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Abstract Corticosteroids (CSs) are standard first‐line therapy for immune thrombocytopenia (ITP). Prolonged exposure is associated with substantial toxicity; thus guidelines recommend avoidance of prolonged CS treatment and early use of second‐line therapies. However, real‐world evidence on ITP treatment patterns remains limited. We aimed to assess real‐world treatment patterns in patients with newly‐diagnosed ITP, using two large US healthcare databases (Explorys and MarketScan) between January 1, 2011 and July 31, 2017. Adults with ITP, ≥12 months of database registration prior to diagnosis, ≥1 ITP treatment, and ≥1 month enrollment following initiation of first ITP treatment were included (n = 4066 Explorys; n = 7837 MarketScan). Information on lines of treatment (LoTs) was collected. As expected, CSs were the most common first‐line treatment (Explorys, 87.9%; MarketScan, 84.5%). However, CSs remained by far the most common treatment (Explorys ≥77%; MarketScan ≥85%) across all subsequent LoTs. Second‐line treatments such as rituximab (12.0% Explorys; 24.5% MarketScan), thrombopoietin receptor agonists (11.3% Explorys; 15.6% MarketScan), and splenectomy (2.5% Explorys; 8.1% MarketScan) were used much less frequently. CS use is widespread in the US in patients with ITP across all LoTs. Quality improvement initiatives are needed to reduce CS exposure and bolster use of second‐line treatments.

Abstract Severe adverse events (AEs) after COVID-19 vaccination are not well studied in randomized controlled trials (RCTs) due to rarity and short follow-up. To monitor the safety of COVID-19 vaccines (“Pfizer” vaccine dose 1 and 2, “Moderna” vaccine dose 1 and 2, and “Janssen” vaccine single dose) in the U.S., especially regarding severe AEs, we compare the relative rankings of these vaccines using both RCT and the Vaccine Adverse Event Reporting System (VAERS) data. The risks of local and systemic AEs were assessed from the three pivotal COVID-19 vaccine trials and also calculated in the VAERS cohort consisting of 559,717 reports between December 14, 2020 and September 17, 2021. AE rankings of the five vaccine groups calculated separately by RCT and VAERS were consistent, especially for systemic AEs. For severe AEs reported in VAERS, the reported risks of thrombosis and GBS after Janssen vaccine were highest. The reported risk of shingles after the first dose of Moderna vaccine was highest, followed by the second dose of the Moderna vaccine. The reported risk of myocarditis was higher after the second dose of Pfizer and Moderna vaccines. The reported risk of anaphylaxis was higher after the first dose of Pfizer vaccine. Limitations of this study are the inherent biases of the spontaneous reporting system data, and only including three pivotal RCTs and no comparison with other active vaccine safety surveillance systems.

Summary: Background: Diagnosing heparin-induced thrombocytopenia (HIT) at the bedside remains challenging, exposing a significant number of patients at risk of delayed diagnosis or overtreatment. We hypothesized that machine-learning algorithms could be utilized to develop a more accurate and user-friendly diagnostic tool that integrates diverse clinical and laboratory information and accounts for complex interactions. Methods: We conducted a prospective cohort study including 1393 patients with suspected HIT between 2018 and 2021 from 10 study centers. Detailed clinical information and laboratory data were collected, and various immunoassays were conducted. The washed platelet heparin-induced platelet activation assay (HIPA) served as the reference standard. Findings: HIPA diagnosed HIT in 119 patients (prevalence 8.5%). The feature selection process in the training dataset (75% of patients) yielded the following predictor variables: (1) immunoassay test result, (2) platelet nadir, (3) unfractionated heparin use, (4) CRP, (5) timing of thrombocytopenia, and (6) other causes of thrombocytopenia. The best performing models were a support vector machine in case of the chemiluminescent immunoassay (CLIA) and the ELISA, as well as a gradient boosting machine in particle-gel immunoassay (PaGIA). In the validation dataset (25% of patients), the AUROC of all models was 0.99 (95% CI: 0.97, 1.00). Compared to the currently recommended diagnostic algorithm (4Ts score, immunoassay), the numbers of false-negative patients were reduced from 12 to 6 (−50.0%; ELISA), 9 to 3 (−66.7%, PaGIA) and 14 to 5 (−64.3%; CLIA). The numbers of false-positive individuals were reduced from 87 to 61 (−29.8%; ELISA), 200 to 63 (−68.5%; PaGIA) and increased from 50 to 63 (+29.0%) for the CLIA. Interpretation: Our user-friendly machine-learning algorithm for the diagnosis of HIT (https://toradi-hit.org) was substantially more accurate than the currently recommended diagnostic algorithm. It has the potential to reduce delayed diagnosis and overtreatment in clinical practice. Future studies shall validate this model in wider settings. Funding: Swiss National Science Foundation (SNSF), and International Society on Thrombosis and Haemostasis (ISTH).

