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Prophylaxis in rare coagulation disorders — Factor XIII deficiency
Thrombosis Research (2006) 118S1, S23 — S28
intl.elsevierhealth.com/journals/thre
REGULAR ARTICLE
Prophylaxis in rare coagulation disorders — Factor XIII deficiency Diane J. Nugent * Division of Hematology, Hemostasis/Thrombosis Research, Children’s Hospital of Orange County, Orange, CA 92868, USA Received 1 February 2006; received in revised form 1 February 2006; accepted 6 February 2006
KEYWORDS Coagulation; Factor XIII; Factor XIII concentrate; Haemorrhage; Prophylaxis
Abstract Factor XIII (FXIII) deficiency is a very rare form of haemophilia resulting in different manifestations of bleeding disorders, but characterised by umbilical stump bleeding in up to 80% of patients. Although originally described as the final enzyme in the clotting cascade, FXIII is now recognised to play a role throughout the clotting process. Treatment with FXIII concentrate (Fibrogammin PR, ZLB Behring) results in the re-establishment of a normal clotting pattern. Prophylaxis studies in France and the USA have demonstrated an excellent response following monthly prophylaxis with this plasma-derived, pasteurised concentrate. Patients with FXIII deficiency have good control of bleeding, with no development of inhibitors, or viral seroconversion. The development of registries such as that in the USA will enable the different manifestations of the disease to be explored. D 2006 Published by Elsevier Ltd.
The clinical relevance of Factor XIII (FXIII) deficiency was described in 1960, following its discovery 16 years earlier. It represents a very rare form of haemophilia that occurs in only one in 3—5 million individuals. FXIII is traditionally described as the final enzyme in the coagulation cascade and is essential for normal haemostasis [1]. Although it was originally described as a fibrin stabilisation factor, knowledge continues to evolve regarding
Abbreviations: FXIII, Factor XIII. * Tel.: +1 714 532 8459; fax: +1 714 532 8771. E-mail address: [email protected]. 0049-3848/$ - see front matter D 2006 Published by Elsevier Ltd. doi:10.1016/j.thromres.2006.02.009
this protein, and it is becoming evident that FXIII plays a role throughout the clotting process. In this presentation, current knowledge about FXIII is reviewed, and details of the ongoing prophylaxis study in the USA are presented.
Natural course of FXIII deficiency Umbilical cord bleeding is the most common manifestation of FXIII deficiency, occurring in up to 80% of patients. The recognition of this characteristic feature in the newborn period is a presenting feature for FXIII deficiency, and a vital
S24 clue for additional specific investigations [2]. Poor wound healing occurs in about 20% of patients with FXIII deficiency. FXIII appears to be vital for haemostasis in the brain, and the incidence of intracranial haemorrhage has been reported in 25—60% of patients, a frequency much higher than that seen in any other congenital bleeding disorder, including the most severe haemophilias and type 3 von Willebrand disease. This manifestation of the disorder represents a significant threat to life and can also result in significant morbidity. There is a very high rate of recurrence in patients who do not receive appropriate prophylaxis. Mucous membrane bleeding and surgical bleeding have also been observed, but are often delayed, probably due to poor clot stability. Moreover, the rate of miscarriage is very high in women with the disorder [3]. It has become evident that the manifestations of FXIII deficiency vary greatly and may not necessarily be characterised by bleeding disorders. The establishment of registries will play an important role in the discovery of these different manifestations.
