一例两种新的ADAMTS13基因突变导致的遗传性血栓性血小板减少性紫癜

Identification of two novel mutations in ADAMTS13 gene in a patient with hereditary thrombotic thrombocytopenic purpura

目的对1例高度可疑的遗传性血栓性血小板减少性紫癜(TTP)患者的vWF裂解蛋白酶(ADAMTS13,vWF-cp)基因突变进行检测,以明确诊断并制定相应的治疗方案。方法用残余胶原结合实验(residual-collagen binding assay)动态检测1例TTP患者ADAMTS13的活性和抑制物水平。用PCR方法扩增ADAMTS13的29个外显子及外显子邻近处的内含子,并直接测序检测突变。对其亲属的基因组DNA在患者突变区域扩增并测序。结果患者ADAMTS13活性降低,未发现抑制物存在。测序显示患者的ADAMTS13的凝血酶敏感蛋白1(TSP1)基序重复区第21外显子碱基2708处和25号外显子碱基3283处出现C→T的错义突变(均为纯合子),分别导致该碱基参与编码的丝氨酸密码子(TCG)变为亮氨酸密码子(TTG)(S903L),精氨酸密码子(CGG)变为色氨酸密码子(TGG)(R1095W)。患者父母上述突变位置处的基因均呈杂合状态,其兄的该段碱基序列正常,并且在采集的25位家族成员中共发现11名上述突变位点的正常携带者。结论该患者是由于ADAMTS13基因纯合子错义突变导致翻译发生错误所致的遗传性TTP。

Objective To investigate the gene mutations of ADAMTS13 in a highly suspected hereditary thromhoeytopenie purpura （TTP） patient, and then make a progressive diagnosis and adjust the plan of therapy. Methods ADAMTS13 activity and inhibitor were determined by residuat-collagen binding assay during several episodes. Genomic DNA extracted from the prohand＇s peripheral blood was used for amplification of 29 exons anti exon/intron boundaries of ADAMTS13 by PCR. The PCR products were screened hy direct sequencing and the gene alterations were further confirmed hy direet sequeneing in her family memhers. Result The activity of the proband＇s ADAMTS13 was significantly reduced while no inhibitor was found. Two novel missense mutations were found in the TSP1 repeated motif domain of ADAMTS13. In both mutations, thymine substituted for eytidine, resulting in the substitution of leueine for serine in nt 2708, exon21 （codon S903L）, and tryptophan for arginine in nt 3283, exon 25 （eodon R1095W）. These two mutations were revealed as each heterozygote in the prohand＇s parents. Conclusion The deficiency of ADAMTS13 caused by two homozygote missense mutations might be responsible for episode of this TTP patient.