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Amegakaryocytic Thrombocytopenia
C H A P T E R
19
Amegakaryocytic Thrombocytopenia D. Meyran*, T. Leblanc*, S. Giraudier**, J.H. Dalle* *Hematology–Immunology Pediatric Department, Robert–Debre Hospital, Paris, France; **Hematology Laboratory, Henri–Mondor Hospital, Paris–Est–Creteil University, Paris, France
INTRODUCTION Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare autosomal recessive bone marrow failure syndrome characterized by severe reduction or absence of megakaryocytes in bone marrow. The diagnosis must be considered in any young patient with a history of early bruising or bleedings with nonimmune thrombocytopenia and no specific physical abnormalities. The diagnosis is confirmed by blood sample and bone marrow examination, determination of platelet volume, dosage of thrombopoietin (TPO), and the identification of mutations in the c-MPL gene. Some patients with mild thrombocytopenia may be missed and only diagnosed later. However, all published patients were diagnosed and reported before adulthood.
Molecular Pathogenesis CAMT is due to mutations on the c-MPL gene resulting in an abnormal TPO receptor without
Congenital and Acquired Bone Marrow Failure http://dx.doi.org/10.1016/B978-0-12-804152-9.00019-1
the binding capacity for TPO. This results in a failure of megakaryopoiesis even if the TPO serum level is markedly elevated [1–10]. As megakaryopoiesis mainly depends on TPO pathway, inadequate binding of TPO to the TPO receptor induces a severe reduction of megakaryocyte number into the bone marrow. However, megakaryopoiesis is not as dependent on TPO as erythropoiesis is on erythropoietin. In fact, megakaryopoiesis may be induced also by the synergistc action of IL-3, IL-6, and SCF. This is in keeping with the observation that mice inactivated for TPO or its receptor, MPL, may still have a residual megakaryopoiesis. This probably also explains why in some CAMT patients, a low and residual megakaryopoiesis persists. TPO receptor is a member of the cytokine receptor superfamily and its functions are not restricted to megakaryopoiesis but also involve other hematopoietic cells and tissues (CD34+, bone marrow, spleen, and fetal liver), thus ensuring a pivotal role in hematopoietic stem cell homeostasis, which explains why associated CAMT
235
Copyright © 2017 Elsevier Inc. All rights reserved.
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19. Amegakaryocytic Thrombocytopenia
mutations can lead to full blown marrow failure with pancytopenia [11–13]. More than 36 different mutations have been described since the first one reported by Kenji Hiara [14] in 1999. Some studies suggested a genotype/phenotype correlation in which null mutations result in severe early thrombocytopenia and rapid progression to pancytopenia (CAMT-I), while missense mutations have led to improvement in platelet counts early in childhood and delayed evolution to aplastic anemia (CAMT-II) [15]. These correlations were partly confirmed by other groups [7,8,16]. However, Savoia in 2007 in a study about five patients did not confirm this finding [9]. Actually, the total number of reported patients is too small to determine whether the risk of aplastic anemia or malignant evolution significantly differs between the two groups. At the molecular level, the vast majority of CAMT patients are due to homozygous or compound heterozygous mutations in MPL [2]. CAMT-associated truncating mutations in MPL principally lead to defective MPL presentation on the cell surface that is responsible for unresponsiveness to TPO [17,18].
