Managing women-specific bleeding in inherited bleeding disorders: A multidisciplinary approach.

INTRODUCTION: Multidisciplinary management of women-specific bleeding is important to preserve quality of life, healthy reproduction and social participation of women and girls with bleeding disorders (WBD). AIM: To support appropriate multidisciplinary care for WBD in haemophilia treatment centres. METHODS: Two case examples are presented and management issues discussed from different health care perspectives, including the nurse, patient, psychologist, gynaecologist, geneticist, psychosexual therapist and haematologist. RESULTS: Woman with bleeding disorders may experience heavy menstruation from menarche onwards. This has a physical and psychosocial impact requiring a multidisciplinary approach. If a woman with an inherited bleeding disorder desires to become pregnant, preconception counselling is essential, to discuss genetic diagnosis, state of the art treatment options for the bleeding disorder in question and possible choices to prevent having an affected child, as well as maternal bleeding risks during conception, delivery and the post-partum period. CONCLUSION: Adequate management and good education of WBD requires a patient-centred multidisciplinary approach with experienced specialists in a haemophilia treatment centre.

Sports participation and physical activity in patients with von Willebrand disease.

INTRODUCTION: Patients with bleeding disorders may experience limitations in sports participation and physical activity. Several studies on sports participation have been performed in haemophilia patients, but studies in patients with von Willebrand disease (VWD) are lacking. AIM: We assessed the sports participation and physical activity of a large cohort of VWD patients. METHODS: Patients were included from the "WiN study." All patients completed a questionnaire on sports participation, physical activity, quality of life and bleeding symptoms (Tosetto bleeding score). RESULTS: From the 798 included patients, 474 had type 1, 301 type 2 and 23 type 3 VWD. The mean age was 39 ± 20 (standard deviation) years. Five hundred and fifty-two patients (69.3%) participated in various types of sports. Type 3 VWD patients more often did not participate in sports due to fear of bleeding and physical impairment, respectively, OR = 13.24 (95% CI: 2.45-71.53) and OR = 5.90 (95% CI: 1.77-19.72). Patients who did not participate in sports due to physical impairment had a higher bleeding score item for joint bleeds 1.0 (±1.6) vs 0.5 (± 1.1) (P = 0.036). Patients with type 3 VWD and patients with a higher bleeding score frequently had severe limitations during daily activities, respectively, OR = 9.84 (95% CI: 2.83-34.24) and OR = 1.08 (95% CI: 1.04-1.12). CONCLUSION: The majority of VWD patients participated in sports. Patients with type 3 VWD, a history of joint bleeds and a more severe bleeding phenotype frequently experienced limitations in sports participation and physical activities during daily life.

Comorbidities associated with higher von Willebrand factor (VWF) levels may explain the age-related increase of VWF in von Willebrand disease.

Some comorbidities, such as hypertension, are associated with higher von Willebrand factor (VWF) levels in the general population. No studies have been conducted to assess this association in patients with von Willebrand disease (VWD). Therefore, we studied this association in patients with type 1 (n = 333) and type 2 (n = 203) VWD from the 'WiN" study. VWF antigen (VWF:Ag) was higher in type 1 VWD patients with hypertension [difference: 0·23 iu/ml, 95% confidence interval (CI): 0·11-0·35], diabetes mellitus (0·11 iu/ml, 95% CI: -0·02 to 0·23), cancer (0·14 iu/ml, 95% CI: 0·03-0·25) and thyroid dysfunction (0·14 iu/ml, 95% CI: 0·03-0·26) than in patients without these comorbidities (all corrected for age, sex and blood group). Similar results were observed for VWF collagen binding capacity (VWF:CB), VWF activity as measured by the VWF monoclonal antibody assay (VWF:Ab) and factor VIII (FVIII) coagulant activity (FVIII:C). In type 1 VWD, age was associated with higher VWF:Ag (0·03 iu/ml; 95% CI: 0·01-0·04), VWF:CB (0·02 iu/ml; 95% CI: 0·00-0·04), VWF:Ab (0·04 iu/ml; 95% CI: 0·02-0·06) and FVIII:C (0·03 iu/ml; 95% CI: 0·01-0·06) per decade increase. After adjustment for relevant comorbidities, these associations were no longer significant. Despite the higher VWF and FVIII levels, type 1 VWD patients with comorbidities had more bleeding episodes, particularly during surgery. There was no association between comorbidities and VWF/FVIII levels or bleeding phenotype in type 2 VWD patients. In conclusion, comorbidities are associated with higher VWF and FVIII levels in type 1 VWD and may explain the age-related increase of VWF and FVIII levels.

von Willebrand factor propeptide and the phenotypic classification of von Willebrand disease.

