Movement behaviour in adults with haemophilia compared to healthy adults.

BACKGROUND: Limited research has been published regarding movement behaviour of adult persons with haemophilia (PWH). It is hypothesized that avoidance of activities and more sedentary behaviour cause poorer physical functioning. AIM: To determine differences in movement behaviour between PWH and healthy adults. METHODS: Movement behaviour was measured with an accelerometer distinguishing between; lying/non-wear, sitting, standing, walking, running and cycling. Time spent on activities was compared between PWH and healthy adults, using absolute time spent on activities and activities as percentage of wear time. RESULTS: One hundred and five PWH (32 mild/moderate with a mean age of 42.8 ± 15.1, severe 42.1 ± 13.6) and 98 healthy adults (mean age 41.9 ± 15.5) showed that adults with severe haemophilia sit and stand more than healthy adults (4.5 [CI 0.6-8.4] and 4.2 [CI 1.8-6.6] h/wk, respectively) and walk and run less (3.4 [CI 1.4-5.3] hours and 33.6 [CI 19.0-41.7] min/wk, respectively). Patients with mild/moderate haemophilia stand more than healthy adults (3.3 [CI 0.1-6.4] h/wk). Differences in sitting between severe haemophilia and healthy adults and differences in standing between mild/moderate haemophilia and healthy adults disappeared when using activities as percentage of wear time. CONCLUSION: Movement behaviour of adults with severe haemophilia differs from healthy adults, mainly due to less walking and less running. No differences were found in other activities and postures or the distribution of movement behaviour over the day. No significant differences were found between adults with mild/moderate haemophilia and healthy adults.

Measuring activities and participation in persons with haemophilia: A systematic review of commonly used instruments.

INTRODUCTION: Monitoring clinical outcome in persons with haemophilia (PWH) is essential in order to provide optimal treatment for individual patients and compare effectiveness of treatment strategies. Experience with measurement of activities and participation in haemophilia is limited and consensus on preferred tools is lacking. AIM: The aim of this study was to give a comprehensive overview of the measurement properties of a selection of commonly used tools developed to assess activities and participation in PWH. METHODS: Electronic databases were searched for articles that reported on reliability, validity or responsiveness of predetermined measurement tools (5 self-reported and 4 performance based measurement tools). Methodological quality of the studies was assessed according to the COSMIN checklist. Best evidence synthesis was used to summarize evidence on the measurement properties. RESULTS: The search resulted in 3453 unique hits. Forty-two articles were included. The self-reported Haemophilia Acitivity List (HAL), Pediatric HAL (PedHAL) and the performance based Functional Independence Score in Haemophilia (FISH) were studied most extensively. Methodological quality of the studies was limited. Measurement error, cross-cultural validity and responsiveness have been insufficiently evaluated. CONCLUSION: Albeit based on limited evidence, the measurement properties of the PedHAL, HAL and FISH are currently considered most satisfactory. Further research needs to focus on measurement error, responsiveness, interpretability and cross-cultural validity of the self-reported tools and validity of performance based tools which are able to assess limitations in sports and leisure activities.

Differential effects of bleeds on the development of arthropathy - basic and applied issues.

Haemophilia is characterized by a spontaneous bleeding tendency, affecting mainly the synovial joints. Recurrent joint bleeds induce a cascade of inflammatory as well as degenerative processes injuring synovium, cartilage and bone. These processes affect each other and may occur in parallel and/or sequentially. Clinically, the effects of joint bleeds are heterogeneous. A marked variability in joint damage is observed in patients with a similar bleeding history. Also late stage effects differ with some patients developing chronic synovitis, and others suffering from osteochondral degeneration called haemophilic arthropathy. This article reviews the current understanding of the pathogenesis of blood-induced joint damage, elaborates on potential explanations for the differential effects of a bleed, and discusses challenges for future research.

Long-term effects of joint bleeding before starting prophylaxis in severe haemophilia.

