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Background. Hereditary bone marrow failure syndromes are a category of biologically different syndromes that can cause cytopenia in at least one hematopoietic cell lineage. Case. We present a 29-week-old male infant who had a low Apgar Score, advanced delivery room resuscitation, widespread petechial rash, and ecchymoses at birth, without any dysmorphic features. Initial laboratory tests revealed bicytopenia (platelet count 7x10 3 /uL, hemoglobin of 3.9 g/dL, neutrophil 2.0x103 /uL) with findings of disseminated intravasculer coagulation (DIC). Imaging studies demonstrated accompanying left-sided congenital pulmonary airway malformation. On the second postnatal week pancytopenia occurred and the bone marrow findings were consistent with congenital amegakaryocytic thrombocytopenia. Further evaluations for differential diagnosis of pancitopenia were performed and the results of congenital viral infections, metabolic and immunologic tests were negative. While supportive treatments were in progress, haploidentical bone marrow transplantation (BMT) was performed from the father at 84th day due to unavailability of HLA-matched relative or nonrelative donor. Whole exome sequencing revealed a novel heterozygous frameshift variation (c.1242dupT [p. Thr538fs]) in exon 8 of the MECOM gene and validated by Sanger sequencing. No variation was detected in the parents genetic analysis. Conclusions. In this report, we present a patient with congenital bone marrow failure successfully treated with haploidentic BMT and describe a novel, de novo pathogenic variant in MECOM gene. © 2022, Turkish National Pediatric Society. All rights reserved.

Immune checkpoint inhibitors (ICIs), despite their ability to potentiate antitumor T-cell responses, may cause various immune-related adverse events. Most cases of thrombocytopenia induced by ICIs have revealed a pathophysiologic mechanism of immune thrombocytopenia with increased platelet destruction and preserved megakaryocytes. Acquired amegakaryocytic thrombocytopenic purpura (AATP) is an unusual disorder characterized by thrombocytopenia with markedly diminished bone marrow megakaryocytes in the presence of otherwise normal hematopoiesis. AATP caused by ICIs has not been reported on. Herein, we present the case of a 79-year-old man diagnosed with squamous cell carcinoma of the lung who developed AATP after two courses of durvalumab, a drug targeting programmed death-ligand 1. Two weeks after the second cycle, his platelet count decreased to 2.1 × 104/μL. After the patient underwent platelet transfusion, his platelet count increased to 8.1 × 104/μL the next day but subsequently decreased repeatedly even after the ICI was discontinued. Six weeks after the second cycle, he developed interstitial pneumonia and was administered prednisolone (50 mg/day). However, thrombocytopenia did not improve. Bone marrow biopsy showed scarce megakaryocytes (< 1 megakaryocyte/10 high-power fields) with preservation of myeloid and erythroid series. Myelodysplasia, myelofibrosis, or metastatic lesions were not observed. Cytogenetic analysis showed a normal male karyotype of 46XY. Hence, the patient received eltrombopag, a thrombopoietin receptor agonist, and his platelet count subsequently improved. After recovery, bone marrow aspiration revealed a normal number of megakaryocytes. AATP is rarely the type of thrombocytopenia induced by ICIs and may be successfully treated with thrombopoietin receptor agonists.

Adult-onset Still's disease (AOSD) sometimes demonstrates hematologic disorder, whereas acquired amegakaryocytic thrombocytopenia (AAT) involvement is extremely rare. We herein report a 67-year-old woman with relapse of AOSD who concomitantly developed AAT. Thrombocytopenia along with high disease activity of AOSD was resistant to high-dose prednisolone, even in combination with methotrexate and tacrolimus. However, alternative treatment with cyclosporine after administering tocilizumab resulted in the improvement of thrombocytopenia, ultimately demonstrating that combination therapy based on suppressing the intractable disease activity of AOSD and subsequently adding a reliable immunosuppressant was required to achieve remission.

Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare inherited bone marrow failure syndrome (IBMFS) that is characterized by severe thrombocytopenia at birth due to ineffective megakaryopoiesis and development towards aplastic anemia during the first years of life. CAMT is not a single monogenetic disorder; rather, many descriptions of CAMT include different entities with different etiologies. CAMT in a narrow sense, which is primarily restricted to the hematopoietic system, is caused mainly by mutations in the gene for the thrombopoietin receptor (MPL), sometimes in the gene for its ligand (THPO). CAMT in association with radio-ulnar synostosis, which is not always clinically apparent, is mostly caused by mutations in MECOM, rarely in HOXA11. Patients affected by other IBMFS - especially Fanconi anemia or dyskeratosis congenita - may be misdiagnosed as having CAMT when they lack typical disease features of these syndromes or have only mild symptoms. This article reviews scientific and clinical aspects of the various disorders associated with the term "CAMT" with a main focus on the disease caused by mutations in the MPL gene.

