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Inherited thrombocytopenias (ITs) are a heterogeneous group of disorders characterized by low platelet count that may result in bleeding tendency. Despite progress being made in defining the genetic causes of ITs, nearly 50% of patients with familial thrombocytopenia are affected with forms of unknown origin. Here, through exome sequencing of 2 siblings with autosomal-recessive thrombocytopenia, we identified biallelic loss-of-function variants in

To the editor: Since the discovery that mutations in the 5′ untranslated region (UTR) of ANKRD26 are responsible for an autosomal-dominant form of thrombocytopenia ( ANKRD26 -RT),[1][1] 21 affected families were reported.[2][2] A study analyzing this series of patients suggested that ANKRD26 -RT

A form of autosomal dominant macrothrombocytopenia is characterized by mild or no clinical symptoms, normal platelet function, and normal megakaryocyte count. Because this condition has so far received little attention, patients are subject to misdiagnosis and inappropriate therapy. To identify the molecular basis of this disease, 12 Italian families were studied by linkage analysis and mutation screening. Flow cytometry evaluations of platelet membrane glycoproteins (GPs) were also performed. Linkage analysis in 2 large families localized the gene to chromosome 17p, in an interval containing an excellent candidate, the GPIbα gene. GPIbα, together with other proteins, constitutes the plasma von Willebrand factor (vWF) receptor, which is altered in Bernard-Soulier syndrome (BSS). In 6 of 12 families, a heterozygous Ala156Val missense substitution was identified. Platelet membrane GP studies were performed in 10 patients. Eight were distinguished by a reduction of GPs comparable to that found in a BSS heterozygous condition, whereas the other 2, without the Ala156Val mutation, had a normal content of platelet GPs. In conclusion, the current study provides evidence that most (10 of 12) patients with an original diagnosis of autosomal dominant macrothrombocytopenia shared clinical and molecular features with the heterozygous BSS phenotype. The remaining 2 affected subjects represented patients with “true” autosomal dominant macrothrombocytopenia; the GPIb/IX/V complex was normally distributed on the surface of their platelets. Thus, the diagnosis of heterozygous BSS must always be suspected in patients with inherited thrombocytopenia and platelet macrocytosis.

Platelet transfusion is currently the primary medical treatment for reducing thrombocytopenia in patients with inherited thrombocytopenias. To evaluate whether stimulating megakaryopoiesis could increase platelet count in these conditions, we treated patients with a severe thrombocytopenia induced by MYH9 mutations (MYH9-related disease) with a nonpeptide thrombopoietin receptor agonist, eltrombopag. Twelve adult patients with MYH9-RD and platelet counts of less than 50 × 109/L received 50 mg of eltrombopag orally per day for 3 weeks. Patients who achieved a platelet count higher than 150 × 109/L stopped therapy, those with 100 to 150 platelets × 109/L continued treatment at the same eltrombopag dose for 3 additional weeks, while those with less than 100 platelets × 109/L increased the eltrombopag dose to 75 mg for 3 weeks. Major responses (platelet count of at least 100 × 109/L or 3 times the baseline value) were obtained in 8 patients, minor responses (platelet counts at least twice the baseline value) in 3. One patient did not respond. Bleeding tendency disappeared in 8 of 10 patients with bleeding symptoms at baseline. Mild adverse events were reported in 2 patients. The availability of thrombopoietin mimetics opened new prospects in the treatment of inherited thrombocytopenias. This study is registered at www.clinicaltrials.gov as NCT01133860 (European Union Drug Regulating Authorities Clinical Trials number 2008-001903-42).