Abstract Background Thrombopoietin receptor agonists (TPO‐RAs) are used to treat primary immune thrombocytopenia (ITP). Some patients have discontinued treatment while maintaining a hemostatic platelet count. Objectives To develop expert consensus on when it is appropriate to consider tapering TPO‐RAs in ITP, how to taper patients off therapy, how to monitor patients after discontinuation, and how to restart therapy. Methods We used a RAND/UCLA modified Delphi panel method. Ratings were completed independently by each expert before and after a meeting. Second‐round ratings were used to develop the panel’s guidance. The panel was double‐blinded: The sponsor and nonchair experts did not know each other’s identities. Results Guidance on when it is appropriate to taper TPO‐RAs in children and adults was developed based on patient platelet count, history of bleeding, intensification of treatment, trauma risk, and use of anticoagulants/platelet inhibitors. For example, it is appropriate to taper TPO‐RAs in patients who have normal/above‐normal platelet counts, have no history of major bleeding, and have not required an intensification of treatment in the past 6 months; it is inappropriate to taper TPO‐RAs in patients with low platelet counts. Duration of ITP, months on TPO‐RA, or timing of platelet response to TPO‐RA did not have an impact on the panel’s guidance on appropriateness to taper. Guidance on how to taper patients off therapy, how to monitor patients after discontinuation, and how to restart therapy is also provided. Conclusion This guidance could support clinical decision making and the development of clinical trials that prospectively test the safety of tapering TPO‐RAs.

Abstract Background The optimal prophylactic preprocedural management of patients with coagulopathy due to liver disease is not known. Objectives Our objective was to compare the efficacy and safety of fresh frozen plasma (FFP) with prothrombin complex concentrate (PCC) in the preprocedural management of patients with coagulopathy of liver disease. Methods We conducted a systematic review to examine published evidence regarding treatment with FFP or PCC in adults with coagulopathy of liver disease undergoing an invasive procedure. Direct comparisons and single‐arm studies were eligible. Efficacy outcomes included major bleeding, mortality, and correction of prothrombin time (PT) and/or international normalized ratio (INR). Safety outcomes included thrombosis and transfusion‐related complications. Results A total of 95 articles were identified for full‐text review. Nine studies were eligible and included in the review. No randomized trials comparing FFP versus PCC were identified. Only two studies directly compared FFP versus PCC. In these studies, PCC appeared to result in higher rates of correction of PT/INR, but bleeding outcomes were not different. In the single‐arm studies, bleeding events appeared low overall. Volume overload was the most common recorded adverse event in patients receiving FFP. Thromboembolic events occurred rarely, but exclusively in the PCC group. Due to heterogeneity in study definitions and bias, meta‐analysis was not possible. Our study found no evidence to favor a specific product over another. Conclusions Insufficient data exist on the effects of FFP versus PCC administration before invasive procedures in patients with coagulopathy of liver disease to make conclusions with respect to relative efficacy or safety.