Structure of FXIII Circulating in plasma, the FXIII molecule is composed of four proteins: two A subunits that contain the catalytic component, activation peptide, and the substrate recognition regions [4], and two B subunits, which bind to the A2 subunits to modulate the survival of these enzymatically active units [5]. Scanning electron microscopy studies have demonstrated the globular form of the A subunits, with the surrounding B subunit depicted as a fibular structure. FXIII plays a role throughout the clotting process. It increases the tensile strength and integrity of the fibrin clot by covalently crosslinking fibrin, fibrinogen and possibly platelet integrin and other molecules. Anti-plasmin inhibitors are also incorporated in the clot by crosslinking. The mechanically stronger clot is more resistant to fibrinolytic enzymes. When thrombin, fibrin and factor XIII complex, the cleavage of the A2 chains is accelerated, thus initiating the Factor XIII activation and facilitating the binding of FXIII to fibrinogen, mainly via the B subunits. The fibrinogen molecule itself can also modify A2 subunit survival. In the final step, calcium activation results in release of the B2 subunits, resulting in the full activation of the enzyme after thrombin cleavage [6]. FXIII is not only found as the A2B2 complex in plasma but also as the A2 enzymatic
D.J. Nugent form in monocytes and platelets, where it interacts with cytoskeletal integrins and matrix proteins. In addition, the enzymatic form is found in placental tissue where it is involved in the maintenance of pregnancy, although the mechanism involved remains unknown.
Degree of heterogeneity in FXIII deficiency The molecular basis of FXIII deficiency is characterised by a high degree of heterogeneity. Different areas of the protein are responsible for different activities of FXIII, and as such, different deletions result in different manifestations of the disease. The heterogeneity of mutations and deletions responsible for FXIII deficiency is demonstrated in Fig. 1. Different deletions or mutations in the subunit A gene may affect thrombin activation, B subunit binding, or calcium activation. This may explain the heterogeneity observed in Factor XIII deficient patients and why some patients may have wound healing problems while others have umbilical cord bleeding or intracranial haemorrhage. Very small changes in gene function may also be responsible for large differences in function. An important example is the Val/Leu polymorphism in position 34. This single amino acid substitution may be associated with increased thrombosis, and a dramatic difference in cross-linking of fibrinogen has been demonstrated between clots made from plasma samples homozygous for each Val34Leu allele. Fibrin clots formed in the presence of Leu34 FXIII have thinner fibres, more branching with smaller pores, and denser permeation, compared with fibrin clots formed in the presence of the Val34 variant. This substitution is currently being investigated as a possible pro-thrombotic risk factor [7]. Several other proteins have also been identified that are substrates for FXIII and targets for crosslinking. These are listed in Table 1, representing proteins important in coagulation and fibrinolysis, adhesive proteins, and contractile or cytoskeletal proteins.
Clot generation in normal and FXIII-deficient individuals The generation of a clot can be represented in a thromboeslastograph. A series of thromboelastographs is shown in Fig. 2. In Fig. 2A, the normal
Prophylaxis in rare coagulation disorders—factor XIII deficiency
Figure 1
Known SNP mutations in Factor XIII, subunit A gene. Adapted from [5].
pattern of clot generation is presented. The size of the clot is represented by the amplitude. The pattern of clot generation in a FXIII-deficient patient (Fig. 2B) is characterized by less clot formation, and a weaker clot that is more easily degraded. The slope of the shoulder, representing the rapidity of clot formation, is markedly changed in the FXIII-deficient individual. After treatment with FXIII concentrate (Fibrogammin PR, 20U/kg), a normal clotting pattern is restored, as demonstrated in Fig. 2C.