Introduction FNAIT is associated with severe bleeding, especially intracranial hemorrhage (ICH), in the fetus and/or newborn. More than 75% of ICHs occur in utero and up to 50% before 32 weeks gestation. The consequences of ICH include death (35%) or serious neurological sequelae in survivors (83%). FNAIT requires prompt identification and treatment antepartum, postpartum and in subsequent pregnancies. An international panel was convened by the International Collaboration for Transfusion Medicine Guidelines (ICTMG) to develop evidence based recommendations for diagnosis and management of FNAIT. Methods The international panel consisted of specialists in adult and pediatric hematology, maternal fetal medicine (MFM), neonatology, methodology, transfusion medicine, and a patient representative. Clinical questions were developed for diagnostic testing, antenatal screening and management, and postnatal interventions. A systematic search for articles published between 1946 and June 2017 in MEDLINE, EMBASE and Cochrane was conducted. Recommendations were formulated based on the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) method which incorporates the quality of the evidence, benefits and risks, and resource utilization. Web conferences and electronic correspondence were used to discuss the results of the systematic reviews and formulate recommendations. Considerations for clinical practice such as dosing of intravenous immunoglobulin (IVIG) and corticosteroids were detailed. Electronic surveys were sent to all members to assess agreement with recommendations. The final guidance document was sent to maternal fetal, hematology and pediatric societies for comments. Results Three systematic reviews (antenatal management, postnatal management and use of laboratory investigations to identify pregnancies at risk) were developed. Antenatal recommendations: Women with FNAIT in a previous pregnancy or sisters of women with FNAIT should be referred to MFM centers. Fetal HPA typing (e.g. HPA-1a/1b) should be performed in HPA-immunized pregnant women when the paternity is unknown or the partner is heterozygous or unavailable for testing. Prenatal HPA-1 typing should preferentially be performed by a non-invasive method e.g. cell-free fetal DNA (cffDNA) in maternal plasma if adequately quality assured. Antenatal IVIG administration to the mother commencing at 12-16 weeks gestation should be offered to all women in a subsequent pregnancy with maternal fetal incompatibility who have had a previous fetus or neonate with FNAIT related ICH. For all other pregnancies with a previous neonate with FNAIT (without ICH), administering antenatal IVIG to the mother should be discussed prior to a subsequent pregnancy or when pregnancy with maternal fetal incompatibility is confirmed. If corticosteroids are used with IVIG, dexamethasone should not be used because of the associated risk of oligohydramnios. Postnatal recommendations: HPA-selected platelets should be made available at delivery for potentially affected infants to increase the neonatal platelet count. If HPA-selected platelets are not immediately available, unselected platelets should be used. In the presence of life-threatening neonatal hemorrhage such as intracranial or gastrointestinal bleeding, platelets should be transfused to maintain platelet counts above 50 to 100x109/L for at least 7 days. In the absence of life-threatening bleeding in a neonate such as intracranial or gastrointestinal bleeding, platelets should be transfused to maintain a platelet count above 30x109/L. Conclusions The intent of this guidance document developed from systematic reviews is to promote best practices in the management of FNAIT. The guideline development group developed algorithms for treatment, podcasts for physicians and patients, pamphlets for patients and a slide set to assist with the implementation of recommendations into practice. This expert panel identified key areas for future research. One is the optimal approach to antenatal management of the next affected pregnancy. Developing biomarkers of fetal severity would be critical to this endeavor. In addition, creating comprehensive screening to identify HPA-1b1b women at risk of FNAIT would advance successful prevention of this disease. Disclosures Bakchoul: German Research Society (DFG): Research Funding; Aspen Germany gGmbH, CLS Behring, Stago gGmbH: Honoraria; Robert Bosch gGmbH: Research Funding. Kjaer:Prophylix Pharma: Equity Ownership. Kjeldsen-Kragh:Prophylix Pharma: Equity Ownership. Oepkes:Towards routine HPA screening in pregnancy: Research Funding. Bussel:Uptodate: Honoraria; Rigel: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Protalex: Consultancy; Amgen Inc.: Consultancy, Research Funding; Prophylix: Consultancy, Research Funding; Momenta: Consultancy. Arnold:Bristol Myers Squibb: Research Funding; Amgen: Consultancy, Research Funding; UCB: Consultancy; Novartis: Consultancy, Research Funding; Bristol Myers Squibb: Research Funding; UCB: Consultancy; Novartis: Consultancy, Research Funding; Amgen: Consultancy, Research Funding. Savoia:Neonatal Alloimmune Thrombocytopenia Registry of the Transfusion Outcomes Research Collaborative (TORC) Australia: Membership on an entity's Board of Directors or advisory committees.

