Six novel missense mutations causing factor X deficiency and application of thrombin generation test

Abstract

Introduction: Inherited factor X (FX) deficiency is a rare hemorrhagic condition characterized by a variable clinical presentation weakly correlating with laboratory phenotype and genotype. Thrombin generation test (TGT) offers potential clinical advantages in the evaluation of hypocoagulable states.

Materials and methods: Five FX assays were performed using clotting, chromogenic and immunological methods. The factor X gene (F10) defects were analyzed by direct sequencing. Thrombin generation (TG) was measured using a standard procedure with commercial reagents at 1 pM and 5 pM of tissue factor (TF). The influence of contact activation on TG at the two TF concentrations was analyzed by the addition of corn trypsin inhibitor (CTI).

Results: Seven missense mutations were identified in the F10 of the four probands with FX deficiency, six of which (Ser425Pro, Ala-29Pro, Phe324Leu, Ala235Thr, Cys111Arg and Met362Thr) were novel and associated with type I FX deficiency. TG measurements at 1 pM TF need the addition of CTI in both healthy individuals and FX-deficient patients. TG parameters of ETP, Peak and Rate correlated well with the FX:C levels and the clinical expressions of the FX-deficient patients at 1 pM TF with CTI. There is a higher sensitivity for FX deficiency at 1 pM TF compared with 5 pM TF in FX-deficient patients.

Conclusions: TGT may serve as a useful laboratory tool to assess the individual clinical manifestation of the patients with FX deficiency and 1 pM TF concentration in the presence of CTI is recommended.