Inhibitor incidence in an unselected cohort of previously untreated patients with severe haemophilia B: a PedNet study.

The incidence of FIX inhibitors in severe hemophilia B (SHB) is not well defined. Frequencies of 3-5% have been reported but most studies to date were small, including patients with different severities, and without prospective follow-up for inhibitor incidence. Study objective was to investigate inhibitor incidence in patients with SHB followed up to 500 exposure days (ED), the frequency of allergic reactions, and the relationship with genotypes. Consecutive previously untreated patients (PUPs) with SHB enrolled into the PedNet cohort were included. Detailed data was collected for the first 50 ED, followed by annual collection of inhibitor status and allergic reactions. Presence of inhibitors was defined by at least two consecutive positive samples. Additionally, data on factor IX gene mutation was collected. 154 PUPs with SHB were included; 75% were followed until 75 ED, and 43% until 500 ED. Inhibitors developed in 14 patients (7 high-titre). Median number of ED at inhibitor manifestation was 11 (IQR 6.5-36.5). Cumulative inhibitor incidence was 9.3% (95%CI 4.4-14.1) at 75 ED, and 10.2% (5.1-15.3) at 500 ED. Allergic reactions occurred in 4 (28.6%) inhibitor patients. Missense mutations were most frequent (46.8%) overall but not associated with inhibitors. Nonsense mutations and deletions with large structural changes comprised all mutations among inhibitor patients and were associated with an inhibitor risk of 26.9% and 33.3%, respectively. In an unselected, well-defined cohort of PUPs with SHB, cumulative inhibitor incidence was 10.2% at 500 ED. Nonsense mutations and large deletions were strongly associated with the risk of inhibitor development. The PedNet Registry is registered at clinicaltrials.gov; identifier: NCT02979119.

Optimizing the management of patients with haemophilia A and inhibitors in the era of emicizumab: Recommendations from a German expert panel.

Standard treatment of haemophilia A is based on replacing the missing coagulation factor VIII (FVIII) to treat and prevent bleeding episodes. The most challenging complication of FVIII therapy is the development of neutralizing antibodies (inhibitors) that can render treatment ineffective. Eradication of the inhibitor through immune tolerance induction (ITI) remains the most effective strategy for managing these patients. Bypassing agents can be used to help restore haemostasis in inhibitor patients. Several novel agents have recently been developed, such as the FVIII mimetic agent emicizumab, which has been effective in reducing the annualized bleeding rate in haemophilia A patients with inhibitors. When coadministered with repetitive high doses of activated prothrombin complex concentrate (ie >100 U/kg/d for ≥24 hours), emicizumab was associated with thrombotic microangiopathy and thrombosis events. As a consequence the United Kingdom Haemophilia Centres Doctors' Organisation (UKHCDO) issued the first guidance on the treatment of bleeding episodes in patients receiving emicizumab. To build on and extend this work, a panel of German haemophilia specialists met to discuss the UK guidance, review current evidence and provide additional guidance for German healthcare professionals on how to optimize the management of patients with haemophilia A receiving emicizumab. Recommendations are provided on the use of bypassing and other agents to manage breakthrough bleeding, ITI in the emicizumab era, haemostatic support during surgery and issues relating to laboratory monitoring.

Symptom patterns in childhood arterial ischemic stroke: Analysis of a population-based study in Germany.

