Measurement of factor XIII activity in plasma

Traumatic intracranial hemorrhage in pediatrics: Implications of factor XIII deficiency and consumptive coagulopathy in abusive head trauma evaluation

For infants that present with intracranial hemorrhage in the setting of suspected abusive head trauma (AHT), the standard recommendation is to perform an evaluation for a bleeding disorder. Factor XIII (FXIII) deficiency is a rare congenital bleeding disorder associated with intracranial hemorrhages in infancy, though testing for FXIII is not commonly included in the initial hemostatic evaluation. The current pediatric literature recognizes that trauma, especially traumatic brain injury, may induce coagulopathy in children, though FXIII is often overlooked as having a role in pediatric trauma-induced coagulopathy. We report an infant that presented with suspected AHT in whom laboratory workup revealed a decreased FXIII level, which was later determined to be caused by consumption in the setting of trauma induced coagulopathy, rather than a congenital disorder. Within the Child Abuse Pediatrics Research Network (CAPNET) database, 85 out of 569 (15 %) children had FXIII testing, 3 of those tested (3.5 %) had absent FXIII activity on qualitative testing, and 2 (2.4 %) children had activity levels below 30 % on quantitative testing. In this article we review the literature on the pathophysiology and treatment of low FXIII in the setting of trauma. This case and literature review demonstrate that FXIII consumption should be considered in the setting of pediatric AHT.

Recombinant Destabilase from Hirudo medicinalis Is Able to Dissolve Human Blood Clots In Vitro

Leeches are amazing animals that can be classified as conditionally poisonous animals since the salivary cocktail they produce is injected directly into the victim, and its components have strictly defined biological purposes, such as preventing blood clot formation. Thrombolytic drugs are mainly aimed at treating newly formed blood clots. Aged clots are stabilized by a large number of isopeptide bonds that prevent the action of thrombolytics. These bonds are destroyed by destabilase, an enzyme of the leech’s salivary glands. Here, we conducted a pilot study to evaluate the feasibility and effectiveness of the use of destabilase in relation to blood clots formed during real pathological processes. We evaluated the isopeptidase activity of destabilase during the formation of a stabilized fibrin clot. We showed that destabilase does not affect the internal and external coagulation cascades. We calculated the dose–response curve and tested the ability of destabilase to destroy isopeptide bonds in natural blood clots. The effect of aged and fresh clots dissolving ability after treatment with destabilase coincided with the morphological characteristics of clots during surgery. Thus, recombinant destabilase can be considered as a potential drug for the treatment of aged clots, which are difficult to treat with known thrombolytics.

Clinical Validation of an Automated Fluorogenic Factor XIII Activity Assay Based on Isopeptidase Activity

Hereditary factor XIII (FXIII) deficiency is a rare autosomal bleeding disorder which can cause life-threatening bleeding. Acquired deficiency can be immune-mediated or due to increased consumption or reduced synthesis. The most commonly used screening test is insensitive, and widely used quantitative assays have analytical limitations. The present study sought to validate Technofluor FXIII Activity, the first isopeptidase-based assay available on a routine coagulation analyser, the Ceveron s100. Linearity was evidenced throughout the measuring range, with correlation coefficients of >0.99, and coefficients of variation for repeatability and reproducibility were <5% and <10%, respectively. A normally distributed reference range of 47.0–135.5 IU/dL was derived from 154 normal donors. Clinical samples with Technofluor FXIII Activity results between 0 and 167.0 IU/dL were assayed with Berichrom^® FXIII Activity, a functional ammonia release assay, and the HemosIL^™ FXIII antigen assay, generating correlations of 0.950 and 0.980, respectively. Experiments with a transglutaminase inhibitor showed that Technofluor FXIII Activity can detect inhibition of enzymatic activity. No interference was exhibited by high levels of haemolysis and lipaemia, and interference by bilirubin was evident at 18 mg/dL, a level commensurate with severe liver disease. Technofluor FXIII Activity is a rapid, accurate and precise assay suitable for routine diagnostic use with fewer interferents than ammonia release FXIII activity assays.