Congenital amegakaryocytic thrombocytopenia caused by deleterious homozygous or compound heterozygous mutations in MPL (CAMT-MPL) is a rare inherited bone marrow failure syndrome presenting as an isolated thrombocytopenia at birth progressing to pancytopenia due to exhaustion of hematopoietic progenitors. The analysis of samples and clinical data from a large cohort of 56 patients with CAMT-MPL resulted in a detailed description of the clinical picture and reliable genotype-phenotype correlations for this rare disease. We extended the spectrum of CAMT causing MPL mutations regarding number (17 novel mutations) and impact. The clinical courses showed a great variability with respect to the severity of thrombocytopenia, the development of pancytopenia and the consequences from bleedings. The most severe clinical problems were (1) intracranial bleedings pre- and perinatally and the resulting long-term consequences, and (2) the development of aplastic anemia in the later course of the disease. An important and new finding was that thrombocytopenia was not detected at birth in a quarter of the patients. The rate of non-hematological abnormalities in CAMT-MPL was higher than described so far. Most of the anomalies were related to the head region (brain anomalies, ocular and orbital anomalies) and consequences of intracranial bleedings. The present study demonstrates a higher variability of clinical courses than described so far and has important implications on diagnosis and therapy. The diagnosis CAMT-MPL has to be considered even for those patients who are inconspicuous in the first months of life or show somatic anomalies typical for other inherited bone marrow failure syndromes.

Acquired amegakaryocytic thrombocytopenia (AATP) is a rare disease characterized by thrombocytopenia and the disappearance of marrow megakaryocytes. A 43-year-old man was admitted because of thrombocytopenia of 1.0×109/L. Bone marrow aspirate demonstrated normal hematopoiesis lacking megakaryocytes, and AATP was diagnosed. The serum concentration of thrombopoietin (TPO) was high (7.72 fmol/mL). Prednisolone (PSL) at 60 mg/day was started and the platelet count recovered to 1,335×109/L; however, excessive megakaryocytopoiesis and subsequent decline in platelet count were noted 14 days later. At the peak platelet count, the TPO remained at 3.79 fmol/mL and returned to a normal level of 0.40 fmol/mL during the period of normal platelet count after PSL tapering. The marked thrombocytosis in response to prednisolone may have been caused by the high TPO after the resolution of suppressed megakaryopoiesis. Marked rebound thrombocytosis beyond 1,000×109/L after successful PSL treatment for AATP has not been previously reported.

Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare, inherited bone marrow failure syndrome. Hematopoietic stem cell transplantation (HSCT) is considered a curative treatment option, but existing descriptions of patient and transplant characteristics and outcomes after related and unrelated donor HSCT are sparse. We describe outcomes after HSCT for congenital amegakaryocytic thrombocytopenia (CAMT; n = 86) from 2000 to 2018. We conducted an analysis of data collected by the Center for International Blood and Marrow Transplant Research on patients with CAMT receiving therapeutic allogeneic HSCT. The predominant donor type was HLA-matched or mismatched unrelated donors (n = 58, 67%). The remaining included HLA-matched sibling (n = 23, 27%) and HLA-mismatched relative (n = 5, 6%). The predominant graft types were bone marrow (n = 53, 62%) and cord blood (n = 25, 29%). The median age at transplantation was 3 years, with 82 of 86 patients being transplanted aged ≤10 years. The 5-year graft failure-free and overall survival were 83% (95% confidence interval [CI], 74-90) and 86% (95% CI, 78-93), respectively. An examination for risk factors confirmed mortality was higher after HLA-mismatched relative and mismatched unrelated donor HSCT compared to HLA-matched sibling and matched unrelated donor HSCT (hazard ratio 3.52, P = .04; 75% versus 93%). The 1-year incidence of graft failure was 19% after HLA-mismatched HSCT (n = 32) compared to 7% after HLA-matched HSCT (n = 54, P = .15). Day-100 grade II-IV acute graft-versus-host disease was 13%, 26%, and 30% after HLA-matched sibling, HLA-matched and mismatched unrelated donor HSCT. The 5-year incidence of chronic graft-versus-host disease was 33% with 24 of 28 patients having received grafts from HLA-matched (n = 13) and mismatched unrelated (n = 11) donors. Although HLA-matched donors are preferred, HLA-mismatched donors also extend survival for CAMT.

Congenital amegakaryocytic thrombocytopenia (CAMT) is an autosomal recessive disorder characterized by severe thrombocytopenia that presents soon after birth and is usually not accompanied by specific somatic malformations [Germeshausen M, Ballmaier M. Best Pract Res Clin Haematol 2021; 34: 101286]. CAMT is more prevalent in females than males [Ballmaier M, Germeshausen M. Semin Thromb Hemost 2011; 37: 673–681; Germeshausen M, Ballmaier M. Haematologica 2021; 106: 2439–2448], in contrast to other congenital bone marrow failure syndromes. Patients with CAMT also exhibit cardiac malformations, cerebellar hypoplasia, growth retardation, and a distinctive facial appearance [Yldrm A T, Güneş B T, Oymak Y, et al. Blood Coagul Fibrinolysis 2015; 26: 337–341], although it remains unknown whether these are related to CAMT. Mutations in the MPL gene, which encodes the thrombopoietin receptor, are the pathogenetic cause of CAMT [Germeshausen M, Ballmaier M. Haematologica 2021; 106: 2439–2448]. Since thrombopoietin is involved in the maintenance of hematopoietic stem cells and megakaryocyte development [Germeshausen M, Ballmaier M. Best Pract Res Clin Haematol 2021; 34: 101286], CAMT may eventually manifest as a hematopoietic failure. Currently, allogeneic hematopoietic stem cell transplantation (HSCT) is the only cure for CAMT. Human leukocyte antigen (HLA)-matched siblings are the first-choice donors for HSCT because transplantations from matched unrelated donors have a low success rate [King S, Germeshausen M, Strauss G, et al. Br J Haematol 2005; 131: 636–644]. Cancio et al. [Cancio M, Hebert K, Kim S, et al. Transplant Cell Ther 2022; 28: 101 e101–101 e106] reviewed 86 patients treated over 18 years and reported that although HLA-mismatched donors can extend the survival of CAMT patients, HLA-matched donors are preferred. The present report describes the successful treatment of a 3-year-old girl with CAMT using haploidentical allogeneic HSCT from the father, even though he harbored a mutant MPL gene.