Prophylaxis for FXIII deficiency Treatment with FXIII concentrate (Fibrogammin PR) results in the re-establishment of a normal clotting pattern. Other products that have been used in the treatment of FXIII deficiency include fresh-frozen plasma and cryoprecipitate, but such products are unsatisfactory due to the risk of blood-borne diseases, such as hepatitis, HIV, and most recently, West Nile virus. Fibrogammin PR is a highly purified, heat-treated lyophilisate obtained from fresh-frozen plasma that can be administered every 4—6 weeks due to its excellent long half-life (5—11 days). Fibrogammin PR is not currently licensed in the USA, but is approved in
Table 1
S25
several other countries including Japan, Germany and the UK. It is recommended at a dose of 10U/kg as prophylaxis, with higher doses of up to 35U/kg prior to surgical procedures. In addition to the treatment or prophylaxis of bleeding disorders associated with FXIII deficiency, Fibrogammin PR has been administered to patients with inflammatory bowel disease, with improvement of bleeding symptoms. In patients with acquired FXIII deficiency, levels of the protein have been found to be very low. Acquired FXIII deficiency is also found in patients following cardio-pulmonary bypass. The first multicentre, prospective study of Fibrogammin PR was conducted in France in 19 patients from 15 centres who were treated for over 2 years [8]. Replacement therapy with Fibrogammin PR was well tolerated and showed a favourable safety profile. The study population was comprised of 14 males and 5 females (a ratio of approximately 3:1), with a mean age of 17 years at inclusion (range 0.05—46.9 years). Sixteen patients received regular infusions during 19—108 weeks, and there were no major bleeds. Response was defined as good to excellent. Patients were followed up for 12—25 months after inclusion and untoward side effects were reported in only two patients: one headache related to menses and one transient urticarial
Substrates for Factor XIII (high affinity for fibrinogen)
Proteins important in coagulation and fibrinolysis
Adhesive proteins
! Factor V ! Plasminogen activator inhibitor-2 ! Alpha-2 anti-plasmin
! ! ! !
Fibronectin Vitronectin von Willebrand Factor Thrombospondin
Contractile/cytoskeletal proteins ! Vinculin ! Heat shock protein 27
S26
D.J. Nugent
Figure 2 Thromboelastographs from a normal individual (A) and a patient with Factor XIII (FXIII) deficiency before (B), and after (C), treatment with FXIII concentrate.
reaction. No patients developed detectable antiFXIII inhibitor [8].
Fibrogammin PR prophylaxis study A prophylaxis programme with Fibrogammin PR has been underway for almost 5 years in patients with congenital FXIII deficiency. The programme involves 61 patients from 50 centres throughout the USA. Thirty-nine patients have been included from a previous Fibrogammin PR compassionateuse study, resulting in a total follow-up time for
some patients of more than 8 years. All patients have been accrued through physician referral and all have Institutional Review Board (IRB) approval. The mean age of the patients is 12.7 years (range 1—74, median 15 years) and the population includes 44 males and 17 females, approaching the 3:1 ratio observed in the French study. Limited pharmacokinetic and inhibitor studies have been performed due to distance constraints in the transport of samples. Samples have been collected at baseline, day 14, and day 28. Calculation of the circulating half-life was based on the Berichrom assay (Dade
Prophylaxis in rare coagulation disorders—factor XIII deficiency Behring). The data of primary interest were the first 12 months on study, but assessment of inhibitors and seroconversion continues. All patients in the study receive prophylaxis monthly. There have been no major bleeds during prophylaxis, although there have been bleeds in 5 patients non-compliant with treatment, who had not received Fibrogammin PR for at least 2 months prior to the bleeding episode. The response to therapy has been good to excellent, and no inhibitors to FXIII have developed, including a patient who underwent tolerance induction prior to entry to the study. It is important to note that no seroconversions have been observed during therapy. Many patients were positive for hepatitis C on entry to the study, but there have been no seroconversions on treatment. The half-life of FXIII following administration of Fibrogammin PR has been similar to that observed for patients administered FXIII in fresh-frozen plasma or cryoprecipitate. Adverse events include headache and some myalgias, but none severe. There have been two deaths on study, both unrelated to the underlying bleeding disorder or to FXIII replacement. Recruitment to the study is ongoing, with continuing assessment of adverse events, serious adverse events, and inhibitor conversion. The pharmacokinetics of FXIII over 28 days is presented in Fig. 3. The upper curve represents the normal control levels of FXIII measured as Factor XIII activities. The lower curve shows the FXIII activities prior to and at various time points following the infusion of Fibrogammin PR. The
S27
limit of detection of FXIII is 5—10%, based on the specificity and sensitivity of the Berichrom assay used. The increase in FXIII levels in the first 24 hours in the FXIII-deficient patient following Fibrogammin PR infusion increased endogenous B subunit production or possibly, to stabilisation of the tetramer with fibrinogen in tissue or on the platelet. It may also reflect mobilisation of FXIII within the platelets, as 50% of circulating FXIII is carried within platelets in normal individuals. The structure—function relationship of the FXIII molecule has implications for levels of the circulating protein and for initiation of, and dosing levels in, prophylaxis. In 17% of patients, for example, the abnormality is in the B subunit, and in these patients, survival of the FXIII molecule will be shorter. Some patients may also have higher levels of FXIII A2 in the platelets, with none or little circulating free in the plasma. Another consideration in the analysis of FXIII in the plasma is the striking variation in results obtained from different assays, for example the Berichrom and the clot solubility assay. Unlike the Berichrom assay, the clot solubility assay is dependent upon endogenous thrombin; thus abnormalities in thrombin binding may also play a part in these differences.