Clinical Manifestation and Diagnosis
neonatal alloimmune thrombocytopenia or idiopathic thrombocytopenic purpura. Due to treatment failure a central thrombocytopenia is suspected. Diagnosis requires the association of thrombocytopenia, reduced or absent bone marrow megakaryocytes, highly elevated TPO serum level, and eventual progression to bone marrow failure. Identification of mutations in cMPL gene confirms the diagnosis since now no other genes have been involved in this disease. However, some patients present with morphologic amegakaryocytosis without c-MPL gene mutation. They are considered as CAMT-III. Some patients with mild thrombocytopenia may be missed during the first years of life and only diagnosed later. However, all published patients were diagnosed and reported before adulthood. Thrombocytopenia progressed to pancytopenia at a median age of 39 months in 68% of reported cases up to 2011 [15]. The projected median age for aplastic anemia was 5 years. However progression to aplastic anemia is seen in over 90% of cases by the age of 13 years. Depending on the authors, CAMT must be divided in two or three different subgroups based on the clinical course [6]: type I is characterized by persistent severe thrombocytopenia (below 50 × 109 L–1) and early evolution to central pancytopenia by 2 years of life; type II is characterized by a transient amelioration of platelet count up to 50 × 109 L–1 but by a subsequent fall, with mean onset of marrow failure at 5 years of age; and type III with ineffective megakaryopoiesis with no genetic defects in the c-MPL gene but is associated to amegakaryocytosis and high TPO serum level. CAMT is also classified as preleukemic disease with a median age of 17 years to overt leukemia. However, reported cases of malignant evolution in CAMT are rare and the risk of malignant transformation seems to be very low as compared to other bone marrow failure syndromes. This may be due to the fact
The clinical presentation is variable but usually hemorrhagic manifestations are severe, specifically when the first symptoms occur during neonatal period. During childbirth, these patients could develop central nervous system hemorrhage with life-threatening prognosis. Infants and children present with hemorrhagic symptoms even before learning to walk, with sometime unusual localizations. Buchanan hemorrhagic score (namely established for idiopathic thrombocytopenic purpura) may be variable from low grade with few purpuric lesions up to grade 5 with life-threatening hemorrhages. However, no hemorrhagic manifestations are pathognomonic of CAMT. The clinical presentation can often be mistaken for fetal/
Introduction
that hematopoietic stem cell transplantation (HSCT) actually prevents the risk of leukemic evolution. To note, although malformations do not classically belong to the clinical picture of CAMT, a few patients have been reported with associated congenital abnormalities, such as septal defect of the heart, eye anomalies, and cerebral malformations including cortical dysplasia, lissencephaly, hypoplastic cerebellar vermis with communication 4th ventricle, and cisterna magna. Indeed the role for TPO in the brain development brain is currently discussed [6,15] and in these patients no MPL mutations were demonstrated. When the clinical features are typical and amegakaryocytosis is demonstrated, there is nearly no differential diagnosis for CAMT. Thrombocytopenia with absent radii, which is systematically associated with bilateral and symmetric radial hypoplasia with normal thumbs, is easy to diagnose. Thrombocytopenia associated with radioulnar synostosis is a very rare condition [19]. Other inherited bone marrow failure (IBMF) syndrome, such as Fanconi anemia, dyskeratosis congenita, and Shwachman–Diamond syndrome may also be considered. Nevertheless, these syndromes usually do not associate a very severe thrombocytopenia to normal counts for other lineages; the distinction may be more difficult at the aplastic stage. Wiskott–Aldrich syndrome with microthrombocytes [low mean platelet volume (MPV) as opposite to CAMT where MPV is normal] associated to immune deficiency and skin lesions may be discussed in male patients but megakaryocytic lineage is actually normal on bone marrow aspiration. To note, very rare cases of alloimmune amegakaryocytosis have been published in infants [20] although this picture has not been reported in recent times. More recently, in neonates in whom a CAMT was discussed, 22q22.11 was demonstrated. Lastly, Noonan
237
patients may present with amekaryocytic thrombocytopenia [21–23]
Laboratory Features Thrombocytopenia is usually severe, the median platelets counts on the first diagnosis of thrombocytopenia is 17 × 109 L–1 with a 4–96 range [15]. Platelets are normal in size (normal MPV) and on blood films [24] and the expression of platelets surface glycoproteins is also normal [9]. There is no other cytopenia at diagnosis. Bone marrow is usually normocellular with absent or severely reduced number of megakaryocytes; other lineages are normal at diagnosis. When still present, the megakaryocytes are often reported as small and immature. To note, as megakaryocyte may be normally present on the first bone marrow aspiration [15], this examination has to be repeated during evolution when diagnosis is highly suspected. TPO levels are very high in CAMT patients and higher than those observed in other hypomegakaryocytosis whatever the etiology. Some other diagnostic tools have been reported but are not currently used in clinical practice [15] In fact, diagnosis is based on isolated severe thrombopenia with normal platelet size and with low number (or absence) of megakaryocytes in the bone marrow. TPO level is measured to confirm the decreased megakaryopoiesis but the highest diagnostic levels is achieved by sequencing the entire coding region of c-MPL gene.