HINTERGRUND: Die zeitliche Verzögerung zwischen Symptombeginn und Diagnose ist eine Herausforderung in der Behandlung von Kindern mit arteriell ischämischem Schlaganfall. Frühere Studien zur klinischen Präsentation beschäftigten sich v. a. mit kumulativen Symptomen. ZIELSETZUNG: Ziel dieser Studie ist es, mögliche Symptommuster aufzuzeigen. METHODEN: In einer aktiven Beobachtungsstudie zwischen 01/2015 und 12/2016 (ESPED-Studie) wurden Kinder mit Erstdiagnose eines arteriell ischämischen Schlaganfalls eingeschlossen. Isoliert auftretende Erstsymptome wurden verschiedenen Symptomkombinationen gegenübergestellt. Zudem wurde untersucht, inwieweit ein als "akut" oder "progredient" klassifiziertes Auftreten der Symptome Rückschlüsse auf die zugrundeliegende Ätiologie erlaubt. ERGEBNISSE: Es wurden 99 Kinder in die Studie eingeschlossen. Unabhängig vom Alter traten überwiegend fokale Symptome auf (86%). Krampfanfälle als Initialsymptom wurden insbesondere bei Säuglingen beschrieben (67%), wohin-gegen diffuse, unspezifische Symptome vor allem bei Vorschulkindern (38%) und älteren Kindern (59%) auftraten. Isoliert traten fokale Symptome bei 37 Kindern auf, 48 Kinder zeigten zusätzlich unspezifische Symptome, darunter auch 9 Kinder mit Krampfanfällen. Isolierte unspezifische Symptome zeigten sich lediglich bei 7 Kindern, 2 Kinder wurden nur mit Krampfanfällen symptomatisch. Die Akuität des Symptombeginns wurde bei 53/78 als "akut" und bei "25/78 Fällen als "progredient" klassifiziert, lieferte jedoch keinen Hinweis auf die zugrundeliegende Ätiologie. SCHLUSSFOLGERUNG: Jedes neue fokal neurologische Defizit sollte unabhängig vom Auftreten (isoliert oder kombiniert, akut oder progredient) an einen kindlichen Schlaganfall denken lassen. BACKGROUND: Time delay between onset of clinical symptoms and diagnosis is a challenge in childhood arterial ischemic stroke. Most previous studies reported cumulative symptoms. OBJECTIVE: We attempted to identify typical symptom patterns and assessed their emergence in childhood stroke. METHODS: Prospective active surveillance in ESPED, a hospital based Pediatric Surveillance Unit for rare diseases in Germany, between January 2015 and December 2016. Case definition: first diagnosis of a radiologically confirmed arterial ischemic stroke. Symptom patterns were identified as occurring in isolation or in combination. We distinguished acute vs. progressive onset. We ascertained risk factors to identify the possible etiology. RESULTS: 99 children with childhood arterial ischemic stroke were reported. Focal symptoms were the predominant presenting feature (86%), independent of age. Seizures were more often seen in infants < 1 year (67%), whereas diffuse symptoms were more present in pre-school children (38%) and older children (59%). 37 children had focal features alone and 48 additional non-specific features, including 9 with seizures. Isolated non-specific features accounted for 7 cases, and 2 children had (focal) seizures as the only symptom. In 77% of all cases at least one risk factor was identified. The emergence of symptoms was acute in 53/78 cases and progressive in 25/78 cases. The pattern of emergence was unrelated to the underlying etiology. CONCLUSIONS: Any new focal neurological deficit in isolation, or associated with seizures or further non-specific symptoms should alert to childhood stroke.

Infrared Thermography as a Non-Invasive Tool to Explore Differences in the Musculoskeletal System of Children with Hemophilia Compared to an Age-Matched Healthy Group.

Recurrent joint bleeds and silent bleeds are the most common clinical feature in patients with hemophilia. Every bleed causes an immediate inflammatory response and is the leading cause of chronic crippling arthropathy. With the help of infrared thermography we wanted to detect early differences between a group of clinical non-symptomatic children with hemophilia (CWH) with no history of clinically detected joint bleeds and a healthy age-matched group of children. This could help to discover early inflammation and help implement early treatment and preventative strategies. It could be demonstrated that infrared thermography is sensitive enough to detect more signs of early inflammatory response in the CWH than in healthy children. It seems to detect more side differences in temperature than clinical examination of silent symptoms detects tender points. Silent symptoms/tender points seem to be combined with early local inflammation. Using such a non-invasive and sensor-based early detection, prevention of overloading and bleeding might be achieved.

Intracranial haemorrhage in children and adolescents with severe haemophilia A or B - the impact of prophylactic treatment.

The discussion of prophylactic therapy in haemophilia is largely focused on joint outcomes. The impact of prophylactic therapy on intracranial haemorrhage (ICH) is less known. This study aimed to analyse ICH in children with haemophilia, with a focus on different prophylaxis regimens and sequelae of ICH. We conducted a multicentre retrospective and prospective study that included 33 haemophilia centres from 20 countries. Inclusion criteria were children and adolescents born between 1993 and 2014, with severe haemophilia A or B without inhibitors. Participants were categorized by prophylaxis regimen: full, partial or none, based on dose and dose frequency of regular infusions. The cohort study included 1515 children: 29 cases of ICH over 8038 patient years were reported. The incidence of ICH in the prophylaxis group, 0·00033 cases of ICH/patient year, was significantly lower compared to the no prophylaxis group, 0·017 cases of ICH/patient year (RR 50·06; P < 0·001) and the partial prophylaxis group, 0·0050 cases of ICH/patient year (RR 14·92; P = 0·007). In the on-demand-group, 8% (2/24) children with ICH died and 33% had long-term sequelae, including intellectual and behavioural problems, paresis and epilepsy. Children on regular, frequent prophylaxis have a low risk of ICH compared to those using non-frequent or no prophylaxis.

