Dysfibrinogenemias Affecting Platelet Aggregation

Congenital dysfibrinogenemia is a rare disease characterized by inherited abnormality in the fibrinogen molecule, resulting in functional defects. Two patients, both with history of thrombotic events, had abnormal coagulation test results. DNA sequencing showed the heterozygous γ Y363N mutation and the heterozygous Aα N106D mutation, respectively. Fibrin polymerization, after addition of either thrombin or reptilase, showed remarkably delayed polymerization in both cases. Fibrinolysis experiments showed slower tPA initiated lysis of clots. Both mutations had a significant effect on platelet aggregation. Aggregation initiated by ADP and TRAP were significantly different. After initiation with ADP (weak activator), the aggregation of platelets from a healthy donor in the presence of fibrinogen with Aα N106D mutation was markedly decreased. The aggregation in the presence of abnormal fibrinogen γ Y363N was significantly decreased at the level of significance P=0.05. Average aggregation response after the addition of ADP was (42 ± 7) % for abnormal fibrinogen γ Y363N, (20 ± 4) % for abnormal fibrinogen Aα N106D, and (55 ± 8) % for normal fibrinogen, respectively. After initiation with TRAP (strong activator), the aggregation of platelets from a healthy donor in the presence of both fibrinogens was significantly decreased at the level of significance P=0.05. Average aggregation response after the addition of TRAP was (60 ± 4) % for abnormal fibrinogen γ Y363N, (63 ± 11) % for abnormal fibrinogen Aα N106D, and (89 ± 10) % for normal fibrinogen, respectively. SEM revealed abnormal clot morphology, with a large number of free ends and narrower fibers. In conclusion, we identified novel mutations in the fibrinogen polymerization pocket "a" ( γ Y363N) and in the fibrinogen coiled-coil region (Aα N106D) causing congenital dysfibrinogenemia associated with thromboses. This work was supported by a grant of The Grant Agency of The Czech Republic nr. P205/12/G118, by a grant of the ERDF OPPK CZ.2.16/3.1.00/28007 and by a grant for conceptual development of The Ministry of Health of the Czech Republic nr. 00023736.