Treatment and Supportive Care
Treatment options in CAMT are highly restricted. Patients with CAMT do not respond to immunoglobulins, corticosteroids, splenectomy, or androgens and to date there is no reported benefit associated with the use of TPO receptor agonists in CAMT. Supportive care is limited to transfusion of blood products for long-life duration.
238
19. Amegakaryocytic Thrombocytopenia
As for other chronic transfusion programs with a possible curative treatment by HSCT, the following rules have to be respected: • Transfusions with compatible irradiated blood products. • Limit platelet transfusions to clinical hemorrhagic symptoms. Do not perform transfusion only for low platelet count without clinical manifestations.
As other chronically transfused patients, CAMT subjects present rather a high risk of graft rejection as 11 and 6 patients (out of 63) received a second and a third HSCT, respectively. Seven out of 10 patients died after a first HSCT from TRM. OS was not significantly different according to donor type and stem-cell source although there was a trend toward higher OS and lower TRM for patients transplanted from sibling donor and with bone marrow as source of cells. Overall CAMT patients have an increased risk for transplant-related toxicity due to prior infections, in case of long duration of aplasia, and due to iron overload consequent to red blood cell transfusions when patients develop pancytopenia. As described by Alter et al., CAMT patients also have an increased risk of clonal evolution overtime [1]. Therefore HSCT should be performed as early as possible during childhood but probably not before 1 year of age in order to avoid excessive toxicity during infancy. As in other nonmalignant diseases, HSCT from alternative donor [defined as less than 10/10 allelic HLA-matched compatibility (HLA-A,-B,-C, -DQ, and -DRB1 typing at the allele level)] or unrelated cord blood has to be considered with caution because of higher expected graft failure and higher TRM than from sibling donor (defined as a family donor who shares the same parental haplotypes as the patient). These HSCT from alternative donor should be performed only at an experimental center and needs to be registered in the international registry dedicated to CAMT or to IBMF, as it appears it is very unlikely to have an international HSCT protocol for this very rare IBMF.
Due to the risk of malignant transformation, a bone marrow examination associated with karyotype monitoring has to be performed once a year. If the patient develops pancytopenia, prophylactic therapy against infectious disease (bacterial and fungal) have to be discussed in order to avoid severe infections that may impair the result or even contraindicate subsequent HSCT.
HSCT As for other IBMF syndromes, HSCT represents the only curative option. A retrospective study was recently conducted by EBMT (Fahd et al., CIBMTR Tandem Meeting, 2014, Dallas, TX, USA); 63 patients (30 males/33 females) were identified. They received 80 HSCT from June 1987 to January 2013 (11 and 6 patients underwent a second or a third HSCT, respectively for primary graft rejection). The median age was 1.3 years (0.12–12.7 years) and 7 years (0.3–17.7 years) at CAMT diagnosis and HSCT, respectively. More than 80% of patients received myeloablative conditioning regimen for the first HSCT. None of conditioning regimens were TBI-based. For the first HSCT, 40% of patients underwent transplantation from sibling donor and 40% from unrelated donor. Seventeen percent of HSCT were performed from unrelated cord blood. The 5-year OS was 76.6% without any difference regarding the type of donor and stem-cell source. Transplant-related mortality (TRM) was about 13% at 3 years.
Source of Stem Cells Bone marrow has been shown to be superior to peripheral blood as a stem-cell source in patients with acquired aplastic anemia undergoing matched sibling or unrelated transplants [25,26]. Bone marrow turned out to be superior to peripheral blood also in HSCT in FA patients
REFERENCES
[27]. Also our EBMT study in CAMT patients showed a trend toward a better outcome when bone marrow was used as a source of cells. Based on these findings it can be inferred that in CAMT also peripheral blood stem cells should be avoided because it is likely to be associated with a higher risk of extensive chronic graft versus host disease (GvHD) compared with bone marrow. In general, these results lead us to recommend bone marrow as the preferred choice of stem cells for all children with IBMF.
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Cell Dose On a similar basis, it seems logical to recommend a cell dose greater than 3 × 108 total nucleated cells/kg of recipient body weight for bone marrow stem cells and greater than 3 × 107 total nucleated cells/kg of recipient body weight before freezing for cord stem cells [28].