Congenital Factor XIII Deficiency With the Presence of Inhibitor: A Case Study

Coagulation factor XIII (FXIII) is a fibrin-stabilizing factor with additional roles in wound healing and interactions between the decidua and fetus. Congenital FXIII deficiency is rare bleeding disorder. Inhibitor development against FXIII in inherited FXIII deficency is also uncommon, but may cause severe, life-threatening bleeding. FXIII is the last step in the coagulation cascade with normal coagulation paramaters (PT, aPTT), the detection of inhibitor to FXIII is quite difficult. The treatment of inhibitor-positive congenital FXIII deficiency is challenging due to the lack of a role of by-pass agents such as FVII. The best known ways of treatment in these cases are the use of high-dose FXIII concentrates and immunosuppression. Herein, we report the management of postoperative bleeding diathesis in a patient with FXIII deficiency who developed inhibitors, and to follow the clinical course of the disease with FXIII concentrate and immunosuppression.

Acquired factor XIII deficiency: A review

Acquired factor XIII (FXIII) deficiency is a rare bleeding disorder that can manifest with spontaneous or delayed life-threatening hemorrhage. Causes of acquired deficiency include immune-mediated inhibition, as well as non-immune FXIII hyperconsumption or hyposynthesis. The occurrence of acquired FXIII deficiency can be idiopathic or may be associated with comorbidities, such as malignancies or autoimmune disorders. Recognition of acquired FXIII deficiency and its underlying cause is imperative, as treatment options vary depending on the etiology. Diagnosis requires quantitative FXIII testing in addition to supplemental inhibitor studies if the clinical situation suggests an immune-mediated pathophysiology. Treatment may involve FXIII replacement, antifibrinolytic administration, and/or inhibitor eradication. However, treatment targets and thresholds are undefined in acquired FXIII deficiency. This review will focus on the clinical characteristics, diagnostic issues and therapeutic options for both immune and non-immune acquired FXIII deficiency. Cases are described to illustrate the clinical features of acquired FXIII deficiency.

Auto- and alloantibodies against factor XIII: laboratory diagnosis and clinical consequences

Acquired FXIII deficiencies caused by autoantibodies against FXIII subunits represent rare but very severe bleeding diatheses. Alloantibodies in FXIII-deficient patients also cause life-threatening bleeding complications, but they develop extremely rarely. In this review we provide an overview of the diagnosis and classification of anti-FXIII antibodies and analyze 48 patients with autoimmune FXIII deficiency and four additional FXIII-deficient patients who developed anti-FXIII alloantibody. The patients were collected from peer-reviewed publications from which relevant data could be extracted. With the exception of two cases the antibodies were directed against FXIII-A. The difficulties in the diagnosis of FXIII deficiency in the presence of anti-FXIII antibodies are discussed and a scheme for the functional classification of the anti-FXIII antibodies is recommended. The three main categories are neutralizing and non-neutralizing antibodies and antibodies with combined effect. The methods being used for detecting and quantifying the inhibitory effect on FXIII activation and on the transglutaminase activity of activated FXIII are summarized and techniques for the classification of neutralizing anti-FXIII antibodies are outlined. The importance of clearance studies in these cases is emphasized. Binding assays, useful for the identification of non-neutralizing and combined type antibodies, were collected from the literature and their informative power is demonstrated by examples. The most frequently occurring bleeding symptoms in patients with anti-FXIII antibodies were soft tissue bleeding; intracranial bleedings also occurred, but less frequently than in inherited FXIII deficiency. Treatment of such patients is extremely challenging; the main aim should be eradication of the antibody.

A large case series on surgical outcomes in congenital factor XIII deficiency patients in Iran

Essentials Data on surgery in factor XIII (FXIII) deficiency patients are scarce and lack standardized guidelines. Variable dosage of 10-50 U kg-1 was given to FXIII deficiency patients undergoing surgery. Surgical outcomes showed excellent hemostasis with a minimal risk of post-operative complications. Surgery can be performed safely in FXIII deficiency patients following FXIII administration.