Perioperative management of hemostasis in children and adolescents.

Invasive procedures in children are in most cases elective and are carried out in otherwise healthy children. While many surgeries are still performed in a hospital, more and more procedures are defined as "outpatient procedures," leading to increased discussion about safety and risks. This review will examine common practices, review the sparse literature and provide recommendations regarding the identification of children with increased bleeding risk, planning for children with known bleeding disorders and strategies for perioperative management. In conclusion, after careful planning, surgeries can be performed safely even in children with known bleeding disorders.

Impact of high-risk thrombophilia status on recurrence among children with a first non-central-venous-catheter-associated VTE: an observational multicentre cohort study.

Deficiency of antithrombin (AT), protein C (PC) or protein S (PS) constitutes a major risk factor for venous thromboembolism (VTE). Individuals at high risk for recurrence who benefit from screening need to be identified. The primary study objective was to determine the individual recurrence risk among children with a first non-central-venous-catheter-associated VTE with respect to their thrombophilia status and to evaluate if the clinical presentation at first VTE onset differs between children with AT, PC or PS deficiency versus no thrombophilia. We calculated the absolute risk of VTE recurrence and event-free-survival adjusted for thrombophilia, age, sex and positive family VTE history in 161 consecutively enrolled paediatric VTE patients. The presence of a deficiency relative to no thrombophilia was evaluated as a potential predictor of recurrence. Predictors for recurrence were AT deficiency (hazard ratio/95% CI: 6·5/2·46-17·2) and female gender (2·6/1·1-6·35). The annual recurrence rates (95% CIs) were 5·4% (2·6-10) in AT-deficient children, 1·3% (0·3-3·8) in patients with PC deficiency, 0·7% (0·08-2·4) in the PS-deficient cohort and 0·9% (0·4-1·8) in patients with no thrombophilia. Positive family VTE history or combined thrombophilias did not predict recurrence. Given the overall annual incidence rate of recurrence of 1·5% we suggest screening for AT deficiency in children with VTE.

Impact of high risk thrombophilia status on recurrence among children and adults with VTE: An observational multicenter cohort study.

BACKGROUND: Antithrombin [AT]-, protein C [PC]- or protein S [PS]-deficiency [D] constitutes a major risk factor for venous thromboembolism [VTE]. Primary study objective was to evaluate if the clinical presentation at first VTE onset differs between children and adults and to compare the individual recurrence risk among patients with respect to age at onset and their thrombophilia status ATD, PCD or PSD. METHODS/PATIENTS/RESULTS: In 137 of 688 consecutively enrolled pediatric and adult VTE patients we calculated the absolute risk of VTE recurrence and event-free-survival adjusted for thrombophilia and positive family VTE history. At first VTE children manifested i) with a lower rate of pulmonary embolism, ii) a higher rate of cerebral vascular events or multiple VTEs, and iii) showed a higher proportion of unprovoked VTE compared to adolescents and adults. Adult patients reported more often a positive VTE history compared to younger study participants. The adjusted odds of recurrence in adults was 2.05 compared to children. CONCLUSION: At disease manifestation children and adults differ with respect to i) thrombotic locations, ii) percentage of unprovoked versus provoked VTE, and iii) different rates of positive VTE family histories. Furthermore, adults showed a two-fold increase risk of VTE recurrence compared to children.

Intensity of factor VIII treatment and inhibitor development in children with severe hemophilia A: the RODIN study.

The objective of this study was to examine the association of the intensity of treatment, ranging from high-dose intensive factor VIII (FVIII) treatment to prophylactic treatment, with the inhibitor incidence among previously untreated patients with severe hemophilia A. This cohort study aimed to include consecutive patients with a FVIII activity < 0.01 IU/mL, born between 2000 and 2010, and observed during their first 75 FVIII exposure days. Intensive FVIII treatment of hemorrhages or surgery at the start of treatment was associated with an increased inhibitor risk (adjusted hazard ratio [aHR], 2.0; 95% confidence interval [CI], 1.3-3.0). High-dose FVIII treatment was associated with a higher inhibitor risk than low-dose FVIII treatment (aHR, 2.3; 95% CI, 1.0-4.8). Prophylaxis was only associated with a decreased overall inhibitor incidence after 20 exposure days of FVIII. The association with prophylaxis was more pronounced in patients with low-risk F8 genotypes than in patients with high-risk F8 genotypes (aHR, 0.61, 95% CI, 0.19-2.0 and aHR, 0.85, 95% CI, 0.51-1.4, respectively). In conclusion, our findings suggest that in previously untreated patients with severe hemophilia A, high-dosed intensive FVIII treatment increases inhibitor risk and prophylactic FVIII treatment decreases inhibitor risk, especially in patients with low-risk F8 mutations.

