Thomas C. Abshire

Prevalence of von Willebrand disease in children: A multiethnic study

OBJECTIVE Von Willebrand disease (vWD) was thought to be a rare disorder until a recent survey reported a prevalence of 0.8% in an ethnically homogenous community in northern Italy. The purpose of this study was to determine the prevalence of vWD in an ethnically heterogenous population. METHODS Von Willebrand factor (vWF) was measured by the ristocetin cofactor method in 600 healthy children, aged 2 to 18 years, seen for routine school physical examinations in a three-state region. Personal and family bleeding symptoms were determined by questionnaire. The diagnosis of vWD required a personal history of bleeding symptoms, an abnormal vWF activity concentration, and a family history of at least one immediate family member with bleeding symptoms. RESULTS A total of 315 subjects were white, 212 were black, 16 were Hispanic, 10 were from other groups, and 47 were biracial. Eight subjects (four black, four white) met the criteria for vWD, for a prevalence of 1.3%. Seven subjects with vWD had blood group O (mean vWF = 32 U/dl; range, 10 to 42 U/dl), and one had blood group A (vWF = 41 U/dl). Children who had blood group O had significantly (p < 0.001) lower vWF activities (median, 83 U/dl, range, 43 to 162 U/dl) than those from non-O blood groups (median, 98 U/dl; range, 51 to 190 U/dl). There were no significant differences in vWF activity by ethnicity. The vWF activity was significantly (p < 0.02) greater for boys than girls in both blood groups. CONCLUSION Von Willebrand disease is the most common congenital hemostatic disorder; its high prevalence is not limited to one ethnic group.

ISTH/SSC bleeding assessment tool: a standardized questionnaire and a proposal for a new bleeding score for inherited bleeding disorders

F . RODEGHIERO,* A . TOSETTO,* T . ABSH IRE , D . M . A R NO L D , B . COLLE R ,§ P . J AMES ,– C. NEUNER T** and D . L I LL ICRAP ON BEHALF OF THE I STH/SSC JOINT VWF AND PER INATAL/ PED IA TR I C HEMOSTA S IS SUB CO MMI TTEES WO RKI NG GRO U P 1 *Department of Cell Therapy and Hematology, San Bortolo Hospital, Vicenza, Italy; Blood Center of Wisconsin, Milwaukee, WI, USA; Michael G DeGroote School of Medicine, Department of Medicine, McMaster University and Canadian Blood Services, Hamilton, Canada; §Allen and Frances Adler Laboratory of Blood and Vascular Diseases, The Rockefeller University New York, NY, USA; –Department of Medicine, Queen s University, Kingston, Canada; **Department of Pediatric Hematology/Oncology, UT Southwestern Medical Center, Dallas, TX, USA; and Department of Pathology and Molecular Medicine, Richardson Laboratory Queen s University, Kingston, Canada

ISTH/SSC bleeding assessment tool

F . RODEGHIERO,* A . TOSETTO,* T . ABSH IRE , D . M . A R NO L D , B . COLLE R ,§ P . J AMES ,– C. NEUNER T** and D . L I LL ICRAP ON BEHALF OF THE I STH/SSC JOINT VWF AND PER INATAL/ PED IA TR I C HEMOSTA S IS SUB CO MMI TTEES WO RKI NG GRO U P 1 *Department of Cell Therapy and Hematology, San Bortolo Hospital, Vicenza, Italy; Blood Center of Wisconsin, Milwaukee, WI, USA; Michael G DeGroote School of Medicine, Department of Medicine, McMaster University and Canadian Blood Services, Hamilton, Canada; §Allen and Frances Adler Laboratory of Blood and Vascular Diseases, The Rockefeller University New York, NY, USA; –Department of Medicine, Queen s University, Kingston, Canada; **Department of Pediatric Hematology/Oncology, UT Southwestern Medical Center, Dallas, TX, USA; and Department of Pathology and Molecular Medicine, Richardson Laboratory Queen s University, Kingston, Canada

Dose effect and efficacy of rFVIIa in the treatment of haemophilia patients with inhibitors: analysis from the Hemophilia and Thrombosis Research Society Registry

