NEW SUBSTITUTION, GAMMA-358-SER-]CYS, IN FIBRINOGEN MILANO-VII CAUSESDEFECTIVE FIBRIN POLYMERIZATION

Fibrinogen Milano VII is a hereditary fibrinogen variant detected in a woman with no clinical symptoms of bleeding or thrombosis. Thrombin a nd reptilase clotting times were prolonged in six family members from three generations. Release of fibrinopeptides A and B was normal. Fibr in polymerization was strongly delayed both in the presence and in the absence of calcium. The structural defect was determined by sequence analysis of a 290-bp fragment of genomic DNA amplified by polymerase c hain reaction and cloned in M13mp19. The triplet TCT coding for the am ino acid residue gamma 358 was found to be replaced by TGT, resulting in the substitutiton gamma 358 Ser --> Cys. Immunoblot analysis demons trated the presence of covalently linked fibrinogen;albumin and fibrin ogen (albumin)(2) complexes. Albumin was released from fibrinogen Mila no VII by limited reduction with 2-mercaptoethanol. Fibrin polymerizat ion was not normalized after removal of albumin from fibrinogen Milano VII, suggesting that the delayed clot formation is not due to steric hindrance caused by bound albumin but by substitution of gamma 358 Ser by Cys itself. Our results indicate that the residue gamma 358 Ser is essential for normal expression of the carboxy terminal polymerizatio n site on the fibrinogen gamma-chain. (C) 1994 by The American Society of Hematology.