Gene copy number variation (CNV) and single nucleotide polymorphisms (SNPs) count as important sources for interindividual differences, including differential responsiveness to infection or predisposition to autoimmune disease as a result of unbalanced immunity. By developing an FCGR-specific multiplex ligationdependent probe amplification assay, we were able to study a notoriously complex and highly homologous region in the hu-

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The TEL (ETV6)؊AML1 (CBFA2) gene fusion is the most common reciprocal chromosomal rearrangement in childhood cancer occurring in Ϸ25% of the most predominant subtype of leukemia-common acute lymphoblastic leukemia. The TEL-AML1 genomic sequence has been characterized in a pair of monozygotic twins diagnosed at ages 3 years, 6 months and 4 years, 10 months with common acute lymphoblastic leukemia. The twin leukemic DNA shared the same unique (or clonotypic) but nonconstitutive TEL-AML1 fusion sequence. The most plausible explanation for this finding is a single cell origin of the TEL-AML fusion in one fetus in utero, probably as a leukemia-initiating mutation, followed by intraplacental metastasis of clonal progeny to the other twin. Clonal identity is further supported by the finding that the leukemic cells in the two twins shared an identical rearranged IGH allele. These data have implications for the etiology and natural history of childhood leukemia.An extraordinary diversity of chromosomal molecular abnormalities has been identified in hematopoietic malignancies (1, 2). Among the most prominent are reciprocal chromosomal translocations that produce, via genetic recombination, inframe fusion genes and hybrid proteins (3, 4). Although details of the mechanisms involved remain to be elucidated, many of these genes encode transcription factors; their novel products are thought to endow clonal advantage via the imposition of an altered pattern of gene regulation (3, 4). One of the most frequent gene fusions so far described is that between TEL (or ETV6) and AML1 (or CBFA2). This rearrangement, although cryptic at the level of chromosome karyotype, occurs in approximately 25% of the predominant subtype of pediatric cancer and leukemia-common acute lymphoblastic leukemia (cALL)-in children diagnosed between the ages of 2 and 10 years (5, 6). The translocation t(12;21)(p13;q22) in ALL consistently involves the fusion of the protein dimerization encoding 5Ј region of the ETS-like gene TEL with almost the entire AML1 gene including its DNA binding region (with homology to Drosophila runt) and transactivation domain (reviewed in ref. 5). The chromosome 12 breakpoints cluster within a single intron of the TEL gene whereas AML1 breaks occur within the large and currently unsized first two introns of the AML1 gene on chromosome 21 (5-7). As with other fusion genes in leukemia, each patient's intronic breakpoints and subsequent fusion sequence are unique, providing a stable genomic marker of the derivative clone of cells. In the context of the etiology and natural history of childhood ALL, a key issue is when and how the TEL-AML1 fusion gene is generated and whether this is an early or initiating event. We report here a molecular analysis of the genomic fusion region of TEL-AML1 in the unusual situation of concordant leukemia in monozygotic twins. This analysis provides unequivocal evidence that this genetic lesion can be acquired during fetal hematopoiesis in utero.

Six percent of pediatric patients with ALL developed symptomatic osteonecrosis during or shortly after treatment. Older age and female sex were risk factors. After a median follow-up of 5 years, 60% of patients had persistent symptoms.

Key Points• Older age, insidious onset, no preceding infection, mild bleeding, and higher platelet count are the strongest risk factors for chronic ITP.• Intravenous immunoglobulin treatment seems to protect against development of chronic ITP.Childhood immune thrombocytopenia (ITP) is a rare autoimmune bleeding disorder. Most children recover within 6 to 12 months, but individual course is difficult to predict. We performed a systematic review and meta-analysis to identify predictors of chronic ITP. We found 1399 articles; after critical appraisal, 54 studies were included. The following predictors of chronic ITP in children, assessed in at least 3 studies, have been identified: female gender (odds ratio [OR] 1.17, 95% confidence interval [CI] 1.04-1.31), older age at presentation (age ‡11 years; OR 2.47, 95% CI 1.94-3.15), no preceding infection or vaccination (OR 3.08,, insidious onset (OR 11.27,), higher platelet counts at presentation ( ‡20 3 10 9 /L: OR 2.15, 95% CI 1.63-2.83), presence of antinuclear antibodies (OR 2.87, 95% 1.57-5.24), and treatment with a combination of methylprednisolone and intravenous immunoglobulin (OR 2.67, 95% CI 1. 44-4.96). Children with mucosal bleeding at diagnosis or treatment with intravenous immunoglobulin alone developed chronic ITP less often (OR 0.39, 95% CI 0.28-0.54 and OR 0.71, 95% CI 0.52-0.97, respectively). The protective effect of intravenous immunoglobulin is remarkable and needs confirmation in prospective randomized trials as well as future laboratory studies to elucidate the mechanism of this effect. (Blood. 2014;124(22):3295-3307) IntroductionChildhood immune thrombocytopenia (ITP) is a rare autoimmune disorder characterized by isolated thrombocytopenia (peripheral blood platelet count ,100 3 10 9 /L) in the absence of other causes that may be associated with thrombocytopenia.1 Most children present with a typical history of acute development of purpura and bruising, often after a mild viral infection. Management of newly diagnosed ITP consists of careful observation, regardless of platelet count. Severe bleeding, occurring in only 3% to 5% of children, 2 requires treatment with corticosteroids, intravenous immunoglobulin (IVIg), or anti-Rhesus-D immunoglobulin, either alone or in combination and, if life threatening, also with platelet and red blood cell transfusions. 3,4 Chronic ITP is currently defined as thrombocytopenia ,100 3 10 9 /L lasting for .12 months.1 About 20% to 25% of children with newly diagnosed ITP will develop chronic disease. Because of the high impact of ITP on a child's everyday life and activities, as well as to decide whether treatment has to be instituted to influence the clinical course of ITP, it is of clinical significance if the course of the disease could be predicted at time of diagnosis.Several clinical, therapeutic, laboratory, and genetic predictors of chronic ITP have been evaluated in children.5-7 A systematic review or meta-analysis, however, has not yet been performed. In this study, we systematically analyzed all...