[2] Ballmaier M, Germeshausen M. Congenital amegakaryocytic thrombocytopenia: clinical presentation, diagnosis, and treatment. Semin Thromb Hemost 2011;37(6):673–81. [3] Freedman MH, Estrov Z. Congenital amegakaryocytic thrombocytopenia: an intrinsic hematopoietic stem cell defect. Am J Pediatr Hematol Oncol 1990;12(2):225–30. [4] Geddis AE. Congenital amegakaryocytic thrombocytopenia and thrombocytopenia with absent radii. Hematol Oncol Clin North Am 2009;23(2):321–31. [5] Geddis AE. Congenital amegakaryocytic thrombocytopenia. Pediatr Blood Cancer 2011;57(2):199–203. [6] King S, Germeshausen M, Strauss G, Welte K, Ballmaier M. Congenital amegakaryocytic thrombocytopenia: a retrospective clinical analysis of 20 patients. Br J Haematol 2005;131(5):636–44. [7] Passos-Coelho JL, Sebastiao M, Gameiro P, Reichert A, Vieira L, Ferreira I, et al. Congenital amegakaryocytic thrombocytopenia—report of a new c-mpl gene missense mutation. Am J Hematol 2007;82(3):240–1. [8] Rose MJ, Nicol KK, Skeens MA, Gross TG, Kerlin BA. Congenital amegakaryocytic thrombocytopenia: the diagnostic importance of combining pathology with molecular genetics. Pediatr Blood Cancer 2008;50(6): 1263–5. [9] Savoia A, Dufour C, Locatelli F, Noris P, Ambaglio C, Rosti V, et al. Congenital amegakaryocytic thrombocytopenia: clinical and biological consequences of five novel mutations. Haematologica 2007;92(9):1186–93. [10] Stoddart MT, Connor P, Germeshausen M, Ballmaier M, Steward CG. Congenital amegakaryocytic thrombocytopenia (CAMT) presenting as severe pancytopenia in the first month of life. Pediatr Blood Cancer 2013;60(9):E94–6. [11] Kobayashi M, Laver JH, Kato T, Miyazaki H, Ogawa M. Thrombopoietin supports proliferation of human primitive hematopoietic cells in synergy with steel factor and/or interleukin-3. Blood 1996;88(2):429–36. [12] Kaushansky K. The molecular mechanisms that control thrombopoiesis. J Clin Invest 2005;115(12):3339–47. [13] Yoshihara H, Arai F, Hosokawa K, Hagiwara T, Takubo K, Nakamura Y, et al. Thrombopoietin/MPL signaling regulates hematopoietic stem cell quiescence and interaction with the osteoblastic niche. Cell Stem Cell 2007;1(6):685–97. [14] Ihara K, Ishii E, Eguchi M, Takada H, Suminoe A, Good RA, et al. Identification of mutations in the c-mpl gene in congenital amegakaryocytic thrombocytopenia. Proc Natl Acad Sci USA 1999;96(6):3132–6. [15] Ballmaier M, Germeshausen M. Advances in the understanding of congenital amegakaryocytic thrombocytopenia. Br J Haematol 2009;146(1):3–16. [16] Muraoka K, Ishii E, Ihara K, Imayoshi M, Miyazaki S, Hara T, et al. Successful bone marrow transplantation
Graft Versus Host Disease Prophylaxis GvHD is one of the most significant complications in nonmalignant diseases and must be avoided. GvHD prophylaxis should include cyclosporin A plus methotrexate. Cyclosporin A should be gradually reduced until it can be discontinued, in the absence of chronic GvHD, 6–12 months after HSCT. These latter recommendations are derived from what has been already published in acquired severe aplastic anemia from sibling donors [29] and unrelated transplantation [30], using bone marrow as a stem-cell source. Pretransplantation serotherapy (either antithymoglobulin or alemtuzumab) is recommended for unrelated donor HSCT, but not for matched sibling donor HSCT because of the associated immunosuppression in the early months post-HSCT, which has the potential for higher TRM and mortality due to opportunistic infections.
References [1] Alter BP. Diagnosis, genetics, and management of inherited bone marrow failure syndromes. Hematology Am Soc Hematol Educ Program 2007;29–39.
