A common mutation, Arg457→Gln, links prothrombin deficiencies in the Puerto Rican population

Abstract

Summary. Five unrelated families with Puerto Rican ancestry were identi®ed as having at least one member with bleeding due to a prothrombin de®ciency. Genetic prothrombin de®ciencies are extremely rare, but at the University of Puerto Rico Hemophilia Center, prothrombin de®ciency is the third most common congenital coagulation factor de®ciency. Because Puerto Rico is relatively isolated, there was a reasonable expectation of a founder effect. Prothrombin genes from probands and their parents were directly sequenced from PCR ampli®ed exons using forward and reverse primers. Four novel prothrombin mutations were identi®ed. The ®rst, a G3A substitution at DNA position 10150 predicting an Arg4573Gln (R457Q) replacement, is common to all ®ve families. In two of the families, the proband children are homozygous for R457Q. In the other three families, the probands are compound heterozygotes for R457Q and one of the other three mutations, which include another point mutation (g16Q), a deletion and a splice junction mutation. The two point mutations have been designated Puerto Rico I and Puerto Rico II. The crystal structure of a-thrombin predicts that the R457Q mutation removes a salt bridge that links the A-and B-chains of thrombin. The primary effect of this defect appears to be destabilization of the circulating prothrombin, creating a moderate hypoprothrombinemia. However, prothrombin antigen/activity ratios indicate a dysprothrombinemia as well, most likely due to the inability of R457Q prothrombin to activate fully to thrombin.

Quality Assessment of Established and Emerging Blood Components for Transfusion

“…In consequence, their deficiencies are recessive and require mutation or inactivation of both gene copies; 50% levels of most coagulation factors, therefore, fail to cause clinically relevant symptoms. Rare individuals with genetic deficiencies of FV, FVII, FX, or FXIII typically do not present with a bleeding diathesis unless their circulating levels of these proteins fall below 0.05 IU/mL [27]; in contrast some individuals with prothrombin deficiency exhibit a bleeding diathesis with activity levels as high as 18.9% [28]. …”

True Congenital Prothrombin Deficiency Due to a ‘New’ Mutation in the Pre-Propeptide (ARG-39 GLN)

“…Reported cases of prothrombin deficiency studied by molecular biology techniques are gathered in table 3. A total of 16 different mutations, including that seen in the proband, have been described in the 19 kindreds [10,11,12,13,14,15,16,17,18]. The same mutation, namely Tyr 44 Cys, was found in two families [15, 17].…”

Prothrombin structure: unanticipated features and opportunities

“…Some of these mutations are buried but point to important determinants of recognition. For example, the severe bleeding reported in prothrombin Puerto Rico (T122M/R457Q) is associated with normal antigen levels [28] and may be due to mutation of R457, a residue in the B chain making a strong ionic interaction with D306 in the A chain [28]. The A chain contains four residues arranged in an ion quartet where R296 is caged by the side chains of E300, D306 and E309.…”

“…Each of the four Ala mutants of the quartet has been reported to activate poorly due to the lack of cleavage by prothrombinase at R271 [29]. Remarkably, prothrombin Denver (E300K and E309K) causes severe bleeding because of direct perturbation of prothrombin activation [30], and so does prothrombin Puerto Rico (T122M/R457Q) [28]. Through the structure of prothrombin, a molecular understanding of the bleeding phenotype associated with naturally occurring mutations becomes possible.…”