The risk of hemophagocytic lymphohistiocytosis in Hermansky-Pudlak syndrome type 2.

Genetic disorders of lymphocyte cytotoxicity predispose patients to hemophagocytic lymphohistiocytosis (HLH). Reduced lymphocyte cytotoxicity has been demonstrated in Hermansky-Pudlak syndrome type 2 (HPS2), but only a single patient was reported who developed HLH. Because that patient also carried a potentially contributing heterozygous RAB27A mutation, the risk for HLH in HPS2 remains unclear. We analyzed susceptibility to HLH in the pearl mouse model of HPS2. After infection with lymphocytic choriomeningitis virus, pearl mice developed all key features of HLH, linked to impaired virus control caused by a moderate defect in CTL cytotoxicity in vivo. However, in contrast to perforin-deficient mice, the disease was transient, and all mice fully recovered and controlled the infection. An additional heterozygous Rab27a mutation did not aggravate the cytotoxicity defect or disease parameters. In the largest survey of 22 HPS2 patients covering 234 patient years, we identified only 1 additional patient with HLH and 2 with incomplete transient HLH-like episodes, although cytotoxicity or degranulation was impaired in all 16 patients tested. HPS2 confers a risk for HLH that is lower than in Griscelli or Chediak-Higashi syndrome, probably because of a milder defect in cytotoxicity. Preemptive hematopoietic stem cell transplantation does not appear justified in HPS2.

Clinical and laboratory characteristics of children with venous thromboembolism and protein C-deficiency: an observational Israeli-German cohort study.

Venous thromboembolism [TE] is a multifactorial disease and protein C deficiency [PCD] constitutes a major risk factor. In the present study the prevalence of PCD and the clinical presentation at TE onset, including neonatal purpura fulminans, in a cohort of children are reported. In 367 unselected children (0·1-19 years) recruited between July 1996 and December 2013, a comprehensive thrombophilia screening was performed along with recording of anamnestic data. Twenty-five of 338 children (7·4%) had PCD. Mean age at first TE onset was 10 years (range 0·1-18). Leading thromboembolic manifestations were neonatal purpura fulminans (n = 5), TE of cerebral veins (n = 3), stroke (n = 2) deep veinthrombosis (DVT) of the leg (n = 10), DVT & pulmonary embolism (n = 2) and DVT & pelvic veins (n = 3). Concomitant risk factors for TE were identified in 12 patients, whereas 13 children spontaneously developed TE. A positive family history of DVT was found in 10 children. In this unselected cohort of paediatric patients with symptomatic TE the overall prevalence of PCD was 7·4%; 1·5% presented with neonatal purpura fulminans. Given its clinical implication for patients and family members, thrombophilia testing should be performed and the benefit of medical or educational interventions should be evaluated in this high-risk population.

Subcutaneous protein C concentrate in the management of severe protein C deficiency--experience from 12 centres.

Since the first description of subcutaneous protein C concentrate as treatment for severe protein C deficiency in 1996, further cases have been reported but there is no uniform approach to this form of treatment. In order to assess the safety and effectiveness of subcutaneous protein C concentrate and suggest recommendations for future use, patients who had received subcutaneous protein C concentrate were identified from the literature, by contacting the manufacturers and by personal communication. Treatment details were available from 14 cases. Apart from one case where the infusion interval was inadvertently increased, no thrombotic events occurred even when doses were subsequently reduced. Initially, a trough protein C level of >0·25 iu/ml should be aimed for. Subsequently, a smaller dose of subcutaneous protein C concentrate, especially if taken with an oral anticoagulant, may be protective maintenance treatment. The treatment was well tolerated with few side effects. Subcutaneous protein C concentrate on its own or combined with an oral anticoagulant appears to be safe and effective as maintenance treatment of severe protein C deficiency. A major advantage is the avoidance of central venous access devices. The incidence of neurodevelopmental handicap was high with blindness affecting the majority of patients.