Congenital amegakaryocytic thrombocytopenia is a rare disorder causing thrombocytopenia that progresses to pancytopenia and bone marrow failure if untreated. It is caused by variants in the MPL gene which encodes the thrombopoeitin receptor. In this report, we review 5 cases of congenital amegakaryocytic thrombocytopenia, all of whom belong to the Mississippi Band of Choctaw Indians. There are 2 common variants in these cases: R90X and R537W. One variant was previously reported only once and had unclear significance at that time. With these variants identified, we hope to improve screening that results in earlier diagnosis in the Choctaw population in the future.

Acquired amegakaryocytic thrombocypenia (AAMT) is an extremely rare hematologic disorder and standard treatment strategy has not been established. We described herein two cases of AAMT who were fully responded to eltrombopag and immunosuppressant. Patient 1 was refractory to steroid, IVIG and recombinant human thrombopoietin (rhTPO). Patient 2 did not respond to high dosage of steroid, IVIG, rhTPO and rituximab. Moreover, his AAMT progressed to aplastic anemia in 5 months. Both patients took eltrombopag and immunosuppressant, then they achieved long-term remission without obvious side effects. Our findings suggest that this combination can be a valuable alternative in AAMT.

Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare autosomal recessive disorder characterized by thrombocytopenia from failure of megakaryopoiesis. The genetic background of CAMT is mutations in the myeloproliferative ligand gene encoding the thrombopoietin receptor. In our patient with CAMT, we identified homozygous missense mutations [c.407C>T (p.P136L)]. The association of CAMT and central nervous system (CNS) abnormalities is uncommon. Here we present a case in which CAMT appears linked to CNS abnormalities (encephalomalacia, global atrophy) and developmental delay related with intrauterine intracranial hemorrhage.

Pembrolizumab is a humanized antibody directed against the programmed death-1 receptor on the cell surface, resulting in a T-cell-mediated immune response against tumor cells that can be complicated by immune-related adverse events. Here we present a novel case of pembrolizumab-induced acquired amegakaryocytic thrombocytopenia (AAT) in a patient with metastatic nasopharyngeal carcinoma. AAT is an incredibly rare and challenging entity for which there is no standardized treatment. We discuss our therapeutic approach using a calcineurin inhibitor and thrombopoietin receptor agonists for successful treatment of AAT and resumption of multiagent cytotoxic chemotherapy.

The congenital amegakaryocytic thrombocytopenia (CAMT) is a syndrome characterized by preservation of granulocytic and erythroid cells during genesis, with a gradual or progressive decrease in the number of megakaryocytic series of cells in the bone marrow. At later times, most patients develop aplastic anemia. It is important to rule out specific causes of thrombocytopenia that develop in the early stages of CAMT. Typically, there are no specific somatic abnormalities that accompany this deadly disease. Here we present three CAMT cases that presented with different clinical diagnoses, with various physical anomalies in two of those cases. The first patient was examined because of a cytomegalovirus infection. The second patient had been referred with a suspected neonatal alloimmune thrombocytopenia, whereas the third patient presented with chronic immune thrombocytopenic purpura. Subsequently, all three patients were diagnosed with CAMT. Two of the patients had physical anomalies. In particular, the first patient had a duplex urinary system. To our knowledge, this is the first patient with CAMT to have a duplicated collecting sysem. The second patient had a secundum atrial septal defect, an atypical facial appearance, and growth retardation. Since CAMT could also be observed outside the neonatal period, the differential diagnosis for thrombocytopenia should be considered for all age groups. Moreover, it should be considered that CAMT may also be accompanied with somatic abnormalities.

Heterozygous mutations in MECOM (MDS1 and EVI1 complex locus) have been reported to be causative of a rare association of congenital amegakaryocytic thrombocytopenia and radioulnar synostosis. Here we report on 12 patients with congenital hypomegakaryocytic thrombocytopenia caused by MECOM mutations (including 10 novel mutations). The mutations affected different functional domains of the EVI1 protein. The spectrum of phenotypes was much broader than initially reported for the first 3 patients; we found familial as well as sporadic cases, and the clinical spectrum ranged from isolated radioulnar synostosis with no or mild hematological involvement to severe bone marrow failure without obvious skeletal abnormality. The clinical picture included radioulnar synostosis, bone marrow failure, clinodactyly, cardiac and renal malformations, B-cell deficiency, and presenile hearing loss. No single clinical manifestation was detected in all patients affected by MECOM mutations. Radioulnar synostosis and B-cell deficiency were observed only in patients with mutations affecting a short region in the C-terminal zinc finger domain of EVI1. We propose the term MECOM-associated syndrome for this heterogeneous hereditary disease and inclusion of MECOM sequencing in the diagnostic workup of congenital bone marrow failure.