Key Points In children with newly diagnosed ITP, IVIg treatment at diagnosis does not result in a lower rate of chronic ITP. Upfront treatment with IVIg led to faster recovery and less severe bleeding events.

Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare disorder of undefined aetiology. The disease presents with severe thrombocytopenia and absence of megakaryocytes in the bone marrow. Furthermore, CAMT patients may develop bone marrow aplasia. To obtain more insight into the mechanism underlying CAMT, five children were analysed. All patients had increased plasma thrombopoietin (Tpo) levels, indicating a platelet production defect. Bone marrow‐derived CD34+ stem cells from three patients were cultured in an in vitro liquid culture system to study megakaryocytopoiesis. CD34+ cells from two of the three patients failed to differentiate into megakaryocytes. The lack of megakaryocyte formation could imply that a defect in the c‐mpl gene, encoding the Tpo receptor, exists. Sequencing of c‐mpl revealed mutations in four of five patients. Three patients had point mutations and/or a deletion in the coding regions of c‐mpl. All point mutations led to an amino acid substitution or to a premature stop codon. In one patient, a homozygous mutation in the last base of intron 10 was found that resulted in loss of a splice site. This study showed that mutations in c‐mpl could be the cause of thrombocytopenia in CAMT in the majority of patients. Furthermore, Tpo has been shown to have an anti‐apoptotic effect on stem cells. Therefore, mutations in c‐mpl might not only affect megakaryocyte formation but may also impair stem cell survival, which could explain the occurrence of bone marrow failure as final outcome in patients with CAMT.

Key Points• CRP enhances IgG-mediated respiratory burst and phagocytosis of platelets in vitro and their clearance in vivo.• CRP levels are increased in ITP patients and correlate with platelet counts and bleeding severity and predict time to recovery.Immune-mediated platelet destruction is most frequently caused by allo-or autoantibodies via Fcg receptor-dependent phagocytosis. Disease severity can be predicted neither by antibody isotype nor by titer, indicating that other factors play a role. Here we show that the acute phase protein C-reactive protein (CRP), a ligand for Fc receptors on phagocytes, enhances antibody-mediated platelet destruction by human phagocytes in vitro and in vivo in mice. Without antiplatelet antibodies, CRP was found to be inert toward platelets, but it bound to phosphorylcholine exposed after oxidation triggered by antiplatelet antibodies, thereby enhancing platelet phagocytosis. CRP levels were significantly elevated in patients with allo-and autoantibody-mediated thrombocytopenias compared with healthy controls. Within a week, intravenous immunoglobulin treatment in children with newly diagnosed immune thrombocytopenia led to significant decrease of CRP levels, increased platelet numbers, and clinically decreased bleeding severity. Furthermore, the higher the level of CRP at diagnosis, the longer it took before stable platelet counts were reached. These data suggest that CRP amplifies antibody-mediated platelet destruction and may in part explain the aggravation of thrombocytopenia on infections. Hence, targeting CRP could offer new therapeutic opportunities for these patients. (Blood. 2015;125(11): 1793-1802 IntroductionFetal or neonatal alloimmune thrombocytopenia (FNAIT) and immune thrombocytopenia (ITP) are both antibody-mediated disorders in which platelets are destroyed mainly through activating immunoglobulin (IgG) Fc receptors on phagocytes in the spleen and liver, eventually resulting in thrombocytopenia. 1 In childhood, ITP is characterized by a typical history of acute development of purpura and bruising in an otherwise healthy child, caused by development of platelet autoantibodies, with an incidence of ;5 in 100 000 children.2 Most children with newly diagnosed ITP will not suffer from serious bleeding and will recover within 12 months. In ;60% of ITP, there is a history of a prior infection. [1][2][3] FNAIT is a potentially destructive disease in pregnancies, with intracerebral hemorrhage (ICH) of the fetus or neonate as the most feared complication, resulting in perinatal death in 1% to 7% or in severe neurological impairments in 14% to 26% of affected pregnancies. [4][5][6][7] FNAIT is caused by maternal IgG platelet alloantibodies, in whites mainly directed against human platelet antigen (HPA)-1a (85%), that cross the placenta and destroy the platelets of the fetus or newborn. Immunization against HPA-1a occurs in ;1:450 random pregnancies. [8][9][10] Although platelet decrement is related to antibody titer in FNAIT, 8,11,12 this correlation is not strict, as cas...