Introduction: Major obstetric hemorrhage (MOH) can develop rapidly and, due to the unique characteristics of maternity patients, early recognition and management can be challenging. Use of blood components in MOH can be life-saving however there is uncertainty about optimal use of these products and the role of adjunctive therapies. The ANZ-MTR generates observational data on current transfusion management and outcomes in critically bleeding patients receiving massive transfusion (MT) across all clinical settings. This study aimed to describe the transfusion strategies used in the MOH population and report their outcomes. Methods: Patients who had a MOH and received a MT (≥5 units of red blood cells [RBC] in 4h) between April 2011 and December 2013 at 15 Australian & NZ hospitals were identified. Data on the type and volume of blood products transfused as well as selected laboratory results and clinical outcomes were reviewed. Results: A total of 154 cases were identified and reviewed, representing 6% of the total ANZ-MTR cohort. Median age was 34 [IQR29-37] years and 99% of women had a Charlson Comorbidity Index score ≤ 1. Table 1 presents the blood products transfused. The median [IQR] fresh frozen plasma (FFP) to RBC ratio and platelets to RBC ratio was 0.6 [0.3-0.8] and 0.1 [0-0.2], respectively. FFP, platelets and cryoprecipitate were transfused in 87%, 66% and 49% of patients. Prothrombinex-HT was administered to 1 patient and 3 patients received rFVIIa. Table 2 presents the laboratory results taken prior to MT onset as well as the lowest and highest result reported within 24hours after the MT onset. Fibrinogen levels following MT onset was available for 121 (79%) patients. Of these, 46% women had a fibrinogen level Table 1. Number of patients and median number of units transfused 24h post-MT onset (n = 154). Blood product n (%) Median units (IQR) Red blood cells 154 (100) 7 [6-10] Fresh frozen plasma 134 (87) 4 [2-6] Platelets 102 (66.2) 1 [0-1] Cryoprecipitate 76 (49.4) 0 [0-5] Table 2. Laboratory values* reported Value prior to MT onset Lowest value 0-24h post-MT onset Highest value 0-24h post-MT onset Hemoglobin (g/L) 102 [81-120], 84 77 [67-90]; 92 108 [95-119]; 92 INR 1.1 [0.9-1.2]; 33 1.1 [.9-1.2]; 72 1.3 [1.1-1.4]; 72 aPPT(s) 31 [28-35]; 39 31 [29-34]; 88 37 [33-46]; 88 Fibrinogen level (g/L) 3.2 [1.6-3.9]; 25 1.9 [1.4-2.6]; 79 2.9 [2.5-3.5]; 79 Platelet Count (109/L) 210 [158-249];84 102 [74-135]; 92 146 [110-190]; 92 pH 7.3 [7.3-7.4]; 22 7.3 [7.2-7.3]; 70 7.4 [7.4-7.5]; 70 *Data are Median [IQR]; % patients with laboratory test available Conclusion: Women with MOH requiring massive transfusion were generally healthier and younger than patients of other clinical contexts in the ANZ-MTR. Although there were few in-hospital deaths reported (1.9%), a large proportion of the cohort required a hysterectomy during their hospital admission. Further information on transfusion practice, including understanding optimal blood component ratios, is required to inform clinical practice and minimize risk in the obstetric setting. Disclosures McLintock: Novo Nordisk Australasia: Honoraria.

