Rapid detection of the factor XIII Val34Leu (163 G-->T) polymorphism by real-time PCR using fluorescence resonance energy transfer detection and melting curve analysis

High prevalence of thrombophilic risk factors in patients with central retinal artery occlusion

INTRODUCTION

Central retinal artery occlusion (CRAO) is a common cause of blindness and visual morbidity. In the majority of cases, it is related to thrombotic embolism. Nevertheless, the role of inherited or acquired thrombophilic risk factors in CRAO pathogenesis has not been comprehensively studied.

METHODS

In 126 CRAO patients (66 [52.4%] men, median age 55 [range: 18-80] years) and 107 matched controls (56 [52.3%] men, median age 53 [range: 34-78] years) we evaluated classical atherosclerotic risk factors, including serum lipid profile and glucose level, analyzed intima-media complex thickness (IMT) of external carotid arteries, and performed transthoracic echocardiography. Furthermore, we established the prevalence of inherited and acquired thrombophilic risk factors, such as factor V Leiden (FVL) and prothrombin 20210 G/A genetic variants, plasma activity of factor (F) VIII, protein C and antithrombin activity, and free protein S levels. We also assessed the presence of antiphospholipid antibodies (APLA) and evaluated blood homocysteine in all enrolled subjects. Additionally, we estimated the occurrence of Val34Leu polymorphism of the A subunit of coagulation factor XIII (FXIII-A) in both groups as a potential thrombosis-protecting factor.

RESULTS

Among traditional atherosclerotic risk components, obesity/overweight and hypercholesterolemia were the most common in the CRAO group and occurred in 103 (81.7%) and 85 (67.5%) patients, respectively. CRAO patients also had elevated IMT and altered echocardiographic parameters, indicating diastolic cardiac dysfunction. In thrombophilia investigations, at least one laboratory risk factor occurred in 72.2% (n = 91) of CRAO patients, with APLA as the most frequent, detected in 38.1% (n = 48) of them (almost seven times more frequent than in controls, p < 0.001). Deficiencies in protein C activity and free protein S levels were also common in the CRAO group, reported in 17.5% (n = 22) and 19.8% (n = 25) of patients, respectively. Interestingly, among two analyzed prothrombotic genetic variants, only the FVL was related to CRAO, with the allelic frequency 2.4 times more prevalent than in controls (p = 0.044). Finally, the CRAO group was characterized by hyperhomocysteinemia, almost twice as common as in controls (p = 0.026). Antithrombin deficiency, elevated FVIII, and FXIII-A Val34Leu polymorphism were not associated with CRAO.

CONCLUSIONS

Our findings suggest that thrombophilia plays a vital role in the pathogenesis of CRAO. Thus, proper laboratory screening should be considered in the primary and secondary prevention of those episodes, with implementing appropriate therapy as needed.

Decreased clot burden is associated with factor XIII Val34Leu polymorphism and better functional outcomes in acute ischemic stroke patients treated with intravenous thrombolysis

BACKGROUND

Intravenous thrombolysis using recombinant tissue plasminogen activator remains the mainstay treatment of acute ischemic stroke (AIS), although endovascular treatment is becoming standard of care in case of large vessel occlusions (LVO). To quantify the thrombus burden in LVO, a semiquantitative CT angiography (CTA) grading system, the clot burden score (CBS) can be used. Here we aimed to study the association between CBS and various hemostasis parameters, and to evaluate which parameters are major determinants of thrombolysis outcome.

METHODS

In this single-centered prospective observational case-control study, 200 anterior circulation AIS patients receiving intravenous thrombolysis treatment without thrombectomy were enrolled: 100 AIS patients with LVO (CBS 0-9) and 100 age- and sex-matched AIS patients without LVO (CBS 10). Fibrinogen, α2-plasmin inhibitor, plasminogen, factor XIII and D-dimer were assessed from blood samples taken before and 24 h after thrombolysis, and FXIII-A Val34Leu was genotyped. CBS was calculated using admission CTA. Short-term outcomes were defined based on the change in NIHSS by day 7, long-term outcomes were assessed according to the modified Rankin scale at 3 months post-event.

