Search

Acquired amegakaryocytic thrombocytopenia (AAMT) is a rare disorder characterized by severe thrombocytopenia resulting from a marked reduction or absence of bone marrow megakaryocytes, and preserved hematopoiesis in other cellular lineages. We report a unique case of AAMT associated with Hodgkin Lymphoma, with spontaneous recovery following multiple cycles of combination chemotherapy. Our case provides evidence that AAMT associated with an underlying lymphoproliferative disorder may spontaneously recover following chemotherapy for the primary disease, and conservative management of thrombocytopenia could be considered in this setting.

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.

Introduction Acquired amegakaryocytic thrombocytopenia (AATP) is a rare bleeding disorder that causes severe thrombocytopenia with preserved hematopoiesis of other cell lineages. Many cases are misdiagnosed and treated as immune thrombocytopenia. Case presentation We report a case of AATP, in a 50-year-old man, that was treated as immune thrombocytopenia for years with no clinical response. The disorder later was diagnosed as AATP after bone marrow biopsy and was successfully treated with cyclosporine. Discussion The exact mechanism of AATP remains unclear; it is suspected to be an immune-mediated process. Patients with AATP present with severe bleeding and thrombocytopenia, which is usually unresponsive to high-dose corticosteroids. There are no standard treatment guidelines for AATP. Cyclosporine and antithymocyte globulin are found to be effective in some cases. The prompt diagnosis of AATP is vital because it carries high mortality because of excessive bleeding, and it can progress into aplastic anemia or myelodysplastic syndrome.

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.

Introduction Acquired amegakaryocytic thrombocytopenia (AAT) is an extremely rare disease characterized by acquired megakaryocytic aplasia or hypoplasia with no other lineage abnormalities. Given limited evidence, the first aim of this study was to describe the characteristics, management and outcome of patients with AAT, the second aim was to examine the therapeutic response through a systematic review of published case reports. Patients and Methods We carried out a retrospective multicenter study through the French Reference Network for Adult Autoimmune Cytopenias, including patients aged > 18 years with acquired thrombocytopenia with a platelet count < 50 x 10 9/L, associated with a megakaryocytes / granulocytes ratio < 50 % on bone marrow, diagnosed from July 2007 to February 2020. Exclusion criteria were: abnormal granular lineage, evidence of dysplasia, bone marrow infiltration by tumor cells or hematologic malignancy, significant karyotype abnormality, and significant paroxysmal nocturnal hemoglobinuria clone. Bone marrow biopsy were centrally reviewed. Patients' medical charts were collected using the standardized form of the referral center for adult immune thrombocytopenia (ITP). Response to treatment was defined according to standardized international criteria for ITP: response (R) and complete response (CR) were respectively defined as platelet count of > 30 × 10 9/L with at least a doubling of the baseline value, and platelet count of > 100 × 10 9/L ; overall response as either R or CR. We performed a systematic review conducted through Medline and Scopus databases from 1970 to April 2021. Cases were included in the analysis if initial platelet count was < 50 x 10 9/L and bone marrow examination was available, demonstrating a megakaryocyte hypoplasia or aplasia with no alternate diagnosis. Results We screened 23 patients reported as thrombocytopenia with absence or decreased megakaryocytes. Eleven patients were excluded because of: presence of megakaryocytes on bone marrow biopsy despite megakaryocytic aplasia on bone marrow aspirate (n=2), absence of bone marrow biopsy (n=4), aplastic or hypoplastic bone marrow (n=3), moderate thrombocytopenia > 50 x 10 9/L (n=1), lack of data (n=1). Twelve patients were included in the analysis. AAT patients had a median age of 52.5 years, 5/12 (41.7%) were female, 6/12 (50%) had a preexisting autoimmune disease (Table 1). All bone marrow biopsies reviewed to date contained CD8+ T-cell infiltrates. Eight patients received a first line treatment with corticosteroids and/or intravenous immunoglobulins (IVIg), a single response was observed. Ten patients received cyclosporine in monotherapy resulting in 4CR, and 1R or in combination with diverse agents with heterogenous responses. Six had received a single therapy with thrombopoietin receptor agonists (TPO-RAs) inducing 4 CR. Eventually, 9 patients (75%) achieved a CR under therapy, obtained with ciclosporin alone in 3 cases, ciclosporin in association with TPO-RA or ATG in 2 cases, cyclophosphamide followed-up by mycophenolate mofetil in 1 case, and TPO-RAs alone in 4 patients (of whom 3 had previously received at least on immunosuppressive therapy). After a median follow up time of 4.0 years (range 1.2 - 11.9), 2 (16%) patients eventually developed an aplastic anemia, 7 and 41.5 months respectively after initial AAT diagnosis. The literature search yielded 108 articles, of which 75 articles reporting 85 cases were included in the final analysis. The pooled analysis of newly reported and historic cases included 97 cases. Overall response rates to corticosteroids and IVIg were respectively 22.4 % and 5.3 % (Table 2). Ciclosporin was used as single agent in 37.1 % of patients, with an overall response rate of 66.7 %. TPO-RAs were used in 9 cases, with a CR in 7 patients (77.8%). Overall, 9/97 patients (9.3 %) experienced an aplastic anemia during the follow-up. The presence of a thymoma was associated with a higher risk of aplastic anemia (OR 6.83 (95%CI 1.22-34.00, p=0.020)). Conclusion Distinguishing AAT from ITP is of significance as the outcome and response to therapy strongly differ. Aplastic anemia may occur in the follow-up but remain rare. Corticosteroids and IVIg are inefficient in most cases, ciclosporin appear to be very effective, TPO-RA could also be an option, as single therapy or in associations. Further data will be needed to define the respective place of these treatments. Figure 1 Figure 1. Disclosures Moulis: Amgen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Argenix: Membership on an entity's Board of Directors or advisory committees; Grifols: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sobi: Membership on an entity's Board of Directors or advisory committees. Ebbo: Grifols: Honoraria, Membership on an entity's Board of Directors or advisory committees; Octapharma: Other: Attendance Grant; Amgen: Honoraria; Sobi: Other: Attendance Grant; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Terriou: Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Haioun: Amgen: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Gilead: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; F. Hoffmann-La Roche Ltd: Honoraria, Research Funding; Servier: Honoraria, Research Funding; Takeda: Honoraria, Research Funding; Miltenyi: Honoraria, Research Funding. Michel: Amgen,Novartis,UCB,Argenx,Rigel: Honoraria. Godeau: Amgen: Consultancy; Novartis: Consultancy; Grifols: Consultancy; Sobi: Consultancy. Mahevas: GSK: Research Funding; Amgen: Honoraria.