INTRODUCTION: Early initiation of prophylaxis in severe haemophilia is critical for effective prevention of arthropathy. However, the optimum time for starting prophylaxis has not been established yet. AIM: This study assessed long-term effects of age at starting prophylaxis and joint bleeding before prophylaxis on haemophilic arthropathy. METHODS: In patients with severe haemophilia (FVIII/IX <0.01 IU mL-1 ), born between 1965 and 2000, haemophilic arthropathy was evaluated on X-rays. Patient groups were compared by multivariable regression analysis, adjusted for bleeding phenotype and lifetime intensity of prophylaxis. RESULTS: One hundred and twenty-four patients were evaluated at a median age of 22 years. When comparing patients according to age at starting prophylaxis, starting before age 6 years was significantly better than starting later (P < 0.01), but no additional benefit of starting before age 3 years was demonstrated. The number of joint bleeds before prophylaxis had a stronger association with arthropathy than age at starting prophylaxis. Starting prophylaxis before the onset of joint bleeding resulted in the best long-term outcome (P ≤ 0.02); starting after one joint bleed appeared to have acceptable long-term outcome. The difference between starting after 0-1 and 2-5 joint bleeds was notable, but statistical significance was not reached (P = 0.15). CONCLUSION: Future research with more patients on early prophylaxis will have to clarify whether starting prophylaxis before joint bleeding is superior.

Silencing of protease-activated receptors attenuates synovitis and cartilage damage following a joint bleed in haemophilic mice.

INTRODUCTION AND AIM: Joint bleeding results in blood-induced arthropathy. We investigate whether a joint bleed alters protease-activated receptor (PAR) expression, and whether treatment with small interfering RNA (siRNA) targeted against PAR1-4 attenuates synovitis and cartilage damage. METHODS: Protease-activated receptor expression was evaluated upon a joint bleed in haemophilic mice and in humans. In addition, mice with a joint bleed were randomized between treatment with PAR1-4 siRNA or control and evaluated for the presence of synovitis and cartilage damage. Also, human cartilage was transfected with PAR1-4 siRNA or control, and evaluated for plasmin-induced cartilage damage. RESULTS: Following a joint bleed, we observed an increase in synovial PAR1, -2 and -4 expression, and an increase in chondrocyte PAR2 and -3 expression in mice (all P < 0.05). Also an increase in synovial PAR1 and chondrocyte PAR4 expression in patients was observed (both P < 0.05). Treatment of a joint bleed in haemophilic mice with PAR1-4 siRNA attenuates synovitis and cartilage damage (both P < 0.01). Treatment of human cartilage tissue explants with PAR1-4 siRNA reduced plasmin-induced cartilage damage (P < 0.01). CONCLUSION: This study demonstrates that synovial and chondrocyte PAR expression is altered upon a joint bleed, and that treatment with PAR1-4 siRNA attenuates synovitis and plasmin-induced cartilage damage.

How do patients and professionals differentiate between intra-articular joint bleeds and acute flare-ups of arthropathy in patients with haemophilia?

INTRODUCTION: The overlap in symptoms between joint bleeds and flare-ups of haemophilia arthropathy (HA) creates difficulties in differentiating between the two conditions. Diagnosis of haemarthrosis is currently empirically made based upon clinical presentations. However, no standard diagnostic criteria are available. To offer appropriate treatment, rapid and accurate diagnosis is essential. Additionally, adequate differentiation can decrease health costs significantly. AIM: The aim of this study was to identify signs and symptoms to differentiate between an intra-articular joint bleed and an acute flare-up of HA in patients with haemophilia and make an initial proposal of items to include in a diagnostic criteria set. METHODS: Six focus group interviews with a total of 13 patients and 15 professionals were carried out. The focus groups were structured following the Nominal Group Technique (NGT). RESULTS: The most important signs and symptoms used to differentiate between joint bleeds and HA were (i) course of the symptoms, (ii) cause of the complaints, (iii) joint history, (iv) type of pain and (v) degree of impairments in range of motion. CONCLUSION: This qualitative study provides insight into signs and symptoms that are currently used to differentiate between joint bleeds and flare-ups of HA. Results of this study can be used to develop a valid and standardized clinical diagnostic criteria set to differentiate between these two conditions. Further research is necessary to validate the signs and symptoms found in this study.

Joint surgery in von Willebrand disease: a multicentre cross-sectional study.