RESULTS

Poor outcomes were significantly more frequent in the CBS 0-9 group. Plasminogen activity on admission was significantly higher in the CBS 0-9 group. In a univariate analysis, significant protective effect of the Leu34 allele against developing larger clots (CBS 0-9) could be demonstrated (OR:0.519; 95%CI:0.298-0.922, p = 0.0227). Multivariate regression analysis revealed that CBS is an independent predictor of short- and long-term functional outcomes, while such effect of the studied hemostasis parameters could not be demonstrated.

CONCLUSIONS

CBS was found to be a significant independent predictor of thrombolysis outcomes. FXIII-A Leu34 carrier status was associated with smaller thrombus burden, which is consistent with the in vitro described whole blood clot mass reducing effects of the allele, but the polymorphism had no effect on thrombolysis outcomes.

The factor XIII-A Val34Leu polymorphism decreases whole blood clot mass at high fibrinogen concentrations

BACKGROUND

Factor XIII (FXIII) promotes fibrin crosslinking and red blood cell (RBC) retention in clots. The FXIII-A polymorphism, Val34Leu, is associated with protection against venous thrombosis. This effect is hypothesized to result from fibrinogen concentration-dependent changes in fibrin structure. Effects of the FXIII-A Val34Leu polymorphism in whole blood clots have not been investigated.

AIM

Characterize effects of FXIII-A Val34Leu polymorphism and fibrinogen on whole blood clots.

METHODS

We isolated platelet-poor plasmas from human donors (FXIIIVal/Val , FXIIIVal/Leu , FXIIILeu/Leu ), reconstituted plasmas with platelets and RBCs, and triggered clotting. We assessed contributions of gender, age, clotting times, thrombin generation, FXIII activity, FXIII-A Val34Leu polymorphism, and fibrinogen to clot mass. We also reconstituted FXIII-depleted plasma with platelets, RBCs, and purified FXIIIVal/Val or FXIIILeu/Leu , varied fibrinogen, and characterized effects on clot mass.

RESULTS

Clot mass was associated with age, fibrinogen, prothrombin time, and thrombin generation. Clots reconstituted with plasmas from individuals with FXIII-AVal/Val and FXIII-AVal/Leu did not differ in mass from clots with FXIII-ALeu/Leu . However, clots containing a 34Val allele demonstrated a fibrinogen concentration-dependent increase in mass, whereas clots with homozygous 34Leu did not. In plasmas with high fibrinogen, mass was higher for clots with 34Val alleles compared with clots with homozygous 34Leu. In clots reconstituted with purified FXIII, increasing fibrinogen enhanced clot mass in the presence of 34Val, but decreased mass in the presence of 34Leu.

CONCLUSIONS

FXIII 34Leu mitigates the effect of elevated fibrinogen on whole blood clot mass. The Val34Leu polymorphism may protect against venous thrombosis by reducing clot mass.

Low factor XIII levels after intravenous thrombolysis predict short-term mortality in ischemic stroke patients

In this observational study we investigated whether levels of factor XIII (FXIII) and its major polymorphisms affect the outcome of thrombolysis by recombinant tissue plasminogen activator (rtPA) in acute ischemic stroke (AIS) patients. Study cohort included 132 consecutive AIS patients undergoing i.v. thrombolysis within 4.5 h of symptom onset. Blood samples taken on admission, immediately after and 24 h after therapy were analyzed for FXIII activity and antigen levels. FXIII-A p.Val34Leu, p.Tyr204Phe, FXIII-B p.His95Arg and intron K(IVS11 + 144) polymorphisms were genotyped. Neurological deficit was assessed using the National Institutes of Health Stroke Scale. Intracranial hemorrhage was classified according to ECASSII criteria. Long-term functional outcome was defined at 3 months post-event by the modified Rankin scale. FXIII levels showed a gradual decrease immediately after thrombolysis and 24 h later, which was not related to therapy-associated bleeding. In a multiple logistic regression model, a FXIII level in the lowest quartile 24 h post-lysis proved to be an independent predictor of mortality by 14 days post-event (OR:4.95, 95% CI:1.31-18.68, p < 0.05). No association was found between the investigated FXIII polymorphisms and therapeutic outcomes. In conclusion, our findings indicate that FXIII levels 24 h after thrombolysis might help to identify patients at increased risk for short-term mortality.