The ratios between von Willebrand factor propeptide (VWFpp) or factor VIII activity ( FVIII: C) and VWF antigen (VWF:Ag) reflect synthesis, secretion, and clearance of VWF. We aimed to define the pathophysiology of 658 patients with type 1, 2, or 3 von Willebrand disease (VWD) with VWF levels ≤30 U/dL from the Willebrand in The Netherlands (WiN) study using the VWFpp/VWF:Ag and FVIII: C/VWF:Ag ratios. We evaluated the use of VWFpp in the classification and diagnosis of VWD. On the basis of the ratios, reduced VWF synthesis was observed in 18% of type 1 and only 2% of type 2 patients. A significant proportion of type 3 patients had detectable VWFpp (41%). These patients had a lower bleeding score than type 3 patients who had a complete absence of VWF:Ag and VWFpp (14.0 vs 19.5; P = .025). The majority of these patients had missense mutations with rapid VWF clearance, whereas type 3 patients with no VWFpp were homozygous for null alleles. In conclusion, VWFpp identified severe type 1 VWD with very low VWF levels in patients who had previously been classified as type 3 VWD. This study underlines the clinical significance of the VWFpp assay in the diagnosis and classification of VWD.

Long-term impact of joint bleeds in von Willebrand disease: a nested case-control study.

Patients with severe von Willebrand disease (VWD) may develop arthropathy after joint bleeds. Information on its prevalence and severity is limited. We aimed to assess the occurrence and severity of arthropathy in VWD and its impact on daily life. VWD patients with and without verified joint bleeds were matched for age, sex and Factor VIII level or von Willebrand Factor activity in a nested case-control study within the Willebrand in the Netherlands study. Assessments included the Hemophilia Joint Health Score (0-124), Pettersson score (0-13 per joint X-ray), Hemophilia Activity List score (0-100), joint pain (Visual Analog Scale 0-10), and the Impact on Participation and Autonomy questionnaire (0-20). Arthropathy was defined as a Hemophilia Joint Health Score of 10 or higher, or a Pettersson score over 3 of at least one joint. We included 48 patients with verified joint bleeds (cases) and 48 controls: 60% males, mean age 46 years (range 18-80), median von Willebrand Factor activity 5 versus 8 IU/dL and Factor VIII 24 versus 36 IU/dL. Arthropathy occurred in 40% of the cases versus 10% of the controls (P<0.01). The cases reported more functional limitations compared to the controls (median Hemophilia Activity List score: 88 vs. 100, P<0.01). Arthropathy was related to joint pain and less social participation (Visual Analog Scale>3: 13 of 19 vs. 3 of 28, P<0.01, and median score on the participation questionnaire 6.1 vs. 0.9, P<0.01). In conclusion, arthropathy occurs in 40% of VWD patients after joint bleeds and is associated with pain, radiological abnormalities, functional limitations, and less social participation (Dutch trial register: NTR4548).

Recombinant long-acting glycoPEGylated factor IX in hemophilia B: a multinational randomized phase 3 trial.

This multinational, randomized, single-blind trial investigated the safety and efficacy of nonacog beta pegol, a recombinant glycoPEGylated factor IX (FIX) with extended half-life, in 74 previously treated patients with hemophilia B (FIX activity ≤2 IU/dL). Patients received prophylaxis for 52 weeks, randomized to either 10 IU/kg or 40 IU/kg once weekly or to on-demand treatment of 28 weeks. No patients developed inhibitors, and no safety concerns were identified. Three hundred forty-five bleeding episodes were treated, with an estimated success rate of 92.2%. The median annualized bleeding rates (ABRs) were 1.04 in the 40 IU/kg prophylaxis group, 2.93 in the 10 IU/kg prophylaxis group, and 15.58 in the on-demand treatment group. In the 40 IU/kg group, 10 (66.7%) of 15 patients experienced no bleeding episodes into target joints compared with 1 (7.7%) of 13 patients in the 10 IU/kg group. Health-related quality of life (HR-QoL) assessed with the EuroQoL-5 Dimensions visual analog scale score improved from a median of 75 to 90 in the 40 IU/kg prophylaxis group. Nonacog beta pegol was well tolerated and efficacious for the treatment of bleeding episodes and was associated with low ABRs in patients receiving prophylaxis. Once-weekly prophylaxis with 40 IU/kg resolved target joint bleeds in 66.7% of the affected patients and improved HR-QoL. This trial was registered at www.clinicaltrials.gov as #NCT01333111.