Summary.  Recombinant activated factor VII (rFVIIa), licensed in 1999 for treatment of haemophilia patients with inhibitors (HI), represents an important advance in the therapeutic armamentarium. Standard bolus dosing ranges from 90 to 120 mcg kg−1 every 2–3 h until arrest of bleeding. As licensure, clinical use of rFVIIa has increased and broadened. Clinicians now use a wide dose range, 90–300 mcg kg−1. High‐dose regimens may optimize thrombin generation or burst, and may allow for prolonged dose interval. The Hemophilia and Thrombosis Research Society (HTRS) maintains a registry database to study haemophilia treatment and related disorders, particularly treatment of acute bleeding in HI, acquired haemophilia, FVII deficiency and von Willebrands disease (VWD). To assess the effect of rFVIIa dose on efficacy and safety in the treatment of acute bleeding in HI, data from the HTRS database from January 2000 through June 2002 were analysed. Bleeding episodes were grouped by bolus rFVIIa dose range: <100, 100–150, 150–200 and >200 mcg kg−1. Investigator‐reported efficacy for the first 72 h of treatment was evaluated. Thirty‐eight congenital HI patients were treated for 555 bleeding episodes. Patient age range was 1–55 years (median: 14). Bleeding episodes were spontaneous (45%), caused by trauma (38%), or because of surgery, dental, diagnostic, or medical procedures (17%); bleeding occurred in joint, muscle, and intra/extracranial sites. Treatment location included: 80% at home, 12% at other facilities (treatment centres, ER, inpatient and OR), and 8% at both home/other facilities. Median total dose given over 72 h was 360 mcg kg−1 (range: 40–4281, mean: 537). Bleeding stopped in 87% of the episodes. Bleeding cessation rate was 84% for the three lower dose groups, and 97% for the highest dose group (P < 0.001). Five patients experienced nine adverse events (AEs). AE rates were <1% for <100, 5% for 100–150, 0% for 150–200, <1% for >200 mcg kg−1 dose group. Decreased therapeutic response accounted for eight of the nine AEs. These data, which represent the most comprehensive report of rFVIIa use since the USA licensure, demonstrate that bleeding episodes in HI patients can be treated safely and effectively at home and that doses up to 346 mcg kg−1 appear to be well‐tolerated. Additionally, rFVIIa doses >200 mcg kg−1 appear to significantly increase efficacy (97% in the high‐dose group, compared with 84% in the lower dose groups). Optimal dosing remains to be determined; specifically, what the lowest effective dose is and whether a single high‐dose bolus eliminates the need for repeated dosing. Recombinant FVIIa appears to have a wide safety margin that may allow dose escalation to address these questions.

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.

Safety update on the use of recombinant factor VIIa and the treatment of congenital and acquired deficiency of factor VIII or IX with inhibitors

Summary.  Recombinant factor VIIa (rFVIIa, NovoSeven®) has been licensed for treatment of haemophilia with inhibitors in Europe since 1996 and in North America since 1999. Overall, approximately 1.5 million doses have since been administered. Safety data from licensure to April 2003 revealed 25 thromboembolic (TE) adverse events (AE) from over 700 000 doses given, a remarkably low incidence of TE events. Recent reports have cited a higher prevalence of TE events with rFVIIa use, especially when used off‐label. This report reviews the TE and fatal events with use of rFVIIa for congenital and acquired haemophilia A or B from May 2003 to December 2006. Approximately 800 000 standard doses of rFVIIa have been administered during this time frame. All clinical trials, spontaneous and solicited reports, as well as a detailed literature review, were included in the data analysis. There were a total of 30 TE events and 6 TE‐associated fatal events. Spontaneous reports captured 14/71 (20%) TE/AE and 2/34 TE‐associated/total fatal events. From solicited reports, 5/40 (12.5%) were associated with a TE and 1/32 TE‐associated fatal events. Literature review revealed 11/19 (58%) TE events and 3/6 TE‐associated fatal events. Despite the use of high‐dose rFVIIa (270 μg kg−1) in some clinical trials and registries, rFVIIa appears safe, when used for congenital and acquired haemophilia. The prevalence of TE associated with rFVIIa use is less than 4/100 000 and a TE‐associated fatal event is also extremely rare. However, use of rFVIIa for off‐label indications should continue to be monitored closely via clinical trials and carefully designed registries.

Neutralizing antibodies against adeno-associated virus examined prospectively in pediatric patients with hemophilia

Recombinant adeno-associated virus (rAAV) is a promising gene delivery vector and has recently been used in patients with hemophilia. One limitation of AAV application is that most humans have experienced wild-type AAV serotype 2 exposure, which frequently generates neutralizing antibodies (NAbs) that may inhibit rAAV2 vector transduction. Employing alternative serotypes of rAAV vectors may circumvent this problem. We investigated the development of NAbs in early childhood by examining sera gathered prospectively from 62 children with hemophilia A, participating in a multi-institutional hemophilia clinical trial (the Joint Outcome Study). Clinical applications in hemophilia therapy have been suggested for serotypes AAV2, AAV5 and AAV8, therefore NAbs against these serotypes were serially assayed over a median follow-up of 4 years. NAbs prevalence increased during early childhood for all serotypes. NAbs against AAV2 (43.5%) were observed more frequently and at higher titers compared with both AAV5 (25.8%) and AAV8 (22.6%). NAbs against AAV5 or AAV8 were rarely observed in the absence of co-prevalent and higher titer AAV2 NAbs, suggesting that NAbs to AAV5 and AAV8 were detected following AAV2 exposure due to partial cross-reactivity of AAV2-directed NAbs. The results may guide rational design of clinical trials using alternative AAV serotypes and suggest that younger patients who are given AAV gene therapy will benefit from the lower prevalence of NAbs.