We report the first case of a patient with hepatitis C virus (HCV) infection and idiopathic thrombocytopenic purpura (ITP), who later developed acquired amegakaryocytic thrombocytopenia (AAMT), with autoantibodies to the thrombopoietin (TPO) receptor (c-Mpl). A 64-year-old woman, with chronic hepatitis C, developed severe thrombocytopenia and was diagnosed with ITP. She died of liver failure. Autopsy revealed cirrhosis and liver carcinoma. In the bone marrow, a marked reduction in the number of megakaryocytes was observed, while other cell lineages were preserved. Therefore, she was diagnosed with AAMT. Additionally, autoantibodies to c-Mpl were detected in her serum. Autoantibodies to c-Mpl are one of the causes of AAMT, acting through inhibition of TPO function, megakaryocytic maturation, and platelet formation. HCV infection induces several autoantibodies. HCV infection might also induce autoantibodies to c-Mpl, resulting in the development of AAMT. This mechanism may be one of the causes of thrombocytopenia in patients with HCV infection.

Although the association of pure red cell aplasia (PRCA) and aplastic anemia with thymoma is well-known, acquired amegakaryocytic thrombocytopenia (AAMT) is not a recognized paraneoplastic manifestation of thymoma. This report discusses a patient with recurrent thymoma complicated by myasthenia gravis, PRCA, and AAMT. Both PRCA and AAMT are diagnosed after a thymoma recurrence, 11 years after complete resection of the initial tumor and 9 months after chemotherapy for the relapsed disease. Both PRCA and AAMT responded to immunosuppression with cyclosporine, corticosteroid, and an abbreviated course of antithymocyte globulin, achieving a very good erythroid response and a complete remission for AAMT, suggesting that AAMT, although extremely rare, can be an immune-mediated paraneoplastic manifestation of thymoma.

Congenital amegakaryocytic thrombocytopenia (CAMT) generally begins at birth with severe thrombocytopenia and progresses to pancytopenia. It is caused by mutations in the thrombopoietin receptor gene, the myeloproliferative leukemia virus oncogene (c-MPL). The association between CAMT and c-MPL mutation type has been reported in the literature. Patients with CAMT have been categorized according to their clinical symptoms caused by different mutations. Missense mutations of c-MPL have been classified as type II and these patients have delayed onset of bone marrow failure compared to type I patients. Here we present a girl with severe clinical course of CAMT II having a missense mutation in exon 4 of the c-MPL gene who was admitted to our hospital with intracranial hemorrhage during the newborn period.Konjenital amegakaryositik trombositopeni (KAMT) genellikle, doğumda ağır trombositopeni ile başlar ve pansitopeniye ilerler. Hastalığın nedeni trombopoetin reseptör geni olan myeloproliferatif lösemi virüs onkogenindeki (c-MPL) mutasyon olup, literatürde KAMT kliniği ile c-MPL mutasyon tipleri arasında ilişki bildirilmiş, hastalar farklı mutasyonların neden olduğu klinik belirtilere göre sınıflandırılmışlardır. c-MPL’nin yanlış anlamlı mutasyonları tip 2 olarak sınıflanmıştır. Bu hastalar tip 1 hastalar ile karşılaştırıldığında kemik iliği yetmezliğinin daha geç başladığı bildirilmiştir. Burada, yenidoğan döneminde intrakranial kanama ile hastanemize başvuran c-MPL geninde ekzon 4’de yanlış anlamlı mutasyonu olan KAMTII tanılı ağır klinik seyirli bir kız sunulmuştur.

Acquired amegakaryocytic thrombocytopenia (AAT) is a hematologic disorder that presents as thrombocytopenia with absent megakaryocytes in the bone marrow. Causes of AAT include toxins, drugs, viral infections, systemic lupus erythematosus, and cytokine deficiencies. Patients with AAT should be followed for possible progression to aplastic anemia or myelodysplastic syndrome. We present a case of a 61-year-old woman with AAT due to occupational chemical exposure.

Congenital amegakaryocytic thrombocytopenia (CAMT) is caused by the loss of thrombopoietin receptor-mediated (MPL-mediated) signaling, which causes severe pancytopenia leading to bone marrow failure with onset of thrombocytopenia and anemia prior to leukopenia. Because Mpl(-/-) mice do not exhibit the human disease phenotype, we used an in vitro disease tracing system with induced pluripotent stem cells (iPSCs) derived from a CAMT patient (CAMT iPSCs) and normal iPSCs to investigate the role of MPL signaling in hematopoiesis. We found that MPL signaling is essential for maintenance of the CD34+ multipotent hematopoietic progenitor (MPP) population and development of the CD41+GPA+ megakaryocyte-erythrocyte progenitor (MEP) population, and its role in the fate decision leading differentiation toward megakaryopoiesis or erythropoiesis differs considerably between normal and CAMT cells. Surprisingly, complimentary transduction of MPL into normal or CAMT iPSCs using a retroviral vector showed that MPL overexpression promoted erythropoiesis in normal CD34+ hematopoietic progenitor cells (HPCs), but impaired erythropoiesis and increased aberrant megakaryocyte production in CAMT iPSC-derived CD34+ HPCs, reflecting a difference in the expression of the transcription factor FLI1. These results demonstrate that impaired transcriptional regulation of the MPL signaling that normally governs megakaryopoiesis and erythropoiesis underlies CAMT.