BACKGROUND: Joint bleeds are reported by 23% of von Willebrand disease (VWD) patients and associated with orthopaedic surgery. Limited data are available on joint surgery in VWD. AIM: To assess the prevalence, indications, management and complications of joint surgery in VWD patients. METHODS: 804 VWD patients with historically lowest von Willebrand factor (VWF) activity ≤30 U dL-1 completed a questionnaire on joint bleeds, joint damage and orthopaedic surgery. We retrieved additional medical file data of patients who underwent surgery on large joints (shoulder, elbow, hip, knee or ankle). RESULTS: 116 out of 804 patients (14%) reported large joint surgery. Compared to VWD patients without previous orthopaedic surgery, these 116 patients reported more frequently a history of joint bleeds and joint damage (41% vs. 20%, P < 0.001 and 61% vs. 20%, P < 0.001). Medical file data on 126 large joint surgeries in 79 VWD patients revealed that this surgery was associated with joint damage due to prior joint bleeds in 24% of the procedures. Preoperative clotting factor correction (CFC) to prevent bleeding was administered in most cases (81%). Documentation on postoperative bleeding was found in 23 surgeries (18%). CONCLUSIONS: Large joint surgery is reported by 14% of VWD patients, related to joint bleeds in 24% and seems associated with bleeding complications frequently despite perioperative CFC.

Biochemical markers of joint tissue damage increase shortly after a joint bleed; an explorative human and canine in vivo study.

OBJECTIVE: Evaluation whether biomarkers of joint damage are sensitive to change shortly after a joint bleed in hemophilia patients and in a canine model of blood-induced joint damage. METHODS: Blood and urine samples were collected from 10 hemophilia patients after they reported a joint bleed: within 2 days, after 3-5 days, and 12-14 days. Additionally, 90 days after the bleed a blood and urine sample was taken and considered to represent baseline condition. Commercial serum and urine biomarker assays were performed: urinary C-terminal telopeptide of type II collagen (uCTX-II), serum cartilage oligomeric matrix protein (sCOMP), serum cartilage cleavage product C1,2C, and serum chondroitin sulfate 846 (sCS846). The same panel of biomarkers was explored in dogs (n = 7) after induction of a first joint bleed by intra-articular blood injections. Biosamples were collected at baseline, day 2, 1 and 2 weeks later. RESULTS: In hemophilia patients, levels of uCTX-II and sCS846 increased 5 days after joint bleeding when compared with baseline (+52%; P = 0.021 and +14%; P = 0.011, respectively). In dogs, uCTX-II increased statistically significant from day 2 to day 7 (from 75% to 155% of baseline; P = 0.018), and sCOMP from baseline to day 2 (+46%; P = 0.028). CONCLUSIONS: This study demonstrates that biochemical markers of joint tissue damage increase shortly after a single joint bleed, both in humans with established hemophilic arthropathy (HA) and in an animal model of joint damage upon a first joint bleed. Biomarkers might be useful in monitoring the impact of a joint bleed and in evaluation of treatment of such bleeds.

Thalidomide for treatment of gastrointestinal bleedings due to angiodysplasia: a case report in acquired von Willebrand syndrome and review of the literature.

INTRODUCTION: Acquired von Willebrand syndrome is a rare bleeding disorder and treatment of the associated gastrointestinal (GI) bleeding due to angiodysplasia is challenging. AIM: The aim of this study was to present a new case on the successful use of thalidomide in a patient with acquired von Willebrand syndrome and recurrent angiodysplasia-related GI bleedings, and to conduct a literature review on the use of thalidomide in patients with GI angiodysplasia. METHODS: A literature review was conducted, searching the electronic databases PubMed, Embase and Cochrane. RESULTS: We present a 75-year-old woman with IgG MGUS-associated acquired von Willebrand syndrome (AVWS) who suffered from recurrent gastrointestinal (GI) bleedings and epistaxis. Treatment with immunoglobulins, desmopressin, Haemate-P and blood transfusions failed to achieve long-term haemostasis. Eventually, after these bleedings relapsed for almost a decade at 1- to 3-month intervals, thalidomide was prescribed. Since then, only one single nose bleed and one single melaena episode had occurred. She currently remains in remission of GI bleeds after 3 years and 3 months follow-up. The literature review revealed a beneficial effect of thalidomide in reducing GI bleeding due to angiodysplasia, including four case reports on inherited von Willebrand disease. CONCLUSION: In conclusion, thalidomide can be a reasonable option for the treatment of recurrent GI bleeding due to angiodysplasia in AVWS and we report for the first time that refractory or relapsing GI bleeding in patients with AVWS can successfully be controlled with thalidomide.

