凝血因子Ⅴ及凝血因子Ⅷ联合缺陷患者四例的基因诊断

目的 对4例FⅤ及FⅧ联合缺陷患者及其家系成员进行基因诊断及分子发病机制研究.方法 测定先证者及家系成员APTT、PT、FⅧ:C及FⅤ:C等进行表型诊断;采用凝血酶生成试验检测先证者及健康对照者的凝血酶生成情况;Tiangen试剂盒法抽提先证者及家系成员全血基因组DNA;平衡酚-乙醚法抽提羊水DNA;PCR扩增4例先证者及家系成员的LMAN1基因及MCFD2基因,用末端标记双脱氧法检测核酸序列查找基因突变.结果 先证者1的APTT显著延长,为88.2 s,PT 延长至19.6 s,FⅧ:C降至24.2%,FⅤ:C为9.1%.先证者2与先证者3为亲姐妹,两人的APTF均明显延长,分别为71.6 s及74.6 s,PT分别延长至22.1 s及18.3 s,FⅧ:C均降低,分别为25%及19.6%,FⅤ:C分别降至7.6%及14.5%.先证者4的AFTT及PT均延长,分别为70.3 s及18.2 s,其FⅦ:C降至15.7%,FV:C降至9.4%,4例先证者的其余实验室表型检测指标均正常,临床诊断为FⅤ及FⅧ联合缺陷性疾病.对先证者1进行LMAN1及MCFD2基因直接测序,显示其LMAN1基因存在双杂合突变:突变1位于第8号外显子,为插入突变:nt912insA(X71661.1),导致第305位氨基酸发生移码突变,并在编码20个氨基酸后终止,其母亲该位点亦为杂合突变;先证者1的另一个杂合突变位于第11号外显子:nt1366C>CT(X71661.1),导致第456位精氨酸发生无义突变(p.Arg456X),其父亲及胎儿该位点均为杂合突变.先证者1及其父母的MCFD2基因测序均未发现突变.先证者2及3的LMAN1基因测序均未发现突变,MCFD2基因直接测序检测发现两者均在该基因的第4号外显子处存在1个纯合突变:nt411T>C(NM_139279),导致第136位异亮氨酸突变成苏氨酸(p.Ile136Thr).先证者2的女儿该位点为杂合突变.先证者4的LMAN1基因测序显示其在该基因的第5号外显子存在1个纯合突变:nt615C>T,导致第202位的精氨酸无义突变;其MCFD2基因测序未发现突变.凝血酶生成试验检测显示4例FⅤ及FⅧ联合缺陷患者的凝血酶生成潜力较健康对照者均有不同程度的下降.结论 先证者1是由LMAN1基因的双杂合突变nt1366C>CT及nt912insA引起,突变分别遗传自其父亲及母亲,对其母亲进行产前基因诊断发现胎儿为1名女性携带者,该胎儿遗传了其父亲的1个杂合突变nt1366C>CT.先证者2及3是由MCFD2基因上的纯合突变(nt411T>C,p.ne136Thr)所导致的.先证者2的女儿遗传了其母亲的一个杂合突变,为携带者.先证者4是由LMAN1基因的纯合无义突变(nt615C>T,p.Arg202X)所导致的.

Genetic diagnosis of four combined deficiency of factor Ⅴ and Ⅷ patients

Objective To investigate the genetic diagnosis and molecular pathogenesis of four patients with combined deficiency of coagulation factor Ⅴ and Ⅷ and their family members. Methods The APPT, FT, FⅤ: C, FⅧ: C were detected for phenotypic diagnosis. Thrombin generation assay was applied to determine the generation condition of thrombin in patients and healthy controls. Cenomic DNA was extracted from peripheral blood using the TianGen RelaxCene Blood DNA System;amniotic fluid DNA was extracted with phenol-ethyl ether method. The LMAN1 and MCFD2 genes were analyzed by PCR. Gene mutations were detected with nucleotid sequences by using end-labeling dideoxy method. Results The APTT of Proband 1 was significantly prolonged to 88. 2s and her PT was prolonged to 19. 6 s. The combined deficiency was identified with FⅧ (FⅧ: C 24. 2% ) and FV(FⅤ: C 9. 1% ). Proband 2 and 3 were sisters. The coagulation studies revealed that both of them had prolonged APTT (71.6 s and 74.6 s respectively) and PT (22. 1 s and 18. 3 s respectively). The combined deficiency of FⅤ (FⅤ: C 7. 6% and 14. 5% respectively) and FⅧ( FⅧ: C 25% and 19.6% respectively) were identified. Proband 4 was detected to have the prolonged APTT (70.3 s),PT (18.2 s) and the deficiency of FⅤ(FⅤ: C 9. 4% ) and FⅧ (15. 7% ). The remaining phenotype indicators test of the 4 probands were normal. The diagnosis for the 4 probands was combined deficiency of factor Ⅴ and Ⅷ. The proband 1 was detected to have compound heterozygous mutations in LMAN1 gene while having the LMAN1 and MCFD2 direct gene sequencing. One mutation was a small insertion located on exon 8 nt912insA (X71661. 1)] that resulted in p. 305frameshiftX20 and her mother was detected to have the same heterozygous mutation on the the locus. The other mutation was located on exon 11: nt1366C > CT ( X71661. 1 ) , p. 456Arg > Stop which was inherited from her father. Amniocyte DNA was detected to have only one heterozygous mutaion nt1366C > CT (X71661. 1) , 456Arg > Stop] inherited from the father. No mutation in MCFD2 gene was found in proband 1 and her parents. The analysis of the MCFD2 gene in proband 2 and 3 revealed a novel homozygous single base substitution (nt411T>C) in exon 4, which results in the exchange of the amino acid isoleucine by the amino acid threonine at amino acid position 136 (p. Ile136Thr). Sequencing of the whole LMAN1 gene showed that the proband 4 had one homozygous nonsence mutation in the exon 5 of the LMAN1 ( nt615C >T,p. 202 Arg> Stop). All of the 4 probands with combined deficiency of FⅤ and FⅧ showed declined endogenous thrombin potential in the thrombin generation tests. Conclusion The combined deficiency of FⅤ and FⅧ in the proband 1 results from the compound heterozygous mutations ( nt1366C > CT and nt912insA) in LMAN1 gene, which are inherited from her parents respectively. The prenatal genetic investigation for the patient mother with preganency indicates that the fetus is a female carrier with one mutation (nt1366C > CT) inherited from the father. The homozygous missence mutation ( nt411T > C, p. Ile136Thr) in the MCFD2 gene accounts for the proband 2 and 3. The daughter of the proband 2 is a carrier with a heterozygous mutation inherited from her mother. The homozygous nonsence mutation in the LMAN1 gene of the proband 4 results in the deficency of F Ⅴ and FⅧ.