R. Liesner

Plasma and albumin-free recombinant factor VIII: pharmacokinetics, efficacy and safety in previously treated pediatric patients.

Summary.  Background: The pharmacokinetics of factor VIII replacement therapy in preschool previously treated patients (PTPs) with hemophilia A have not been well characterized. Objectives: To assess the pharmacokinetics, efficacy and safety of a plasma‐free recombinant FVIII concentrate, ADVATE [Antihemophilic Factor (Recombinant), Plasma/Albumin‐Free Method, rAHF‐PFM], in children < 6 years of age with severe hemophilia. Patients/methods: Fifty‐two boys, one girl, mean (± SD) age 3.1 ± 1.5 years and ≥ 50 days of prior FVIII exposure, were enrolled in a prospective study of ADVATE rAHF‐PFM at 23 centers. Results: The mean terminal phase half‐life (t1/2) was 9.88 ± 1.89 h, and the mean adjusted in vivo recovery (IVR) was 1.90 ± 0.43 IU dL−1 (IU kg−1)−1. Over the 1–6‐year age range, t1/2 of rAHF‐PFM increased by 0.40 h year−1. IVR increased by 0.095IU dL−1(IU kg−1)−1 (kg m−2)−1 in relation to body mass index (BMI). Patients primarily received prophylaxis. Median (range) annual joint bleeds were 0.0 (0.0–5.8), 0.0 (0.0–6.1) and 14.2 (0.0–34.5) for standard prophylaxis, modified prophylaxis and on‐demand treatment, respectively. Bleeds were managed in 90% (319/354) of episodes with one or two rAHF‐PFM infusions; response was rated excellent/good in 93.8% of episodes. Over a median 156 exposure days, no FVIII inhibitors were detected and no related severe adverse events or unusual non‐serious adverse events were seen. Conclusions: Children < 6 years of age appear to have shorter FVIII t1/2 and lower IVR values than older subjects. However, these parameters increased with age (t1/2) and BMI (adjusted IVR), respectively. rAHF‐PFM was clinically effective and well tolerated, with no signs of increased immunogenicity in previously treated young children with hemophilia A.

Inherited prothrombotic states and ischaemic stroke in childhood

OBJECTIVE To investigate the prevalence of currently recognised inherited prothrombotic states in a population of children with arterial stroke. METHODS Children with arterial stroke presenting to a tertiary level paediatric neurology centre between 1990 and 1996 were investigated for inherited prothrombotic states. RESULTS Sixty seven children with arterial stroke were investigated. Abnormalities were initially identified in 16 patients; however, only eight children (12%) had an inherited prothrombotic state. This was type 1 protein S deficiency in one patient, the factor V Leiden mutation in six, and activated protein C resistance (without the factor V Leiden mutation) in one. The prevalence of the factor V Leiden mutation was not significantly higher in children with arterial stroke (12%) than in a control population of children without thrombosis attending the same institution (5.2%; Fisher’s exact test, p=0.19; difference in prevalence between patients and controls (95% confidence interval)=6.8% (−2.78% to 16.8%)). CONCLUSIONS Currently recognised inherited prothrombotic tendencies were rarely associated with stroke in this group of children, although larger numbers of patients would be needed to confirm this. Age appropriate normal values should be used when interpreting the results of a prothrombotic screen. Prothrombotic abnormalities seen acutely are as often transient as inherited. Longitudinal assessment and family studies are required before low concentrations of an anticoagulant protein found acutely can be attributed to an inherited abnormality.

Von Willebrand factor--cleaving protease activity in congenital thrombotic thrombocytopenic purpura.

Thrombotic thrombocytopenic purpura (TTP) is characterized by microangiopathic haemolytic anaemia (MAHA), thrombocytopenia, fluctuating neurological impairment, renal dysfunction and fever. Both acquired and congenital forms are recognized. Recurrent episodes, which may be predictable (occurring every 21–28 d), are seen in congenital disease and may be treated by infusion with fresh‐frozen plasma (FFP). Congenital TTP has recently been associated with deficiency of a novel von Willebrand factor (VWF)‐cleaving protease. To investigate whether residual protease activity dictates clinical manifestations, we determined protease activity in three patients with congenital TTP of varying severity. Intrinsic VWF‐cleaving protease activity of a range of plasma‐derived products was also assessed as one patient had been successfully maintained for many years, initially using an intermediate‐purity factor VIII concentrate (Kryobulin) and then cryoprecipitate. All three patients had a severe absolute deficiency of VWF‐cleaving protease activity (< 3%) up to 5 months after clinical symptoms. Three relatives were also found to have a mild reduction in protease activity (25–50%). Nevertheless, the intrinsic VWF‐cleaving protease activity of plasma‐derived products correlated with their clinical efficacy: significant (100%) protease activity was found in FFP, cryosupernatant, solvent–detergent‐treated plasma, cryoprecipitate and Kryobulin. Two clinically ineffective factor VIII products (Fahndi and Haemate P) possessed only low protease activity (6·25% and 12·5% respectively). Although this suggests that VWF‐cleaving protease activity is central to the pathogenesis of congenital TTP, either small differences in protease activity below 3% or hitherto unknown factors have a profound influence on clinical phenotype. The possible use of factor VIII concentrates in the treatment of this condition also warrants further investigation.

