Congenital hypofibrinogenemia associated with γK232T

We have previously reported a case of congenital hypofibrinogenemia caused by a novel heterozygous A -> C transition at nucleotide 5864 of FGG, leading to the K232T substitution in the fibrinogen Upsilon-chain. However, the pathogenic mechanism is still unclear. To further reveal its molecular basis, we examined the effects of Upsilon K232T substitution on fibrinogen synthesis, stability, and secretion through in vitro expression of mutant Upsilon 232T in Chinese hamster ovary (CHO) cells. Quantitative RT-PCR of the variant Upsilon-chain mRNA showed that the Upsilon 232T transcribed the variant cDNA. Enzyme-linked immunosorbent assay and Western blot analysis of the cell lysates and culture media showed that the CHO cells transfected with successfully synthesized the variant fibrinogen, but failed to secrete it into the culture medium. Furthermore, fibrinogen purified from the plasma of patient showed a normal thrombin-catalyzed fibrin polymerization, also indicating the impeding secretion of variant Upsilon 232T fibrinogen. In conclusion, our data reveal that the Upsilon K232T is responsible for the congenital hypofibrinogenaemia through interfering with the correct secretion of fibrinogen.