Severe neonatal protein C deficiency: Prevalence and thrombotic risk

Severe deficiencies of protein C, a pivotal coagulation-regulatory protein, have been reported in neonates as an apparently transient condition. In this prospective study, cord blood was collected at 193 deliveries and assays of protein C were correlated with clinical status, other coagulation results, and outcome. Protein C levels of less than 0.1 unit/ml were found most frequently in preterm infants with respiratory distress, infants of diabetic mothers, and infants of twin gestations. Levels of protein C correlated with levels of factor VIII activity but did not correlate with markers of consumptive coagulopathy. A protein C level less than 0.1 unit/ml was significantly correlated with the subsequent onset of thrombosis, even when the effects of gestational age and birth weight were excluded. Low cord blood levels of protein C may reflect delayed maturation or increased turnover in certain infants and appear to convey an independent risk of thrombosis, but the critical concentration of protein C necessary to maintain neonatal hemostasis is not known.

Sites of initial bleeding episodes, mode of delivery and age of diagnosis in babies with haemophilia diagnosed before the age of 2 years: a report from The Centers for Disease Control and Prevention’s (CDC) Universal Data Collection (UDC) project

Summary.  Lack of detailed natural history and outcomes data for neonates and toddlers with haemophilia hampers the provision of optimal management of the disorder. We report an analysis of prospective data collected from 580 neonates and toddlers aged 0–2 years with haemophilia enrolled in the Universal Data Collection (UDC) surveillance project of the Centers for Disease Control and Prevention (CDC). This study focuses on a cohort of babies with haemophilia whose diagnosis was established before the age of two. The mode of delivery, type and severity of haemophilia, onset and timing of haemorrhages, site(s) of bleeding, provision of prophylaxis with coagulation factor replacement therapy, and the role played by the federally funded Haemophilia Treatment Centers (HTC) in the management of these infants with haemophilia were evaluated. Seventy‐five per cent of haemophilic infants were diagnosed early, in the first month of life, especially those with a family history or whose mothers were known carriers; infants of maternal carriers were more likely to be delivered by C‐section. Involvement of an HTC prior to delivery resulted in avoidance of the use of assisted deliveries with vacuum and forceps. Bleeding from the circumcision site was the most common haemorrhagic complication, followed by intra‐ and extra‐cranial haemorrhages and bleeding from heel stick blood sampling. Eight per cent of the infants were administered factor concentrate within 24 h of birth; more than half were treated to prevent bleeding. This study highlights the significant rate and the sites of initial bleeding unique to very young children with haemophilia and underscores the need for research to identify optimal evidence‐based recommendations for their management.

Incidence and prognostic significance of MDM2 oncoprotein overexpression in relapsed childhood acute lymphoblastic leukemia

MDM2 overexpression by pediatric ALL cells at initial diagnosis has been linked to poor response to therapy. In the present study, we evaluated the incidence of MDM2 overexpression by ALL cells from pediatric patients at first relapse and compared MDM2 protein levels with in vitro response to adriamycin and with duration of initial complete remission (CR1). Since an important role of MDM2 in enhancing cell proliferation and survival appears to be inhibition of p53 activity, we also evaluated the status of p53 in these patients’ leukemic cells. MDM2 protein levels were determined by Western blot analysis of leukemic bone marrow cells obtained from 42 patients with B cell precursor (BCP) ALL who relapsed during or following therapy on standard POG ALL protocols. Twelve of 42 (29%) cases have MDM2 levels ⩾10-fold higher than those detected in normal bone marrow mononuclear (NMMC) cells, which express relatively low levels of protein. Thirty cases (71%) expressed MDM2 at levels <10-fold those in nmmc, including 24 mdm2-negative cases (57%). P53 mutations were detected by single-strand conformation polymorphism analysis in two cases. Overexpression of mdm2 (⩾10-fold) was significantly correlated with adriamycin resistance and decreased duration of cr1. Eight of 12 (75%) overexpressers showed high levels of in vitro resistance to adriamycin, compared to four of 30 (13%) non-overexpressers (P < 0.005). The median cr1 for mdm2 overexpressers was 20.5 months (range: 3–75 months) compared to 41 months (range: 8–98 months) for non-overexpressers (P < 0.01). Four of 42 patients failed to achieve cr following re-induction: leukemic cells from three of these patients either overexpressed mdm2 or contained a mutant p53. These results indicate that overexpression of mdm2 plays a significant role in refractory pediatric all and is associated with early relapse, adriamycin resistance, and failure to respond to re-induction therapy.