Fibrinogen anomalies and disease. A clinical update

The precipitous increase in the number of structurally defined fibrinogen defects in recent years has resulted from application of high performance liquid chromatography in combination with peptide mapping and sequencing procedures. More recently, application of DNA sequence of polymerase chain reaction products has accelerated the pace of identification of mutations. Highly frequent defects are Arg substitutions, accounting for eight mutation sites substituted by Cys or His and less frequently by Ser. Amino acid substitutions at different positions on all three chains have pointed to possible structures with polymerization-related functions. Also, substitutions yielding consensus sequences resulted in extra glycosylations of the appropriate Asn in four different mutation sites; the impaired polymerization was reported associated with undue bleeding in two of these. Among informative defects have been those of homozygous probands with A alpha 16Arg----His and A alpha 16Arg----Cys in that failure of release of peptide A (but not of B), as shown with A alpha 16Arg----Cys, resulted in markedly delayed polymerization of such fibrin monomers, in general agreement with conclusions reached in studies of normal fibrin. This dysfunction, as well as the slow rate of release of A shown with A alpha 16Arg----His, was associated with clinically significant hemorrhagic diathesis (in the homozygous probands), consistent with the known physiologic importance of peptide A cleavage in normal hemostasis. Also, defects on the A alpha 17-19 sequence resulting in impaired polymerization are consistent with the known role of this segment in polymerization. Of similar interest have been defects within a B beta chain span encoded its exon 2. Two defects resulting in impaired polymerization and thrombin binding were associated with clinical thrombosis commencing in early life, and this lends strong support to other evidence suggesting a role in polymerization and in noncatalytic thrombin binding by this B beta chain segment. Thrombosis associated with A alpha 554Arg----Cys in a heterozygous proband with impaired tPA interaction is unique and may shed light on this poorly understood but important interaction among fibrin, plasminogen, and tPA. A group of different defects within the gamma 275-375 sequence have pointed to a polymerization role, evidenced by delayed gelation and impaired binding of mutant D to normal fibrin E. An unusual example is a 15 residue insertion between gamma 350 and 351 resulting in impaired polymerization, gamma chain crosslinking, and platelet aggregation support and is associated with hemorrhagic diathesis and poor healing.(ABSTRACT TRUNCATED AT 400 WORDS)