Coronary artery calcification in hemophilia A: no evidence for a protective effect of factor VIII deficiency on atherosclerosis.

OBJECTIVE: Ischemic heart disease mortality is lower in hemophilia patients than in the general male population. As coagulation plays a role in the inflammatory pathways involved in atherogenesis, we investigated whether the clotting factor deficiency protects hemophilia patients from developing atherosclerosis. METHODS AND RESULTS: Coronary artery calcification, measured with multidetector-row computed tomography, was compared between 42 men, ≥59 years, with severe or moderate hemophilia A, and 613 nonhemophilic men from the Rotterdam Study, a prospective population-based study. None of the study subjects were HIV infected or had a history of cardiovascular disease. Coronary artery calcification was quantified by calculating the Agatston score and calcification mass. Data were analyzed using linear regression. Mean difference (ß) of the natural log-transformed Agatston score between men with and without hemophilia was 0.141 (95% CI -0.602 to 0.885, P=0.709). Results did not change after adjustment for age, body mass index, hypercholesterolemia, hypertension, and use of antidiabetic medication (ß=0.525, 95% CI -0.202 to 1.252, P=0.157). Comparable results were found for calcification mass. CONCLUSION: The extent of coronary artery atherosclerosis is comparable between elderly men with and without hemophilia. Results from this study underline the importance of screening and treating atherosclerosis risk factors in hemophilia patients.

History of non-fatal cardiovascular disease in a cohort of Dutch and British patients with haemophilia.

OBJECTIVE: Cardiovascular disease (CVD) mortality is reported to be lower in haemophilia patients than in the general population, but information on the occurrence of non-fatal CVD is lacking. The aim of our study was to assess CVD history in a cohort of living haemophilia patients. METHODS: Retrospective data on the occurrence of myocardial infarction, angina pectoris, ischaemic stroke and intracranial bleeding in 709 living Dutch and British haemophilia patients aged 30 yr or older were analysed and compared with the general age-matched male population. RESULTS: There was a trend towards a lower cumulative incidence of myocardial infarction (1.7% vs. 4.0%) and ischaemic stroke (0% vs. 1.5%) in patients with severe haemophilia than in the general population, while the occurrence of angina pectoris was similar (3.2 vs. 3.7%). As expected, the cumulative incidence of intracranial bleeding was, on the other hand, significantly increased in haemophilia patients (1.6% vs. 0.4% in the general population). CONCLUSION: Our results suggest a protective effect of severe haemophilia against acute ischaemic CVD.

Hepatitis C virus in hemophilia: Health-related quality of life after successful treatment in the sixth Hemophilia in the Netherlands study.

INTRODUCTION: Persons with hemophilia and hepatitis C virus (HCV) infection have a lower health-related quality of life (HRQoL) than those never HCV infected. However, it is unknown whether HRQoL after HCV eradication is comparable to individuals never HCV infected. We aimed to compare HRQoL between HCV-cured and never chronically HCV-infected persons with hemophilia. METHODS: All persons with hemophilia in the Netherlands were invited for a nationwide study conducted in 2018-2019. For the current analysis, participants born before 1992 with data on HRQoL and HCV status were included. HCV status was collected from medical records. HRQoL was measured by RAND-36 questionnaire, with a minimally important difference set at 4.0 points. Multivariable linear regression was used to adjust for age, hemophilia severity, HIV status, and self-reported joint impairment. RESULTS: In total, 486 persons were eligible; 180 were HCV cured and 306 never chronically HCV infected. Compared with those never HCV infected, HCV-cured individuals were older (57 vs. 53 years), more often had severe hemophilia (67% vs. 21%), and reported more impaired joints (median 3 vs. 0). Compared with those never HCV infected, adjusted RAND-36 domain scores of HCV-cured individuals cured were lower on all RAND-36 domains except Pain, ranging from a difference of 4.5 (95% CI, -8.8 to -0.3) for Physical functioning to 11.3 (95% CI, -19.4 to -3.1) for Role limitations due to physical problems. CONCLUSION: Despite effective HCV treatment, HRQoL of HCV-cured persons with hemophilia is still lower than HRQoL of those never chronically HCV-infected on all RAND-36 domains. This implies that careful psychosocial follow-up and support are indicated.