Conclusion In conclusion, the response to prophylaxis with FXIII has been excellent, without the development of inhibitors, nor evidence of seroconversion. FXIII
Figure 3 Pharmacokinetics (PK) of Factor XIII (FXIII) in patients from the US prophylaxis study. OD, optical density; Per Inf, pre-infusion. The ELISA is not as helpful in this setting as the polyclonal reagents will detect the B subunit even in the absence of the A subunits.
S28 administered as Fibrogammin PR represents a convenient means of administration for patients and families with low risk for blood-borne diseases. There is also a decreased risk of allergic reactions or sensitisation to other plasma proteins compared with other sources of FXIII. The study continues in the USA.
Acknowledgements With special acknowledgement of the contribution of Dr. Amy Lovejoy and Dr. Jorge DiPaola as fellows and now colleagues in the community caring for patients with Factor XIII deficiency. In addition, special recognition is given to Kathy Birschbach, Marianne McDaniel, Christine Nguyen and Vicki Giraldin whose continual support and dedication have changed the lives of our patients with bleeding disorders. Many thanks to Dr. Sandra Cox for her excellent writing and editorial input in all aspects of this report.
References [1] Lorand L, Losowsky MS, Miloszewski K. Human factor XIII: fibrin stabilizing factor. In: Spaet TH, editor. Progress in Haemostasis and Thrombosis, vol. 5. New York, NY7 Grune and Stratton Inc;, 1980. p. 245 – 89.
D.J. Nugent [2] Anwar R, Minford A, Gallivan L, Trinh CH, Markham AF. Delayed umbilical bleeding — a presenting feature for factor XIII deficiency: clinical features, genetics, and management. Pediatrics 2002;109:32 – 8. [3] Anwar R, Miloszewski KJ. Factor XIII deficiency. Br J Haematol 1999;107:468 – 84. [4] Yee VC, Pedersen LC, Le Trong I, Bishop PD, Stenkamp RE, Teller DC. Three-dimensional structure of a transglutaminase: human blood coagulation factor XIII. Proc Natl Acad Sci 1994;91:7296 – 300. [5] Ichinose A. Physiopathology and regulation of factor XIII. Thromb Haemost 2001;86:57 – 65. [6] Arie ¨ns RAS, Lai T-S, Weisel JW, Greenberg CS, Grant PJ. Role of factor XIII in fibrin clot formation and effects of genetic polymorphisms. Blood 2002;100:743 – 54. [7] Arie ¨ns RA, Philippou H, Nagaswami C, Weisel JW, Lane DA, Grant PJ. The factor XIII V34L polymorphism accelerates thrombin activation of factor XIII and affects cross-linked fibrin structure. Blood 2000;96:988 – 95. [8] Dreyfus M, Arnuti B, Beurrier P, Borg JY, Clayssens S, Girardel JM, et al. Safety and efficacy of Fibrogammin PR for the treatment of patients with severe FXIII deficiency. J Thromb Haemost 2003;1(S1):P0299 [Abstract].