SUMMARY

Background The lack of accepted standardized surgical guidelines leads to dependence on the treating physicians' and centers' experiences. Aim Our aim is to evaluate the surgical outcomes of a large group of congenital factor XIII deficiency (FXIIID) patients. Methods A case series study was conducted prior to surgery on congenital FXIIID patients in two major referral centers located in Iran from 2010 to 2016. All patients were on prophylaxis using plasma factor XIII concentrate (10 U kg-1 , every 28 days) except for three patients. Single doses of 10 U kg-1 or 30 U kg-1 plasma factor XIII concentrate were given before a minor procedure and circumcision, respectively. Two doses of plasma factor XIII concentrate, one 30 U kg-1 prior to the procedure and the second dose of 30 U kg-1 on postoperative day 3, were given for major surgery. The dose was 50 U kg-1 both before and after neurosurgical procedures. Results One hundred and sixty-two FXIIID patients underwent minor, major and obstetrical/gynecological surgeries. Median age of the patients was 14 years (ages ranged 15 days to 47 years). The male-to-female ratio was 89/73. Five postoperative complications, two bleeding and three thrombosis, were recorded. Conclusion Our study showed excellent hemostasis in FXIIID patients undergoing surgeries. During the period of these surgeries, we observed only 1.8% postoperative complications. Surgery can be performed safely in FXIIID patients, and our proposed treatment regimens lead to adequate hemostatic coverage with minimal risk, for both minor and major surgeries.

Factor XIII deficiency diagnosis: Challenges and tools

Factor XIII deficiency (FXIIID) is a rare hereditary bleeding disorder arising from heterogeneous mutations, which can lead to life-threatening hemorrhage. The diagnosis of FXIIID is challenging due to normal standard coagulation assays requiring specific FXIII assays for diagnosis, which is especially difficult in developing countries. This report presents an overview of FXIIID diagnosis and laboratory methods and suggests an algorithm to improve diagnostic efficiency and prevent missed or delayed FXIIID diagnosis. Assays measuring FXIII activity: The currently available assays utilized to diagnose FXIIID, including an overview of their complexity, reliability, sensitivity, and specificity, as well as mutational analysis are reviewed. The use of a FXIII inhibitor assay is described. Diagnostic tools in FXIIID: Many laboratories are not equipped with quantitative FXIII activity assays, and if available, limitations in lower activity ranges are important to consider. Clot solubility tests are not standardized, have a low sensitivity, and are therefore not recommended as routine screening test; however, they are the first screening test in almost all coagulation laboratories in developing countries. To minimize the number of patients with undiagnosed FXIIID, test quality should be improved in less well-equipped laboratories. Common country-specific mutations may facilitate diagnosis through targeted genetic analysis in reference laboratories in suspected cases. However, genetic analysis may not be feasible in every country and may miss spontaneous mutations. Centralized FXIII activity measurements should also be considered. An algorithm for diagnosis of FXIIID including different approaches dependent upon laboratory capability is proposed.

Minimal factor XIII activity level to prevent major spontaneous bleeds

Essentials A strong association between bleeding severity and FXIII activity level (FXIII:C) was shown. The range 5-30 IU dL-1 of FXIII:C was associated with a high variability of bleeding severity. The PROspective study confirmed the association between FXIII:C activity and bleeding severity.

A FXIII

C of 15 IU dL-1 is a proposed target to start prophylaxis for prevention of major bleeding.

SUMMARY

Background Congenital factor XIII (FXIII) deficiency is a rare bleeding disorder associated with significant bleeding manifestations. The European Network of Rare Bleeding Disorders (EN-RBD) study, performed from 2007 to 2010, showed a strong association between bleeding severity and FXIII activity in plasma of patients with FXIII deficiency. Among these patients, variable levels of FXIII activity, from undetectable to 30%, were associated with a wide range of bleeding severity. Objectives and patients The present cross-sectional study, in the frame of the PRO-RBDD project, a prospective cohort study, analyzed data of 64 patients with FXIII deficiency and different types of clinical and laboratory severity. Results The results of this analysis confirmed that FXIII coagulant activity in plasma is well associated with clinical severity of patients. In addition, 15 IU dL-1 of FXIII activity was identified to be the level under which the probability of spontaneous major bleeding sharply increases (from 50% for levels of 15 IU dL-1 to more than 90% for levels of 5 IU dL-1 or lower). Conclusion The PRO-RBDD study suggests a FXIII coagulant activity level of 15 IU dL-1 as a target to start prophylaxis in order to prevent major bleedings, such as central nervous system or gastrointestinal tract hemorrhages.