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[17]
[18]
[19]
[20] [21]
[22]
[23]
[24]
19. Amegakaryocytic Thrombocytopenia
in a patient with c-mpl-mutated congenital amegakaryocytic thrombocytopenia from a carrier donor. Pediatr Transplant 2005;9(1):101–3. Ballmaier M, Germeshausen M, Schulze H, Cherkaoui K, Lang S, Gaudig A, et al. c-Mpl mutations are the cause of congenital amegakaryocytic thrombocytopenia. Blood 2001;97(1):139–46. Varghese LN, Zhang JG, Young SN, Willson TA, Alexander WS, Nicola NA, et al. Functional characterization of c-Mpl ectodomain mutations that underlie congenital amegakaryocytic thrombocytopenia. Growth Factors 2014;32(1):18–26. Thompson AA, Nguyen LT. Amegakaryocytic thrombocytopenia and radio-ulnar synostosis are associated with HOXA11 mutation. Nature Genet 2000;26(4): 397–8. Bizzaro N, Dianese G. Neonatal alloimmune amegakaryocytosis. Case report. Vox Sang 1988;54(2):112–4. Christensen RD, Wiedmeier SE, Yaish HM. A neonate with congenital amegakaryocytic thrombocytopenia associated with a chromosomal microdeletion at 21q22.11 including the gene RUNX1. J Perinatol 2013;33(3):242–4. Christensen RD, Yaish HM, Leon EL, Sola-Visner MC, Agrawal PB. A de novo T73I mutation in PTPN11 in a neonate with severe and prolonged congenital thrombocytopenia and Noonan syndrome. Neonatology 2013;104(1):1–5. Evans DG, Lonsdale RN, Patton MA. Cutaneous lymphangioma and amegakaryocytic thrombocytopenia in Noonan syndrome. Clin Genet 1991;39(3):228–32. Drachman JG. Inherited thrombocytopenia: when a low platelet count does not mean ITP. Blood 2004;103(2):390–8.
[25] Eapen M, Le Rademacher J, Antin JH, Champlin RE, Carreras J, Fay J, et al. Effect of stem cell source on outcomes after unrelated donor transplantation in severe aplastic anemia. Blood 2011;118(9): 2618–21. [26] Bacigalupo A, Socie G, Schrezenmeier H, Tichelli A, Locasciulli A, Fuehrer M, et al. Bone marrow versus peripheral blood as the stem cell source for sibling transplants in acquired aplastic anemia: survival advantage for bone marrow in all age groups. Haematologica 2012;97(8):1142–8. [27] Peffault de Latour R, Porcher R, Dalle JH, Aljurf M, Korthof ET, Svahn J, et al. Allogeneic hematopoietic stem cell transplantation in Fanconi anemia: the European Group for Blood and Marrow Transplantation experience. Blood 2013;122(26):4279–86. [28] Gluckman E, Ruggeri A, Volt F, Cunha R, Boudjedir K, Rocha V. Milestones in umbilical cord blood transplantation. Br J Haematol 2011;154(4):441–7. [29] Locatelli F, Bruno B, Zecca M, Van-Lint MT, McCann S, Arcese W, et al. Cyclosporin A and shortterm methotrexate versus cyclosporin A as graft versus host disease prophylaxis in patients with severe aplastic anemia given allogeneic bone marrow transplantation from an HLA-identical sibling: results of a GITMO/EBMT randomized trial. Blood 2000;96(5): 1690–7. [30] Bacigalupo A, Socie G, Lanino E, Prete A, Locatelli F, Locasciulli A, et al. Fludarabine, cyclophosphamide, antithymocyte globulin, with or without low dose total body irradiation, for alternative donor transplants, in acquired severe aplastic anemia: a retrospective study from the EBMT-SAA Working Party. Haematologica 2010;95(6):976–82.
19
Amegakaryocytic Thrombocytopenia D. Meyran*, T. Leblanc*, S. Giraudier**, J.H. Dalle* *Hematology–Immunology Pediatric Department, Robert–Debre Hospital, Paris, France; **Hematology Laboratory, Henri–Mondor Hospital, Paris–Est–Creteil University, Paris, France
INTRODUCTION Congenital amegakaryocytic thrombocytopenia (CAMT) is a rare autosomal recessive bone marrow failure syndrome characterized by severe reduction or absence of megakaryocytes in bone marrow. The diagnosis must be considered in any young patient with a history of early bruising or bleedings with nonimmune thrombocytopenia and no specific physical abnormalities. The diagnosis is confirmed by blood sample and bone marrow examination, determination of platelet volume, dosage of thrombopoietin (TPO), and the identification of mutations in the c-MPL gene. Some patients with mild thrombocytopenia may be missed and only diagnosed later. However, all published patients were diagnosed and reported before adulthood.