Effect of factor XIII levels and polymorphisms on the risk of myocardial infarction in young patients

Factor XIII (FXIII) stabilizes and protects the fibrin network. Its role in myocardial infarction (MI) is still to be clarified. To evaluate the association of FXIII levels with MI in young patients and to investigate how the FXIII-A p.Val34Leu, FXIII-B p.His95Arg, and IVS11, c.1952 + 144 C>G (Intron K) polymorphisms influence FXIII levels and MI risk. Patients with ST elevation MI below 40 years of age (MI, n = 119), age-matched clinical controls (CC, n = 101) without MI and coronary artery disease, and healthy controls (HC, n = 120) were investigated for FXIII activity, FXIII-A₂B₂, FXIII-B concentrations and for the polymorphisms. FXIII activity and FXIII-A₂B₂ antigen were significantly elevated in MI. FXIII activity and antigen were significantly elevated in Arg95, while decreased in Intron K "G" carriers. Smoking had an independent increasing effect on FXIII activity and FXIII-A₂B₂ antigen. Intron K C>G polymorphism significantly decreased the risk of MI in patients with elevated fibrinogen. Among the investigated factors Intron K C>G polymorphism and smoking have the most powerful effect on FXIII levels and on the risk of MI in the young. The effect of smoking on coronary thrombus formation may partially be attributed to its FXIII increasing effect.

Regulation of plasma factor XIII levels in healthy individuals; a major impact by subunit B intron K c.1952+144 C>G polymorphism

BACKGROUND

The regulation of plasma factor XIII (FXIII) levels in healthy individuals has been only partially explored. The identification of major non-genetic and genetic regulatory factors might provide important information on the contribution of FXIII to the risk of cardio/cerebrovascular diseases.

OBJECTIVES

To determine the effect of age, smoking, BMI, fibrinogen concentration on plasma FXIII activity, complex FXIII antigen (FXIII-A₂B₂) and total FXIII-B subunit (tFXIII-B) level, to correlate FXIII-B level with the other two FXIII parameters and to assess the variation of FXIII levels in carriers of major FXIII subunit polymorphisms.

METHODS

268 healthy individuals were enrolled in the study. FXIII activity was measured by the ammonia release assay; FXIII-A₂B₂ and tFXIII-B were determined by ELISAs. FXIII-A p.Val34Leu, FXIII-B p.His95Arg and FXIII-B intron K c.1952+144 C>G polymorphisms were identified by RT-PCR using melting point analysis with fluorescence resonance energy transfer detection.

RESULTS

All investigated FXIII parameters showed significant positive correlation with age and fibrinogen level; gender and BMI influenced only tFXIII-B. A highly significant positive correlation was demonstrated between tFXIII-B and the other FXIII parameters. FXIII-A p.Val34Leu polymorphism had only slight, if any effect on FXIII levels. The FXIII-B Arg95 allele moderately increased all three FXIII parameters, but the effect became statistically significant only after adjustment. The FXIII-B intron K G allele drastically decreased FXIII levels, and it seemed to be in synergism with the FXIII-A Leu34 allele.

CONCLUSIONS

Plasma FXIII levels are subjected to multifactorial regulation, in which age, fibrinogen level and FXIII-B intron K polymorphism are major determinants.

Factor XIII-A subunit Val34Leu polymorphism in fatal atherothrombotic ischemic stroke