Detection of Factor XIII deficiency: data from multicentre exercises amongst UK NEQAS and PRO-RBDD project laboratories

INTRODUCTION

FXIII deficiency is a rare bleeding disorders, and specific FXIII assays are recommended to detect this deficiency. We investigated the performance and accuracy of FXIII investigations in two exercises, comparing centres enrolled in the PRO-RBDD project (prospective data collection on patients with fibrinogen and Factor XIII deficiencies), and UK NEQAS BC centres.

METHODS

Samples from a FXIII deficient subject and a normal donor were sent to participating centres, to investigate for FXIII deficiency, and interpret their results. Median, coefficient of variation and range were determined.

RESULTS

Results were returned from 98 UK NEQAS BC and 28 PRO-RBDD centres. Up to 40% of UK NEQAS BC and 52% of PRO-RBDD centres reported clot solubility results - with diagnostic errors by two NEQAS BC centres (false negatives for the FXIII deficient sample) and one PRO-RBDD centre (false positive for the normal sample). Over 70% of UK NEQAS BC centres and PRO-RBDD centres performed FXIII assays. Median results were similar between the two groups, with the exception of sample 3 in survey 2 (5.5 vs. 14.0 μ/dl for UK NEQAS BC and PRO-RBDD centres respectively, P < 0.001). Diagnostic errors were made by 2 UK NEQAS BC centres.

CONCLUSION

Approximately 70% of centres now employ FXIII assays, complying with international recommendations. However, solubility tests continue to be used. Our data show this can be successful, depending on the sensitivity of the method in use. Diagnostic errors are made by centres using both solubility screens and FXIII assays, and laboratories should ensure good quality assurance procedures to improve diagnostic accuracy.

Severe bleeding diatheses in an elderly patient with combined type autoantibody against factor XIII A subunit; novel approach to the diagnosis and classification of anti-factor XIII antibodies

INTRODUCTION

Acquired factor XIII (FXIII) deficiency due to autoantibody is a rare, severe bleeding diathesis. Its laboratory diagnosis and classification represents a difficult task.

AIM

Introduction of novel approaches into the diagnosis and characterization of anti-FXIII autoantibody and demonstration of their use in the diagnosis of a patient with autoimmune FXIII deficiency.

METHODS

Factor XIII activity, FXIII antigen levels and the titre of anti-FXIII-A antibody were monitored throughout the course of the disease. FXIII activity was measured by ammonia release assay; FXIII-A₂ B₂ complex, total and free FXIII-B concentrations were determined by ELISAs. The binding constant for the interaction of the autoantibody with recombinant FXIII-A₂ (rFXIII-A₂ ) and FXIII-A₂ B₂ was determined by surface plasmon resonance (SPR). The inhibitory capacity of IgG was expressed as the concentration exerting 50% inhibition of FXIII activation/activity (IC50). The truncation of FXIII-A by thrombin was monitored by western blotting. The inhibition of Ca²⁺ -induced FXIII activation and active FXIII (FXIIIa) were assessed by FXIII activity assay.

RESULTS

The antibody bound to rFXIII-A₂ and FXIII-A₂ B₂ with high affinity and accelerated the decay of supplemented FXIII concentrate. An IC50 value of 170.1 μg IgG·mL^-1 indicated effective FXIII neutralization. The main neutralizing effect of the autoantibody was the inhibition of FXIIIa. After 2 months, due to combined therapeutic modalities, the autoantibody disappeared and FXIII activity significantly elevated.