Objective To determine whether specific c-Mpl mutations might respond to thrombopoietin receptor agonists. Materials and Methods We created cell line models of type II c-Mpl mutations identified in congenital amegakaryocytic thrombocytopenia. We selected F104S c-Mpl for further study because it exhibited surface expression of the receptor. We measured proliferation of cell lines expressing wild-type or F104S c-Mpl in response to thrombopoetin receptor agonists targeting the extracellular (m-AMP4) or transmembrane (LGD-4665) domains of the receptor by 1-methyltetrazole-5-thiol assay. We measured thrombopoietin binding to the mutant receptor using an in vitro thrombopoietin uptake assay and identified F104 as a potentially critical residue for the interaction between the receptor and its ligand by aligning thrombopoietin and erythropoietin receptors from multiple species. Results Cells expressing F104S c-Mpl proliferated in response to LGD-4665, but not thrombopoietin or m-AMP4. Compared to thrombopoietin, LGD-4665 stimulates signaling with delayed kinetics in both wild-type and F104S c-Mpl−expressing cells. Although F104S c-Mpl is expressed on the cell surface in our BaF3 cell line model, the mutant receptor does not bind thrombopoietin. Comparison to the erythropoietin receptor suggests that F104 engages in hydrogen-bonding interactions that are critical for binding to thrombopoietin. Conclusions These findings suggest that a small subset of patients with congenital amegakaryocytic thrombocytopenia might respond to treatment with thrombopoietin receptor agonists, but that responsiveness will depend on the type of mutation and agonist used. We postulate that F104 is critical for thrombopoietin binding. The kinetics of signaling in response to a transmembrane domain−binding agonist are delayed in comparison to thrombopoietin.

Mutations in the human myeloproliferative leukemia (MPL) protein gene are known to cause congenital amegakaryocytic thrombocytopenia (CAMT). The prognosis of this heritable disorder is poor and bone marrow transplantation is the only effective treatment. Here, by using the TALEN (transcription activator-like effector nuclease) technology, we created a zebrafish mpl mutant to model human CAMT. Disruption of zebrafish mpl lead to a severe reduction in thrombocytes and a high bleeding tendency, as well as deficiencies in adult hematopoietic stem/progenitor cells. We further demonstrated that thrombocytopenia in mpl mutant zebrafish was caused by impaired Tpo/Mpl/Jak2 signaling, resulting in reduced proliferation of thrombocyte precursors. These results indicate that mpl mutant zebrafish develop thrombocytopenia resembling the human CAMT. To utilize fully zebrafish to study thrombocyte biology and thrombocytopenia disorders, we generated a transgenic reporter line Tg(mpl:eGFP)smu4, in which green fluorescent protein (GFP) expression was driven by the mpl promoter. Detailed characterization of Tg(mpl:eGFP)smu4 fish confirmed that the thrombocyte lineage was specifically marked by GFP expression. In conclusion, we generated the first transmissible congenital thrombocytopenia zebrafish model mimicking human CAMT and a thrombocyte-specific transgenic line. Together with Tg(mpl:eGFP)smu4, mpl mutant zebrafish provide a useful tool for drug screening and study of thrombocytopoiesis.

Objective To genetically and functionally characterize mutations of c-Mpl that lead to thrombocytopenia in a child with congenital amegakaryocytic thrombocytopenia. Materials and Methods We identified two c-Mpl mutations in a child with clinical features of congenital amegakaryocytic thrombocytopenia, one a previously described mutation in the extracellular domain (R102P) and the other a novel mutation leading to truncation of the receptor after the box 1 homology domain (541Stop). Cell line models were created to examine the ability of the mutant receptors to signal in response to thrombopoietin and thrombopoietin-like agonists. Results Data from cell-line models indicate that c-Mpl R102P does not support significant signaling in response to thrombopoietin due to impaired trafficking of the mutant receptor to the cell surface. Alternative thrombopoietic agents do not circumvent this block to signaling, likely due to the inaccessibility of the receptor. In addition, previous data indicate that c-Mpl 541Stop does not support intracellular signaling due to the loss of critical intracellular domains. Conclusions This case demonstrates two different mechanisms by which c-Mpl mutations can impair thrombopoietin signaling, and suggests that mutations in the extracellular domain will not be rescued by c-Mpl agonists if they interfere with normal receptor expression.

Congenital amegakaryocytic thrombocytopenia (CAMT, MIM #604498) is a rare inherited bone marrow failure syndrome presenting as isolated hypomegakaryocytic thrombocytopenia at birth without other characteristic physical anomalies. Most of the patients develop a severe aplastic anemia and trilineage cytopenia during the first years of life and hematopoietic stem cell transplantation is the only curative treatment. In most of the cases the disease is caused by homozygous or compound heterozygous mutations in the gene MPL encoding the receptor for the hematopoietic growth factor thrombopoietin. The present review summarizes clinical and laboratory data for 96 patients with CAMT, reported since 1990.