A genome-wide association study identifies a gene network of ADAMTS genes in the predisposition to pediatric stroke.

Pediatric stroke is a rare but highly penetrant disease with a strong genetic background. Although there are an increasing number of genome-wide association studies (GWASs) for stroke in adults, such studies for stroke of pediatric onset are lacking. Here we report the results of the first GWAS on pediatric stroke using a large cohort of 270 family-based trios. GWAS was performed using the Illumina 370 CNV single nucleotide polymorphisms array and analyzed using the transmission disequilibrium test as implemented in PLINK. An enrichment analysis was performed to identify additional true association signals among lower P value signals and searched for cumulatively associated genes within protein interaction data using dmGWAS. We observed clustering of association signals in 4 genes belonging to one family of metalloproteinases at high (ADAMTS12, P = 2.9 × 10(-6); ADAMTS2, P = 8.0 × 10(-6)) and moderate (ADAMTS13, P = 9.3 × 10(-4); ADAMTS17, P = 8.5 × 10(-4)) significance levels. Over-representation and gene-network analyses highlight the importance of the extracellular matrix in conjunction with members of the phosphoinositide and calcium signaling pathways in the susceptibility for pediatric stroke. Associated extracellular matrix components, such as ADAMTS proteins, in combination with misbalanced coagulation signals as unveiled by gene network analysis suggest a major role of postnatal vascular injury with subsequent thrombus formation as the leading cause of pediatric stroke.

Determinants of bleeding before and during immune tolerance in 222 boys with severe hemophilia A and inhibitors >5 BU.

ABSTRACT: Prevention of bleeding and its consequences is the main goal of hemophilia treatment and determines treatment choices for patients who develop inhibitors. To assess bleeding before and during immune tolerance induction (ITI) and its association with ITI regimen and inhibitor titer, we selected and analyzed data on patients receiving high-titer inhibitors from the international prospective PedNet cohort study. In total, 222 patients with severe hemophilia A and inhibitor titers of >5 Bethesda units (BU) were followed from the first positive to the first negative inhibitor result (median overall follow-up, 1.7 years). Mean annual (joint) bleeding rates (AJBR) and 95% confidence intervals (CIs) were compared according to treatment and inhibitor titer using multivariable negative binomial regression. Before ITI, 115 patients showed an ABR of 6.1 (5.0-7.4) and an AJBR 2.6 (2.1-3.2). Bleeding was independent of inhibitor titer. During ITI, 202 patients had an ABR of 4.4 (3.9-5.1) and an AJBR of 1.7 (1.5-2.0). AJBR during ITI increased with inhibitor titer (hazard ratio [HR] for ≥200 BU vs 5 to 39 BU [4.9; CI, 3.2-7.4]) and decreased with daily ITI infusions (HR, 0.4; CI, 0.3-0.6) or activated prothrombin complex concentrate prophylaxis (HR, 0.4; CI, 0.2-0.8), whereas ITI dose and recombinant activated factor VII prophylaxis did not independently affect bleeding. These data provide evidence for a protective effect of repeated FVIII infusions (ITI) on bleeding in patients who have developed inhibitors; these data should be used to plan ITI and/or serve as a comparator for prophylaxis with nonreplacement therapy.

Novel mutation in Hermansky-Pudlak syndrome type 2 with mild immunological phenotype.

Patients with Hermansky-Pudlak syndrome type 2 (HPS2) present with oculocutaneous albinism, nystagmus, prolonged bleeding time, and increased susceptibility to infections. Twelve HPS2 patients with mutations in the ß3A-subunit of the cytosolic adaptor-related protein complex 3 (AP3B1, also called HPS2) have been described so far. Here, we report on a patient with oculocutaneous albinism who developed a life-threatening bleeding after tonsillectomy. She presented with moderate neutropenia and reduced granulopoiesis. Analyzing patient's impaired platelet function using electron microscopy and flow cytometry led to the diagnosis of HPS2. Flow cytometric analysis of the patient's platelets showed already elevated CD63 expression on resting platelets with no further increase after thrombin stimulation. Natural killer (NK) cell degranulation was partially impaired but target cell lysis of NK cells and cytotoxic T-lymphocytes (CTLs) were normal and the patient did not develop signs of hemophagocytic syndrome. Molecular genetic analyses revealed a novel 2 bp-deletion (c.3222_3223delTG) in the last exon of AP3B1 causing a frameshift and a prolonged altered protein. The location of the deletion at the very C-terminal end may prevent a complete loss of the HPS2 protein leading to a less pronounced severity of immunodeficiency than in other HPS2 patients.

