OBJECTIVETo identify the genotype and pathogenesis in four Chinese pedigrees with Factor Ⅻ deficiency.

METHODSActivated partial thromboplastin time (APTT), FⅫ procoagulant activity (FⅫ∶C), FⅫ antigen（FⅫ∶Ag）and other coagulant parameters were detected. The FⅫ deficiency Pedigree members,all exons,boundary introns including the splice junctions of the FⅫ gene were amplified with Polymerase chain reaction (PCR). Expression plasmids were constructed by mutagenesis based on the wild-type and transfected into COS7 cells. FⅫ∶C and FⅫ∶Ag of the expression levels were tested in the supernatant and cell lysate.

RESULTSThe four probands presented prolonged APTT with all the values of FⅫ∶C and FⅫ∶Ag were low to 2% and 1%, respectively. There were common 46C/T polymorphism in the promoter regions of FⅫ gene in four pedigrees. Proband A was heterozygous for two mutations, g.5741-5742delCA (His101Gln) and g.7142insertC (Lys346Gln). Proband B was a heterozygous deletion mutation g.6800-6808del9bp. The results of the transfection revealed that FⅫ∶Ag in cell lysates and conditioned media protein FⅫ6800-6808del9bp were 85.6% and 51.9%. The FⅫ∶C in the conditioned media was 56.4%. Proband C was a heterozygous mutation g.8699G>A(Gly542Ser). Proband D was a homozygous mutation 8699G>A, whose parents with consanguineous marriage.

CONCLUSIONFour mutations, g.5741-5742delCA, g.7142insertC, g.6800-6808del9bp and g.8699G>A with 46C/T polymorphism in the promoter regions of FⅫ gene, were identified in the four Factor Ⅻ deficiency pedigrees. The two mutations g.5741-5742delCA and g.6800-6808del9bp were first found in China. FⅫ 6800-6808del9bp expressed in vitro suggested that almost normal proteinum synthesis but defect proteinum secretion.