CONCLUSION

The anti-FXIII-A autoantibody exerted a combined effect including inhibition of FXIIIa and acceleration of FXIII decay in the plasma. IC50 and binding constant determinations added important information to the characterization of the autoantibody.

Agreement between factor XIII activity and antigen assays in measurement of factor XIII: A French multicenter study of 147 human plasma samples

INTRODUCTION

Factor XIII (FXIII) deficiency is a rare hemorrhagic disorder whose early diagnosis is crucial for appropriate treatment and prophylactic supplementation in cases of severe deficiency. International guidelines recommend a quantitative FXIII activity assay as first-line screening test. FXIII antigen measurement may be performed to establish the subtype of FXIII deficiency (FXIIID) when activity is decreased.

METHODS

The aim of this multicenter study was to evaluate the analytical and diagnostic levels of performance of a new latex immunoassay, K-Assay^® FXIII reagent from Stago, for first-line measurement of FXIII antigen. Results were compared to those obtained with the Berichrom^® FXIII chromogenic assay for measurement of FXIII activity. Of the 147 patient plasma samples, 138 were selected for analysis.

RESULTS

The accuracy was very good, with intercenter reproducibility close to 7%. Five groups were defined on FXIII activity level (<5% (n = 5), 5%-30% (n = 23), 30%-60% (n = 17), 60%-120% (n = 69), above 120% (n = 24)), without statistical differences between activity and antigen levels (P value >0.05). Correlation of the K-Assay^® with the Berichrom^® FXIII activity results was excellent (r = 0.919). Good agreement was established by the Bland and Altman method, with a bias of +9.4% on all samples, and of -1.4% for FXIII levels lower than 30%. One patient with afibrinogenemia showed low levels of Berichrom^® FXIII activity but normal antigen level and clot solubility as expected.

CONCLUSIONS

The measurement of FXIII antigen using the K-Assay^® is a reliable first-line tool for detection of FXIII deficiency when an activity assay is not available.

Assessment of Factor XIII

Blood coagulation factor XIII (FXIII) is essential for maintaining hemostasis. The absence of FXIII results in severe bleeding diathesis, which without prophylaxis frequently leads to fatal bleeding. As the usual hemostasis screening tests remain normal, the diagnosis of FXIII deficiency needs specific tests. Here, we describe FXIII activity determination by the ammonia release assay, which is the first-line test in the diagnostic algorithm for FXIII deficiency. The method for another activity test, the undeservedly rarely used fibrin cross-linking assay, is also presented. Further tests used for the classification of FXIII deficiencies, measurement of FXIII activity in platelets, ELISAs for the measurement of complex plasma FXIII (FXIII-A₂B₂) antigen and for FXIII-A₂ in plasma and platelets are also included. Detailed description of the methods for the detection and measurement of neutralizing auto- and alloantibodies is also provided.

Neutralizing autoantibody against factor XIII A subunit resulted in severe bleeding diathesis with a fatal outcome - characterization of the antibody

Essentials Autoantibody against factor XIII (FXIII) is a rare but severe acquired hemorrhagic diathesis. In an elderly patient, anti-FXIII-A antibody led to severe bleedings with fatal outcome. The neutralizing autoantibody bound to FXIII with high affinity (Ka≈10(9) m(-1) ). The dominant effect of the autoantibody was the inhibition of activated FXIII.

SUMMARY

Autoantibodies may develop against the catalytic A subunit of factor XIII (FXIII-A) or the carrier B subunit (FXIII-B). Autoimmune FXIII-A deficiency was diagnosed in an elderly (75 years) patient with severe bleeding symptoms. The patient had 3% FXIII activity, and unmeasurable FXIII-A2 B2 and FXIII-A antigens in the plasma, whereas, in the platelet lysate, activity and FXIII-A antigen values were normal. As revealed by western blotting, FXIII antigen was present in the plasma, but the autoantibody interfered with the immunoassays. A mixing study indicated the presence of inhibitor with a titer of 63.2 Bethesda units (BU). The patient's IgG bound to FXIII-A2 B2 and to FXIII-A2 with equally high affinity (Ka in the range of 10(9) m(-1) ). It exerted a multiple inhibitory effect on FXIII activation/activity (IC50: 50 μg mL(-1) ). Immunosupressive therapy gradually decreased the autoantibody titer to 8.0 BU, but FXIII activity remained very low, and, owing to recurrent bleeding, the patient died.