Catheter Ablation for Atrial Fibrillation in Patients with Hemophilia or von Willebrand Disease.

Background Management of atrial fibrillation (AF) is complex in patients with bleeding disorders. Catheter ablation such as pulmonary vein isolation (PVI) has been suggested in cases with bleeding disorders. However, data on safety are missing. This report describes the outcome of PVI in patients with bleeding disorders. Methods A retrospective study in our hemophilia treatment center of patients who underwent a PVI in 2014 to 2018. PVI was done according to local protocol. Clotting factor was given periprocedural. Postprocedural anticoagulation was given for at least 4 weeks, with clotting factor suppletion if needed to maintain factor VIII (FVIII) levels >0.20 IU/mL. Results and Discussion Five patients with hemophilia and one with von Willebrand disease were included. Eight PVIs were performed. Target FVIII levels (>0.80 IU/mL) were met before the procedure. Postprocedural anticoagulation was given: vitamin K antagonist (VKA) or direct oral anticoagulant (DOAC) dabigatran. All patients obtained long-term sinus rhythm, in two patients after a second PVI. However, late recurrent AF occurred in one patient after 42 months. A notable incidence of groin bleeds was observed: two of eight interventions (25%) compared with 0.9% in the general population. Bleeding seemed to be related to agitation, early mobilization, and bridging of VKA with low molecular weight heparin (LMWH). No relevant bleeding was observed when on DOAC therapy. Conclusion PVI seems to be effective in the case of bleeding disorders. To reduce the groin bleeds agitation and early mobilization should be avoided and DOAC is preferred over bridging VKA with LMWH.

The Impact of Hepatitis C Virus Direct-Acting Antivirals on Patient-Reported Outcomes: A Dutch Prospective Cohort Study.

INTRODUCTION: Pegylated interferon-based therapy for hepatitis C virus (HCV) negatively impacts nutritional state and patient-reported outcomes (PROs) such as health-related quality of life (HRQL). Clinical trials with direct-acting antivirals (DAAs) report significant PRO improvement but real-world data are still scarce. METHODS: Prospective cohort study recruiting HCV patients treated with DAAs in 2015-2016. Data at baseline, end of treatment (EOT) and 12 weeks thereafter (FU12) included: patient-reported medication adherence; SF-36; Karnofsky Performance Status; paid labour productivity; physical exercise level; nutritional state [by body mass index (BMI) and Jamar hand grip strength (HGS)] and Beliefs about Medicines Questionnaire. Potential factors predicting these PROs were evaluated with multiple regression analysis. RESULTS: A total of 68 patients were enrolled: 85% male, median age 57 years, 80% genotype 1, 40% cirrhotics, 46% haemophilia. Both cure rate and patient-reported adherence were 97%. SF-36 Physical Component Summary did not change (43.2 ± 11.9, 44.9 ± 10.3 and 44.7 ± 10.9 at baseline, EOT and FU12, p = 0.71). In contrast, SF-36 mental component summary (MCS) decreased transiently during therapy (49.2 ± 11.9, 44.6 ± 10.3 and 49.9 ± 12.6 at baseline, EOT and FU12, p < 0.01). Concomitant ribavirin-use was the only independent predictor of decreased SF-36 MCS. BMI (25.7 ± 4.5 and 25.6 ± 4.4 at baseline and EOT, p = 0.8) and Jamar HGS (39.7 ± 13.0, 37.4 ± 11.9 and 37.9 ± 13.8 at baseline, EOT and FU12, p = 0.56) did not change. CONCLUSION: Our study reveals concomitant ribavirin as the only independent predictor of transient decrease in SF-36 mental HRQL during DAA therapy. In contrast to interferon-based therapy, DAAs do not affect BMI or Jamar HGS.

Long-Term Outcome after Joint Bleeds in Von Willebrand Disease Compared to Haemophilia A: A Post Hoc Analysis.