International audience; Thrombopoietin (Tpo) and its receptor (Mpl) are the principal regulators of early and late thrombopoiesis and hematopoietic stem cell maintenance. Mutations in MPL can drastically impair its function and be a contributing factor in multiple hematologic malignancies, including congenital amegakaryocytic thrombocytopenia (CAMT). CAMT is characterized by severe thrombocytopenia at birth, which progresses to bone marrow failure and pancytopenia. Here we report unique familial cases of CAMT that presented with a previously unreported MPL mutation: T814C (W272R) in the background of the activating MPL G117T (K39N or Baltimore) mutation. Confocal microscopy, proliferation and surface biotinylation assays, co-immunoprecipitation, and western blotting analysis were used to elucidate the function and trafficking of Mpl mutants. Results showed that Mpl protein bearing the W272R mutation, alone or together with the K39N mutation, lacks detectable surface expression while being strongly colocalized with the endoplasmic reticulum (ER) marker calreticulin. Both WT and K39N-mutated Mpl were found to be signaling competent, but single or double mutants bearing W272R were unresponsive to Tpo. Function of the deficient Mpl receptor could be rescued by using 2 separate approaches: (1) GRASP55 overexpression, which partially restored Tpo-induced signaling of mutant Mpl by activating an autophagy-dependent secretory pathway and thus forcing ER-trapped immature receptors to traffic to the cell surface; and (2) CRISPR-Cas9 gene editing used to repair MPL T814C mutation in transfected cell lines and primary umbilical cord blood–derived CD34+ cells. We demonstrate proof of principle for rescue of mutant Mpl function by using gene editing of primary hematopoietic stem cells, which indicates direct therapeutic applications for CAMT patients.

