一个遗传性凝血因子Ⅶ缺陷症家系F7基因信号肽区L12R和3＇＇非翻译区c11814-insAA复合性突变与表型分析

Analysis of Phenotype and L12R Mutation in Signal Peptide and 3'Non-translation Region c11814-insAA Mutation of F7 Gene in a Family with Hereditary Coagulation Factor Ⅶ Deficiency

目的:通过对一个遗传性凝血因子Ⅶ(FⅦ)缺陷症患者家系成员表型与基因型分析,研究其基因突变与临床表型的关系,探讨其分子发病机制。方法:对先证者及其父母进行活化部分凝血酶时间(APTT)、凝血酶原时间(PT)、纤维蛋白原和FⅦ活性(FⅦ:C)、FⅦ抗原(FⅦ:Ag)检测,对其F7基因的全部外显子及侧翼、启动子区进行测序,以寻找致病基因突变。根据信号肽预测数据库构建包含所发现突变的FVII蛋白分子模型,进行功能预测,推断其对蛋白合成和功能的影响。结果:先证者APTT正常,PT明显延长(58.3 s),FⅦ:C显著下降(1.1%),FⅦ:Ag重度降低(0.9%),其父母的APTT、PT、FⅦ:C和FⅦ:Ag均在正常范围内。先证者和其父亲的F7基因第1a外显子第556位核苷酸发生杂合性T/G突变,导致相应氨基酸由亮氨酸(L)变成精氨酸(R),即L12R。功能预测分析提示,L12R突变影响到信号肽区不同区域的分割及其相应功能,进而导致成熟蛋白质的合成减少和因子活性明显降低。同时,先证者F7基因还存在自发性3'非翻译区c11814-ins AA杂合性突变,而其父母均无此突变。结论:发现1例F7基因L12R突变,位于信号肽区的该杂合突变是导致此例遗传性FVII缺乏症发生的主要分子基础,而位于3'非翻译区的自发性c11814-ins AA突变则进一步造成了FⅦ合成的减低。

Objective： To examine one young female patient with hereditary FVII deficiency and her family members, to observe the gene mutation and clinical phenotype, and to investigate the molecular mechanism of the dysfunction. Methods ： Prothrombin time （ PT）, activated partial thromoploastin time （ APTT）, fibrinogen （Fg） and F VI[ activity （FVII：C） and FVII antigen （FVII：Ag） were tested. The gene mutations were sought by DNA sequencing for all of the exons and flanks, 5＇ and 3＇ non-translation region of F7 gene. To confirm the role of the found gene mutation, the reverse sequence were determined with Chromas software. To infer the influence of the mutation on the synthesis and function of FVII protein, the FVII protein molecule model containing the found mutation was constructed and the function prediction was performed by the signal peptide prediction database. Results- Compared with the normal population, the proband＇s PT value was significantly prolonged, and the ratio % FⅦ： C and that of FVII： Ag were significantly decreased by 1. 1% and 0.9%, respectively. The PT, APTT, FⅦ：C and FVII：Ag of the proband＇s parents were both normal. Heterozygous 556th nucleotide mutations T/G were found in the proband＇s and his father＇s exon 1A of F7 gene, with codon CTG turning into CGG, corresponding leucine （L） into arginine （R）, i. e Leul2Arg. Function prediction showed that L12R mutations affected the segmentation of different parts of the signal peptide and its corresponding function, which could result in the decline in the mature protein synthesis and its activity obviously. In addition, a spontaneous 3＇ untranslated region c11814-insAA heterozygous mutation was detected in the proband＇s F7 gene, while her parents didn＇t possess this mutation. Conclusion： A new hererozygous mutation （L12R） located in signal peptide of F＇/gene is the primary molecular basis of the case with hereditary FVII deficiency. At the same time, the proband＇s spontaneous 3＇ non-translation region c11814-insAA mutation may lead to the further reduetion of the FⅦ synthesis.