To the Editor: Fanconi anemia (FA) is an autosomal recessive disease characterized by bone marrow failure and cancer susceptibility. At least eight complementation groups for FA have been identified, and the genes corresponding to groups A, C, and G have been cloned. An understanding of the

Abstract 2214 Bernard-Soulier syndrome (BSS) has been historically described as an autosomal recessive disease, and more than 50 different mutations have been identified in homozygous or double-heterozygous patients. However, a few reports have suggested that BSS may be occasionally transmitted in an autosomal-dominant fashion. In 2001, we described six Italian families that were previously diagnosed with Mediterranean macrothrombocytopenia and possessed the monoallelic c.515C>T transition in the GPIBA gene, which results in a p.Ala156Val substitution (Bolzano mutation) in GPIb alpha (Savoia et al, Blood 2001;97:1330–5) Since 2001, we have searched for this mutation in all patients referred to us for a non-syndromic, autosomal dominant form of inherited macrothrombocytopenia of unknown origin. Screening for the c.515C>T mutation identified 42 carriers and genetic molecular testing in all of the available relatives indicated that this mutation was present in 61 additional individuals. When the 42 families described here are added to the 6 families previously described, our database of 210 pedigrees of inherited thrombocytopenia includes 48 families with monoallelic, dominant BSS caused by the Bolzano mutation; 22 of the pedigrees have MYH9-related disease, 21 have thrombocytopenia 2 caused by ANKRD26 mutations (Noris et al, Blood 2011;117:6673–80), and 10 pedigrees have the classic biallelic, recessive form of BSS (Savoia et al, Haematologica 2011;96:417-23). Our experience therefore indicates that the Bolzano mutation is the most frequent cause of inherited thrombocytopenia in Italy. Analyses of the geographic origin of affected pedigrees and haplotypes indicated that this mutation originated in southern Italy. The bleeding tendency was variable, with 42% of the cases presenting recurrent, spontaneous hemorrhages that only rarely were severe (5 patients required medical intervention and platelet transfusions). 19 women delivered 32 children (vaginal and caesarean births) with no platelet transfusions, and excessive bleeding was reported in one case only. None of the patients experienced abnormal bleeding associated with dental extractions or surgery. Thrombocytopenia was usually mild (a few subjects even had normal platelet counts), and electronic counters overestimated the degree of platelet deficiency with respect to manual counting with optical microscopy in a Neubauer chamber (Table 1). Platelets were larger than normal in most patients, and their GPIb/IX/V content was 50% of controls. However, in vitro platelet aggregation in response to ristocetin 1.5 mg/mL was defective only in 22% of cases. The serum thrombopoietin level was two-fold greater than that of healthy subjects and similar to that observed in a case series of patients with ITP. Beta 1-tubulin polymorphisms, which have been associated with platelet size and function (Freson et al, Blood 2005;106:2356–62), did not explain the variation in clinical and laboratory features of our patients. In conclusion, our study indicates that the monoallelic Bolzano mutation is a frequent cause of macrothrombocytopenia in Italy and that this mutation induces a mild form of BSS that is often misdiagnosed with ITP. Further analyses in other countries will reveal whether this form of the disease is exclusive to Italy or if it also affects other populations.Table 1.Platelet count and size in patients with the Bolzano mutation in GPIb alpha.PatientsControlsmean±SD (range)Manual platelet count, x10e9/L114±36† (42–184)276±50 (170–420)Impedance platelet count, x10e9/L89±33**† (21–147)255±53 (141–396)Optical platelet count, x10e9/L103±32*† (21–162)280±54 (164–412)MPV, fL, by optical counter15±1.7† (9.7–17.8)8.2±0.8 (7.1–11.1)MPD, um, by optical microscopy3.6±0.5† (2.6–5.1)2.4±0.3 (1.9–3.4)*: p Disclosures: Cattaneo: Eli Lilly Daiichi Sankyo: Honoraria; AstraZeneca: Honoraria, Research Funding.

Abstract 1163 Inherited thrombocytopenias are rare genetic disorders which frequently represent a diagnostic challenge, even after extensive diagnostic work-up. This is due to the requirement of specialized laboratory tests and to the fact that the underlying disease-causing mutation remains in many cases still unknown. Increasing knowledge regarding the molecular etiology of inherited thrombocytopenias contributes both to patient diagnosis, prognosis and genetic counseling and may lead to the identification of novel regulators of platelet production. Recently, mutations in the ANKRD26 gene have been described, which underlie inherited thrombocytopenias with normal platelet size. We applied a previously proposed algorithm (Haematologica 2003; 88: 582–592) and developed a twining program in collaboration with a specialized center to improve the diagnostic yield in a cohort of patients in Argentina. Based on this algorithm, patients were classified according both to the presence or absence of clinical or laboratory features other than thrombocytopenia and to platelet size. Simple laboratory tests, such as platelet function studies, peripheral blood smear and flow cytometry were performed in all cases, while confirmatory tests were performed according to initial diagnostic suspicion, and included analysis of non-muscle myosin heavy chain IIA distribution in neutrophils by immunofluorescence and mutational screening of candidate genes, such as MYH9, RUNX1, MPL, WASP, GPIBA and ANKRD26. Studies unavailable at the local institution were performed in a specialized center in the setting of the twining program. Thirty-five patients, belonging to 14 pedigrees, were included, age 32 (4–72) years old, 20 were female. Platelet count was 83 (5–170)×109/L, 49% were classified as macrothrombocytopenia, 46% had normal platelet size while 6% harboured small platelets. In the latter, a diagnosis of X-linked thrombocytopenia secondary to WASP mutation was made. Four pedigrees with macrothrombocytopenia had MYH9-related disease, one had Bernard-Soulier syndrome, while in four other, no molecular diagnosis was reached. Among pedigrees with normal platelet size, one had FPD/LMA due to RUNX1 mutation, whereas the c.-127A>G mutation in 5'UTR region of the ANKRD26 gene was detected in another family. In addition, a working diagnosis of familial ITP was made in a three-generation pedigree who had autosomal dominant thrombocytopenia and normal platelet size, based on the finding of shortened platelet life-span and complete response to splenectomy. Overall, a molecular diagnosis was established in 9 of 14 (64%) pedigrees, and MYH9-RD comprised the most frequent single disorder. Application of this diagnostic algorithm proved feasible in a resource-limited setting, as data provided by careful medical history and simple laboratory tests allowed to identify patients in whom further, specialized studies were justified. Collaboration of a specialized center was essential for molecular diagnosis and proved invaluable to build local capacities. Disclosures: No relevant conflicts of interest to declare.