Molecular Pathogenesis CAMT is due to mutations on the c-MPL gene resulting in an abnormal TPO receptor without
Congenital and Acquired Bone Marrow Failure http://dx.doi.org/10.1016/B978-0-12-804152-9.00019-1
the binding capacity for TPO. This results in a failure of megakaryopoiesis even if the TPO serum level is markedly elevated [1–10]. As megakaryopoiesis mainly depends on TPO pathway, inadequate binding of TPO to the TPO receptor induces a severe reduction of megakaryocyte number into the bone marrow. However, megakaryopoiesis is not as dependent on TPO as erythropoiesis is on erythropoietin. In fact, megakaryopoiesis may be induced also by the synergistc action of IL-3, IL-6, and SCF. This is in keeping with the observation that mice inactivated for TPO or its receptor, MPL, may still have a residual megakaryopoiesis. This probably also explains why in some CAMT patients, a low and residual megakaryopoiesis persists. TPO receptor is a member of the cytokine receptor superfamily and its functions are not restricted to megakaryopoiesis but also involve other hematopoietic cells and tissues (CD34+, bone marrow, spleen, and fetal liver), thus ensuring a pivotal role in hematopoietic stem cell homeostasis, which explains why associated CAMT
235
Copyright © 2017 Elsevier Inc. All rights reserved.
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mutations can lead to full blown marrow failure with pancytopenia [11–13]. More than 36 different mutations have been described since the first one reported by Kenji Hiara [14] in 1999. Some studies suggested a genotype/phenotype correlation in which null mutations result in severe early thrombocytopenia and rapid progression to pancytopenia (CAMT-I), while missense mutations have led to improvement in platelet counts early in childhood and delayed evolution to aplastic anemia (CAMT-II) [15]. These correlations were partly confirmed by other groups [7,8,16]. However, Savoia in 2007 in a study about five patients did not confirm this finding [9]. Actually, the total number of reported patients is too small to determine whether the risk of aplastic anemia or malignant evolution significantly differs between the two groups. At the molecular level, the vast majority of CAMT patients are due to homozygous or compound heterozygous mutations in MPL [2]. CAMT-associated truncating mutations in MPL principally lead to defective MPL presentation on the cell surface that is responsible for unresponsiveness to TPO [17,18].
Clinical Manifestation and Diagnosis
neonatal alloimmune thrombocytopenia or idiopathic thrombocytopenic purpura. Due to treatment failure a central thrombocytopenia is suspected. Diagnosis requires the association of thrombocytopenia, reduced or absent bone marrow megakaryocytes, highly elevated TPO serum level, and eventual progression to bone marrow failure. Identification of mutations in cMPL gene confirms the diagnosis since now no other genes have been involved in this disease. However, some patients present with morphologic amegakaryocytosis without c-MPL gene mutation. They are considered as CAMT-III. Some patients with mild thrombocytopenia may be missed during the first years of life and only diagnosed later. However, all published patients were diagnosed and reported before adulthood. Thrombocytopenia progressed to pancytopenia at a median age of 39 months in 68% of reported cases up to 2011 [15]. The projected median age for aplastic anemia was 5 years. However progression to aplastic anemia is seen in over 90% of cases by the age of 13 years. Depending on the authors, CAMT must be divided in two or three different subgroups based on the clinical course [6]: type I is characterized by persistent severe thrombocytopenia (below 50 × 109 L–1) and early evolution to central pancytopenia by 2 years of life; type II is characterized by a transient amelioration of platelet count up to 50 × 109 L–1 but by a subsequent fall, with mean onset of marrow failure at 5 years of age; and type III with ineffective megakaryopoiesis with no genetic defects in the c-MPL gene but is associated to amegakaryocytosis and high TPO serum level. CAMT is also classified as preleukemic disease with a median age of 17 years to overt leukemia. However, reported cases of malignant evolution in CAMT are rare and the risk of malignant transformation seems to be very low as compared to other bone marrow failure syndromes. This may be due to the fact
