[Fibrinogen Bern III: a further case of hereditary fibrinogen variants with substitution A alpha 16 Arg----Cys].

A heterozygous hereditary fibrinogen variant, fibrinogen Bern III, has been characterized. The proposita and her daughter showed prolonged thrombin time and reptilase time, as well as a markedly reduced fibrinogen concentration as determined by functional clotting assay. Fibrinogen was purified from the proposita's plasma and subjected to biochemical characterization. The delayed fibrin formation was shown to result from impaired release of fibrinopeptide A. Thrombin was found to cleave an extended fibrinopeptide A (A alpha 1-19) from the reduced polypeptide chains of the abnormal fibrinogen. Amino acid analysis of this fragment indicated that the arginine residue, located at the physiological thrombin cleavage site, was replaced by cysteine. The functional defect of the fibrinogen variant Bern III is due to the amino acid substitution A alpha 16 Arg----Cys.