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PubMed2002

Hypoproteinemia in severe childhood atopic dermatitis: a serious complication.

As a complication of atopic dermatitis (AD), the incidence of hypoproteinemia is increasing among infants with severe AD in Japan. It can be a life-threatening condition owing to hypovolemic shock as a result of hypoproteinemia and vascular infarction as a result of thrombocythemia. However, the pathophysiology of this condition remains unclear. The objectives of the present study were two-fold. The first objective was to determine the main route of protein loss, i.e. through the damaged skin or the gastrointestinal tract, or as a result of insufficient food intake. The second objective was to identify whether allergy or infection was the cause of severe skin inflammation. Fifteen patients with AD were enrolled who had serum protein levels of 3.2-5.8 g/dl. Specific immunoglobulin E (IgE) and skin test to allergens, stool eosinophils, alpha1-antitrypsin clearance, skin Staphylococcus aureus colonization and superantigens (SAgs) produced by the organism, serum SAg-specific IgE antibodies, serum interleukin (IL)-5, IL-6, IL-12, and interferon-gamma (IFN-gamma) were evaluated. Prominent serous skin discharge was seen in all of the patients and was found to have almost the same protein concentration as serum. Marked thrombocytosis, with a maximum of 1,060 x 103/ml, was seen. Skin culture revealed S. aureus colonization in all patients. SAg-producing S. aureus were found in 84.6% of the patients. The concentration of serum IL-5 was significantly increased and correlated well with the blood eosinophil count. Hence, the main route of protein loss was believed to be through damaged skin. The cause of severe inflammation was thought to be a combination of allergic inflammation and skin colonization by SAg-producing S. aureus. Serum cytokines showed a T helper 2 (Th2) T-cell-mediated pattern. To prevent hypovolemic shock, vascular occlusion, and growth retardation, it is of vital importance to diagnose hypoproteinemia at an early stage and start appropriate therapy.

Adolescent↗
PubMed2002

Modulation of platelet caspases and life-span by anti-platelet antibodies in mice.

Anti-platelet antibodies are known to contribute to some types of thrombocytopenia. In this work we investigated anti-platelet antibodies with opposite influence upon activation and kinetics of platelet caspases. A rabbit anti-platelet antibody induced a profound thrombocytopenia, which was associated with an increase of microparticles in plasma and an activation of platelet caspases, as detected by the binding of a carboxyfluorescein-labeled fluoromethyl ketone probe (FAM-VAD-fmk). Furthermore, microparticles and thrombocytopenia were prevented by the injection of a caspase inhibitor ZVAD-fmk. In contrast, an anti-CD18 mAb (M18.2) induced a thrombocytosis, due to an increased platelet life-span and which was evident in wild-type (+/+), but not in CD18-/- or CD87-/-, mice indicating a requirement of these two surface molecules. Activation of caspases was decreased in platelets from mice injected with the M 18.2 mAb, as evidenced by a decreased binding of the VAD probe, detected by flow cytometry, or an increase in the level of pro-caspase-3, seen on Western blots. These observations indicate firstly, that anti-platelet antibodies can either promote or inhibit activation of platelet caspases, and secondly, that the activation of caspases regulates platelet life-span.

Animals↗
PubMed2002

Treatment of relapsed idiopathic thrombocytopenic purpura with the anti-CD20 monoclonal antibody rituximab: a pilot study.