Abstract Background Second‐line treatment for immune thrombocytopenia (ITP) is not well reported for patients treated in real‐world clinical settings. Objective The purpose of this study was to compare outcomes of four second‐line treatments for ITP. Patients/methods Included adult patients had at least two medical records containing ITP diagnoses and second‐line eltrombopag, romiplostim, rituximab, or splenectomy. Date of treatment initiation or splenectomy was set as index date, between July 1, 2008, and March 31, 2017. Patients had first‐line corticosteroid or intravenous immune globulin treatment and continuous database activity from 6 months before to 12 months after index. Patient characteristics, treatment patterns, platelet counts, bleeding‐related episodes (BREs), and thrombotic events (TEs) were compared by second‐line treatment cohort. Results The sample included 3332 patients (mean age, 60.5 years; 52.3% female): eltrombopag (5.8%), romiplostim (9.9%), rituximab (73.3%), and splenectomy (11.0%). Patients having splenectomy were younger, more likely female and commercially insured, and less likely to require a third line of treatment than medical regimen cohorts. Proportions of patients having treatment‐free (≥180 days with no second‐line index or rescue agent) periods varied significantly (P = .01) by regimen: 33% for eltrombopag, 23% for romiplostim, 26% for rituximab, and 17% for splenectomy. All regimens significantly improved platelet counts, while TE and BRE rates differed significantly (P = .03 and P = .01, respectively) when all treatment groups were compared. Conclusions Over an average 7‐year follow‐up, all second‐line regimens improved platelet counts, but eltrombopag yielded the highest proportion of patients with completely treatment‐free periods of at least 180 days.

Abstract Although arterial and venous thromboembolic disorders are among the most frequent causes of mortality and morbidity, there has been little description of how the composition of thrombi and emboli depends on their vascular origin and age. We quantified the structure and composition of arterial and venous thrombi and pulmonary emboli using high-resolution scanning electron microscopy. Arterial thrombi contained a surprisingly large amount of fibrin, in addition to platelets. The composition of pulmonary emboli mirrored the most distal part of venous thrombi from which they originated, which differed from the structure of the body and head of the same thrombi. All thrombi and emboli contained few biconcave red blood cells but many polyhedrocytes or related forms of compressed red blood cells, demonstrating that these structures are a signature of clot contraction in vivo. Polyhedrocytes and intermediate forms comprised the major constituents of venous thrombi and pulmonary emboli. The structures within all of the thrombi and emboli were very tightly packed, in contrast to clots formed in vitro. There are distinctive, reproducible differences among arterial and venous thrombi and emboli related to their origin, destination and duration, which may have clinical implications for the understanding and treatment of thrombotic disorders.

Abstract Background Microfluidic clotting assays permit drug action studies for hemophilia therapeutics under flow. However, limited availability of patient samples and Inter‐donor variability limit the application of such assays, especially with many patients on prophylaxis. Objective To develop approaches to phenocopy hemophilia using modified healthy blood in microfluidic assays. Methods Corn trypsin inhibitor (4 µg/mL)‐treated healthy blood was dosed with either anti–factor VIII (FVIII; hemophilia A model) or a recombinant factor IX (FIX) missense variant (FIX‐V181T; hemophilia B model). Treated blood was perfused at 100 s−1 wall shear rate over collagen/tissue factor (TF) or collagen/factor XIa (FXIa). Results Anti‐FVIII partially blocked fibrin production on collagen/TF, but completely blocked fibrin production on collagen/FXIa, a phenotype reversed with 1 µmol/L bispecific antibody (emicizumab), which binds FIXa and factor X. As expected, emicizumab had no significant effect on healthy blood (no anti‐FVIII present) perfused over collagen/FXIa. The efficacy of emicizumab in anti‐FVIII‐treated healthy blood phenocopied the action of emicizumab in the blood of a patient with hemophilia A perfused over collagen/FXIa. Interestingly, a patient‐derived FVIII‐neutralizing antibody reduced fibrin production when added to healthy blood perfused over collagen/FXIa. For low TF surfaces, reFIX‐V181T (50 µg/mL) fully blocked platelet and fibrin deposition, a phenotype fully reversed with anti‐TFPI. Conclusion Two new microfluidic hemophilia A and B models demonstrate the potency of anti‐TF pathway inhibitor, emicizumab, and a patient‐derived inhibitory antibody. Using collagen/FXIa‐coated surfaces resulted in reliable and highly sensitive hemophilia models.