Measurement of factor XIII (FXIII) activity by an automatic ammonia release assay using iodoacetamide blank-procedure: no more overestimation in the low activity range and better detection of severe FXIII deficiencies

Background:

Laboratory investigation with specific factor XIII (FXIII) assays plays a crucial role in diagnosis of FXIII deficiency. According to the International Society on Thrombosis and Hemostasis (ISTH), it is necessary a blank sample with iodoacetamide, provided by the kit or locally prepared, when the ammonia release assays are used, to avoid FXIII activity overestimation.

Methods:

In this study we set up a modification of the Berichrom FXIII chromogenic assay, in which iodoacetamide was added by the BCS analyzer in the reaction mixture of the blank sample, without modifications of the original reagents. We analyzed 100 plasma samples of outpatients with clinical symptoms suggestive of a bleeding diathesis (20 samples had FXIII activity <20%).

Results:

In all samples blank subtraction significantly reduced FXIII activity, mostly in the low activity range group (from 10.1% to 2.4%, p<0.0001). In this group correction with iodoacetamide also increased the agreement with the immunoassay and allowed FXIII activity measure up to 0%.

Conclusions:

Despite the low number of samples included in the study, the described automatic procedure seemed to decrease FXIII activity overestimation and, especially for low activity range samples (<20%), to improve the agreement between FXIII activity and concentration. Our data suggested that iodoacetamide correction could allow the detection of severe FXIII deficiencies (activity <5%) otherwise undiagnosed using the original method.

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).

Use of Factor XIII (FXIII) concentrate in patients with congenital FXIII deficiency undergoing surgical procedures

BACKGROUND

Patients with congenital Factor XIII (FXIII) deficiency have impaired fibrin stabilization and are at high risk for surgical bleeding. Data regarding the use of FXIII concentrates before and during surgery are lacking. The objective of this study was to report the use of plasma-derived FXIII concentrate (Corifact in the United States; Fibrogammin P in other countries) in patients with congenital FXIII deficiency undergoing surgical procedures.

STUDY DESIGN AND METHODS

FXIII concentrate at preoperative doses ranging from 25 to 40 U/kg was administered to six patients with congenital FXIII deficiency undergoing major or minor surgeries.

RESULTS

FXIII concentrate was administered immediately before surgery for five surgical cases; three of these patients achieved excellent hemostasis during and after surgery, while two had intraoperative bleeding. In one surgical case, a regular prophylactic dose of FXIII concentrate was administered to the patient 1 week before minor surgery. FXIII concentrate provided rapid replacement of FXIII activity. In all but one of the patients given a dose of FXIII designed to increase FXIII levels more than 50%, there was satisfactory intraoperative and postoperative hemostasis. One patient undergoing aortic valve replacement on cardiopulmonary bypass (CPB) was the exception. Intraoperative bleeding in this patient was associated with lower-than-expected blood levels of FXIII.

CONCLUSION

Preoperative plasma-derived FXIII concentrate allowed for sufficient hemostasis in most patients with FXIII deficiencies. Additional doses were necessary to achieve hemostasis in one patient who underwent a CPB procedure.

