Fibrinogen bastia (gamma 318 Asp -> Tyr) a novel abnormal fibrinogen characterized by defective fibrin polymerization

A new congenital dysfibrinogen, Fibrinogen Bastia, was discovered in a 20-y ear-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-cl otting time related to a delayed thrombin-induced fibrin polymerization. Bo th 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 gamma-chain since by SDS-PAGE performed acc ording to the method of Laemmli two gamma-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 gamma-chain against plasmin digestion, suggestin g that the anomaly is located in the C-terminal part of the gamma-chain. Se quence analysis of PCR-amplified genomic DNA fragments of the propositus de monstrated a single base substitution (G --> T) in the exon VIII of the gam ma chain gene, resulting in the amino acid substitution 318 Asp (GAC) --> T yr (TAC). The PCR clones were recloned and 50% of them contained the mutati on, indicating that the patient was heterozygous. These data indicate that residue Asp 318 is important for normal fibrin Polymerization and the prote ctive effect of calcium ions against plasmin degradation of the C-terminal part of the gamma-chain.