Four Cases of Aaplha Dysfibrinogenemia in Childhood

Introduction

Hemostasis in childhood differs from that of adults; and the hemostatic system is still developing during childhood. These differences offer a protective advantage to children with hemorrhagic and thrombotic complications. Plasma levels of coagulation factors (except for fibrinogen, factor V and factor VIII), as well as plasma levels of protein C, protein S and antithrombin are reduced. Hereditary dysfibrinogenemia is a rare disorder wherein an inherited abnormality in fibrinogen structure may result in defective fibrin function and/or structure. Clinical symptoms may vary from asymptomatic to life-threatening bleeding complications. Venous or arterial thrombotic complications occur extremely rarely during childhood. Fibrinogen, a key component in hemostasis, is a 340-kDa glycoprotein. The molecule consists of three different pairs of polypeptide chains (Aa, Bb, and g) each encoded by a distinct gene (FGA, FGB, and FGG). N-terminal parts of the Aa chain - fibrinopeptides A and the Bb chain - fibrinopeptides B are situated in the central part of the molecule and block polymerization of the molecules. Conversion of fibrinogen to fibrin occurs after the cleavage of N-terminal fibrinopeptides by the serine protease thrombin. Correct conformation of fibrinopeptides is important for the cleavage by thrombin.

Methods

Routine coagulation tests were performed with citrated plasma samples on a STA-R coagulation analyzer. The functional fibrinogen level was measured by the Clauss method. Total fibrinogen level was determined by an immunoturbidimetric assay performed on a UV-2401PC spectrophotometer. Fibrin polymerization induced by either thrombin or reptilase and fibrinolysis experiments were obtained by the turbidimetrical method. Fibrinopeptide release was measured as a function of time; and the fibrinopeptides were determined by the reversed-phase, high-performance liquid chromatography (RP-HPLC) method. The purified genomic DNA was amplified by polymerase chain reaction, using specific primers; and dideoxysequencing was performed with Dye Terminator Cycle Sequencing with a Quick Start kit and a CEQ 8000 genetic analysis system).

Results

We have examined four unrelated children suspected dysfibrinogenemia. The first patient was a 5-yr old boy with prolonged thrombin time and low functional fibrinogen level. He presented with easy bruising and epistaxis. Genetic analysis revealed a heterozygous substitution Aalpha R16H. The second patient was a 13-yr old girl with prolonged thrombin and reptilase times and low functional fibrinogen level. She presented with menorrhagia. Genetic analysis revealed a heterozygous substitution Aalpha G17V. The third patient was a 12-yr old asymptomatic boy. Genetic analysis revealed a heterozygous substitution Aalpha R16H. Kinetics of fibrinopeptide release was impaired in all these cases. The fourth patient was a 3-yr old girl with low functional fibrinogen level. She presented with easy bruising. Genetic analysis revealed a heterozygous substitution Aalpha K448N. All patients presented with impaired fibrin polymerization.

Conclusion

All patients were found to be heterozygous for point mutations in FGA gene. Three mutations were found in the site of fibrinopeptide cleavage and one in the alphaC-domain. Mutations had different clinical manifestations from asymptomatic to bleeding. Mutations Aalpha Arg16His and Aalpha Gly17Val are among the most common fibrinogen mutations and both decelerate fibrinopeptide A cleavage from mutant fibrinogens. We describe here a novel previously unreported mutation Aalpha Lys448Asn affecting fibrin formation.

Acknowledgment

This work was supported by the project of the Ministry of Health of the Czech Republic for conceptual development of the research organization 00023736, by Grant from the Academy of Sciences, Czech Republic (P205/12/G118), and by ERDF OPPK CZ.2.16/3.1.00/28007.