Abstract Heparin‐induced thrombocytopenia (HIT) is a life‐threatening pathologic reaction to heparin‐based products. Diagnosis of this condition can be confounded by other comorbidities or by acute illness—oftentimes presenting challenging clinical dilemmas, particularly in critically ill patients. A 67‐year‐old woman was admitted with liver failure and severe hyperbilirubinemia. She developed thrombocytopenia after prophylactic heparin exposure. Subsequent quantitative latex immunoturbidimetric assay (LIA) HIT antibody testing was intermediately positive. Confirmatory serotonin release assay testing subsequently returned negative. Platelet factor4–dependent P‐selectin expression assay also returned negative, suggesting false positivity of the initial LIA tests. Concern was raised that hyperbilirubinemia (total bilirubin, 55.5 mg/dL) interfered with the original assay. Further testing with a separate HIT ELISA assay, which includes multiple washes and dilutions of the serum in order to effectively remove bilirubin, returned negative. Medical providers must consider the possibility of false‐positive LIA testing when evaluating for HIT in the setting of severe hyperbilirubinemia.

Abstract Corticosteroids remain a crucial component of first‐line therapy for immune thrombocytopenia (ITP) due to low cost, high initial response rates, and acceptable short‐term tolerability. However, extended and recurrent use of corticosteroids is associated with substantial toxicity. Survey studies indicate that >95% of patients with ITP treated with corticosteroids report adverse effects, more than one‐third of whom require reduction or discontinuation of treatment. In light of the heavy treatment burden of prolonged corticosteroid exposure, clinical practice guidelines recommend limiting corticosteroid treatment to no more than 6 weeks in adults with ITP receiving initial therapy. For patients who require subsequent therapy, clinical practice guidelines recommend treatments more suitable for long‐term disease control such as thrombopoietin receptor agonists, rituximab, other immune‐modulating medications, or splenectomy, rather than repeated courses of corticosteroids. Despite these recommendations, real‐world evidence suggests that corticosteroids remain the most frequently used treatment for adults with ITP, not only in the first line, but also in the second and third line. In this review, we summarize evidence on the efficacy, safety, and tolerability of corticosteroids; discuss the problem of overuse; and suggest strategies for curtailing the excessive use of corticosteroids in adults with ITP.

Abstract: Background: Despite an increase in the number of therapies available to treat patients with immune thrombocytopenia (ITP), there are minimal data from randomized trials to assist physicians with the management of patients.Objective: These evidence-based guidelines of the American Society of Hematology (ASH) are intended to support patients, clinicians, and other health care professionals in their decisions about the management of ITP.Methods: In 2015, ASH formed a multidisciplinary guideline panel that included 8 adult clinical experts, 5 pediatric clinical experts, 2 methodologists with expertise in ITP, and 2 patient representatives. The panel was balanced to minimize potential bias from conflicts of interest. The panel reviewed the ASH 2011 guideline recommendations and prioritized questions. The panel used the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach, including evidence-to-decision frameworks, to appraise evidence (up to May 2017) and formulate recommendations.Results: The panel agreed on 21 recommendations covering management of ITP in adults and children with newly diagnosed, persistent, and chronic disease refractory to first-line therapy who have non–life-threatening bleeding. Management approaches included: observation, corticosteroids, IV immunoglobulin, anti-D immunoglobulin, rituximab, splenectomy, and thrombopoietin receptor agonists.Conclusions: There was a lack of evidence to support strong recommendations for various management approaches. In general, strategies that avoided medication side effects were favored. A large focus was placed on shared decision-making, especially with regard to second-line therapy. Future research should apply standard corticosteroid-dosing regimens, report patient-reported outcomes, and include cost-analysis evaluations.

