The molecular defect in the abnormal
fibrinogen Dusart (Paris V) that is associated with
thrombophilia was determined by sequence analysis of genomic
DNA that had been amplified using the polymerase chain reaction. The propositus was heterozygous for a single base change (C-->T) in the A alpha-chain gene, resulting in the amino acid substitution A alpha 554 Arg-->Cys. Restriction analysis of the amplified
DNA derived from the family members showed that his father and his two sons were also heterozygous. Electron microscopic studies on
fibrin formed from purified
fibrinogen Dusart demonstrated fibers that were much thinner than in normal
fibrin. In contrast to the previously observed defective binding of
plasminogen, the binding of
thrombospondin to immobilized
fibrinogen Dusart was similar to that of normal
fibrinogen. Immunoblot analysis of plasma
fibrinogen demonstrated that a substantial part of the
fibrinogen Dusart molecules were
disulfide-linked to
albumin. The plasma of the affected family members also contained
fibrinogen-
albumin complexes. Furthermore, small amounts of high molecular weight complexes containing
fibrinogen were detected in all the heterozygous individuals. These data indicate that the molecular abnormality in
fibrinogen Dusart (A alpha 554 Arg-->Cys) results in defective lateral association of the
fibrin fibers and
disulfide-linked complex formation with
albumin, and is associated with a family history of recurrent
thrombosis in the affected individuals.