We performed a prospective pilot study on 12 patients to evaluate the efficacy of the anti-CD20 monoclonal antibody rituximab in relapsed idiopathic thrombocytopenic purpura (ITP). Inclusion criteria were relapse of ITP with a thrombocyte count <20 000 micro L-1 and unsuccessful corticosteroid treatment. Eleven patients had a previous splenectomy, five patients had unsuccessful cytotoxic treatment, and six patients were refractory to intravenous immunoglobulins before rituximab therapy. Response criteria were as follows. Complete remission (CR): normalization of thrombocyte count for at least 30 d. Partial remission (PR): an increase of thrombocytes to above 30 000 microL(-1) for at least 30 d. Minor response (MR): any increase above 30 000 microL(-1) for less than 30 d but more than 10 d. No response (NR): failure to achieve any of the above responses. Treatment plan: We administered 375 mg m(-2) of rituximab once weekly on up to four consecutive weeks, unless there was early CR. Five patients (41%) achieved CR, two patients (17%) PR, and two patients MR (overall response rate 75%, median follow-up of responders 320 d). Four CR patients are ongoing; one CR patient relapsed after 6 months. Adverse events included excessive thrombocytosis in one patient as well as minor infusion-related (grade I) toxicities in four patients. We conclude that rituximab is a promising agent in the treatment of relapsed ITP.

Adult↗
PubMed2002

Double Ph-positive megakaryoblastic transformation of chronic myeloid leukemia.

A 64-yr-old Japanese man presented with mild anemia, leukocytosis, and thrombocytosis in November 1999. A diagnosis of chronic myeloid leukemia was made with a positive Ph chromosome, and interferon alpha treatment was started, 6 million units a day. Two years later, in October 2001, the patient developed leukocytosis, an increased LDH level, and large blasts with basophilic cytoplasm with cytoplasmic projections appeared in the peripheral blood. Bone marrow aspiration revealed increased blasts (59.6%). These blasts were negative on peroxidase stain, positive on acid phosphatase, and weakly positive on alpha naphthyl butyrate esterase stain and periodic acid-Schiff stain. Immunohistochemical staining with monoclonal antibodies revealed that these blasts were strongly positive with anti-CD41 (glycoprotein IIb/IIIa), weakly positive with CD7, CD33, and CD34, and negative with other monoclonal antibodies. A diagnosis of megakaryoblastic transformation from chronic myeloid leukemia was therefore made. Two-color fluorescence in situ hybridization (FISH) for portions of the major-bcr and abl genes from bone marrow cells revealed two fused signals in 90.6% and one fused signal in 5.8% of 106 cells. A cytogenetic study revealed that bone marrow cells were 69, XYY, +6, -7, +8, -9, t(9;22)(q34;q11), +11, +13, -15, -16, dic(17;18)(p11;p11), -18, +19, +21, der(22)t(9;22) in six of nine examined cells. These findings confirmed that these megakaryoblasts originated from megakaryocytes of the chronic myeloid leukemia clone.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2003

Acute myelogenous leukemia in an adult with thrombocytopenia with absent radii syndrome.

Acute myelogenous leukemia with t(8;21)(q22;q22) developed in a 42-yr-old woman having thrombocytopenia with absent radii syndrome (TARS). Standard induction and postremission therapies were safely administered. With each successive chemotherapy, the onset of platelet recovery was not delayed, but peak platelet counts were persistently suppressed. Nine months after achieving complete hematologic and cytogenetic remission, she remains severely thrombocytopenic (platelet count 6-12 x 109/L). She is, however, asymptomatic and transfusion independent. Of interest is the transient normalization of platelet count (rebound relative thrombocytosis). Our report and review of the literature suggests that TARS, contrary to previous belief, may be associated with increased risk of acute leukemia.

Abnormalities, Multiple↗
PubMed1996

Recombinant human interleukin 6 in metastatic renal cell cancer: a phase II trial.

A phase II trial investigating the anti-tumour effects of recombinant human interleukin 6 (rhIL-6) in patients with metastatic renal cell cancer was carried out. RhIL-6 (150 microgram) was administered as a daily subcutaneous injection for 42 consecutive days on an outpatient basis. Forty-nine patients were studied, 12 with and 37 without previous immunotherapy. Forty patients were evaluable for response. A partial remission was noted in two patients, stable disease in 17 and progressive disease in 21. Toxicity was moderate and reversible and consisted mainly of fever, flu-like symptoms, nausea, weight loss and hepatotoxicity. Anaemia, leucocytosis and thrombocytosis and induction of acute phase protein synthesis were noted in most patients. In 15% of the patients anti-IL-6 antibodies developed, and were neutralising in only one patient. Baseline plasma IL-6 concentrations did not correlate with tumour behaviour before or after rhIL-6 treatment. In conclusion, rhIL-6 can be safely administered on an outpatient basis for prolonged period of time and has moderate, reversible toxicity. Its administration induces IL-6-antibody production in only a minority of patients. Antitmour effects of rhIL-6 in metastatic renal cancer are limited.