Major surgery is associated with an increased risk of venous thromboembolism (VTE), thus the application of mechanical or pharmacologic prophylaxis is recommended. The incidence of VTE in patients with inherited platelet disorders (IPD) undergoing surgical procedures is unknown and no information on the current use and safety of thromboprophylaxis, particularly of low-molecular-weight-heparin in these patients is available. Here we explored the approach to thromboprophylaxis and thrombotic outcomes in IPD patients undergoing surgery at VTE-risk participating in the multicenter SPATA study. We evaluated 210 surgical procedures carried out in 155 patients with well-defined forms of IPD (VTE-risk: 31% high, 28.6% intermediate, 25.2% low, 15.2% very low). The use of thromboprophylaxis was low (23.3% of procedures), with higher prevalence in orthopedic and gynecological surgeries, and was related to VTE-risk. The most frequently employed thromboprophylaxis was mechanical and appeared to be effective, as no patients developed thrombosis, including patients belonging to the highest VTE-risk classes. Low-molecular-weight-heparin use was low (10.5%) and it did not influence the incidence of post-surgical bleeding or of antihemorrhagic prohemostatic interventions use. Two thromboembolic events were registered, both occurring after high VTE-risk procedures in patients who did not receive thromboprophylaxis (4.7%). Our findings suggest that VTE incidence is low in patients with IPD undergoing surgery at VTE-risk and that it is predicted by the Caprini score. Mechanical thromboprophylaxis may be of benefit in patients with IPD undergoing invasive procedures at VTE-risk and low-molecular-weight-heparin should be considered for major surgery.

Background:. Individuals with hemophilia undergoing hip or knee arthroplasty are at risk for complications such as bleeding and infection. However, data on hospital length of stay (LOS) and readmission rates compared with nonhemophilic controls are lacking. This study compared the complication rates, LOS, and unplanned 30-day readmission rates between patients with hemophilia and nonhemophilic controls. Methods:. This retrospective cohort study used the Pennsylvania Health Care Cost Containment Council (PHC4) database from 2007 to 2015 to compare outcomes in patients with hemophilia and nonhemophilic controls undergoing partial and total hip arthroplasty, knee arthroplasty, and revision knee arthroplasty. Results:. A total of 118 patients with hemophilia and 3,811 controls were identified. Compared with controls, patients with hemophilia had a higher risk of bleeding complications after hip procedures (38.7% versus 16.1%, p = 0.003), a higher risk of surgical site infection after knee procedures (8.1% versus 1.1%, p < 0.001), longer median LOS after hip (6 versus 3 days, p < 0.001) and knee (5 versus 3 days, p < 0.001) procedures, and higher rates of unplanned 30-day readmission after hip (22.6% versus 4.1%, p < 0.001) and knee (10.3% versus 4.5%, p = 0.018) procedures. The most common reason for unplanned 30-day readmission in patients with hemophilia was bleeding or the patient’s underlying coagulopathy (25.1%). Conclusions:. Patients with hemophilia undergoing hip or knee arthroplasty had a higher incidence of postoperative bleeding (hip procedures) and surgical site infections (knee procedures), longer LOS, and higher rates of unplanned 30-day readmission compared with nonhemophilic controls. Key limitations of our study include the potential for inaccurate coding, the relatively small number of patients in the hemophilia cohort, and the uneven distribution of procedure type in the hemophilia and control cohorts. Level of Evidence:. Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Abstract: Men with hemophilia were initially thought to be protected from cardiovascular disease (CVD), but it is now clear that atherothrombotic events occur. The primary objective of the CVD in Hemophilia study was to determine the prevalence of CVD and CVD risk factors in US older men with moderate and severe hemophilia and to compare findings with those reported in age-comparable men in the Atherosclerosis Risk in Communities (ARIC) cohort. We hypothesized if lower factor levels are protective from CVD, we would see a difference in CVD rates between more severely affected and unaffected men. Beginning in October 2012, 200 patients with moderate or severe hemophilia A or B (factor VIII or IX level ≤ 5%), aged 54 to 73 years, were enrolled at 19 US hemophilia treatment centers. Data were collected from patient interview and medical records. A fasting blood sample and electrocardiogram (ECG) were obtained and assayed and read centrally. CVD was defined as any angina, any myocardial infarction by ECG or physician diagnosis, any self-reported nonhemorrhagic stroke or transient ischemic attack verified by physicians, or any history of coronary bypass graft surgery or coronary artery angioplasty. CVD risk factors were common in the population. Compared with men of similar age in the ARIC cohort, patients with hemophilia had significantly less CVD (15% vs 25.8%; P < .001). However, on an individual patient level, CVD events occur and efforts to prevent cardiovascular events are warranted. Few men were receiving secondary prophylaxis with low-dose aspirin, despite published opinion that it can be used safely in this patient population.

