New molecular defects in the γ subdomain of fibrinogen D-domain in four cases of (hypo)dysfibrinogenemia: fibrinogen variants Hannover VI, Homburg VII, Stuttgart and Suhl

Summary Four new molecular abnormalities in the γ subdomain of the D domain elucidated in three unrelated thrombophilic patients and in one asymptomatic case of hypofibrinogenemia are reported: fibrinogen Suhl, γ 326,Cys →Tyr, fibrinogen Hannover VI, γ 336 Met →Ile, fibrinogen Stuttgart, γ 345, Asn→Asp and fibrinogen Homburg VII, γ354,Tyr→Cys. In all cases, fibrin polymerization in plasma is impaired. In the case of fibrinogen Suhl, there was a normalization of fibrin polymerization in plasma at higher Ca2+ concentration. The protective effect of Ca2+ on plasmic degradation of fibrinogen was incomplete with all three variants. The fibrinogen molecules in variants Homburg VII and Suhl contain covalently bound albumin. Fibrin clot structure was abnormal in case of variant Homburg VII, with finer and more branched fibers forming a less porous clot. Experimental data indicate possible effects of the molecular abnormalities on Ca2+-binding, D-E interaction and lateral association of protofibrils.