The clinical presentation is variable but usually hemorrhagic manifestations are severe, specifically when the first symptoms occur during neonatal period. During childbirth, these patients could develop central nervous system hemorrhage with life-threatening prognosis. Infants and children present with hemorrhagic symptoms even before learning to walk, with sometime unusual localizations. Buchanan hemorrhagic score (namely established for idiopathic thrombocytopenic purpura) may be variable from low grade with few purpuric lesions up to grade 5 with life-threatening hemorrhages. However, no hemorrhagic manifestations are pathognomonic of CAMT. The clinical presentation can often be mistaken for fetal/
Introduction
that hematopoietic stem cell transplantation (HSCT) actually prevents the risk of leukemic evolution. To note, although malformations do not classically belong to the clinical picture of CAMT, a few patients have been reported with associated congenital abnormalities, such as septal defect of the heart, eye anomalies, and cerebral malformations including cortical dysplasia, lissencephaly, hypoplastic cerebellar vermis with communication 4th ventricle, and cisterna magna. Indeed the role for TPO in the brain development brain is currently discussed [6,15] and in these patients no MPL mutations were demonstrated. When the clinical features are typical and amegakaryocytosis is demonstrated, there is nearly no differential diagnosis for CAMT. Thrombocytopenia with absent radii, which is systematically associated with bilateral and symmetric radial hypoplasia with normal thumbs, is easy to diagnose. Thrombocytopenia associated with radioulnar synostosis is a very rare condition [19]. Other inherited bone marrow failure (IBMF) syndrome, such as Fanconi anemia, dyskeratosis congenita, and Shwachman–Diamond syndrome may also be considered. Nevertheless, these syndromes usually do not associate a very severe thrombocytopenia to normal counts for other lineages; the distinction may be more difficult at the aplastic stage. Wiskott–Aldrich syndrome with microthrombocytes [low mean platelet volume (MPV) as opposite to CAMT where MPV is normal] associated to immune deficiency and skin lesions may be discussed in male patients but megakaryocytic lineage is actually normal on bone marrow aspiration. To note, very rare cases of alloimmune amegakaryocytosis have been published in infants [20] although this picture has not been reported in recent times. More recently, in neonates in whom a CAMT was discussed, 22q22.11 was demonstrated. Lastly, Noonan
237
patients may present with amekaryocytic thrombocytopenia [21–23]
Laboratory Features Thrombocytopenia is usually severe, the median platelets counts on the first diagnosis of thrombocytopenia is 17 × 109 L–1 with a 4–96 range [15]. Platelets are normal in size (normal MPV) and on blood films [24] and the expression of platelets surface glycoproteins is also normal [9]. There is no other cytopenia at diagnosis. Bone marrow is usually normocellular with absent or severely reduced number of megakaryocytes; other lineages are normal at diagnosis. When still present, the megakaryocytes are often reported as small and immature. To note, as megakaryocyte may be normally present on the first bone marrow aspiration [15], this examination has to be repeated during evolution when diagnosis is highly suspected. TPO levels are very high in CAMT patients and higher than those observed in other hypomegakaryocytosis whatever the etiology. Some other diagnostic tools have been reported but are not currently used in clinical practice [15] In fact, diagnosis is based on isolated severe thrombopenia with normal platelet size and with low number (or absence) of megakaryocytes in the bone marrow. TPO level is measured to confirm the decreased megakaryopoiesis but the highest diagnostic levels is achieved by sequencing the entire coding region of c-MPL gene.
Treatment and Supportive Care
Treatment options in CAMT are highly restricted. Patients with CAMT do not respond to immunoglobulins, corticosteroids, splenectomy, or androgens and to date there is no reported benefit associated with the use of TPO receptor agonists in CAMT. Supportive care is limited to transfusion of blood products for long-life duration.
238
19. Amegakaryocytic Thrombocytopenia
As for other chronic transfusion programs with a possible curative treatment by HSCT, the following rules have to be respected: • Transfusions with compatible irradiated blood products. • Limit platelet transfusions to clinical hemorrhagic symptoms. Do not perform transfusion only for low platelet count without clinical manifestations.