Factor XIII (FXIII) is a regulator of fibrinolysis and clot firmness. Val34Leu polymorphism of its potentially active A subunit (FXIII-A) leads to faster activation of FXIII, influences clot structure and provides a moderate protection against coronary artery disease. The effect of FXIII-A Val34Leu polymorphism on the risk of atherothrombotic ischemic stroke (AIS) has been investigated in a few studies with contradictory results. In all previous studies, only patients surviving AIS were enrolled and sex-specific effects were not explored. In this retrospective multicenter cohort, we investigated the effect of FXIII-A Val34Leu polymorphism on the risk of fatal AIS in women and men. DNA isolation and genetic determinations in the case of 316 patients who died of AIS were carried out on paraffin-embedded tissue specimens. Genetic analyses for population controls, patients with history of AIS and sex-matched controls were performed on extracted genomic DNA from peripheral blood leukocytes. The prevalence of homozygous wild-type, and heterozygous genotypes, Leu34 carriers and Leu34 allele was not different significantly between the patients with fatal AIS and their respective controls. Logistic regression analysis with age as co-variant demonstrated that in women, homozygous presentation of Leu34 allele represented a more than three-fold increased risk of AIS with fatal outcome. The results demonstrate that FXIII-A Val34Leu polymorphism does not influence the occurrence of AIS, but has an effect on the severity of its outcome. This effect is sex-specific and in homozygous women, the prothrombotic/antifibrinolytic effects of FXIII-A Val34Leu polymorphism seem to prevail.

Controlled assembly of peptide-functionalized gold nanoparticles for label-free detection of blood coagulation Factor XIII activity

A highly sensitive label-free assay for the determination of blood coagulation Factor XIII activity is demonstrated through the controlled assembly of peptide-functionalized gold nanoparticles (AuNPs). Activated Factor XIII catalyzes the formation of covalent crosslinking between peptide chains through ε-(γ-glutamyl)-lysine bonds leading to the aggregation of the AuNPs and consequently a red-shift of the localized surface plasmon resonance. The selective engineering of nanoscale order over AuNP crosslinking via the formation of isopeptide bonds provides a new approach toward the design of nanoassemblies with precise control on the molecular level. The colorimetric assay reported here provides direct qualitative and quantitative analysis of Factor XIII activity with a limit of detection of 0.01 U mL(-1).

Factor XIII B subunit polymorphisms and the risk of coronary artery disease

The aim of the case-control study was to explore the effect of coagulation factor XIII (FXIII) B subunit (FXIII-B) polymorphisms on the risk of coronary artery disease, and on FXIII levels. In the study, 687 patients admitted for coronary angiography to investigate suspected coronary artery disease and 994 individuals representing the Hungarian population were enrolled. The patients were classified according to the presence of significant coronary atherosclerosis (CAS) and history of myocardial infarction (MI). The F13B gene was genotyped for p.His95Arg and for intron K nt29756 C>G polymorphisms; the latter results in the replacement of 10 C-terminal amino acids by 25 novel amino acids. The p.His95Arg polymorphism did not influence the risk of CAS or MI. The FXIII-B intron K nt29756 G allele provided significant protection against CAS and MI in patients with a fibrinogen level in the upper tertile. However, this effect prevailed only in the presence of the FXIII-A Leu34 allele, and a synergism between the two polymorphisms was revealed. Carriers of the intron K nt29756 G allele had significantly lower FXIII levels, and FXIII levels in the lower tertile provided significant protection against MI. It is suggested that the protective effect of the combined polymorphisms is related to decreased FXIII levels.

Effect of the Gas6 c.834+7G>A polymorphism and the interaction of known risk factors on AMD pathogenesis in Hungarian patients

Age-related macular degeneration (AMD) is the leading cause of blindness in the elderly in the developed world. Numerous genetic factors contribute to the development of the multifactorial disease. We performed a case-control study to assess the risk conferred by known and candidate genetic polymorphisms on the development of AMD. We searched for genetic interactions and for differences in dry and wet AMD etiology. We enrolled 213 patients with exudative, 67 patients with dry AMD and 106 age and ethnically matched controls. Altogether 12 polymorphisms in Apolipoprotein E, complement factor H, complement factor I, complement component 3, blood coagulation factor XIII, HTRA1, LOC387715, Gas6 and MerTK genes were tested. No association was found between either the exudative or the dry form and the polymorphisms in the Apolipoprotein E, complement factor I, FXIII and MerTK genes. Gas6 c.834+7G>A polymorphism was found to be significantly protective irrespective of other genotypes, reducing the odds of wet type AMD by a half (OR = 0.50, 95%CI: 0.26–0.97, p = 0.04). Multiple regression models revealed an interesting genetic interaction in the dry AMD subgroup. In the absence of C3 risk allele, mutant genotypes of both CFH and HTRA1 behaved as strongly significant risk factors (OR = 7.96, 95%CI: 2.39 = 26.50, p = 0.0007, and OR = 36.02, 95%CI: 3.30–393.02, p = 0.0033, respectively), but reduced to neutrality otherwise. The risk allele of C3 was observed to carry a significant risk in the simultaneous absence of homozygous CFH and HTRA1 polymorphisms only, in which case it was associated with a near-five-fold relative increase in the odds of dry type AMD (OR = 4.93, 95%CI: 1.98–12.25, p = 0.0006). Our results suggest a protective role of Gas6 c.834+7G>A polymorphism in exudative AMD development. In addition, novel genetic interactions were revealed between CFH, HTRA1 and C3 polymorphisms that might contribute to the pathogenesis of dry AMD.

