[Fibrinogen Zürich I: defective fibrinopeptide-A release].

Fibrinogen Zurich I (FZI) is characterized by delayed fibrin monomer aggregation. It has been previously shown that the patient fibrinogen is composed of two populations of molecules, one aggregating normally and the other not aggregating at all but interfering with the aggregation of the normal population. By use of a radioimmunoassay for fibrinopeptide A (FPA), only approximately half of the expected FPA could be recovered after thrombin and Defibrase proteolysis. Even after exhaustive proteolysis with 2 thrombin units of Defibrase, no further release of FPA could be obtained. The defective FPA release was confirmed by measurement of the N-terminal Gly/Tyr ratio. It may be assumed that the abnormal aggregation of one fraction of FZI is due to the defective FPA release from this fraction.