Summary
A new congenital dysfibrinogen, Fibrinogen Bastia, was discovered in a 20-year-old
woman with no clinical symptoms. The plasma thrombin-clotting time was severely prolonged.
The functional plasma fibrinogen concentration was low (0.2 mg/ml), whereas the immunological
concentration was normal (2.9 mg/ml). Purified fibrinogen Bastia displayed a markedly
prolonged thrombin-clotting time related to a delayed thrombin-induced fibrin polymerization.
Both the thrombin-clotting time and the fibrin polymerization were partially corrected
by the addition of calcium ions. The anomaly of fibrinogen Bastia was found to be
located in the γ-chain since by SDS-PAGE performed according to the method of Laemmli
two γ-chains were detected, one normal and one with an apparently lower molecular
weight. Furthermore, analysis of plasmin degradation products demonstrated that calcium
ions only partially protect fibrinogen Bastia γ-chain against plasmin digestion, suggesting
that the anomaly is located in the C-terminal part of the γ-chain. Sequence analysis
of PCR-amplified genomic DNA fragments of the propositus demonstrated a single base
substitution (G → T) in the exon VIII of the γ chain gene, resulting in the amino
acid substitution 318 Asp (GAC) → Tyr (TAC). The PCR clones were recloned and 50%
of them contained the mutation, indicating that the patient was heterozygous. These
data indicate that residue Asp 318 is important for normal fibrin polymerization and
the protective effect of calcium ions against plasmin degradation of the C-terminal
part of the γ-chain.
Key Words
Fibrinogen - dysfibrinogenemia - plasmin degradation products - fibrin polymerization