Congenital amegakaryocytic thrombocytopenia (CAMT) is an inherited disorder characterized at birth by thrombocytopenia with reduced megakaryocytes, which evolves into generalized bone marrow aplasia during childhood. Although CAMT is genetically heterogeneous, mutations of MPL , the gene encoding for the receptor of thrombopoietin (THPO), are the only known disease‐causing alterations. We identified a family with three children affected with CAMT caused by a homozygous mutation (p.R119C) of the THPO gene. Functional studies showed that p.R119C affects not only ability of the cytokine to stimulate MPL but also its release, which is consistent with the relatively low serum THPO levels measured in patients. In all the three affected children, treatment with the THPO‐mimetic romiplostim induced trilineage hematological responses, remission of bleeding and infections, and transfusion independence, which were maintained after up to 6.5 years of observation. Recognizing patients with THPO mutations among those with juvenile bone marrow failure is essential to provide them with appropriate substitutive therapy and prevent the use of invasive and unnecessary treatments, such as hematopoietic stem cell transplantation or immunosuppression.

Acquired Amegakaryocytic thrombocytopenia (AAT) is a rare hematological disorder characterized by bleeding and severe thrombocytopenia with marked reduction or absence of megakaryocytes in the bone marrow. Prompt recognition of this condition is essential as the condition does not respond to steroids and immunoglobulins, instead responds better to immunosupressives like Azathioprine, Rituximab, Cyclosporine, Mycophenolate, Antithymocyte globulin alone or in combination with other drugs. We report such a rare case of AAT with rapid clinical remission by cyclosporine treatment.

We here describe a case involving a 67-yearold female patient who was referred to our hospital due to severe anemia (hemoglobin, 5.0 g/dL), thrombocytopenia (platelet count, 0.6 × 104/μL), and a mediastinal shadow with calcification noted on X-ray. On admission, an anterior mediastinal tumor was detected, and bone marrow biopsy revealed few megakaryocytes and severely reduced numbers of erythroid cells. The diagnosis was thymoma with pure red cell aplasia (PRCA) and acquired amegakaryocytic thrombocytopenia (AAMT). On Day 8 of admission, the patient received immunosuppressive therapy together with cyclosporine for the 2 severe hematologic diseases, which were stabilized within 2 months. Subsequently, total thymectomy was performed. The diagnosis of the tumor invading the left lung was invasive thymoma, Masaoka- Koga stage III. The histological diagnosis was World Health Organization type AB. Thymoma accompanied with PRCA and AAMT is very rare, and, based on our case, immunotherapeutic therapy for the hematologic disorders should precede surgical intervention.

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 rare hematological disorder causing severe thrombocytopenia and bleeding. Previous in vitro studies postulated both cell-mediated suppression of megakaryocytopoiesis in early megakaryocytic progenitor cells and humoral-mediated suppression by anti-thrombopoietin antibodies as possible etiologies of AAT. Patients with AAT usually present with severe bleeding and thrombocytopenia that is unresponsive to steroids and intravenous immunoglobulin (IVIG). Although standard guidelines have not been established for management of AAT, a few case reports have indicated a response to immunosuppressive treatment. The prompt recognition of this disease entity is essential in view of the substantial risk of morbidity and mortality from excessive bleeding. We report a case of AAT successfully treated with equine antithymocyte globulin (ATG) and cyclosporine (CSP).

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.

We report a rare case of myelodysplastic syndrome that presented early as amegakaryocytic thrombocytopenia in a collodion baby, which is a rare congenital disorder characterized by thick, taut membrane resembling oiled parchment or collodion, which is subsequently shed. To our knowledge, this is the first reported case of a collodion baby who presented with amegakaryocytic thrombocytopenia and who has a significant family history of the same condition. We document the rarity of this possible association and also the need for further study to establish whether a causal relationship exists.

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.

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.

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.

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 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.

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.

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.

