中文摘要：

目的对1例遗传性凝血因子Ⅻ（FⅫ）缺陷症家系进行基因分析，探讨其发病的分子机制。方法用尿素溶解法和Berichrom kit检测患者及其家系成员血浆FⅫ的活性．用火箭电泳和酶联免疫吸附试验测定FⅫ抗原含量。PCR法扩增FⅫA基因的所有外显子和侧翼序列．DNA测序分析基因异常，用直接测序法和限制性内切酶（SfaNⅠ、NspⅠ）分析80名正常人相应序列的PCR产物以排除基因多态性。应用生物信息学软件对所鉴定的突变进行分子模建，探讨其致病的分子机制。结果患者纤维蛋白凝块在5mol／L尿素中30min内完全溶解，加入正常人血浆后则24h不溶解，患者血浆FⅫ活性为0，FⅫA抗原含量〈2％，FⅫB抗原含量在正常范围。家系成员中其父母和外祖母血浆FⅫ活性和FⅫA抗原约为正常人一半。在患者FⅫA基因外显子15中发现两处杂合异常，分别位于177246位碱基（C→T，导：致Arg703→Trp）和177286位碱摹（A→G，导致His716→Arg），直接测序和酶切分析两种方法均排除了基因多态性。患者的母亲与外祖母为Arg703→Trp杂合子，患者的父亲为His716→Arg杂合子．分子模建分析表明，Arg703和His716两个位点突变后均可导致barrel2与core结构域之间距离和结合能力的政变，使蛋白质发生错误折叠，稳定性降低。His716→Arg还可能影响酶的催化活性基因的空间结构形成。结论FⅫA基因外显子15上Arg703→Trp、His716→Arg复合杂合突变影响了蛋白质的正确折叠和稳定性，造成患者FⅫ抗原和活性的缺失。此复合杂合错义突变是一种未报道过的新的突变类型。

英文摘要：

Objective To identify the genetic defect of inherited coagulation factor Ⅻ （FⅫ） deficiency in a Chinese family and to explore its molecular mechanism. Methods The activity and antigen of plasma FⅫ were measured by photometric test and enzyme-linked immunosorbent assay, and rocket-electro- phoresis, respectively. All the exons and exon-intron boundaries of the FⅫA subunit gene were amplified by PCR and then DNA sequencing was performed. Restriction endonuclease analysis was used for the PCR products of the family members and 80 healthy donors to exclude gene polymorphism. Results Rapid dissolution of the proband＇ s fibrin clot occurred within 30 minutes, and antigen of his plasma FⅫ was significantly decreased, two compound heterozygous missense mutations （ a C to T transition at nucleotide 177 246 which caused Arg703Trp, and a A to G transition at nucleotide 177 286 which caused His716Arg） in exon 15 of FⅫ A subunit gene were found. The possibility of gene polymorphism was excluded by restriction endonuclease analysing. Each of these two missense mutations was respectively found in his mother and father. Molecular modeling based on 3D crystallographic data predicted that the mutant protein decreased stability and was likely to be rapidly degraded. Conclusions The inherited FⅫ deficiency in the Chinese family is caused by two compound heterozygous missense mutations ——Arg703Trp and His716Arg in the FⅫA subunit, which to our knowledge, are reported for the first time.