Acute-Phase Reaction↗
PubMed2005

Granulocyte-colony stimulating factor- and interleukin 6-producing diffuse deciduoid peritoneal mesothelioma.

An autopsy case of granulocyte colony-stimulating factor (G-CSF)- and interleukin-6 (IL-6)-producing diffuse deciduoid peritoneal mesothelioma is reported. The patient was a 70-year-old man with abdominal distension and weight loss in the year prior to his death. Laboratory data suggested severe inflammation with marked leukocytosis, thrombocytosis and elevated serum levels of C-reactive protein, G-CSF and IL-6. Imaging studies showed an expansive mass occupying the entire abdomen and pelvic cavity. Histological diagnosis of tissue taken by needle biopsy was difficult due to the unusual sarcomatoid-appearance of the tumor. In addition, there was severe infiltration of numerous neutrophilic leukocytes. An autopsy revealed that the diffuse peritoneal tumor had a fresh fishmeat-like appearance with focal mucinous degeneration and entirely encased the abdominal organs. Histological examination showed a sheet-like proliferation of tumor cells with large ovoid or polygonal cytoplasm, large atypical nuclei and obvious nucleoli. The tumor cells showed abundant glycogen and hyaluronic acid, and were immunoreactive to cytokeratin, calretinin, epithelial membrane antigen (EMA), CA-125, and focally to vimentin. The tumor cells were immunoreactive to G-CSF and IL-6. Electron microscopy revealed long, slender microvilli on the tumor cell surface. This tumor was diagnosed as a G-CSF- and IL-6-producing, diffuse deciduoid mesothelioma. We report this case with special reference to the differential diagnosis of deciduoid peritoneal mesothelioma with paraneoplastic syndrome.

Aged↗
PubMed2002

A transcription-factor-binding surface of coactivator p300 is required for haematopoiesis.

The coactivators CBP (Cre-element binding protein (CREB)-binding protein) and its paralogue p300 are thought to supply adaptor molecule and protein acetyltransferase functions to many transcription factors that regulate gene expression. Normal development requires CBP and p300, and mutations in these genes are found in haematopoietic and epithelial tumours. It is unclear, however, which functions of CBP and p300 are essential in vivo. Here we show that the protein-binding KIX domains of CBP and p300 have nonredundant functions in mice. In mice homozygous for point mutations in the KIX domain of p300 designed to disrupt the binding surface for the transcription factors c-Myb and CREB, multilineage defects occur in haematopoiesis, including anaemia, B-cell deficiency, thymic hypoplasia, megakaryocytosis and thrombocytosis. By contrast, age-matched mice homozygous for identical mutations in the KIX domain of CBP are essentially normal. There is a synergistic genetic interaction between mutations in c-Myb and mutations in the KIX domain of p300, which suggests that the binding of c-Myb to this domain of p300 is crucial for the development and function of megakaryocytes. Thus, conserved domains in two highly related coactivators have contrasting roles in haematopoiesis.

Amino Acid Sequence↗
PubMed2005

A unique clonal JAK2 mutation leading to constitutive signalling causes polycythaemia vera.