Congenital amegakaryocytic thrombocytopenia (MIM #604498) (CAMT) is a rare inherited disease presenting as severe thrombocytopenia in infancy. Untreated, many CAMT patients develop aplastic anemia within the first decade of life; the only effective treatment of CAMT is bone marrow transplantation. CAMT is the result of the presence of homozygous or compound heterozygous mutations in the thrombopoietin receptor-encoding gene, MPL. We report here the identification and characterization of a founder mutation in MPL in the Ashkenazi Jewish (AJ) population. This mutation, termed c.79+2T>A, is a T to A transversion in the invariant second base of the intron 1 donor splice site. Analysis of a random sample of 2018 individuals of AJ descent revealed a carrier frequency of approximately 1 in 75. Genotyping of six loci adjacent to the MPL gene in the proband and in the 27 individuals identified as carriers of the c.79+2T>A mutation revealed that the presence of this mutation in the AJ population is due to a single founder. The observed carrier frequency predicts an incidence of CAMT in the AJ population of approximately 1 in 22,500 pregnancies. The identification of this mutation will enable population carrier testing and will facilitate the identification and treatment of individuals homozygous for this mutation.

We report a 6-year-old girl with amegakaryocytic thrombocytopenia, the first case of this rare congenital disorder not to have an MPL gene mutation. Although no mutations were identified in MPL, Mpl protein was absent in the platelets and TPO induced phosphorylation of the Janus tyrosine kinase 2 (Jak2) was not detected. In addition to the defect of Mpl, the patient demonstrated markedly reduced expression of glycoprotein VI (GPVI) in contrast to normal expression of other platelet-specific proteins GPIb alpha, GPIb beta, and GPIIb. To explore the causes for the absence of Mpl, the entire coding region of Jak2 and AML1 were sequenced and no mutations were identified. To our knowledge, this is the first report that describes a case of amegakaryocytic thrombocytopenia that is not caused by a mutation in MPL and demonstrates the severe impairment of GPVI expression on platelets.

Thrombocytopenia is a relatively common clinical problem in hospitalized neonates, and it is critical to distinguish infants who have rare congenital thrombocytopenias from those who have acquired disorders. Two well-described inherited thrombocytopenia syndromes that present in the newborn period are congenital amegakaryocytic thrombocytopenia (CAMT) and thrombocytopenia with absent radii (TAR). Although both are characterized by severe (< 50,000/microL) thrombocytopenia at birth, the molecular mechanisms underlying these disorders and their clinical presentations and courses are distinct. CAMT is an autosomal recessive disorder caused by mutations in the thrombopoietin (TPO) receptor c-Mpl. TAR is a syndrome of variable inheritance and unclear genetic etiology consisting of thrombocytopenia in association with bilateral absent radii and frequently additional congenital abnormalities. This article summarizes the current understanding of the pathophysiology and clinical course of CAMT and TAR.

Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare autosomal recessive bone marrow failure, caused by MPL gene mutations. The combination of CAMT and central nervous system abnormalities is uncommon. We describe a case with a homozygous missense MPL gene mutation and polymicrogyria, underdevelopment of the cerebellum, and multiple intracranial hemorrhages.

Acquired amegakaryocytic thrombocytopenia (AAT), a rare entity characterized by severe thrombocytopenia and the absence of megakaryocytes in the bone marrow, may mimic or precede the diagnosis of aplastic anemia (AA). Here, we describe a patient who presented with apparent Epstein-Barr virus (EBV)-associated immune thrombocytopenia resistant to several lines of therapies, which was in fact a form of AAT with some features of AA. He eventually responded to therapy with eltrombopag, cyclosporine A (CSA), and antithymocyte globulin (ATG) and recovered completely. EBV infection is known to cause a variety of benign and malignant hematologic disorders, including bone marrow failure. However, to the best of our knowledge, this is the first case report of EBV-associated AAT. Treatment options for AAT are still not well defined, and even response to eltrombopag together with CSA and ATG does not always imply successful therapy. The natural history of EBV infection may well be sufficient to explain unexpected eventual recovery.

Acquired amegakaryocytic thrombocytopenia (AAT) is a rare disorder, characterized by severe thrombocytopenia and selective, marked decrease or absence of megakaryocytes in the bone marrow. We describe a 29-year-old female with adult onset Still's disease preceding a diagnosis of AAT and autoimmune hemolytic anemia, which was successfully treated with cyclosporine. This is the first case of AAT in a patient with adult onset Still's disease.

Thrombocytopenia in the newborn period can signify an inherited platelet disorder. Congenital amegakaryocytic thrombocytopenia (CAMT) and thrombocytopenia with absent radii (TAR) share features of isolated thrombocytopenia, reduced or absent marrow megakaryocytes, impaired responsiveness to thrombopoietin (TPO), and high plasma TPO levels. These disorders are most readily distinguished from each other by the finding of radial aplasia in TAR and the presence of c-MPL mutations in CAMT. In addition, their long-term outcomes are strikingly different: the development of trilineage marrow failure in CAMT in contrast to the general improvement of thrombocytopenia in TAR. The differential diagnosis for CAMT and TAR also includes other congenital disorders in which thrombocytopenia and radial abnormalities can be seen. In this article we will review our molecular and clinical understanding of these two inherited disorders of amegakaryocytosis.

A rare case of acquired amegakaryocytic thrombocytopenia (AATP) in a 35-year-old woman who presented with anaemia and thrombocytopenia at 22 weeks gestation. The first diagnostic impression was of an evolving aplastic anaemia; however, the patient was simultaneously diagnosed with severe vitamin B12 deficiency in the setting of vegetarianism. Once the cyanocobalamin deficiency was corrected, a repeat bone marrow biopsy revealed an isolated depletion of megakaryocytes, which suggested the diagnosis of AATP. Supportive care was provided for her anaemia and thrombocytopenia and she delivered a healthy baby girl with a normal platelet count. The patient was subsequently started on romiplostim with steady improvement in her platelet counts. This rare AATP case presentation highlights the importance of a well-structured diagnostic approach to thrombocytopenia during pregnancy and supports the successful use of thrombopoietin agonists for the management of AATP.

Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare bone marrow failure syndrome characterised by isolated thrombocytopenia because of ineffective megakaryocytopoiesis at birth. In the last 10 years, we collected data from 20 patients diagnosed with CAMT based on a severe thrombocytopenia since birth and absent or markedly decreased numbers of megakaryocytes in the bone marrow. Fanconi's anaemia and thrombocytopenia absent radii syndrome were ruled out for all patients. We retrospectively compared the clinical courses, laboratory findings and treatment outcome. Development of pancytopenia was observed in 14 of the patients, only one patient presented with an isolated thrombocytopenia over a period of over 14 years. One boy died from bleeding complications. We defined two groups of patients according to the course of platelet counts during the first year of life, which also differed in the course of development of pancytopenia. Physical anomalies in addition to haematopoiesis were found in a number of patients: two children presented with cardiac defects, six with growth abnormalities, and four with retardation of psychomotor development. Fifteen patients were treated with haematopoietic stem cell transplantation, four of whom died of transplantation-related events.

Acquired amegakaryocytic thrombocytopenia (AAMT) is an entity characterized by severe thrombocytopenia with a significantly reduced number of megakaryocytes in the bone marrow. AAMT is rare and poorly defined. Therefore, standard treatment is not well established. In general, steroids are considered the frontline treatment while anti-thymocyte globulin and cyclosporine are reported to be effective in scattered reports. We report a case of AAMT which was successfully treated with azathioprine 3 mg/kg/day. The clinical bleeding tendency resolved after treatment for 4 weeks and complete remission was documented after 6 weeks. Azathioprine treatment for AAMT is low risk, convenient, and cost-effective. Our successful experience suggests that azathioprine is potentially the treatment of choice after steroid failure.

The use of HSCT is the only potentially curative treatment for CAMT, but access is limited by the availability of suitable donors. We report five consecutive patients with CAMT who received MAC and partially HLA-mismatched, UCBT (unrelated, n = 4). Median times to neutrophil (>500/μL) and platelet (≥20 000 and ≥50 000/μL) engraftment were 19, 57, and 70 days, respectively. Acute GvHD, grade II, developed in one patient, who subsequently developed limited chronic GvHD. At median follow-up of 14 yr, all patients are alive with sustained donor cell engraftment. To our knowledge, this is the largest single-center series of UCBT for patients with this disease and suggests that UCBT is a successful curative option for patients with CAMT.

We observed a neonate who had severe thrombocytopenia wherein evaluations for neonatal immune-mediated thrombocytopenia and congenital infections were negative, and the marrow findings were consistent with congenital amegakaryocytic thrombocytopenia (CAMT). A genomic microarray identified a microdeletion at 21q22.11 including the gene RUNX1. Two somewhat similar cases were recently reported, but with multiple congenital anomalies that are not present in our case. We propose that a 21q22 deletion resulting in RUNX1 haploinsufficiency can produce a phenotype similar to CAMT with various associated anomalies depending on which adjacent genes are absent or disrupted.

Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare inherited disorder that presents with thrombocytopenia in infancy and evolves into bone marrow failure over time. Allogeneic hematopoietic stem cell transplant remains the only curative treatment option. We report our experience with identical twin sisters diagnosed with CAMT and treated successfully with matched unrelated donor bone marrow transplants. Before the transplant, 1 twin developed pancytopenia, whereas the other had a relatively benign clinical course. Choice of conditioning regimens was based on their pretransplant bone marrow cellularity and presence or absence of panyhypoplasia. Both twins tolerated the procedure well with no significant complications.

Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare autosomal recessive disorder characterized by thrombocytopenia from failure of megakaryopoiesis. CAMT is one of the bone marrow failure syndromes, and the disease progression may involve other lineages leading to pancytopenia. The genetic background of CAMT is mutations in the MPL gene encoding the thrombopoietin receptor. Here, we describe a Korean male with CAMT. Molecular genetic analyses by direct sequencing revealed that he was compound heterozygous for two nonsense mutations in MPL, Tyr63X (c.189C>A), and Arg357X (c.1069C>T), the latter being a novel mutation. Pediatr Blood Cancer 2011;56:??–??. © 2010 Wiley-Liss, Inc.

Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare disorder expressed in infancy and characterized by isolated thrombocytopenia and megakaryocytopenia with no physical anomalies. Our previous hematological analysis indicated similarities between human CAMT and murine c-mpl (thrombopoietin receptor) deficiency. Because the c-mpl gene was considered as one of the candidate genes for this disorder, we analyzed the genomic sequence of the c-mpl gene of a 10-year-old Japanese girl with CAMT. We detected two heterozygous point mutations: a C-to-T transition at the cDNA nucleotide position 556 (Q186X) in exon 4 and a single nucleotide deletion of thymine at position 1,499 (1,499 delT) in exon 10. Both mutations were predicted to result in a prematurely terminated c-Mpl protein, which, if translated, lacks all intracellular domains essential for signal transduction. Each of the mutations was segregated from the patient’s parents. Accordingly, the patient was a compound heterozygote for two mutations of the c-mpl gene, each derived from one of the parents. The present study suggests that at least a certain type of CAMT is caused by the c-mpl mutation, which disrupts the function of thrombopoietin receptor.

