新的纯合子Leu519Arg导致的遗传性凝血因子Ⅻ缺陷症家系分析

A novel homozygous mutation LeuSlgArg in one pedigree with congenital factor Ⅻ deficiency

目的对一个遗传性凝血因子Ⅻ（FⅫ）缺陷症家系进行FⅫ基因突变的分析和家系调查，探讨其分子发病机制。方法检测先证者及其家系成员活化部分凝血活酶时间（APTT）、凝血酶原时间（PT）、凝血因子Ⅷ活性（FⅧ：C）、凝血因子Ⅸ活性（FⅨ：C）、FⅪ活性（FⅪ：C）、凝血因子Ⅻ活性（FⅫ：C）和FⅫ抗原（FⅫ：Ag）含量等进行表型诊断；用DNA直接测序法分析先证者FⅫ基因所有14个外显子、侧翼、5′和3′非翻译区及家系成员相应的突变位点区域，用反向测序证实所发生的突变。选择100名健康体检者作对照。结果先证者APTT明显延长为106．4S，先证者二女儿和外孙女APTT略延长，分别为42．8s和43．6s，家系其他成员APTT无明显延长；先证者及其儿子、大女儿、二女儿、外孙女的FⅫ：c明显减低，分别为2．0％、23．0％、23．0％、24．0％和23．0％，FⅫ：Ag含量分别为1．0％、21．0％、23．0％、23．0％和23．0％，表现为交叉反应物质（CRM）阴性。基因测序发现先证者FⅫ基因启动子区为46T／T型及13号外显子存在c．1556T〉C纯合突变，导致Leu519Arg；先证者儿子、大女儿、二女儿及外孙女为46C／T型，并且发现存在c．1556T〉G杂合突变；先证者妻子启动子区C／C型，且无上述基因突变。结论该家系发现的FⅫ基因13号外显子区c．1556T〉G尚未见报道。c．1556T〉G影响了FⅫ催化功能，与FⅫ水平的降低有关。

To analyze the mutations of F12 genein one pedigree with congenital factor FⅫ （FⅫ） deficiency, and investigatethe molecular mechanisms of FⅫ deficiency. Methods Activated partial thromboplastin time （ APTT）, Prothrombin time （ PT）, FⅫ activity （ FⅫ ： C ）, FⅫ antigen （ FⅫ ： Ag） and other coagulant parameters were tested in the proband and his family members. 5′ and 3′ UTR, all exons and their exon - intron boundaries of F12 gene were analyzed by direct sequencing. The detected mutations were confirmed by reverse sequencing. 100 healthy persons were as normal controls. Results The proband showed a markedly prolonged APTT （ 106. 4s） , the FⅫ： C and FⅫ： Ag were 2. 0% and 1. 0% , respectively. Hissecond daughter and granddaughter had slightly prolonged APTT, and other family members are normal. The FⅫ：C and FⅫ：Ag of family members were also decreased （his son, 23.0% and 21. 0% ; his elder daughter, 23.0% and 23.0% ; his second daughter,24.0% and 23.0% ; hisgranddaughter, 23.0% and 23.0% ）. The phenotype of all members is consistent with cross -reactive material negative. Nucleotide sequencing analysis showed that the proband had missense mutations in the F12 gene, including one homozygous mutationc. 1556T 〉 G （p. LeuS19Arg ） and a commonly reported single nucleotide polymorphism site within the promoter region of the F12 gene （46T/T）. Sequencing results from the proband children demonstrate them as carriers of a heterozygous missense mutation. The proband＇s wife is normal and with 46C/C in the promoter region. Conclusion The c. 1556T 〉 G in exon 13 is a novel mutation. This mutation affects FⅫcatalytic function, associated with a reduced level of FⅫ.