SERPINC1 gene.