Acquired amegakaryocytic thrombocytopenia (AAMT) is a rare disease that causes severe bleeding. The pathogenesis and treatment of AAMT have not yet been defined. We report the case of a 60-year-old woman diagnosed with AAMT, who presented with severe thrombocytopenia, gastroin­testinal bleeding, and significantly reduced bone marrow megakaryocytes. The patient was treated with methylprednisolone, cyclosporin, and intravenous immunoglobulin. After 2 weeks of treatment, her platelet count started to increase, and her bone marrow megakaryocyte count had normalized 3 months after diagnosis. At the time of diagnosis, the patient was seropositive for anti-c-mpl antibody but was seen to be seronegative once the platelet count recovered. In contrast, anti-c-mpl antibodies were not detected in the serum of 3 patients with idiopathic thrombocytopenic purpura. This case study suggests that anti-c-mpl antibody plays an important role in the development of AAMT, and that intensive immunosuppressive treatment is required for autoantibody clearance and recovery of megakaryocyte count.

Congenital amegakaryocytic thrombocytopenia (MIM #604498) is an extremely rare inherited bone marrow failure syndrome, usually presenting as a severe thrombocytopenia at birth due to ineffective megakaryocytopoiesis and no characteristic physical anomalies. Usually the isolated thrombocytopenia progresses to pancytopenia during the first years of life. The only curative therapy to date is haematopoietic stem cell transplantation. Most of the cases of congenital amegakaryocytic thrombocytopenia are caused by defective expression or function of the thrombopoietin receptor due to homozygous or compound heterozygous mutations in the gene MPL. The essential roles of thrombopoietin as a lineage specific regulator of platelet production and as a regulator of haematopoietic stem cell function are reflected in the haematological defects seen in affected individuals.

CAMT is a bone marrow failure syndrome that usually presents with isolated thrombocytopenia soon after birth. HSCT is curative, and MAC is associated with increased transplant-related morbidity and mortality, especially in the unrelated setting. We used a RIC regimen with alemtuzumab, fludarabine, and melphalan in a seven-month-old patient with CAMT who underwent a MUD HSCT. The transplant was well tolerated with few complications. Neutrophil and platelet engraftment occurred on day +12 and +29, respectively, and she had 100% donor chimerisms on days +19.

T-cell-depleted hematopoietic SCT from unrelated donors for the treatment of congenital amegakaryocytic thrombocytopenia

Congenital amegakaryocytic thrombocytopenia (CAMT, OMIM 604498) is an autosomal recessive disorder characterized by absent or reduced number of megakaryocytes in the bone marrow (BM) since birth, elevated serum levels of thrombopoietin (TPO), and very low platelet count. Prognosis of CAMT patients

Congenital amegakaryocytic thrombocytopenia is an extremely rare disorder for which bone marrow transplantation offers the only possibility for cure. The pathophysiology is unclear. Two children with familial amegakaryocytic thrombocytopenia underwent unrelated donor transplantation (bone marrow in one, umbilical cord blood in the second) after a preparative regimen of cyclophosphamide and total body irradiation. Both patients failed initial engraftment, required further donor stem cell infusions and are currently well with sustained engraftment, 16 months and 7 months after transplantation, respectively. The difficulty in achieving engraftment of unrelated donor stem cells in these children suggests that in future cases additional measures to achieve engraftment may be necessary, for example, a more aggressive preparative regimen or an increased stem cell dose.

Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare disorder that presents with severe thrombocytopenia and absence of megakaryocytes in the bone marrow. The disease may develop into bone marrow aplasia. Genetic defects in the gene encoding the thrombopoietin (Tpo) receptor, MPL, are the cause of this disease. In a previous study, we identified four missense mutations in CAMT patients, predicting Arg102Pro, Pro136His, Arg257Cys and Pro635Leu. To investigate whether these mutations result in defective Tpo-binding and/or signalling, full-length wildtype and mutant MPL were transduced into K562 cells. Expression levels and the ability to activate the mitogen-activated protein kinase, Janus kinase-signal transducer and activator of transcription and phosphoinositide-3 kinase pathways upon Tpo-binding were studied. The results predicted that MPL carrying the P136H or P635L mutation was not properly expressed, whereas the R102P and R257C mutations resulted in impaired signal transduction. Our results indicate that a severe clinical course may be expected when these mutations lead to absent Mpl expression or signalling in CAMT patients with missense mutations.

Congenital Amegakaryocytic Thrombocytopenia (CAMT) is a rare bone marrow failure syndrome that presents with isolated thrombocytopenia within the first year of life. Classic diagnostic bone marrow findings reveal absent or significantly decreased megakaryocytes with otherwise normal marrow cellularity. We present a newborn with thrombocytopenia whose initial bone marrow aspirate showed an appropriate number of megakaryocytes. CAMT was subsequently diagnosed after molecular testing demonstrated a mutation in the thrombopoietin receptor. The presence of a normal number of megakaryocytes on an initial bone marrow aspirate should not exclude CAMT from the differential diagnosis of thrombocytopenia within the first year of life. Pediatr Blood Cancer 2008;50:1263–1265. © 2008 Wiley-Liss, Inc.