Thrombomodulin-dependent effect of factor V Leiden mutation on the cross-linking of α2-plasmin inhibitor to fibrin and its consequences on fibrinolysis

INTRODUCTION

It has been shown that thrombomodulin (TM) considerably delays factor XIII (FXIII) activation and this effect is abrogated by Factor V Leiden (FV(Leiden)) mutation. The aim of the study was to explore the effect of TM on the cross-linking of α(2)-plasmin inhibitor (α(2)-PI) to fibrin in plasma samples of different FV genotypes and how this effect is related to the impaired fibrinolysis of FV(Leiden) carriers.

METHODS

In the plasma samples of fifteen individuals with different FV genotypes and in FV deficient plasma supplemented with wild type FV or FV(Leiden) coagulation was initiated by recombinant human tissue factor and phospholipids with or without recombinant human TM (rhTM). In the recovered clots the extent of α(2)-PI-fibrin cross-linking was evaluated by Western blotting and quantitative densitometry. The effect of rhTM on tissue plasminogen activator (tPA) induced clot lysis was measured by turbidimetric method.

RESULTS

rhTM significantly delayed the formation of α(2)-PI-fibrin α-chain heterodimers/oligomers in plasma samples containing wild type FV. This effect of rhTM was impaired in the presence of FV(Leiden). rhTM delayed tPA-induced clot lysis and this effect of rhTM was more pronounced in plasma containing FV(Leiden). When TAFIa was inhibited by potato carboxypeptidase inhibitor, rhTM accelerated clot lysis in the presence of wild type FV, which is explained by the delayed α(2)-PI-fibrin cross-linking. This effect of rhTM did not prevail in the presence of FV(Leiden).

CONCLUSION

FV(Leiden) abrogates the delaying effect of rhTM on α(2)-PI-fibrin cross-linking, which contributes to the impaired fibrinolysis observed in FV(Leiden) carriers.

Thrombomodulin-dependent effect of factor VLeiden mutation on factor XIII activation

INTRODUCTION

Factor V Leiden mutation (FV(Leiden)) is associated with impaired down-regulation of activated FV procoagulant activity and loss of FV anticoagulant function that result in an increased risk of venous thromboembolism. As the downstream effects of FV(Leiden) on clot formation and fibrinolyis have only partially been revealed, we investigated its effect on the activation of factor XIII (FXIII) and the cross-linking of fibrin.

METHODS

In the plasma samples of fifteen healthy individuals with known FV genotypes coagulation was initiated by recombinant human tissue factor and phospholipids with or without recombinant human thrombomodulin (rhTM). FV deficient plasma supplemented with purified wild type FV or FV(Leiden) were also investigated. Clots were recovered and analyzed by SDS-PAGE and quantitative densitometric evaluation of Western blots.

RESULTS

rhTM considerably delayed the activation of FXIII in the plasma from FV wild type individuals. This effect of rhTM was significantly impaired in the plasma from FV(Leiden) carriers. The results were confirmed in experiments with FV deficient plasma supplemented by FV prepared from wild type individuals or FV(Leiden) homozygotes. Fibrin γ-chain dimerization was also considerably delayed by rhTM in plasma samples from individuals without Leiden mutation, but not in plasma samples from FV(Leiden) heterozygotes or homozygotes. The difference between heterozygotes and homozygotes was not statistically significant.