Homozygous thermolabile variant of the methylenetetrahy‐drofolate reductase gene: a potential risk factor for hyperhomo‐cysteinaemia, CVD, and stroke in childhood

In this study of 118 children (median age 5.1 years; range 6 months to 17 years) with ischaemic stroke or transient ischaemic attack (TIA), 22 children (19%) were homozygous for the thermolabile variant of the methylenetetrahydrofolate reductase allele (t‐MTHFR), compared with nine of 78 (12%) of a reference population (p=0.18, OR 1.76, 95% CI 0.76 to 4.04). Of those with cerebrovascular disease (CVD), 17 of 84 were homozygous for the t‐MTHFR allele (p=0.13 compared with the reference population (OR 1.95, 95% CI 0.81 to 4.65). There was a significant (p<0.025) increment of plasma total homocysteine concentration in homozygotes for the t‐MTHFR allele compared with heterozygotes, negatives for the t‐MTHFR allele, and control children with no history of stroke. In four of 12 homozygotes for the t‐MTHFR allele, plasma homocysteine levels were raised, compared with three of 38 of those who were negative or heterozygous (p=0.047; OR 5.8, 95% CI 1.1 to 31.2). Homozygotes for the t‐MTHFR allele were significantly more likely to have a recurrent event than those who were negative or heterozygous (Cox regression p=0.031, hazard ratio 2.18, 95% CI 1.08 to 4.42). These data suggest that homozygosity for the t‐MTHFR allele is associated with raised homocysteine levels in children and is a risk factor for primary and secondary stroke and TIA.

Increased anticardiolipin antibody IgG titers do not predict recurrent stroke or TIA in children

Background: Increased anticardiolipin antibody (ACLA) immunoglobulin (Ig) G titers are commonly found in children with arterial ischemic stroke (AIS) or TIA (AIS/TIA). The associated risk of recurrent thromboembolism is unknown. Objective: To determine the risk of recurrent thromboembolism associated with persistently increased ACLA titers of the IgG isotype in children with AIS/TIA. Methods: The authors studied a cohort of children surviving first AIS/TIA tested by standardized ELISA for β2-glycoprotein I-dependent ACLA of the IgG isotype. Children with ACLA titers >15 IgG phospholipid (GPL) units (per manufacturer’s cutoff point) on more than two occasions ≥6 weeks apart were classified as ACLA-positive (ACLA+) and compared with ACLA-negative (ACLA−) children with respect to recurrent thromboembolic events (AIS/TIA, sinovenous thrombosis, and extracerebral thromboembolism). Results: The authors recruited 34 ACLA+ children and 151 ACLA− children. Most ACLA+ children (30/34; 88%) had ACLA titers ≤40 GPL units. During the follow-up period (median duration, 2.8 years for ACLA+ children and 3.0 years for ACLA− children), AIS/TIA recurred in 26% of ACLA+ children and in 38% of ACLA− children; none developed sinovenous thrombosis or extracerebral thromboembolism. Based on survival analysis, this difference was nonsignificant (p = 0.54). Using binary partition evaluation, no titer criteria for ACLA positivity (range, 0 to 60 GPL units) predicted recurrent AIS/TIA. Conclusion: In children surviving arterial ischemic stroke/TIA, increased anticardiolipin antibody immunoglobulin G titers do not predict recurrent thromboembolism.

Recombinant factor VIII Fc fusion protein for the prevention and treatment of bleeding in children with severe hemophilia A

Prophylactic factor replacement, which prevents hemarthroses and thereby reduces the musculoskeletal disease burden in children with hemophilia A, requires frequent intravenous infusions (three to four times weekly).

Factor XIII - an under diagnosed deficiency - are we using the right assays?

