Study on the molecular mechanism of the inherited factor X deficiency in three unrelated families / 中华检验医学杂志

ABSTRACT

Objective To identify the clinical features, the molecular diagnosis and the molecular mechanism of three unrelated factor X deficiency families. Methods Three probands were male and the diagnosis was validated by coagulant parameters. The F X coagulation activity ( F X∶ C ) and antigen (FX∶ Ag) were tested by clotting test and ELISA method. The cross-corrected test was used to rule out the inhibitor of FX in plasma. Thrombin generation test was evaluated. The antigen and the molecule weight of the FX in plasma were measured with western blotting. Gene mutations were analyzed in the probands and their family members with PCR and DNA sequencing. FX expression plasmids were constructed and transientby being transfected into 293T cells. FX C and FX Ag of the expression products were tested. Results APTT and PT in proband 1 were obviously prolonged, 113.4 s and 62.3 s, respectively. And there was no inhibitor in plasma. The thrombin generation was lower compared to normal reference. APTT and PT in proband 2 were 56. 5 s and 28.7 s. There was no inhibitor in the plasma. The thrombin generation was 1 101.5 nmol · min. APTT and PT in proband 3 were 117.3 s and 44. 3 s. The thrombin generation was 782.5 nmol · min. FX∶ C and FX∶ Ag in proband 1 were 1.4% and 3.6%, with a homozygous mutation in FX gene (Ser425→Pro). In vitro expression of the mutation showed a normal synthesis in the cell but secretion dysfuntion. In proband 2 F X C and F X Ag were 2. 2% and 5. 5%, with two heterozygous mutations in FX gene (Ala-29→Pro and Phe324→Leu). The Ala-29 → Pro mutation led to significantly reduced expressions of FX in both cell lysate and cell culture supernatants compared to wild-type plasmid,(41.32 ±5.21 )% and(6. 30 ± 1.84)% respectively. However Phe324→Leu mutation almost did not affect the FX synthesis. FX C and FX Ag in proband 3 were 2. 2% and 35%, with two heterozygous mutations in FX gene( Ala235→Thr and Arg347→Cys). The expressions of these two mutant FX proteins in cell lysate were similar to those of wild-type but obviously lower in the supernatant. Conclusions Five mutations of F X gene are found in this study. These mutations (Ser425Pro, Phe324Leu, Ala235Thr and Arg347Cys)can not affect F X protein synthesis. However Ala-29Pro mutation can reduce F X protein synthesis and cause secretion dysfunction.