Myeloproliferative disorders are clonal haematopoietic stem cell malignancies characterized by independency or hypersensitivity of haematopoietic progenitors to numerous cytokines. The molecular basis of most myeloproliferative disorders is unknown. On the basis of the model of chronic myeloid leukaemia, it is expected that a constitutive tyrosine kinase activity could be at the origin of these diseases. Polycythaemia vera is an acquired myeloproliferative disorder, characterized by the presence of polycythaemia diversely associated with thrombocytosis, leukocytosis and splenomegaly. Polycythaemia vera progenitors are hypersensitive to erythropoietin and other cytokines. Here, we describe a clonal and recurrent mutation in the JH2 pseudo-kinase domain of the Janus kinase 2 (JAK2) gene in most (> 80%) polycythaemia vera patients. The mutation, a valine-to-phenylalanine substitution at amino acid position 617, leads to constitutive tyrosine phosphorylation activity that promotes cytokine hypersensitivity and induces erythrocytosis in a mouse model. As this mutation is also found in other myeloproliferative disorders, this unique mutation will permit a new molecular classification of these disorders and novel therapeutical approaches.

Animals↗
PubMed1998

Fibroblast growth factor 2 control of vascular tone.

Vascular tone control is essential in blood pressure regulation, shock, ischemia-reperfusion, inflammation, vessel injury/repair, wound healing, temperature regulation, digestion, exercise physiology, and metabolism. Here we show that a well-known growth factor, FGF2, long thought to be involved in many developmental and homeostatic processes, including growth of the tissue layers of vessel walls, functions in vascular tone control. Fgf2 knockout mice are morphologically normal and display decreased vascular smooth muscle contractility, low blood pressure and thrombocytosis. Following intra-arterial mechanical injury, FGF2-deficient vessels undergo a normal hyperplastic response. These results force us to reconsider the function of FGF2 in vascular development and homeostasis in terms of vascular tone control.

Animals↗
PubMed2000

Thymidine kinase gene therapy with concomitant topotecan chemotherapy for recurrent ovarian cancer.

INTRODUCTION: Patients with recurrent ovarian cancer were treated with a replication-deficient recombinant adenovirus containing the herpes simplex virus thymidine kinase gene administered intraperitoneally (i.p.) followed by administration of an anti-herpetic prodrug and topotecan. MATERIALS AND METHODS: A total of 10 patients with stage IIIc epithelial ovarian cancer underwent secondary debulking to < or =0.5 cm residual tumor. Patients with normal i.p. flow received i.p. delivery of adenovirus. Two patients each were treated on dose level 1 (2 x 10(10) vector particles (VP)), dose level 2 (2 x 10(11) VP), and dose level 3 (2 x 10(12) VP); four patients were treated on dose level 4 (2 x 10(13) VP). Acyclovir and topotecan were started 24 hours after vector delivery. RESULTS: No patient treated at any dose level incurred unanticipated toxic effects, and all side effects resolved. The most common adverse event was myelosuppression: grade 3 or 4 thrombocytopenia with grade 2-4 anemia in three patients and grade 3 or 4 neutropenia in eight patients. Three patients developed thrombocytosis and three patients had a mild elevation of serum glutamic pyruvic transaminase/alanine aminotransferase. Temperature elevations that were not associated with detectable infection occurred in two patients. DISCUSSION: I.p. delivery of adenoviral vector with concomitant topotecan chemotherapy was well tolerated without significant lasting toxicities. Side effects were independent of the dose of adenoviral vector.

Acyclovir↗
PubMed1997

Study of the thrombopoitin receptor in essential thrombocythemia.

Essential thrombocythemia (ET) is a myeloproliferative disorder associated with megakaryocytic hyperplasia and thrombocytosis. In this disease, in vitro autonomous growth of megakaryocytic colonies has been demonstrated by various investigators. This phenomenon is impaired by the inhibition of the thrombopoietin/c-mpl pathway. In order to evaluate the potential role of mutations of the receptor gene in the origin of this autonomous growth, we compared the expression of c-mpl mRNA isoforms in platelets derived from ET patients and normal subjects. Overlapping c-mpl PCR fragments derived from four ET patients were sequenced to search for small mutations. In the 10 ET and five normal samples we studied, relative expression of the c-mpl isoforms was identical. New variants of Mpl-P and K isoforms, Mpl-P2 and K2 were detected. Cloning of these isoforms indicated that they are produced by alternative splicing of exon 9 sequences shared by Mpl-P and K. Their predicted amino acid sequence would be deleted by 24 aminoacids, upstream of the WSSWS box of the second domain of c-mpl. Two sequence variations, leading to DNA restriction polymorphisms, were present in the extracellular and Mpl-K intracytoplasmic domains. Both were present in normal and ET samples, excluding mutations of c-mpl as a cause of ET.