Association of thymoma with myasthenia gravis, pure red cell aplasia, and aplastic anemia is well documented. However, thymoma complicated by acquired amegakaryocytic thrombocytopenia (AAMT) is rarely reported. Here, we present a case of a 60-year-old male with past medical history of recurrent invasive thymoma who presented with cough and blood in sputum. He was found to have severe normocytic normochromic anemia and thrombocytopenia that did not improve with intravenous steroids or multiple transfusions of red cells and platelets. Subsequent bone marrow biopsy showed severely depleted megakaryocytes and erythroid precursor cells with relative myeloid hyperplasia suggestive of amegakaryocytic thrombocytopenia and red cell aplasia. He was started on oral cyclosporine but subsequently developed leukopenia and refused any further treatment or diagnostic procedures and left the hospital against medical advice. AAMT, thus, may be a very early presentation of impending aplastic anemia, and treating physicians need to be aware of this entity.

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

Amegakaryocytic thrombocytopenia (AMT) is a rare and often fatal disorder of infancy and childhood presenting with isolated thrombocytopenia that progresses to marrow failure. The defect in thrombopoiesis is not well understood nor is the etiology of the progressive marrow failure. No standard modality of treatment exists. Here, we evaluated the capacity of marrow cells isolated from five patients with AMT and progressive marrow failure to generate megakaryocyte progenitor cells (CFU-MK). These in vitro studies demonstrated assayable numbers of CFU-MK from all patient bone marrows that responded in vitro to the addition of interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), or the combination of both. These findings suggest that the defect in AMT might be partially correctable by the administration of these cytokines. A Phase I/II trial of in vivo administration of these same hematopoietins in the identical patients was conducted in which no significant toxicity was observed. IL-3 but not GM-CSF administration resulted in improved platelet counts in two patients and decreased bleeding and transfusion requirement in the remaining three. No clinical benefit was observed when GM-CSF was administered after IL-3 pretreatment. Prolonged IL-3 administration has resulted in platelet increases in an additional two patients. In vitro responsiveness of CFU- MK to either cytokine did not predict the degree of clinical response. Although the optimal dose and schedule of IL-3 either alone or in combination remains to be established, this study suggests that IL-3 may contribute to the treatment of patients with AMT.

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.

BACKGROUND AND OBJECTIVES: Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare, autosomal recessive disorder induced by mutations of the gene coding for thrombopoietin (TPO) receptor (c-MPL). Patients initially present with isolated thrombocytopenia that subsequently progresses into pancytopenia. Although the mechanisms leading to aplasia are unknown, the age of onset has been reported to depend on the severity of the c-MPL functional defect. To improve our knowledge in this field, we studied clinical and biological features of five new patients. DESIGN AND METHODS: We diagnosed five CAMT patients, identified c-MPL mutations, including five novel alterations and investigated relationships between mutations and their clinical-biological consequences. RESULTS: In all cases, platelet c-MPL and bone marrow colonies were reduced, while serum TPO levels were elevated. We also documented that the percentage of bone marrow cells expressing tumor necrosis factor-a and interferon-g was increased during pancytopenia as compared to in controls, suggesting that, as in other bone marrow failure diseases, these inhibitory cytokines contributed to the pancytopenia. Contrary to previously published data, we found no evidence of correlations between different types of mutations and the clinical course. INTERPRETATION AND CONCLUSIONS: These results suggest that therapies, such as hematopoietic stem cell transplantation, which are potentially curative although associated with a risk of treatment-related mortality, should not be postponed even in those CAMT patients whose c-MPL mutations might predict residual activity of the TPO receptor.

Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare inherited bone marrow failure syndrome (IBMFS) characterized by decreased or absent numbers of megakaryocytes and is not associated with congenital malformations. It is an autosomal recessive disorder with mutations in the thrombopoietin receptor c-MPL, presenting at birth with severe isolated thrombocytopenia. Given the increased risk of life threatening hemorrhage, close monitoring and supportive care with regular platelet transfusions is usually required. The severity of the MPL mutation may predict the clinical course of children with CAMT. Null mutations may rapidly progress to pancytopenia and aplastic anemia, while more modest functional loss of receptor function cause a transient increase in platelet count to > 50,000/µL during the first year of life with later progression to pancytopenia. Moreover, like other IBMFSs, CAMT has been referred to as a cancer predisposition syndrome. Allogeneic hematopoietic stem cell transplant (HSCT) offers the only curative option. We present our institutional experience of three patients with CAMT who underwent matched unrelated HSCT early in the course of the disease when their presenting problem was isolated thrombocytopenia without pancytopenia, marrow failure or clonal evolution. We have used a fully ablative regimen with busulfan 1 mg/kg/dose for 16 doses (days -9, -8, -7, and -6), cyclophosphamide 50 mg/kg/dose for 4 doses (days -5, -4, -3, and -2) and alemtuzumab 3 mg/day (weight-based dosage) for 4 doses (days -5, -4, -3, and -2). Cyclosporine and mini methotrexate (on days +1, +3, +6 and +11) were given for GVHD prophylaxis. The first two patients were siblings with persistent thrombocytopenia at birth, the first of whom had compound heterozygous mutations (c.256dupC and c.391+5 G>C) in the MPL gene. Both parents were carriers and the second sibling was diagnosed prenatally with the same mutations. No other phenotypic abnormalities were noted and testing for Fanconi anemia was negative. The siblings were transplanted with matched unrelated donors at 12 months and 14 months respectively. Our third patient was diagnosed prenatally with germinal matrix hemorrhage and vetriculomegaly. He was noted to have thrombocytopenia after birth. He was treated initially for presumed neonatal alloimmune thrombocytopenia. Sequencing of the MPL gene revealed two compound heterozygous missense mutations (R257C and R102P). The patient was transplanted with a matched unrelated donor at the age of 11 months. All patients tolerated the transplant with minimal toxicity, durable engraftment, and no acute or chronic GVHD. The first two siblings are approximately 4 years and 2 years post HSCT and the third patient is past day 100. Previous reports of HSCT for CAMT that used matched unrelated donors recorded poor outcomes, with a high rate of graft failure. Although our current study is small in size, the results suggest that a HSCT following a fully ablative regimen containing alemtuzumab and performed early in the course of the disease may produce better outcomes, and will avoid the complications associated with marrow failure and clonal abnormalities. Disclosures Allen: Roche: Consultancy, Other: unpaid; NovImmune: Consultancy, Other: unpaid. Heslop:Celgene: Other: Collaborative research agreement; Cell Medica: Other: Licensing Agreement. Brenner:Celgene: Other: Collaborative Research Agreement; Cell Medica: Other: Licensing Agreement; Bluebird Bio: Equity Ownership, Membership on an entity's Board of Directors or advisory committees.