Long-term outcome after joint bleeds in von Willebrand disease (VWD) (von Willebrand factor activity ≤ 30 IU/dL) could differ from moderate or severe haemophilia A (HA) (factor VIII [FVIII] 1-5 IU/dL or FVIII < 1 IU/dL). We performed a post hoc analysis on Haemophilia Joint Health Score (HJHS, 0-124), X-ray Pettersson scores (PS, 0-13/joint) and the Haemophilia Activities List (HAL, 0-100), using multivariable regression to adjust for age (rate ratio [RR] or odds ratio [OR] [95% confidence interval]). We included 48 VWD (median age, 47 years, type 3 VWD, n = 19), 39 moderate HA (median, 39 years) and 59 severe HA patients (median, 25 years) with documented joint bleeds. VWD patients suffered repeated bleeding (lifetime > 5/joint) less often than moderate and severe HA patients (52% vs. 77% vs. 98%). HJHS and PS in VWD were similar to moderate HA (median HJHS 5 vs. 6, RR 0.9 [0.5-1.4] and PS > 3 of ≥ 1 joint OR 0.3 [0.1-1.4]), but better than in severe HA patients (median HJHS 5 vs. 9, RR 1.8 [1.1-2.9]; PS > 3 in any joint OR 0.1 [0.0-0.3]). Self-reported limitations in activities were comparable across VWD, moderate HA (HAL score < 95: 67% vs. 49%; OR 1.4 [0.5-3.6]) and young adults with severe HA (67% vs. 48%; OR 1.7 [0.7-4.4]). Despite fewer joint bleeds, joint outcome after joint bleeds was similar in VWD and moderate HA patients. Type 3 VWD patients had worst joint outcome, comparable to younger intensively treated severe HA patients. Limitations in activities occurred as often in VWD as in both moderate and severe HA.

Joint assessment in von Willebrand disease. Validation of the Haemophilia Joint Health score and Haemophilia Activities List.

Assessment of clinical outcome after joint bleeding is essential to identify joint damage and optimise treatment, to prevent disability. However, disease-specific tools to assess the musculoskeletal status in patients with von Willebrand disease (VWD) are lacking. We aimed to determine validity and reliability of the Haemophilia Joint Health Score (HJHS) and Haemophilia Activities List (HAL) in patients with Von Willebrand disease (VWD). Ninety-six patients with VWD were included (mean age 46 years) of whom 27 had more than five documented joint bleeds. The HJHS was performed in all patients and all patients completed the HAL and Impact on Participation and Autonomy (IPA) questionnaires. Health-related quality of life (SF36) results were obtained from the prior 'Willebrand in the Netherlands' study. Joint X-rays of knees, elbows and ankles were scored according to Pettersson (PS). Internal consistency of the HJHS (Cronbach's α (α)=0.75) and HAL (α=0.89) were good. Inter-observer agreement of the HJHS was good (ICC 0.84; Limits of Agreement ± 10.3). The HJHS showed acceptable correlation with the X-ray PS (Spearman's r (rs)>0.60 all joints) and HAL (rs=0.71). The HAL also showed acceptable correlation with the SF36 physical functioning (rs=0.65) and IPA (rs=0.69). Hypothesis testing showed adequate discriminative power of both instruments: in patients with a history of >5 versus ≤ 5 joint bleeds (median HJHS 10 vs 2 (p<0.01); median HAL 77 vs 98 (p<0.01)), independent from age. In conclusion, both the HJHS and HAL are feasible to assess clinical outcome after joint bleeds in VWD.

Hepatitis C and health-related quality of life among patients with hemophilia.

Hepatitis C has a negative effect on health-related quality of life (HRQoL). It is not clear whether hepatitis C affects HRQoL of patients with hemophilia. The objective of this study was to assess the effect of hepatitis C virus (HCV) infection on HRQoL in patients with hemophilia. A cross-sectional study was performed among all registered hemophilia patients in the Netherlands. HRQoL was determined by using the self-administered SF-36 questionnaire. Patients were eligible for the study if they completed the SF-36, had been treated with clotting factor products before 1992, and had reported their hepatitis C status. Data on the severity of hemophilia were obtained from the hemophilia treatment centers. The validity of the self-reported data on hepatitis C status was verified in a random sample of 92 (15%) patients; 92% reported their hepatitis C status correctly. Fifty-five percent (333/602) of the study population had a current HCV infection. All eight domains of the SF-36 were lower in patients with a current HCV infection than they were in patients who had never been infected with HCV. After adjustment for age, severity of hemophilia, human immunodeficiency virus (HIV) status, employment status, and joint limitations, hepatitis C infection was associated with a decrease of HRQoL on the domains of general health (difference 6.9 [95% confidence interval (C.I.) 2.7 to 11.2]) and vitality (3.8 [95% C.I. 0.1 to 7.7]). Hemophilia patients infected with HCV scored lower on the HRQoL domains of general health and vitality than hemophilia patients who had never been infected with HCV.