Impact of thrombophilia on risk of arterial ischemic stroke or cerebral sinovenous thrombosis in neonates and children: a systematic review and meta-analysis of observational studies.

BACKGROUND: The aim of this study was to estimate the impact of thrombophilia on risk of first childhood stroke through a meta-analysis of published observational studies. METHODS AND RESULTS: A systematic search of electronic databases (Medline via PubMed, EMBASE, OVID, Web of Science, The Cochrane Library) for studies published from 1970 to 2009 was conducted. Data on year of publication, study design, country of origin, number of patients/control subjects, ethnicity, stroke type (arterial ischemic stroke [AIS], cerebral venous sinus thrombosis [CSVT]) were abstracted. Publication bias indicator and heterogeneity across studies were evaluated, and summary odds ratios (ORs) and 95% confidence intervals (CIs) were calculated with fixed-effects or random-effects models. Twenty-two of 185 references met inclusion criteria. Thus, 1764 patients (arterial ischemic stroke [AIS], 1526; cerebral sinus venous thrombosis [CSVT], 238) and 2799 control subjects (neonate to 18 years of age) were enrolled. No significant heterogeneity was discerned across studies, and no publication bias was detected. A statistically significant association with first stroke was demonstrated for each thrombophilia trait evaluated, with no difference found between AIS and CSVT. Summary ORs (fixed-effects model) were as follows: antithrombin deficiency, 7.06 (95% CI, 2.44 to 22.42); protein C deficiency, 8.76 (95% CI, 4.53 to 16.96); protein S deficiency, 3.20 (95% CI, 1.22 to 8.40), factor V G1691A, 3.26 (95% CI, 2.59 to 4.10); factor II G20210A, 2.43 (95% CI, 1.67 to 3.51); MTHFR C677T (AIS), 1.58 (95% CI, 1.20 to 2.08); antiphospholipid antibodies (AIS), 6.95 (95% CI, 3.67 to 13.14); elevated lipoprotein(a), 6.27 (95% CI, 4.52 to 8.69), and combined thrombophilias, 11.86 (95% CI, 5.93 to 23.73). In the 6 exclusively perinatal AIS studies, summary ORs were as follows: factor V, 3.56 (95% CI, 2.29 to 5.53); and factor II, 2.02 (95% CI, 1.02 to 3.99). CONCLUSIONS: The present meta-analysis indicates that thrombophilias serve as risk factors for incident stroke. However, the impact of thrombophilias on outcome and recurrence risk needs to be further investigated.

Safety and efficacy of low molecular weight heparins in children: a systematic review of the literature and meta-analysis of single-arm studies.

Within the last two decades low molecular weight heparins (LMWH) have gained increasing widespread use as anticoagulants in children. The use of LMWH has been implemented into clinical care even though there is a lack of firm evidence on the efficacy and safety of LMWH in this population due to the absence of sufficiently powered randomized controlled trials. In the absence of clinical trials, we performed a meta-analysis of available single-arm studies using LMWH in children. A systematic search of electronic databases (Medline, EMBASE, OVID, Web of Science, The Cochrane Library) for studies published from 1980 to 2010 was conducted using keywords in combination both as MeSH terms and text words. Two authors independently screened citations and those meeting a priori defined inclusion criteria were retained. Data on year of publication, study design, country of origin, number of patients, ethnicity, venous thromboembolic events type, and frequency of recurrence and major bleedings were abstracted. Pooled incidence rates (IR) including 95% confidence intervals (95% CIs) on efficacy and safety data of LMWH administration on primary prophylaxis, as well as on secondary prophylaxis in children following symptomatic thromboembolism (TE) were shown. We included 2251 pediatric patients derived from 35 single-arm studies from 12 study countries who were eligible for analysis in the present systematic review. Pooled incidence rates (95% CI) to develop first TE on primary prophylaxis, further TE event on LMWH secondary prophylaxis, or a major bleeding event on LMWH were 0.047 (0.023 to 0.091), 0.052 (0.037 to 0.073) for efficacy, and 0.054 (0.039 to 0.074) for safety (treatment data only), respectively. Efficacy and safety data are comparable with adult data. The present systematic review suggests that use of LMWH in children as primary prophylaxis and in treatment of symptomatic thrombosis is effective and safe. However, properly designed randomized controlled trials are needed.