Background Inherited thrombophilias are well‐established predisposing factors for venous thromboembolism, but their role in arterial thrombosis, such as arterial ischemic stroke, remains uncertain. We aimed to evaluate the association between inherited thrombophilia (factor V Leiden, prothrombin G20210A mutation, protein C deficiency, protein S deficiency, and antithrombin deficiency) and risk of arterial ischemic stroke in adults. Methods and Results We searched PubMed, EMBASE, and Cochrane Library Databases from inception to December 31, 2018. We included case‐control or cohort studies of adults reporting the prevalence of inherited thrombophilias in those with arterial ischemic stroke and subjects without arterial ischemic stroke. Two reviewers (T.C., E.D.) independently searched the literature and extracted data. Pooled odds ratios (ORs) and 95% CIs were calculated using random‐effects model. We identified 68 eligible studies, which collectively enrolled 11 916 stroke patients and 96 057 controls. The number of studies reporting factor V Leiden, prothrombin G20210A mutation, protein C deficiency, protein S deficiency, and antithrombin deficiency were 56, 45, 15, 17, and 12, respectively. Compared with controls, patients with arterial ischemic stroke were significantly more likely to have the following inherited thrombophilias: factor V Leiden (OR, 1.25; 95% CI, 1.08–1.44; I2=0%), prothrombin G20210A mutation (OR, 1.48; 95% CI, 1.22–1.80; I2=0%), protein C deficiency (OR, 2.13; 95% CI, 1.16–3.90; I2=0%), and protein S deficiency (OR, 2.26; 95% CI, 1.34–3.80; I2=8.8%). Statistical significance was not reached for antithrombin deficiency (OR, 1.25; 95% CI, 0.58–2.67; I2=8.8%). Conclusions Inherited thrombophilias (factor V Leiden, prothrombin G20210A mutation, protein C deficiency, and protein S deficiency) are associated with an increased risk of arterial ischemic stroke in adults. The implications of these findings with respect to clinical management of patients with ischemic stroke require further investigation.

Abstract: Heparin-induced thrombocytopenia (HIT) is a thrombotic disorder initiated by antibodies to complexes between platelet factor 4 (PF4) and heparin. The risk of recurrent thromboembolism persists after heparin is cleared and platelet activation leading to release of PF4 has dissipated. We asked whether antigenic complexes between polyphosphates and PF4 released from activated platelets might intensify or sustain the prothrombotic phenotype of HIT. PF4 forms stable, ultralarge complexes with polyphosphates of various sizes, including those released from platelets, which are recognized by the HIT-like monoclonal KKO, an immunoglobulin G2bκ monoclonal heparin/PF4 binding antibody, and by human HIT antibodies. KKO helps to protect PF4/polyphosphate complexes from degradation by phosphatases. Complement is activated when HIT antibodies bind to PF4/polyphosphate complexes and PF4 reverses the inhibition of complement by polyphosphates. Polyphosphates and PF4 are stored primarily in separate granules in resting platelets, but they colocalize when the cells are activated. Platelets activated by subaggregating doses of thrombin receptor activating peptide release polyphosphates and PF4, which form antigenic complexes that allow KKO to further activate platelets in the absence of heparin and exogenous PF4. These studies suggest that thrombin- or immune complex–mediated release of endogenous antigenic PF4/polyphosphate complexes from platelets may augment the prothrombotic risk of HIT and perpetuate the risk of thrombosis after heparin has been discontinued.