Factor VIII half-life and clinical phenotype of severe hemophilia A.

BACKGROUND AND OBJECTIVES: Patients with severe hemophilia A have considerably different factor VIII half-lives. Whether this is associated with their clinical characteristics has not been reported. The aim of this study was to describe the association of factor VIII half-lives with treatment and clinical characteristics of patients with severe hemophilia A, who have been treated with individually tailored prophylaxis. DESIGN AND METHODS: Patients were selected from a single-center cohort of 214 patients with severe hemophilia, born between 1944 and 1995. To improve efficiency we measured factor VIII half-life in 42 patients selected from the extremes of the distribution of phenotypes of severe hemophilia. We assessed information on life-long joint bleeds and clotting factor consumption. Orthopedic outcome was assessed by the Pettersson score. RESULTS: Among these patients with severe hemophilia, factor VIII half-life ranged from 7.4-20.4 hours (median 11.8 hours). A one-hour increase in factor VIII half-life was associated with 96 (95% confidence interval (CI) 2 -190) IU less clotting factor use per kg per year. Age was an important determinant of factor VIII half-life, and explained a large part of the association between factor VIII half-life and clotting factor consumption. The median number of joint bleeds per year and arthropathy were similar for patients with different half-lives. INTERPRETATION AND CONCLUSIONS: Among patients with severe hemophilia, treated prophylactically with clotting factor, those with a shorter factor VIII half-life required slightly more clotting factor to prevent joint bleeds and subsequent arthropathy than similar patients with a longer factor VIII half-life.

Changes in bleeding patterns in von Willebrand disease after institution of long-term replacement therapy: results from the von Willebrand Disease Prophylaxis Network.

Clinically, the leading symptom in von Willebrand disease (VWD) is bleeding, chiefly of mucosal type, for example, epistaxis, gingival, or gastrointestinal bleeding, and menorrhagia. In severe forms of VWD with secondary deficiency of factor VIII, spontaneous joint bleeding, resembling that observed in severe haemophilia A, may also be observed. The bleeding patterns of VWD can affect quality of life, and may be life-threatening. The von Willebrand Disease Prophylaxis Network is an international study group formed with the goal of investigating the role of prophylaxis in clinically severe VWD. The objective of the present study is to investigate the response to prophylaxis focusing primarily on epistaxis, joint bleeding, gastrointestinal bleeding, and heavy bleeding associated with menses. Data from 105 subjects, 10 enrolled in a prospective study and 95 in a retrospective study between 2008 and 2013, were available for analysis. The median annualized rate reductions in bleeding were significant for epistaxis (P < 0.0001), gastrointestinal bleeding (P = 0.0003), joint bleeding (P < 0.0001), and menorrhagia (P = 0.008). Doses on a group level were approximately the same prior to and during prophylaxis, but more patients with gastrointestinal bleeding had prophylaxis three or more times per week as well as higher dosages. Our study, which primarily used retrospective data, indicates that prospective studies are needed to better delineate the doses and dose intervals that should be used for prophylactic treatment of VWD.

Age at first treatment and immune tolerance to factor VIII in severe hemophilia.

Findings from a recent study suggest that earlier start of treatment with factor VIII in patients with severe hemophilia is associated with a higher risk to develop inhibitors. We set out to assess the association between age of first administration of clotting factor VIII and the risk to develop inhibitors in infants with severe hemophilia A. This work was a cohort study, carried out in the national hemophilia treatment center. The study included eighty-one consecutive patients with severe hemophilia A who received their first dose of factor VIII between 1975 and 1998. Patients were followed until their last visit in 2001 or 2002. The average follow-up was 16 years (range 3-26). Persistent inhibitory antibodies developed in 12 of 81 patients (15%). Cumulative incidence at 100 exposure days was 34% (95% confidence interval 7-61%) in patients starting therapy before the age of 6 months, 20% (4-36%) in patients starting therapy between 6 months and 1 year, 13% (0-27%) in those starting therapy between 1 and 1.5 years, and 0% in those who started therapy beyond 1.5 years of age (p for trend 0.03). Our findings confirm that age of first factor VIII administration in children with severe hemophilia A is inversely associated with the risk to develop antibodies against factor VIII. The role of confounding factors such as the type of factor VIII mutation and environmental factors needs to be evaluated.