Continuous infusion of recombinant factor VIII formulated with sucrose in surgery: non-interventional, observational study in patients with severe haemophilia A.

In haemophilia A, continuous infusion (CI) of FVIII perioperatively provides a more constant FVIII level than conventional bolus injections, avoiding low trough levels that could increase bleeding risk. Due to the low number of surgical cases in clinical trials, especially in haemophilia, more information on the clinical practice of CI from observational studies is helpful. We aimed to evaluate the effectiveness and safety of CI with recombinant factor VIII formulated with sucrose (rFVIII-FS) in a typical surgery practice setting. This was a non-interventional study in 12 centres. Patients with severe haemophilia A who received rFVIII-FS by CI during and after surgery were included in this study if they had more than 150 exposure days (EDs) to any FVIII product and had no history of inhibitors before CI. Patients were observed during the entire course of CI, with monitoring up to 3 months thereafter. Twenty-five patients with 28 surgeries were included in the analysis. Median age was 51.7 (range 10-75). Most (75%; 21/25) patients underwent orthopaedic surgeries. The median dose of rFVIII-FS consumed during CI was 376 IU kg(-1) (range 157.9-3605.6 IU kg(-1)) with a greater median dose for orthopaedic surgeries (424.0 IU kg(-1)) compared to non-orthopaedic surgeries (278.5 IU kg(-1)). 95% of all FVIII measurements (214/224) were on target. Efficacy and tolerability were rated as good/excellent in 89.3% (25/28) of surgeries. No inhibitors were observed during or after surgery. This study demonstrates the effectiveness of CI with rFVIII-FS during surgery in patients with severe haemophilia A in a clinical practice setting.

Joint bleeds in von Willebrand disease patients have significant impact on quality of life and joint integrity: a cross-sectional study.

BACKGROUND: Joint bleeds (JB) are reported in a minority of patients with von Willebrand disease (VWD) but may lead to structural joint damage. Prevalence, severity and impact of JB in VWD are largely unknown. OBJECTIVES: The aim of this study was to assess JB prevalence, onset, treatment and impact on health-related quality of life (HR-QoL) and joint integrity in moderate and severe VWD. METHODS: In the Willebrand in the Netherlands study 804 moderate and severe VWD patients [von Willebrand factor (VWF) activity ≤30U dL(-1)] completed a questionnaire on occurrence, sites and consequences of JB. To analyse JB number, onset, treatment and impact on joint integrity we additionally performed a patient-control study on medical file data comparing patients with JB to age, gender, factor VIII (FVIII)- and VWF activity matched VWD patients without JB. RESULTS: Of all VWD patients 23% (184/804) self-reported JB. These 184 patients reported joint damage more often (54% vs. 18%, P < 0.001) and had lower HR-QoL (SF36, P < 0.05) compared to VWD patients not reporting JB. Of 55 patients with available JB data, 65% had the first JB before age 16. These 55 patients used more clotting factor concentrate (CFC; median dose 43 vs. 0 IE FVIII kg(-1) year(-1) , P < 0.001), more often had X-ray joint damage (44% vs. 11%, P = 0.001] and chronic joint pain (44% vs. 18%, P = 0.008) compared to 55 control VWD patients without JB. CONCLUSION: In conclusion, joint bleeds are reported by 23% of moderate and severe VWD patients, mostly start in childhood, are associated with more CFC use, joint pain, lower HR-QoL and significantly more radiological and self-reported joint damage.

Factor VIII concentrate infusion in patients with haemophilia results in decreased von Willebrand factor and ADAMTS-13 activity.

The effects of coagulation factor concentrate infusion on restoring secondary haemostasis in patients with haemophilia are obvious. It is not known whether coagulation factor concentrate infusion affects primary haemostasis or induces an acute inflammatory response. In this study, the influence of a factor VIII (FVIII) concentrate bolus infusion on platelet activation and responsiveness, endothelial activation, and inflammation in adult patients with severe haemophilia A was assessed. VWF showed a mild, but significant decrease 15 min after FVIII infusion (85.02 IU dL(-1)) vs. before infusion (92.04 IU dL(-1) ; P = 0.017), while ADAMTS-13 levels also show a mild but significant decrease from 66.1 ng mL(-1) before infusion, to 53.9 ng mL(-1) (P = 0.012) 15 min after and 50.8 ng mL(-1) (P = 0.050) 60 min after infusion. Platelet P-selectin expression decreased 15 min (33.3 AU) and 60 min (38.7 AU) after infusion compared to before infusion (41.3 AU; P = 0.018 and 0.036). In conclusion, a single infusion of a high dose FVIII concentrate in haemophilia A patients may influence primary haemostasis by decreasing VWF, ADAMTS-13 and the number of circulating activated platelets. These effects possibly occur as a consequence of binding of the infused FVIII to VWF, influencing its processing. When treating severe haemophilia A patients with coagulation concentrate infusion, one should realize this does not merely correct FVIII levels but also may influence primary haemostasis.