Abstract 707FN2 Bernard-Soulier syndrome (BSS) is an extremely rare inherited bleeding disorder characterized by a defect of the GPIb/IX/V complex, which is essential for hemostasis, as the GPIbα subunit binds to subendothelial von Willebrand factor. Since the identification of the first mutation in 1990, almost one hundred cases carrying mutations in the GP1BA, GP1BB, and GP9 genes have been described. Most of the mutations prevent the coordinated association of the complex or binding to the von Willebrand factor. BSS is usually transmitted as a recessive trait with giant platelets and severe bleeding tendency. However, there are families with a dominant mild form, in which the affected individuals have only moderate macrothrombocytopenia and bleeding tendency. A correct definition of the clinical and laboratory features, together with accurate genotype/ phenotype correlation studies, remains essential for understanding the molecular basis of the disease and managing patients appropriately. Moreover, it is important to understand the variability of clinical manifestations. Since BSS is rare with an estimated prevalence of 1:1,000,000, an International Consortium has recently been established to collect a large series of cases and families worldwide. At present, the Consortium has been compiling data from 165 unrelated families, of which 50% have not been previously described. In this cohort, the molecular genetic testing reveals more than 30 novel mutations, confirming the wide spectrum of alterations responsible for the disease. Data from 65 unrelated families (69 patients) mainly from France, Italy and Japan show that 23 have mutations in GP9 and 29 in GP1BB. In the remaining 13 families, the defective gene is GP1BA. In agreement with the view that BSS is an extremely rare disease, 53 probands carried homozygous mutations, 10 are compound heterozygous, and 2 hemizygous because of a 22q11 deletion of the DiGeorge syndrome. The mean age of patients at diagnosis was 18 years (range 0–75 years) of which 27 were males and 38 females. Misdiagnosis of autoimmune thrombocytopenia was frequent and 26 patients were previously treated with steroids, intravenous immunoglobulins and/or splenectomy. Except two Japanese cases without any bleeding manifestations, patients presented with a variable bleeding diathesis measured by the World health Organization bleeding scale: grades 1, 2, 3 and 4 in 9, 18, 19 and 10 patients, respectively. The mean platelet count was 64×109/L (range 24–130) as determined by microscopy. In contrast, using a cell counter, thrombocytopenia was more severe (45×109/L; range 5–125). The mean platelet mean diameter was larger than in controls and varied from 2.9 to 7.5 mm. Ristocetin-induced platelet agglutination was absent or lower than 22% of normal response in all patients. Flow cytometry revealed a defective expression of the GPIb/IX/V expression in all patients. Correlating between expression data and gene affected, we found that the expression of GP1ba was often undetectable in patients with GP1BA mutations whereas it was higher, 8% and 17%, in patients with mutations of GP1BB and GP9, respectively. Instead, the GPIX mean level was 14%, 8% and 25% in patients with GP9, GP1BB and GP1BA mutations. The expression of GPV was higher than that of the other subunits, being more than 30% regardless of which gene was mutated. This is the largest cohort of BSS patients characterized to date. These patients together with the other 100 cases not yet included in the BSS database will enable correlations of the molecular genetic defects, receptor expression and clinical manifestations observed in BSS patients. Disclosures: Zieger: CSL Behring Hattersheim: Research Funding.