Antithrombotic treatment puts patients at risk of major bleeding. Fast and adequate response to anticoagulant-associated bleeding may not only stop the bleeding but prevent severe complications. However, practical treatment algorithms to guide physicians in emergency situations are lacking. Important principles that arise from management of bleeding in general are (a) implementation of an in-house algorithm, (b) rapid identification and treatment of the bleeding source, (c) adequate fluid resuscitation, (d) consideration of the application of tranexamic acid and (e) appropriate coagulation testing. We present an algorithm for anticoagulant-associated bleeding and urgent surgery, derived from available data and recommendations, and implemented at our institution. Decisions regarding reversal agents or postponing surgery are based on two questions: the occurrence of a life-threatening bleed or urgent indication for surgery, and the presence of a relevant drug level. Immediate application of reversal agents is suggested if the clinical situation is urgent and laboratory test results are delayed or unavailable. A relevant anticoagulant drug level is required in all other cases. We discuss appropriate laboratory assays for all commonly available anticoagulants, report respective target ranges or expected values, discuss time intervals before surgery, and present critical cut-off values to be used as decision criteria. Specific and unspecific reversal agents for all anticoagulants including the direct oral anticoagulants will be presented. We aim to provide practical guidance for physicians in emergency situations. In addition, we summarise and discuss available experimental and clinical data as well as recommendations provided by scientific societies, authorities and manufacturers.

Pregnancy in women with inherited thrombocytopenias is a major matter of concern as both the mothers and the newborns are potentially at risk of bleeding. However, medical management of this condition cannot be based on evidence because of the lack of consistent information in the literature. To advance knowledge on this matter, we performed a multicentric, retrospective study evaluating 339 pregnancies in 181 women with 13 different forms of inherited thrombocytopenia. Neither the degree of thrombocytopenia nor the severity of bleeding tendency worsened during pregnancy and the course of pregnancy did not differ from that of healthy subjects in terms of miscarriages, fetal bleeding and pre-term births. The degree of thrombocytopenia in the babies was similar to that in the mother. Only 7 of 156 affected newborns had delivery-related bleeding, but 2 of them died of cerebral hemorrhage. The frequency of delivery-related maternal bleeding ranged from 6.8% to 14.2% depending on the definition of abnormal blood loss, suggesting that the risk of abnormal blood loss was increased with respect to the general population. However, no mother died or had to undergo hysterectomy to arrest bleeding. The search for parameters predicting delivery-related bleeding in the mother suggested that hemorrhages requiring blood transfusion were more frequent in women with history of severe bleedings before pregnancy and with platelet count at delivery below 50 × 109/L.

The JAK2V617F allele has recently been identified in patients with polycythemia vera (PV), essential thrombocytosis (ET), and myelofibrosis with myeloid metaplasia (MF). Subsequent analysis has shown that constitutive activation of the JAK-STAT signal transduction pathway is an important pathogenetic event in these patients, and that enzymatic inhibition of JAK2V617F may be of therapeutic benefit in this context. However, a significant proportion of patients with ET or MF are JAK2V617F-negative. We hypothesized that activation of the JAK-STAT pathway might also occur as a consequence of activating mutations in certain hematopoietic-specific cytokine receptors, including the erythropoietin receptor (EPOR), the thrombopoietin receptor (MPL), or the granulocyte-colony stimulating factor receptor (GCSFR).DNA sequence analysis of the exons encoding the transmembrane and juxtamembrane domains of EPOR, MPL, and GCSFR, and comparison with germline DNA derived from buccal swabs, identified a somatic activating mutation in the transmembrane domain of MPL (W515L) in 9% (4/45) of JAKV617F-negative MF. Expression of MPLW515L in 32D, UT7, or Ba/F3 cells conferred cytokine-independent growth and thrombopoietin hypersensitivity, and resulted in constitutive phosphorylation of JAK2, STAT3, STAT5, AKT, and ERK. Furthermore, a small molecule JAK kinase inhibitor inhibited MPLW515L-mediated proliferation and JAK-STAT signaling in vitro. In a murine bone marrow transplant assay, expression of MPLW515L, but not wild-type MPL, resulted in a fully penetrant myeloproliferative disorder characterized by marked thrombocytosis (Plt count 1.9-4.0 x 10(12)/L), marked splenomegaly due to extramedullary hematopoiesis, and increased reticulin fibrosis.Activation of JAK-STAT signaling via MPLW515L is an important pathogenetic event in patients with JAK2V617F-negative MF. The bone marrow transplant model of MPLW515L-mediated myeloproliferative disorders (MPD) exhibits certain features of human MF, including extramedullary hematopoiesis, splenomegaly, and megakaryocytic proliferation. Further analysis of positive and negative regulators of the JAK-STAT pathway is warranted in JAK2V617F-negative MPD.