Introduction: Thrombopoietin (Tpo) and its receptor, Mpl, are the principal regulators of early and late thrombopoiesis. Mutations in MPL can drastically impair its function and be a contributing factor in chronic thrombocytosis and in congenital amegakaryocytic thrombocytopenia (CAMT). CAMT is a rare inherited syndrome characterized by thrombocytopenia at birth, progressing to bone marrow failure and pancytopenia. The functional impact of CAMT mutations on Mpl signaling/trafficking is yet to be determined and could be relevant to multiple hematologic malignancies. Here we report unique familial cases of CAMT presenting with a previously unreported MPL mutation: T814C (W272R) in the background of the MPL K39N (Baltimore mutation), known to cause hereditary thrombocytosis (HT). Patients: Consanguineous parents and their eldest daughter, all heterozygous for Mpl K39N/W272R, do not present any signs of disease. Their monozygotic twin daughters presented at birth with severe thrombocytopenia (platelet counts: 12,000/L and 14,000/L), low hemoglobin levels (10.4 mg/dL and 7.8 mg/dL) and very high Tpo levels (3,650 pg/mL and 3115 pg/mL). Bone marrow smears performed 19 days after birth showed severe megakaryocytopenia (only 1 megakaryocyte (MK) seen). Bone marrow colony formation assays yielded 3 and 9 MK colonies vs 84 MK colonies/105 mononuclear cells for the control, leading to a diagnosis of CAMT type I. Whole blood sequencing revealed the presence of a homozygous double MPL K39N/W272R mutation. One of the twins died after bone marrow transplant. A younger male sibling, homozygous for MPL K39N/W272R mutation, has also been diagnosed with CAMT type I. Objectives: This study focuses on the functional characterization of the novel MPL W272R and K39N/W272R mutations and in vitro genetic engineering as a potential therapeutic option for CAMT. Methods: Human megakaryoblastic UT-7 and murine Ba/F3 cells stably expressing human wild-type (WT) Mpl or K39N, W272R or doubly mutated K39N/W272R Mpl fused to mNeonGreen were used as models. Confocal microscopy, proliferation and surface biotinylation assays, as well as co-immunoprecipitation (co-IP) and western blotting analysis, were used to elucidate the function and trafficking of Mpl mutants. CRISPR/Cas9 genetic engineering was used to repair mutant MPL and rescue its function. Results: Confocal microscopy shows that a significant fraction of chimeric WT Mpl protein reaches the cell surface. Significant surface expression is also noted for Mpl K39N. In contrast, the chimeric Mpl protein bearing the W272R mutation, alone or together with the K39N mutation, showed no detectable surface expression of the Tpo receptor. These results were confirmed by surface biotinylation assay. Co-expression of WT CALR fused to RFP, used as an ER marker, showed significantly higher co-localization (Pearson's R value) with mutant Mpl than with WT Mpl, evidence that the large majority of receptors were retained within the ER. We also evaluated Tpo signaling through the JAK/STAT, MAPK and PI3K pathways and Tpo-induced proliferation. Both WT and K39N-mutated Mpl were competent for signaling, while single or double mutants bearing W272R were unresponsive to Tpo. Tpo-induced signaling was partially restored via GRASP55 over-expression (forcing ER-trapped Mpl to traffic to the cell surface). Genetic engineering performed on cells carrying the W272R mutation restored the WT sequence and the response to Tpo, with similar cell proliferation as WT Mpl cells. In addition, co-IP studies indicate that Jak2 associates strongly with WT Mpl and Mpl K39N but not with Mpl W272R. Conclusion: We report a new mutation of Mpl (W272R) present in cis with HT-causing K39N mutation in the context of CAMT. The absence of symptoms in the Mpl K39N/W272R-mutated parents (found to be heterozygous) can be explained by the opposite (apparently neutralizing) effects of the two mutations on the trafficking and signaling of Mpl, as shown by confocal microscopy, western blotting and proliferation assays. In children homozygous for Mpl K39N/W272R, the W272R mutation prevented Mpl binding of Jak2 and expression at cell surface, rendering Tpo signaling impossible despite the presence of the K39N mutation. Function of the deficient Mpl receptor could be rescued using two separate approaches: CRISPR/Cas9 genetic engineering and GRASP55 over-expression. Cell-permeable Tpo analogs will also be tested. Disclosures No relevant conflicts of interest to declare.

Congenital amegakaryocytic thrombocytopenia (CAMT) is an unusual cause of thrombocytopenia without radial or other congenital anomalies in the newborn. Generalized bone marrow dysfunction developing later in life has been reported. We present a 13-month-old girl who was diagnosed as having congenital amegakaryocytic thrombocytopenia and was successfully treated with allogeneic peripheral stem cell transplantation (PSCT) from her fully matched sibling donor. The neutrophil engraftment was on post transplant day 12 and platelet engraftment was on day 14. Her last hemogram revealed platelets of 168 × 109/l 20 months post transplant. Bone Marrow Transplantation (2000) 26, 571–572.

Objective An 11-year-old girl, presenting with fatigue and bruising, was found to be profoundly pancytopenic. Bone marrow exam and clinical evaluation were consistent with aplastic anemia. Family members were studied as potential stem cell donors, revealing that both younger siblings displayed significant thrombocytopenia, whereas both parents had normal blood counts. We evaluated this pedigree to understand the unusually late presentation of congenital amegakaryocytic thrombocytopenia (CAMT). Materials and Methods The coding region and the intron/exon junctions of MPL were sequenced from each family member. Vectors representing each of the mutations were constructed and tested for the ability to support growth of Baf3/Mpl(mutant) cells. Results All three siblings had elevated thrombopoietin levels. Analysis of genomic DNA demonstrated that each parent had mutations/polymorphisms in a single MPL allele and that each child was a compound heterozygote, having inherited both abnormal alleles. The maternal allele encoded a mutation of the donor splice-junction at the exon-3/intron-3 boundary. A mini-gene construct encoding normal vs mutant versions of the intron-3 donor-site demonstrated that physiologic splicing was significantly reduced in the mutant construct. Conclusions Mutations that incompletely eliminate Mpl expression/function may result in delayed diagnosis of CAMT and confusion with aplastic anemia.