杂合突变导致遗传性FⅫ缺陷症一家系

Identification of a novel heterozygous mutation in a pedigree with hereditary coagulation factor Ⅻ deficiency

目的 对1个遗传性凝血因子Ⅻ（coagulation factorⅫ,FⅫ）缺陷症家系进行基因突变检测,了解其分子发病机制.方法 检测先证者及其家系成员的活化部分凝血活酶时间（activated partial thromboplastin time,APTT）、血浆FⅫ活性（FⅫactivity,FⅫ∶C）和血浆FⅫ抗原（FⅫantigen,FⅫ∶Ag）含量等表型指标;用DNA测序法检测先证者FⅫ基因的全部14个外显子及侧翼序列,发现突变位点则予反向测序证实;针对先证者的突变位点,对该家系成员进行相应的基因突变检测.结果 先证者和其儿子APTT、FⅫ∶C和FⅫ∶Ag明显异常,分别为121.5 s、5％、6.8％和98.5s、9％、12.2％,同时纤溶酶原活性（plasminogen activity,PLG∶A）均略高于正常参考值范围;其他家系成员中,除其小女儿和外孙的FⅫ∶C略低外（分别为64％和60％）,其他成员FⅫ∶C均在正常参考值范围（72％～113％）内.先证者和其儿子的FⅫ基因第13外显子发生了g.8597G＞A杂合突变,导致p.Asp538Asn错义突变,FⅫ启动子区46C/T多态性均为TT基因型;其他4名家系成员中均未见g.8597G＞A杂合突变,有3名成员启动子区为46C/T位点为CT基因型和1名成员为TT基因型.结论 该家系中发现的FⅫ基因第13外显子g.8597G＞A突变为一种新突变.此杂合突变导致的p.Asp538Asn错义突变是该家系遗传性FⅫ缺陷症的分子发病机制;p.Asp538Asn和46TT基因型与家系成员的FⅫ水平明显降低有关.

Objective To identify potential mutation underlying hereditary coagulation factor Ⅻ （F Ⅻ） deficiency in a pedigree and explore its molecular pathogenesis：Methods Activated partial thromboplastin time （APTT）,FⅫ activity （FⅫ ∶ C） and FⅫ antigen（FⅫ ∶ Ag） and other coagulant parameters of the proband and 5 family members were measured.Potential mutations in the 14 exons and intron-exon boundaries of the FⅫ gene were screened with polymerase chain reaction （PCR） and direct DNA sequencing.Suspected mutations were confirmed with reverse sequencing.Corresponding PCR fragments from other family members were also sequenced.Results APPT of the proband and his son were significantly prolonged to 121.5 s and 98.5 s,respectively.FⅫ ∶ C and FⅫ ∶ Ag of the proband and his son have reduced to 5%,6.8% and 9%,12.2%,respectively.Plasma plasminogen activity （PLG ∶ A） in both individuals was slightly higher than the normal reference range.FⅫ ∶ C of his second daughter and grandson were slightly reduced to 64% and 60%.FⅫ ∶ C of the other family members were all in the normal range （72 %-113 %）.A heterozygous missense mutation;g.8597G〉 A,was identified in exon 13 of the FⅫⅫgene in the proband,which resulted in an p.Asp538Asn substitution.For the promoter regions of the FⅫgene,the genotype of the proband was 46TT.The same mutations and 46T/T were also found in the proband＇s son but not in other members of the family.The genotypes of the proband＇s spouse,eldest daughter and grandson were 46CT,and his second daughter was 46TT.Conclusion The heterozygous mutation of g.8597G〉A identified in exon 13 of FⅫ gene is a novel mutation.Heterozygous p.Asp538Asn mutation and 46TT in the FⅫ gene can cause hereditary FⅫ deficiency,which was probably responsible for the low FⅫ concentrations in this pedigree.