Summary.  Background:  The clot solubility test is the most widely used method for detection of factor (F)XIII deficiency. However, it will only detect severe deficiencies; consequently mild deficiencies and heterozygous states are probably under diagnosed. Objective: As an alternative first‐line screening test, we assessed an automated quantitative ammonia release assay (QARA). Patients/methods: Inter‐assay imprecision was evaluated with commercial normal and pathological control plasmas (10 replicates on each of 5 days). Using the QARA and other commercial assays a comparative assessment of congenital (FXIII range < 1–70 u dL−1, n = 9) and acquired (n = 43) deficiencies was made. We also investigated the prevalence of acquired deficiencies in hospitalized patients using residual samples from adult patients (n = 1004) and from a paediatric intensive care unit (ICU, n = 56). Results: Assay imprecision was acceptably low (normal control: mean 86.6 u dL−1; cv = 2.0%; pathological control: mean 27.5 u dL−1; cv = 3.8%). Using an iodoacetamide blanking procedure, the QARA results (FXIII range < 1–70 u dL−1) exhibited close agreement with those from an immuno‐turbidometric FXIII A‐subunit (FXIII‐A) method. There was also good correlation (R2 ≥ 0.89) between the QARA (range 20–180 u dL−1), a second chromogenic assay, the FXIII‐A and FXIII A+B‐subunit ELISA. We found that 21% of samples from adult patients had FXIII levels < 70 u dL−1 (mean normal ± 2 SD 73–161 u dL−1) with 6% < 50 u dL−1. Within the paediatric ICU samples, 52% were < 70 u dL−1, with 21% < 50 u dL−1. Conclusions: Our data demonstrates that the automated assay is sensitive, highly reproducible and the results from clinical samples suggest that acquired FXIII deficiency is a relatively common phenomenon in hospital patients after surgery and in ICU.

A phenotype–genotype correlation of ADAMTS13 mutations in congenital thrombotic thrombocytopenic purpura patients treated in the United Kingdom

Summary.  Background:  ADAMTS13 mutations play a role in thrombotic thrombocytopenic purpura (TTP) pathogenesis.

Prospective observational cohort studies for studying rare diseases: the European PedNet Haemophilia Registry

Haemophilia is a rare disease. To improve knowledge, prospective studies of large numbers of subjects are needed. To establish a large well‐documented birth cohort of patients with haemophilia enabling studies on early presentation, side effects and outcome of treatment. Twenty‐one haemophilia treatment centres have been collecting data on all children with haemophilia with FVIII/IX levels up to 25% born from 2000 onwards. Another eight centres collected data on severe haemophilia A only. At baseline, details on delivery and diagnosis, gene mutation, family history of haemophilia and inhibitors are collected. For the first 75 exposure days, date, reason, dose and product are recorded for each infusion. Clinically relevant inhibitors are defined as follows: at least two positive inhibitor titres and a FVIII/IX recovery <66% of expected. For inhibitor patients, results of all inhibitor‐ and recovery tests are collected. For continued treatment, data on bleeding, surgery, prophylaxis and clotting factor consumption are collected annually. Data are downloaded for analysis annually. In May 2013, a total of 1094 patients were included: 701 with severe, 146 with moderate and 247 with mild haemophilia. Gene defect data were available for 87.6% of patients with severe haemophilia A. The first analysis, performed in May 2011, lead to two landmark publications. The outcome of this large collaborative research confirms its value for the improvement of haemophilia care. High‐quality prospective observational cohorts form an ideal source to study natural history and treatment in rare diseases such as haemophilia.

The incidence of factor VIII inhibitors in severe haemophilia A following a major switch from full-length to B-domain-deleted factor VIII: a prospective cohort comparison

Although it has been suggested that switching of factor VIII (FVIII) products may increase inhibitor formation this is disputed. Half of UK patients changed rFVIII brands because of national contracting in 2010, presenting an opportunity to compare inhibitor incidence of switchers with non‐switchers. Centres were requested to test all the patients for inhibitors prior to the switching date and 6‐monthly thereafter. Positive and negative inhibitor test data were also collected to analyse for testing bias. A total of 1198 patients with severe haemophilia A and treated with Advate, Kogenate/Helixate or Refacto AF preswitch were included in the analysis, of whom 516 switched to Refacto‐AF and 682 did not switch products. Five new inhibitors were reported amongst previously treated patients (>50 exposure days) with a median titre at the time of detection of 1.25 BU mL−1 (IQR 0.7–23.05). One inhibitor occurred in a non‐switcher using Kogenate, an incidence of 1.5 per 1000 treatment‐years (95% CI 0.2–10.5). Four inhibitors arose in patients who had switched from Kogenate (two) or Advate (two) to ReFacto‐AF, an incidence of 7.8 per 1000 treatment‐years (95% CI 2.9–20.8). These incidence rates did not differ significantly from one another (incidence rate ratio 5.3 (95% CI 0.5–260.3) or from the historical rate of 6.05 inhibitors/1000 treatment‐years (95% CI 5.18–7.06). Only one inhibitor (non‐switcher) persisted. Non‐switchers were significantly older (P = 0.03), and used significantly less FVIII per year (P = 0.005) prior to switching. Following switching, factor usage increased similarly (P = 0.53) in both groups. Switching from FLRFVIII to Refacto‐AF (BDDRFVIII) was not associated with an increased inhibitor development.