intl.elsevierhealth.com/journals/thre
REGULAR ARTICLE
Prophylaxis in rare coagulation disorders — Factor XIII deficiency Diane J. Nugent * Division of Hematology, Hemostasis/Thrombosis Research, Children’s Hospital of Orange County, Orange, CA 92868, USA Received 1 February 2006; received in revised form 1 February 2006; accepted 6 February 2006
KEYWORDS Coagulation; Factor XIII; Factor XIII concentrate; Haemorrhage; Prophylaxis
Abstract Factor XIII (FXIII) deficiency is a very rare form of haemophilia resulting in different manifestations of bleeding disorders, but characterised by umbilical stump bleeding in up to 80% of patients. Although originally described as the final enzyme in the clotting cascade, FXIII is now recognised to play a role throughout the clotting process. Treatment with FXIII concentrate (Fibrogammin PR, ZLB Behring) results in the re-establishment of a normal clotting pattern. Prophylaxis studies in France and the USA have demonstrated an excellent response following monthly prophylaxis with this plasma-derived, pasteurised concentrate. Patients with FXIII deficiency have good control of bleeding, with no development of inhibitors, or viral seroconversion. The development of registries such as that in the USA will enable the different manifestations of the disease to be explored. D 2006 Published by Elsevier Ltd.
The clinical relevance of Factor XIII (FXIII) deficiency was described in 1960, following its discovery 16 years earlier. It represents a very rare form of haemophilia that occurs in only one in 3—5 million individuals. FXIII is traditionally described as the final enzyme in the coagulation cascade and is essential for normal haemostasis [1]. Although it was originally described as a fibrin stabilisation factor, knowledge continues to evolve regarding
Abbreviations: FXIII, Factor XIII. * Tel.: +1 714 532 8459; fax: +1 714 532 8771. E-mail address: [email protected]. 0049-3848/$ - see front matter D 2006 Published by Elsevier Ltd. doi:10.1016/j.thromres.2006.02.009
this protein, and it is becoming evident that FXIII plays a role throughout the clotting process. In this presentation, current knowledge about FXIII is reviewed, and details of the ongoing prophylaxis study in the USA are presented.
Natural course of FXIII deficiency Umbilical cord bleeding is the most common manifestation of FXIII deficiency, occurring in up to 80% of patients. The recognition of this characteristic feature in the newborn period is a presenting feature for FXIII deficiency, and a vital
S24 clue for additional specific investigations [2]. Poor wound healing occurs in about 20% of patients with FXIII deficiency. FXIII appears to be vital for haemostasis in the brain, and the incidence of intracranial haemorrhage has been reported in 25—60% of patients, a frequency much higher than that seen in any other congenital bleeding disorder, including the most severe haemophilias and type 3 von Willebrand disease. This manifestation of the disorder represents a significant threat to life and can also result in significant morbidity. There is a very high rate of recurrence in patients who do not receive appropriate prophylaxis. Mucous membrane bleeding and surgical bleeding have also been observed, but are often delayed, probably due to poor clot stability. Moreover, the rate of miscarriage is very high in women with the disorder [3]. It has become evident that the manifestations of FXIII deficiency vary greatly and may not necessarily be characterised by bleeding disorders. The establishment of registries will play an important role in the discovery of these different manifestations.
