GENETIC-ANALYSIS AND FUNCTIONAL-CHARACTERIZATION OF PROTHROMBINS CORPUS-CHRISTI (ARG382-CYS), DHAHRAN (ARG271-HIS), AND HYPOPROTHROMBINEMIA

The structural abnormalities and functional characteristics of dysfunc tional prothrombin variants in two new kindreds have been determined. Prothrombin Corpus Christi (family 1) was purified and found to have m arkedly reduced fibrinogen clotting activity, yet normal amidolytic an d near-normal platelet aggregating activity. A transition (C to T) at nucleotide position 8885, present in the heterozygous form in affected family members, resulted in the substitution of Cys for Arg 382. This substitution results in the loss of a positive charge within the fibr inogen-binding exosite of thrombin, thus accounting for the observed f unctional defect. A heterozygous C to T transition was also present at position 19994 in other family members with a hypoprothrombinemic phe notype. This mutation results in the replacement of Gin 541 (CAA) by a premature stop codon (TAA). Prothrombin Dhahran (family 2) was found to have markedly reduced fibrinogen clotting activity, but normal amid olytic activity. Affected family members were found to have a G to A t ransition at nucleotide position 7312 resulting in the substitution of His for Arg 271. This substitution results in the abolition of a fact or Xa cleavage site, yielding meizothrombin rather than thrombin, on a ctivation of prothrombin Dhahran by factor Xa. All but one of the abov e mutations occur at CpG dinucleotides, thus further supporting the ob servation of a high incidence of CpG transitions in hereditary dysprot hrombinemia. The significant bleeding tendencies of individuals homozy gous for prothrombin Dhahran (prothrombin clotting activity 5% to 7%) contrast sharply with the absence of significant chronic bleeding in t he proband expressing prothrombin Corpus Christi (prothrombin clotting activity 2%). Our findings underscore the capacity of thrombin to con tribute to clinical hemostasis by mechanisms other than its fibrinogen clotting activity. (C) 1996 by The American Society of Hematology.