CONCLUSION

The highly diminished delaying effect of TM on FXIII activation and on the cross-linking of fibrin in FV(Leiden) carriers might represent a novel mechanism contributing to the increased thrombosis risk of these individuals.

Study of 18 functional hemostatic polymorphisms in mucocutaneous bleeding disorders

Hereditary disorders of primary hemostasis, characterized by mucocutaneous bleeding (MCB), are highly prevalent in children. Few cases are clearly monogenic, but the overwhelming majority are classified as mild bleeding disorders, with wide clinical and laboratory heterogeneity suggestive of complex polygenic diseases. In this framework, and by homology with venous thrombosis, some functional polymorphisms affecting the hemostatic system should be considered. We evaluated the role of 18 common hemostatic polymorphisms on the occurrence and severity of MCB in a case-control study including 269 patients and 286 matched controls consecutively recruited. FV Leiden was associated with milder bleeding severity, assessed by a standardized bleeding score (p = 0.013). Multivariate analysis revealed that three additional polymorphisms protected against MCB (F13 Leu34, OR = 0.66; 95% CI, 0.47-0.94; p = 0.024; VKORC1 1173T, OR = 0.59; 95% CI, 0.40-0.87; p = 0.009; and non-O blood group alleles, OR = 0.59; 95% CI, 0.41-0.86; p = 0.006). When combined, these polymorphisms showed an additive protection (OR = 0.24; 95% CI, 0.11-0.52), supporting the polygenic nature of MCB. Our data suggest that some common polymorphisms affecting hemostasis-related genes could protect from bleeding.

The rules of variation: amino acid exchange according to the rotating circular genetic code

General guidelines for the molecular basis of functional variation are presented while focused on the rotating circular genetic code and allowable exchanges that make it resistant to genetic diseases under normal conditions. The rules of variation, bioinformatics aids for preventative medicine, are: (1) same position in the four quadrants for hydrophobic codons, (2) same or contiguous position in two quadrants for synonymous or related codons, and (3) same quadrant for equivalent codons. To preserve protein function, amino acid exchange according to the first rule takes into account the positional homology of essential hydrophobic amino acids with every codon with a central uracil in the four quadrants, the second rule includes codons for identical, acidic, or their amidic amino acids present in two quadrants, and the third rule, the smaller, aromatic, stop codons, and basic amino acids, each in proximity within a 90 degree angle. I also define codifying genes and palindromati, CTCGTGCCGAATTCGGCACGAG.

A real-time multiplex SNP melting assay to discriminate individuals

A method that quickly and inexpensively differentiates crime scene samples from multiple donors would expedite casework analysis by allowing the selection of probative items requiring comprehensive testing. This new method need not be perfectly definitive nor give a complete 13 locus short tandem repeat (STR) profile; it simply must be able to differentiate between most victim and suspect samples. We describe the development of multiplex, single nucleotide polymorphism (SNP), fluorescence resonance energy transfer-based real-time polymerase chain reaction (PCR) assays to fulfill this need. Dual probes, one fluorescently labeled and the other labeled with a quencher, are monitored during a melt analysis to reveal an increase in fluorescence, which allows the assessment of the two SNP alleles. Two alternate 6-plex assays (with and without gender determination) have been developed for the six-color RG6000 real-time instrument (Corbett Robotics, Inc.) and one seven SNP plus gender assay (performed as two 4-plex assays, one with gender the other without) have been developed for use in four/five color real-time instruments. This technique can discriminate between 95% and 99% of samples from different individuals. This assay is fast (approximately 2 h), much less expensive than STR analysis, and uses a real-time PCR instrument which is found in most forensic and molecular biology labs.

Decreased factor XIII levels in factor XIII A subunit Leu34 homozygous patients with coronary artery disease

INTRODUCTION

The effect of factor XIII A subunit (FXIII-A) Val34Leu polymorphism on the risk of coronary artery disease (CAD) has been extensively studied. In this study we investigated how FXIII-A Val34Leu genotypes influence plasma factor XIII levels in patients with coronary sclerosis (CS) and myocardial infarction (MI) and how fibrinogen level modulates this effect.