Coagulation factor XIII deficiency. Diagnosis, prevalence and management of inherited and acquired forms

The plasma circulating zymogenic coagulation factor XIII (FXIII) is a protransglutaminase, which upon activation by thrombin and calcium cross-links preformed fibrin clots/fibrinolytic inhibitors making them mechanically stable and less susceptible to fibrinolysis. The zymogenic plasma FXIII molecule is a heterotetramer composed of two catalytic FXIII-A and two protective FXIII-B subunits. Factor XIII deficiency resulting from inherited or acquired causes can result in pathological bleeding episodes. A diverse spectrum of mutations have been reported in the F13A1 and F13B genes which cause inherited severe FXIII deficiency. The inherited severe FXIII deficiency, which is a rare coagulation disorder with a prevalence of 1 in 4 million has been the prime focus of clinical and genetic investigations owing to the severity of the bleeding phenotype associated with it. Recently however, with a growing understanding into the pleiotropic roles of FXIII, the fairly frequent milder form of FXIII deficiency caused by heterozygous mutations has become one of the subjects of investigative research. The acquired form of FXIII deficiency is usually caused by generation of autoantibodies or hyperconsumption in other disease states such as disseminated intravascular coagulation. Here, we update the knowledge about the pathophysiology of factor XIII deficiency and its therapeutic options.

Factor XIII deficiency: complete phenotypic characterization of two cases with novel causative mutations

Coagulation factor XIII (FXIII) exists as heterotetramer (FXIII-A₂B₂) in the plasma and as dimer (FXIII-A₂) in cells. Activated FXIII mechanically stabilizes fibrin and protects it from fibrinolysis by cross-linking fibrin chains and α₂-plasmin inhibitor to fibrin. FXIII is essential to maintaining haemostasis, and its deficiency causes severe bleeding diathesis. Due to improper laboratory practices, FXIII deficiency is considered the most under-diagnosed bleeding disorder. The aim of this study was to demonstrate in two cases how FXIII deficiency is properly diagnosed and classified, and to compare results of laboratory analysis and clinical symptoms. FXIII activity from plasma and platelets was measured by a modified ammonia release assay, while FXIII-A₂B₂, FXIII-A and FXIII-B antigens were determined by ELISA. The exon-intron boundaries and the promoter region of F13A1 gene were amplified by PCR and the amplified products were analysed by direct fluorescent sequencing. FXIII-A mRNA in platelets was determined by RT-qPCR. Two children with severe bleeding symptoms were investigated. In both cases FXIII activity and FXIII-A antigen were undetectable in the plasma and platelet lysate. In the plasma no FXIII-A₂B₂ antigen was found, while FXIII-B antigen was >30% in both cases. Proband1 was a compound heterozygote possessing a known missense mutation (c.980G>A, p.Arg326Gln) and a novel splice-site mutation (c.1112+2T>C). Proband2 was homozygote for a novel single nucleotide deletion (c.212delA) leading to early stop codon. The discovered mutations explain the severity of clinical symptoms and the laboratory data. Methods precise in the low activity/antigen range are required to draw valid conclusion on phenotype-genotype relationship.

Factor XIIIa generation assay: a tool for studying factor XIII function in plasma

Triggering the extrinsic coagulation pathway in plasma and using a fluorogenic factor XIIIa (FXIIIa) substrate for continuously monitoring FXIIIa activity, an FXIIIa generation curve is obtained. The parameters area under the curve (AUC), time to peak (TTP), and concentration at peak (CP) were calculated. In dilutions of normal plasma in FXIII-deficient plasma, AUC and CP showed linear dose-response relationships, whereas TTP increased from 9.9 min for 25% FXIII to 11.6 min for 100% FXIII. Three FXIII-A preparations (rFXIII, rFXIII(V34L), and cellular FXIII [cFXIII]) showed a linear dose response for AUC and CP. The TTP increased slightly for rFXIII from 13.5 to 15.0 min, but surprisingly for cFXIII TTP increased concentration dependently from 13.5 to 28.7 min. Adding 5 μg/ml FXIII-B at a concentration of 1U of FXIII-A increased the AUC for rFXIII(V34L) and cFXIII by approximately 20% and accelerated TTP from 27.3 to 20.8 min for cFVIII, indicating a supportive function of FXIII-B in orientating cFXIII-A for thrombin cleavage. A commercial assay quantifying FXIII after complete activation in a restricted time window did not reveal differences in the cFXIII preparation with or without FXIII-B. The FXIIIa generation assay provides additional information about activation and function of FXIII. This advantage was underlined in experiments with an irreversible FXIIIa inhibitor.