Stimulation of naïve monocytes and PBMCs with coagulation proteases results in thrombin-mediated and PAR-1-dependent cytokine release and cell proliferation in PBMCs only.

Protease-activated receptors (PARs) are stimulated by proteolytic cleavage of their extracellular domain. Coagulation proteases, such as FVIIa, the binary TF-FVIIa complex, free FXa, the ternary TF-FVIIa-FXa complex and thrombin, are able to stimulate PARs. Whereas the role of PARs on platelets is well known, their function in naïve monocytes and peripheral blood mononuclear cells (PBMCs) is largely unknown. This is of interest because PAR-mediated interactions of coagulation proteases with monocytes and PBMCs in diseases with an increased activation of coagulation may promote inflammation. To evaluate PAR-mediated inflammatory reactions in naïve monocytes and PBMCs stimulated with coagulation proteases. For this, PAR expression at protein and RNA level on naïve monocytes and PBMCs was evaluated with flow cytometry and RT-PCR. In addition, cytokine release (IL-1ß, IL-6, IL-8, IL-10, TNF-α) in stimulated naïve and PBMC cell cultures was determined. In this study, it is demonstrated that naïve monocytes express all four PARs at the mRNA level, and PAR-1, -3 and -4 at the protein level. Stimulation of naïve monocytes with coagulation proteases did not result in alterations in PAR expression or in the induction of inflammation involved cytokines like interleukin-1ß (IL-1ß), interleukin-6 (IL-6), interleukin-8, interleukin-10 or tumour necrosis factor-α. In contrast, stimulation of PBMCs with coagulation proteases resulted in thrombin-mediated induction of IL-1ß and IL-6 cytokine production and PBMC cell proliferation in a PAR-1-dependent manner. These data demonstrate that naïve monocytes are not triggered by coagulation proteases, whereas thrombin is able to elicit pro-inflammatory events in a PAR-1-dependent manner in PBMCs.

Cardiac catheterization and intervention in haemophilia patients: prospective evaluation of the 2009 institutional guideline.

Ageing haemophilia patients are increasingly confronted with ischaemic heart disease (IHD). Treatment is complex because of the delicate equilibrium between bleeding and thrombosis. In 2009, we developed an institutional guideline on how to treat IHD in this patient population. The aim of this study was to evaluate feasibility and safety of this guideline. Haemophilia patients who underwent coronary angiography or percutaneous coronary intervention between January 2009 and June 2012 were included in the current case series. Nine diagnostic or therapeutic cardiac catheterizations were performed in six haemophilia patients. One patient with moderate haemophilia B was included, whereas the other patients had mild haemophilia A. In six of nine procedures, access to the circulation was gained via the radial artery. Only bare-metal stents were implanted, after which dual antiplatelet treatment was given for at least 4 weeks. During cardiac catheterization/intervention and dual antiplatelet treatment, clotting factor levels were corrected. No thrombotic or clinically relevant bleeding complications occurred. In one patient, a low-titre inhibitor recurred 10 months after catheterization. In-stent restenosis was diagnosed in one patient. This case series indicates that treatment according to the guideline is feasible and safe. Furthermore, based on the case series and developments in new guidelines for non-haemophilic patients with IHD, some adjustments on the 2009 guideline are proposed.

Obesity in haemophilia patients: effect on bleeding frequency, clotting factor concentrate usage, and haemostatic and fibrinolytic parameters.