PATIENTS AND METHODS

955 consecutive patients admitted for coronary angiography were categorized according to the presence or absence of significant CS and the history of MI. The frequency of FXIII-A Val34Leu polymorphism, fibrinogen, FXIII activity and antigen levels were determined.

RESULTS AND CONCLUSIONS

CS or MI decreased FXIII levels in patients homozygous for FXIII-A Leu34 allele, but not in heterozygous or wild type patients. In the subgroup of patients with CS, but without the history of MI no significant effect was detected, which suggests that MI has a more prominent role. The specific activity of plasma FXIII was independent of FXIII-A Val34Leu genotype. FXIII and fibrinogen levels significantly correlated in CS+ and MI+ patients. In MI+ patients of Leu/Val or Leu/Leu genotypes and with fibrinogen levels in the lowest quartile, FXIII levels were lower than in the same patient groups, but with higher fibrinogen level. The low-scale continuous activation of blood coagulation in CAD patients could lead to parallel FXIII and fibrinogen consumption. As the same amount of thrombin activates more Leu34 FXIII than Val34 FXIII, increased FXIII consumption might be responsible for the decreased FXIII levels in Leu34 homozygous CAD patients.

Modulation of the risk of coronary sclerosis/myocardial infarction by the interaction between factor XIII subunit A Val34Leu polymorphism and fibrinogen concentration in the high risk Hungarian population

INTRODUCTION

The results on the association of factor XIII (FXIII) A subunit (FXIII-A) Val34Leu polymorphism with the risk of myocardial infarction (MI) are rather inconclusive. The original paper and confirmatory reports demonstrated a protective effect of the mutation, but results demonstrating the lack of protection have also been published. Gene-gene and gene-environmental interactions have been proposed to be responsible for the opposing results. As the rate of change in fibrin clot permeability with increasing fibrinogen concentrations decreased stepwise with increasing number of Leu34 alleles it was proposed that the protection by Val34Leu polymorphism become effective only at higher fibrinogen concentrations. However, this hypothesis has not been tested on patients with coronary artery disease.

PATIENTS AND METHODS

955 consecutive patients admitted for coronary angiography were categorized according to the presence or absence of significant coronary sclerosis (CS) and according to positive or negative history of MI. The frequency of FXIII-A Val34Leu polymorphism, and a number of risk factors, including fibrinogen were determined in the patients. FXIII-A Val34Leu polymorphism was also investigated in a population control group of 1146 subjects.

RESULTS

The presence of FXIII-A Leu34 allele or homozygous Leu34 genotype did not change the risk of CS or MI in the general Hungarian population. However, when patients with fibrinogen level in the upper quartile were separately investigated, the Leu34 allele provided a statistically significant protection against MI.

CONCLUSIONS

Fibrinogen concentration modulates the effect of Leu34 allele on the risk of MI; its protective effect emerges at increasing fibrinogen concentration.

The combined effect of fibrin formation and factor XIII A subunit Val34Leu polymorphism on the activation of factor XIII in whole plasma

The first step in the activation of blood coagulation factor XIII (FXIII) is the proteolytic cleavage of the potentially active A subunit (FXIII-A) by thrombin at Arg37-Gly38. Both fibrin formation and FXIII-A Val34Leu polymorphism influence the rate of proteolytic activation of purified factor XIII, however their relative importance and interaction in determining the time of onset and the rate of FXIII activation in whole plasma have not yet been explored. In the present study it was shown that in plasma, fibrin formation preceded the truncation of FXIII-A by thrombin, the activation process took place exclusively on the surface of newly formed fibrin and activated FXIII remained associated with the fibrin clot. The time of fibrin formation closely correlated with the time of FXIII activation, while there was no significant relationship between the time of FXIII activation and FXIII-A Val34Leu genotype. However, in the case of Leu34 variant the lag phase between fibrin formation and FXIII-A truncation was significantly shorter than in the case of Val34 variant. The results suggest that in whole plasma the onset of FXIII activation is determined by fibrin formation, while the rate of activation is modulated by Val34Leu polymorphism.