Genetic polymorphism of the B subunit of human coagulation factor XIII in Japanese

Novel aspects of blood coagulation factor XIII. I. Structure, distribution, activation, and function

Blood coagulation factor XIII (FXIII) is a protransglutaminase that becomes activated by the concerted action of thrombin and Ca2+ in the final stage of the clotting cascade. In addition to plasma, FXIII also occurs in platelets, monocytes, and monocyte-derived macrophages. While the plasma factor is a heterotetramer consisting of paired A and B subunits (A2B2), its cellular counterpart lacks the B subunits and is a homodimer of potentially active A subunits (A2). The gene coding for the A and B subunits has been localized to chromosomes 6p24-25 and 1q31-32.1, respectively. The genomic as well as the primary protein structure of both subunits has been established, and most recently the three-dimensional structure of recombinant cellular FXIII has also been revealed. Monocytes/macrophages synthesize their own FXIII, and very likely FXIII in platelets is synthesized by the megakaryocytes. Cells of bone marrow origin seem to be the primary site for the synthesis of subunit A in plasma FXIII, but hepatocytes might also contribute. The B subunit of plasma FXIII is synthesized in the liver. Plasma FXIII circulates in association with its substrate precursor, fibrinogen. Fibrin(ogen) has an important regulatory role in the activation of plasma FXIII. The most important steps of the activation of plasma FXIII are the proteolytic removal of activation peptide by thrombin, the dissociation of subunits A and B, and the exposure of the originally buried active site on the free A subunits. The end result of this process is the formation of an active transglutaminase, which cross-links peptide chains through epsilon(gamma-glutamyl)lysyl isopeptide bonds. Cellular FXIII in platelets becomes activated through a nonproteolytic process. When intracytoplasmic Ca2+ is raised during platelet activation, the zymogen--in the absence of subunit B--assumes an active configuration. The protein substrates of activated FXIII include components of the clotting-fibrinolytic system, adhesive and contractile proteins. The main physiological function of plasma FXIII is to cross-link fibrin and protect it from the fibrinolytic plasmin. The latter effect is achieved mainly by covalently linking alpha 2 antiplasmin, the most potent physiological inhibitor of plasmin, to fibrin. Plasma FXIII seems to be involved in wound healing and tissue repair, and it is essential to maintaining pregnancy. Cellular FXIII, if exposed to the surface of the cells, might support or perhaps take over the hemostatic functions of plasma FXIII; however, its intracellular role has remained mostly unexplored.

Factor XIII: inherited and acquired deficiency

Factor XIII (XIII), an enzyme found in plasma (present as a pro-enzyme), platelets and monocytes, is essential for normal haemostasis. It may also have a role to play in the processes of wound healing and tissue repair. Inherited XIII deficiency results in a life-long, severe bleeding diathesis which, if untreated, carries a very high risk of death in early life from intracranial bleeding. XIII is a zymogen requiring thrombin and calcium for activation. In plasma, XIII has two subunits: the 'a' subunit, which is the active enzyme, and the 'b' subunit which is a carrier protein. Activated XIII modifies the structure of clot by covalently crosslinking fibrin through an epsilon (gamma-glutamyl)lysine link. It also crosslinks other proteins, including fibronectin and alpha-2-plasmin inhibitor (alpha-2PI), into the clot through the same link. Clot modified by XIII is physically stronger, relatively more resistant to fibrinolysis and may be a more suitable medium for the ingrowth of fibroblasts. Inheritance of factor XIII is autosomal recessive. The majority of patients with the inherited defect show no XIII activity and absence of 'a' subunit protein in plasma, platelets and monocytes. At the molecular level, the defect is not a major gene rearrangement or deletion, but most likely a single point mutation which may be different in each family. Because of the severity of the bleeding diathesis, prophylaxis is desirable and has been shown to be very effective as the in vivo half-life of plasma XIII is long, and low plasma levels are sufficient for haemostasis. Acquired inhibitors have been reported in only two cases with inherited XIII deficiency. Acquired XIII deficiency has been described in a variety of diseases and bleeding has been controlled by therapy with large doses of XIII in such conditions as Henoch-Schönlein purpura, various forms of colitis, erosive gastritis and some forms of leukaemia. Large dose XIII therapy has also been used in an endeavour to promote wound healing after surgery and bone union in non-healing fractures. The use of XIII in these conditions remains controversial. Very rarely a bleeding diathesis results from the development of a specific inhibitor to XIII arising de novo, often as a complication in the course of a disease or in association with long-term drug therapy. The bleeding diathesis in these patients is difficult to treat.

Population genetics of coagulation factor XIIIB in three ethnic groups of Singapore

The distribution of plasma coagulation factor XXIIB polymorphism was determined by PAG isoelectric focusing and immunoblotting in a group of 670 subjects comprising 375 Chinese, 110 Malays and 185 Indians. The frequencies of FXIIIB*1, FXIIIB*2, and FXIIIB*3 were found to be 0.27, 0.03 and 0.70 in the Chinese; 0.33, 0.05 and 0.64 in the Malays and 0.58, 0.08 and 0.33 in the Indians. The phenotypic distribution of FXIIIB alleles was at Hardy-Weinberg equilibrium in all three populations. A two-dimensional principal-components analysis on the basis of three common alleles at the FXIIIB locus among 19 populations, so far studied, clearly differentiates the Negroid, Mongoloid and Caucasoid populations into three major groups with the exception of Amerindians (Minnesota) and US Blacks showing some Caucasoid influence.

Genetic polymorphism of coagulation factor XIII B subunit in the Japanese population: description of three new rare alleles

Polyacrylamide gel isoelectric focusing (PAGIEF) of neuraminidase-treated EDTA plasma samples followed by electroblotting with enzyme immunoassay was performed to further investigate coagulation factor XIII B subunit (FXIII B) polymorphism. In 435 Japanese subjects PAGIEF patterns of FXIII B were classified into five common and three rare allotypes. This suggested that the FXIII B*2 allele existed in the Japanese population in the same manner as in Caucasians. Three new rare allotypes were considered to be controlled by three rare alleles which were designated FXIII B*13, FXIII B*14, and FXIII B*15, respectively. The gene frequencies calculated from 435 Japanese subjects were FXIII B*1 = 0.2977, FXIII B*2 = 0.0184, FXIII B*3 = 0.6805, FXIII B*13 = 0.0011, FXIII B*14 = 0.0011, and FXIII B*15 = 0.0011, respectively.

No evidence for linkage between the loci for coagulation factor XIII-A and HLA

The linkage analysis between the locus for coagulation factor XIII-A (F13A) and HLA region genes (HLA-A, -C, -B) was performed. In males, the maximum of lod scores between F13A and HLA was 0.33 at 0 = 0.30, and in females lod scores were negative at all values of 0. The results provided no evidence for close linkage between F13A and HLA genes.

Genetic heterogeneity of the B subunit of coagulation factor XIII: resolution of type 2

An apparent discrepancy in phenotyping the genetic polymorphism at the FXIIIB locus by electrophoresis or isoelectric focusing has been investigated. The data indicate that the product of the type 2 allele, which can be detected by agarose electrophoresis, is not resolved from the product of the type 1 allele by isoelectric focusing. The understanding of this problem has previously been confused by the absence or very low frequency of the type 2 allele in Japanese populations studied by isoelectric focusing and electrophoresis. An alternative enzyme-linked immunoblotting technique is described which substantially improves the method for phenotyping products of the FXIIIB locus after electrophoresis.