Structure of FXIII Circulating in plasma, the FXIII molecule is composed of four proteins: two A subunits that contain the catalytic component, activation peptide, and the substrate recognition regions [4], and two B subunits, which bind to the A2 subunits to modulate the survival of these enzymatically active units [5]. Scanning electron microscopy studies have demonstrated the globular form of the A subunits, with the surrounding B subunit depicted as a fibular structure. FXIII plays a role throughout the clotting process. It increases the tensile strength and integrity of the fibrin clot by covalently crosslinking fibrin, fibrinogen and possibly platelet integrin and other molecules. Anti-plasmin inhibitors are also incorporated in the clot by crosslinking. The mechanically stronger clot is more resistant to fibrinolytic enzymes. When thrombin, fibrin and factor XIII complex, the cleavage of the A2 chains is accelerated, thus initiating the Factor XIII activation and facilitating the binding of FXIII to fibrinogen, mainly via the B subunits. The fibrinogen molecule itself can also modify A2 subunit survival. In the final step, calcium activation results in release of the B2 subunits, resulting in the full activation of the enzyme after thrombin cleavage [6]. FXIII is not only found as the A2B2 complex in plasma but also as the A2 enzymatic
D.J. Nugent form in monocytes and platelets, where it interacts with cytoskeletal integrins and matrix proteins. In addition, the enzymatic form is found in placental tissue where it is involved in the maintenance of pregnancy, although the mechanism involved remains unknown.
Degree of heterogeneity in FXIII deficiency The molecular basis of FXIII deficiency is characterised by a high degree of heterogeneity. Different areas of the protein are responsible for different activities of FXIII, and as such, different deletions result in different manifestations of the disease. The heterogeneity of mutations and deletions responsible for FXIII deficiency is demonstrated in Fig. 1. Different deletions or mutations in the subunit A gene may affect thrombin activation, B subunit binding, or calcium activation. This may explain the heterogeneity observed in Factor XIII deficient patients and why some patients may have wound healing problems while others have umbilical cord bleeding or intracranial haemorrhage. Very small changes in gene function may also be responsible for large differences in function. An important example is the Val/Leu polymorphism in position 34. This single amino acid substitution may be associated with increased thrombosis, and a dramatic difference in cross-linking of fibrinogen has been demonstrated between clots made from plasma samples homozygous for each Val34Leu allele. Fibrin clots formed in the presence of Leu34 FXIII have thinner fibres, more branching with smaller pores, and denser permeation, compared with fibrin clots formed in the presence of the Val34 variant. This substitution is currently being investigated as a possible pro-thrombotic risk factor [7]. Several other proteins have also been identified that are substrates for FXIII and targets for crosslinking. These are listed in Table 1, representing proteins important in coagulation and fibrinolysis, adhesive proteins, and contractile or cytoskeletal proteins.
Clot generation in normal and FXIII-deficient individuals The generation of a clot can be represented in a thromboeslastograph. A series of thromboelastographs is shown in Fig. 2. In Fig. 2A, the normal
Prophylaxis in rare coagulation disorders—factor XIII deficiency
Figure 1
Known SNP mutations in Factor XIII, subunit A gene. Adapted from [5].
pattern of clot generation is presented. The size of the clot is represented by the amplitude. The pattern of clot generation in a FXIII-deficient patient (Fig. 2B) is characterized by less clot formation, and a weaker clot that is more easily degraded. The slope of the shoulder, representing the rapidity of clot formation, is markedly changed in the FXIII-deficient individual. After treatment with FXIII concentrate (Fibrogammin PR, 20U/kg), a normal clotting pattern is restored, as demonstrated in Fig. 2C.