As other chronically transfused patients, CAMT subjects present rather a high risk of graft rejection as 11 and 6 patients (out of 63) received a second and a third HSCT, respectively. Seven out of 10 patients died after a first HSCT from TRM. OS was not significantly different according to donor type and stem-cell source although there was a trend toward higher OS and lower TRM for patients transplanted from sibling donor and with bone marrow as source of cells. Overall CAMT patients have an increased risk for transplant-related toxicity due to prior infections, in case of long duration of aplasia, and due to iron overload consequent to red blood cell transfusions when patients develop pancytopenia. As described by Alter et al., CAMT patients also have an increased risk of clonal evolution overtime [1]. Therefore HSCT should be performed as early as possible during childhood but probably not before 1 year of age in order to avoid excessive toxicity during infancy. As in other nonmalignant diseases, HSCT from alternative donor [defined as less than 10/10 allelic HLA-matched compatibility (HLA-A,-B,-C, -DQ, and -DRB1 typing at the allele level)] or unrelated cord blood has to be considered with caution because of higher expected graft failure and higher TRM than from sibling donor (defined as a family donor who shares the same parental haplotypes as the patient). These HSCT from alternative donor should be performed only at an experimental center and needs to be registered in the international registry dedicated to CAMT or to IBMF, as it appears it is very unlikely to have an international HSCT protocol for this very rare IBMF.
Due to the risk of malignant transformation, a bone marrow examination associated with karyotype monitoring has to be performed once a year. If the patient develops pancytopenia, prophylactic therapy against infectious disease (bacterial and fungal) have to be discussed in order to avoid severe infections that may impair the result or even contraindicate subsequent HSCT.
HSCT As for other IBMF syndromes, HSCT represents the only curative option. A retrospective study was recently conducted by EBMT (Fahd et al., CIBMTR Tandem Meeting, 2014, Dallas, TX, USA); 63 patients (30 males/33 females) were identified. They received 80 HSCT from June 1987 to January 2013 (11 and 6 patients underwent a second or a third HSCT, respectively for primary graft rejection). The median age was 1.3 years (0.12–12.7 years) and 7 years (0.3–17.7 years) at CAMT diagnosis and HSCT, respectively. More than 80% of patients received myeloablative conditioning regimen for the first HSCT. None of conditioning regimens were TBI-based. For the first HSCT, 40% of patients underwent transplantation from sibling donor and 40% from unrelated donor. Seventeen percent of HSCT were performed from unrelated cord blood. The 5-year OS was 76.6% without any difference regarding the type of donor and stem-cell source. Transplant-related mortality (TRM) was about 13% at 3 years.
Source of Stem Cells Bone marrow has been shown to be superior to peripheral blood as a stem-cell source in patients with acquired aplastic anemia undergoing matched sibling or unrelated transplants [25,26]. Bone marrow turned out to be superior to peripheral blood also in HSCT in FA patients
REFERENCES
[27]. Also our EBMT study in CAMT patients showed a trend toward a better outcome when bone marrow was used as a source of cells. Based on these findings it can be inferred that in CAMT also peripheral blood stem cells should be avoided because it is likely to be associated with a higher risk of extensive chronic graft versus host disease (GvHD) compared with bone marrow. In general, these results lead us to recommend bone marrow as the preferred choice of stem cells for all children with IBMF.
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Cell Dose On a similar basis, it seems logical to recommend a cell dose greater than 3 × 108 total nucleated cells/kg of recipient body weight for bone marrow stem cells and greater than 3 × 107 total nucleated cells/kg of recipient body weight before freezing for cord stem cells [28].
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Graft Versus Host Disease Prophylaxis GvHD is one of the most significant complications in nonmalignant diseases and must be avoided. GvHD prophylaxis should include cyclosporin A plus methotrexate. Cyclosporin A should be gradually reduced until it can be discontinued, in the absence of chronic GvHD, 6–12 months after HSCT. These latter recommendations are derived from what has been already published in acquired severe aplastic anemia from sibling donors [29] and unrelated transplantation [30], using bone marrow as a stem-cell source. Pretransplantation serotherapy (either antithymoglobulin or alemtuzumab) is recommended for unrelated donor HSCT, but not for matched sibling donor HSCT because of the associated immunosuppression in the early months post-HSCT, which has the potential for higher TRM and mortality due to opportunistic infections.
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