Abstract 2533 MYH9-Related Disease (MYH9-RD) is one of the less rare forms of inherited thrombocytopenia. It derives from mutations of the gene MYH9 for the heavy chain of nonmuscle myosin IIA and is characterized by congenital macrothrombocytopenia variably associated with young-adult onset of hearing loss, cataract, and a severe proteinuric nephropathy. Only platelet transfusions are available for increasing platelet counts in this condition, but they expose to the risks of acute reactions, transmission of infectious diseases, and refractoriness to subsequent platelet transfusions. Moreover, this treatment suffers from scarceness of blood donors. Novel thrombopoiesis-stimulating agents have been developed and 2 of them, eltrombopag and romiplostin, have been approved for increasing platelet count in a few forms of acquired thrombocytopenia. Since it has been recently shown that megakaryocytes of patients with MYH9-RD respond in vitro to TPO stimulation, we reasoned that TPO-mimetics could be effective also in this condition and decided to test the effect of eltrombopag. Therefore, we performed a phase II, multicentre, open-label, dose escalation trial. Twelve adult patients with a platelet count lower than 50×10e9/L and a diagnosis of MYH9-RD confirmed by identification of the causative MYH9 mutations received orally eltrombopag 50 mg daily for 21 days (Revolade®, GSK). Patients with platelet counts lower than 100×10e9/L at day 21 increased eltrombopag to 75 mg daily for 21 additional days. Patients with platelet counts between 100 and 150×10e9/L at day 21 continued eltrombopag 50 mg daily for the following 21 days, while patients with more than 150×10e9 platelets/L stopped therapy. The primary endpoints were the achievement of a platelet count over 100×10e9/L or at least three times the baseline value (major response), or at least twice the baseline value but less than major response (minor response). Secondary end points included safety and tolerability, and the reduction of bleeding tendency. After 3 weeks at the eltrombopag dose of 50 mg daily, 3 patients achieved platelet counts of 150×10e9/L or more and stopped therapy. Two had a platelet counts between 100 and 150×10e9/L and continued treatment at the same dosage, while 7 had less than 100×10e9 platelets/L and received eltrombopag 75 mg daily for 3 weeks. A major response was obtained in 8 patients (67%), in 5 of them after 3 weeks of eltrombopag 50 mg daily, and in 3 cases after 3 additional weeks at the dose of 75 mg. Three patients (25%) achieved a minor response, 1 after 3 weeks at 50 mg daily, and 2 after 3 additional weeks at 75 mg. In one patient the treatment resulted in no response. Mean platelet count at the end of treatment was significantly higher than at baseline (105 versus 31×10e9 platelets/L, p=0.0022). In the 11 patients that achieved major or minor responses, mean platelet count was still higher than baseline 15 days after discontinuation of the drug, while it returned to levels near baseline 15 days later. Platelet size did not change either during treatment or after its cessation, and this indicates that the increases in platelet count were paralleled by corresponding increases in total platelet mass. The extent of platelet aggregation was within the normal range after all tested agonists in 5 of the 7 patients that achieved platelet counts higher than 100×10e9/L, while it was slightly reduced after ADP and collagen in 2 patients. Mean serum TPO level was higher than the normal range and this figure did not change neither during treatment with eltrombopag nor after its discontinuation. Ten of 12 patients had grade 1 or 2 bleeding symptoms, as measured by the WHO bleeding scale, at baseline, while 2 were asymptomatic. Upon treatment, bleeding diathesis quickly ameliorated and disappeared in 8 cases, while it remained unchanged in the only patient with no response to eltrombopag and in another one with a minor response. The benefit in terms of bleeding diathesis lasted well beyond treatment discontinuation. Treatment was well tolerated in all cases, with only two patients reporting mild and transient headache and one patient suffering from transient dry mouth at the beginning of treatment. In conclusion, 50–75 mg of eltrombopag per day increased platelet count and reduced bleeding tendency in most patients with MYH9-RD. Further research is required to ascertain whether TPO mimetics are effective also in other forms of inherited thrombocytopenia. Disclosures: Off Label Use: Eltrombopag for MYH9-related disease.