Prophylaxis for FXIII deficiency Treatment with FXIII concentrate (Fibrogammin PR) results in the re-establishment of a normal clotting pattern. Other products that have been used in the treatment of FXIII deficiency include fresh-frozen plasma and cryoprecipitate, but such products are unsatisfactory due to the risk of blood-borne diseases, such as hepatitis, HIV, and most recently, West Nile virus. Fibrogammin PR is a highly purified, heat-treated lyophilisate obtained from fresh-frozen plasma that can be administered every 4—6 weeks due to its excellent long half-life (5—11 days). Fibrogammin PR is not currently licensed in the USA, but is approved in
Table 1
S25
several other countries including Japan, Germany and the UK. It is recommended at a dose of 10U/kg as prophylaxis, with higher doses of up to 35U/kg prior to surgical procedures. In addition to the treatment or prophylaxis of bleeding disorders associated with FXIII deficiency, Fibrogammin PR has been administered to patients with inflammatory bowel disease, with improvement of bleeding symptoms. In patients with acquired FXIII deficiency, levels of the protein have been found to be very low. Acquired FXIII deficiency is also found in patients following cardio-pulmonary bypass. The first multicentre, prospective study of Fibrogammin PR was conducted in France in 19 patients from 15 centres who were treated for over 2 years [8]. Replacement therapy with Fibrogammin PR was well tolerated and showed a favourable safety profile. The study population was comprised of 14 males and 5 females (a ratio of approximately 3:1), with a mean age of 17 years at inclusion (range 0.05—46.9 years). Sixteen patients received regular infusions during 19—108 weeks, and there were no major bleeds. Response was defined as good to excellent. Patients were followed up for 12—25 months after inclusion and untoward side effects were reported in only two patients: one headache related to menses and one transient urticarial
Substrates for Factor XIII (high affinity for fibrinogen)
Proteins important in coagulation and fibrinolysis
Adhesive proteins
! Factor V ! Plasminogen activator inhibitor-2 ! Alpha-2 anti-plasmin
! ! ! !
Fibronectin Vitronectin von Willebrand Factor Thrombospondin
Contractile/cytoskeletal proteins ! Vinculin ! Heat shock protein 27
S26
D.J. Nugent
Figure 2 Thromboelastographs from a normal individual (A) and a patient with Factor XIII (FXIII) deficiency before (B), and after (C), treatment with FXIII concentrate.
reaction. No patients developed detectable antiFXIII inhibitor [8].
Fibrogammin PR prophylaxis study A prophylaxis programme with Fibrogammin PR has been underway for almost 5 years in patients with congenital FXIII deficiency. The programme involves 61 patients from 50 centres throughout the USA. Thirty-nine patients have been included from a previous Fibrogammin PR compassionateuse study, resulting in a total follow-up time for
some patients of more than 8 years. All patients have been accrued through physician referral and all have Institutional Review Board (IRB) approval. The mean age of the patients is 12.7 years (range 1—74, median 15 years) and the population includes 44 males and 17 females, approaching the 3:1 ratio observed in the French study. Limited pharmacokinetic and inhibitor studies have been performed due to distance constraints in the transport of samples. Samples have been collected at baseline, day 14, and day 28. Calculation of the circulating half-life was based on the Berichrom assay (Dade
Prophylaxis in rare coagulation disorders—factor XIII deficiency Behring). The data of primary interest were the first 12 months on study, but assessment of inhibitors and seroconversion continues. All patients in the study receive prophylaxis monthly. There have been no major bleeds during prophylaxis, although there have been bleeds in 5 patients non-compliant with treatment, who had not received Fibrogammin PR for at least 2 months prior to the bleeding episode. The response to therapy has been good to excellent, and no inhibitors to FXIII have developed, including a patient who underwent tolerance induction prior to entry to the study. It is important to note that no seroconversions have been observed during therapy. Many patients were positive for hepatitis C on entry to the study, but there have been no seroconversions on treatment. The half-life of FXIII following administration of Fibrogammin PR has been similar to that observed for patients administered FXIII in fresh-frozen plasma or cryoprecipitate. Adverse events include headache and some myalgias, but none severe. There have been two deaths on study, both unrelated to the underlying bleeding disorder or to FXIII replacement. Recruitment to the study is ongoing, with continuing assessment of adverse events, serious adverse events, and inhibitor conversion. The pharmacokinetics of FXIII over 28 days is presented in Fig. 3. The upper curve represents the normal control levels of FXIII measured as Factor XIII activities. The lower curve shows the FXIII activities prior to and at various time points following the infusion of Fibrogammin PR. The
S27
limit of detection of FXIII is 5—10%, based on the specificity and sensitivity of the Berichrom assay used. The increase in FXIII levels in the first 24 hours in the FXIII-deficient patient following Fibrogammin PR infusion increased endogenous B subunit production or possibly, to stabilisation of the tetramer with fibrinogen in tissue or on the platelet. It may also reflect mobilisation of FXIII within the platelets, as 50% of circulating FXIII is carried within platelets in normal individuals. The structure—function relationship of the FXIII molecule has implications for levels of the circulating protein and for initiation of, and dosing levels in, prophylaxis. In 17% of patients, for example, the abnormality is in the B subunit, and in these patients, survival of the FXIII molecule will be shorter. Some patients may also have higher levels of FXIII A2 in the platelets, with none or little circulating free in the plasma. Another consideration in the analysis of FXIII in the plasma is the striking variation in results obtained from different assays, for example the Berichrom and the clot solubility assay. Unlike the Berichrom assay, the clot solubility assay is dependent upon endogenous thrombin; thus abnormalities in thrombin binding may also play a part in these differences.