The prevalence of obesity in patients with haemophilia (PWH) is increasing. We investigated the effect of obesity on bleeding frequency and clotting factor concentrate (CFC) usage in PWH and assessed whether prothrombotic changes observed in obesity differ between controls and PWH. Number of bleeds and CFC usage were compared between obese (N = 51) and non-obese (N = 46) haemophilia A patients. Markers of haemostasis and fibrinolysis were compared between PWH, and gender-, age- and body mass index (BMI)-matched non-haemophilic controls (N = 91). Median number of bleeds/patient-month was comparable between obese and non-obese patients with severe haemophilia (P = 0.791). Obese patients with severe haemophilia used 1.4 times more CFC/patient-month than non-obese patients (P = 0.036). When adjusting for weight this difference disappeared (P = 0.451). von Willebrand factor plasma concentration (VWF:Ag), factor VIII activity and endogenous thrombin potential were higher in obese than in non-obese controls. Obesity did not influence these markers in PWH. Plasminogen activator inhibitor type 1 levels were higher in obese vs. non-obese PWH (P < 0.001), whereas levels were comparable between PWH and controls (P = 0.912). Plasmin-α2-antiplasmin complex (PAP) levels appeared to be lower in obese vs. non-obese subjects, both within controls (P = 0.011) and PWH (P = 0.008). However, in PWH, PAP levels were higher than in controls (P < 0.001). Obesity is associated with an increase in net CFC usage in PWH, but has no effect on bleeding frequency. In addition, obesity attenuates hyperfibrinolysis in PWH. Future research investigating whether obese PWH need CFC treatment dosed on weight or whether a lower dosage would suffice to prevent and treat bleedings is needed.

Identification and expression of iron regulators in human synovium: evidence for upregulation in haemophilic arthropathy compared to rheumatoid arthritis, osteoarthritis, and healthy controls.

Recurrent joint bleeding is the most common manifestation of severe haemophilia resulting in haemophilic arthropathy (HA). Iron plays a central role in the pathogenesis of the two main features of HA: synovitis and cartilage destruction. The aim of this study was to investigate the synovial presence of the iron regulator proteins ferroportin (FPN), hepcidin, haemoglobin scavenger receptor CD163 (CD163), feline leukaemia virus subgroup C (FLVCR), and heme carrier protein 1 (HCP-1). A comparison of the expression in HA with rheumatoid arthritis (RA), osteoarthritis (OA), and healthy controls (HC) is made. Synovial expression of iron regulators was investigated by immunohistochemistry in human synovial tissue and in a murine haemophilia model. We demonstrate for the first time the synovial presence of the investigated iron regulator proteins. Expression of the iron regulator proteins FPN, CD163, FLVCR, and HCP-1 was enhanced in HA in comparison to RA, OA, and HC synovium. In addition, in a murine haemophilia model of acute joint bleeding, synovial expression of FPN, CD163, and HCP-1 was increased. In both human and murine experiment, synovial expression of hepcidin was not altered. These findings indicate the presence of iron regulator proteins in the synovium, demonstrate an enhanced expression of FPN, CD163, FLVCR, and HCP-1 in HA, and suggest a synovial adaptation mechanism to maintain synovial iron homeostasis in HA.

Risk of inhibitor development in mild haemophilia A increases with age.

Mild haemophilia A is a rare disease with a relatively mild phenotype. Treatment with factor VIII (FVIII) is indicated after trauma or for surgery only. FVIII infusion may result in the development of inhibiting antibodies against FVIII. This study describes the relation between age and other risk factors for inhibitor development in mild haemophilia. A retrospective cohort study was conducted among all patients with mild haemophilia (FVIII 0.05-0.40 IU mL(-1)) registered at the van Creveldkliniek, University Medical Centre Utrecht, The Netherlands. Data on peak treatment with FVIII, gene mutation and history of inhibitor development were obtained from patient files from the period between 1st January 1970 and 31st December 2009. A total of 231 out of 297 (78%) patients had at least one exposure to FVIII, of whom 14 (6.1%) developed an inhibitor to FVIII at a median age of 66 years after a median of 50 exposure days (ED). Age at first exposure, age at peak treatment, number of peak treatments and Arg593Cys mutation were significantly associated with the development of an inhibitor, while continuous infusion with FVIII was not. Although the incidence of inhibitors in mild haemophilia is low, it increases with age and peak treatments. With increasing age patients with mild haemophilia will suffer from co-morbidity more frequently, requiring surgical interventions and exposing them to an increased risk of inhibitor development. Especially patients with a change of arginine in cysteine at 593 are at risk for inhibitor development.