Conclusion In conclusion, the response to prophylaxis with FXIII has been excellent, without the development of inhibitors, nor evidence of seroconversion. FXIII
Figure 3 Pharmacokinetics (PK) of Factor XIII (FXIII) in patients from the US prophylaxis study. OD, optical density; Per Inf, pre-infusion. The ELISA is not as helpful in this setting as the polyclonal reagents will detect the B subunit even in the absence of the A subunits.
S28 administered as Fibrogammin PR represents a convenient means of administration for patients and families with low risk for blood-borne diseases. There is also a decreased risk of allergic reactions or sensitisation to other plasma proteins compared with other sources of FXIII. The study continues in the USA.
Acknowledgements With special acknowledgement of the contribution of Dr. Amy Lovejoy and Dr. Jorge DiPaola as fellows and now colleagues in the community caring for patients with Factor XIII deficiency. In addition, special recognition is given to Kathy Birschbach, Marianne McDaniel, Christine Nguyen and Vicki Giraldin whose continual support and dedication have changed the lives of our patients with bleeding disorders. Many thanks to Dr. Sandra Cox for her excellent writing and editorial input in all aspects of this report.
References [1] Lorand L, Losowsky MS, Miloszewski K. Human factor XIII: fibrin stabilizing factor. In: Spaet TH, editor. Progress in Haemostasis and Thrombosis, vol. 5. New York, NY7 Grune and Stratton Inc;, 1980. p. 245 – 89.
D.J. Nugent [2] Anwar R, Minford A, Gallivan L, Trinh CH, Markham AF. Delayed umbilical bleeding — a presenting feature for factor XIII deficiency: clinical features, genetics, and management. Pediatrics 2002;109:32 – 8. [3] Anwar R, Miloszewski KJ. Factor XIII deficiency. Br J Haematol 1999;107:468 – 84. [4] Yee VC, Pedersen LC, Le Trong I, Bishop PD, Stenkamp RE, Teller DC. Three-dimensional structure of a transglutaminase: human blood coagulation factor XIII. Proc Natl Acad Sci 1994;91:7296 – 300. [5] Ichinose A. Physiopathology and regulation of factor XIII. Thromb Haemost 2001;86:57 – 65. [6] Arie ¨ns RAS, Lai T-S, Weisel JW, Greenberg CS, Grant PJ. Role of factor XIII in fibrin clot formation and effects of genetic polymorphisms. Blood 2002;100:743 – 54. [7] Arie ¨ns RA, Philippou H, Nagaswami C, Weisel JW, Lane DA, Grant PJ. The factor XIII V34L polymorphism accelerates thrombin activation of factor XIII and affects cross-linked fibrin structure. Blood 2000;96:988 – 95. [8] Dreyfus M, Arnuti B, Beurrier P, Borg JY, Clayssens S, Girardel JM, et al. Safety and efficacy of Fibrogammin PR for the treatment of patients with severe FXIII deficiency. J Thromb Haemost 2003;1(S1):P0299 [Abstract].