Amino Acid Sequence↗
PubMed1998

All-trans retinoic acid (ATRA) in patients with chronic myeloid leukemia in the chronic phase.

Since in vitro observations indicated that all-trans retinoic acid (ATRA), especially in combination with IFNalpha, can exert significant suppressive effects on Ph+ cells, we investigated the effects and the pharmacokinetic profile of ATRA in a selected cohort of patients with Ph+ chronic myeloid leukemia (CML) in chronic phase. Eighteen patients were treated with ATRA at a dose of 80 mg/m2/day (p.o.), divided into two equal doses after meals, for 7 consecutive days every other week for a maximum of 12 courses (1 course = 1 week on and 1 week off). Pharmacokinetic profiles of ATRA were evaluated during intermittent therapy on days 1 and 7 of course 1; on day 1 of course 2; on day 1 of course 6. Out of the 18 patients treated with ATRA, 11 (61%) went off study before the sixth course of treatment because of progressive hyperleukocytosis (seven cases), or thrombocytosis (one case), or refusal (three cases). Seven (39%) patients completed the first six courses (12 weeks) of treatment with ATRA and two of them (11%) maintained a white blood cell (WBC) <10 x 10[9]/l which was induced by the pretreatment with hydroxyurea. One patient completed the 12th course of ATRA maintaining WBC <10 x 10(9)/l, platelets <500 x 10(9)/l and spleen not palpable. The treatment with ATRA was well tolerated and only one patient discontinued the therapy because of non-hematological side-effects. The area under the concentration-time curve (AUC) decreased significantly (P< 0.001) during the first week of therapy. By adopting an intermittent dosing regimen, 1 week on/ 1 week off (1 course), at the start of courses 2 and 6, we obtained the ATRA AUCs equivalent to the ones achieved on day 1 of course 1. In conclusion, our results showed that ATRA alone appeared to be unable to control the WBC expansion in the CML patients in chronic phase. Moreover, it did not induce any remarkable cytoreductive effects on the platelet count and on the hemoglobin level. The major interest of ATRA would be in combination with other therapies. If ATRA was given in combination with IFNalpha or other agents, dose reduction of these would not be planned. On the basis of the pharmacokinetic profile, ATRA should be administered intermittently rather than continuously.

Adult↗
PubMed1999

Initial (prefibrotic) stages of idiopathic (primary) myelofibrosis (IMF) - a clinicopathological study.

A clinicopathological follow-up study including sequential bone marrow biopsies was performed on 79 patients with idiopathic (primary) myelofibrosis (IMF) to characterize initial (prefibrotic) stages and to elucidate whether development of fibrosis was accompanied by corresponding clinical findings. For this purpose our cohort of patients was divided into two groups of which the first presented with the generally accepted signs and symptoms of IMF (group I; n = 60). Most patients of the second group (group II; n = 19) showed mild to moderate therapy-refractory anemia, minimal to slight splenomegaly and frequently thrombocytosis, but no bone marrow fibrosis at onset. Hematopoiesis was consistent with a striking hypercellularity in comparison to the age-related involution by adipose tissue, a conspicuous clustering and histotopographic dislocation of megakaryocytes, a neutrophil granulocytic proliferation and a reduction of erythropoietic islets with arrest of maturation. Most remarkable was the dysplastic cytology of megakaryocytes with a definitive deviation of differentiation resulting in bizarre forms. Follow-up examinations revealed that at later stages group II patients were not distinguishable from the first group with more advanced IMF. For this reason, these patients were regarded as presenting initial, prefibrotic IMF characterized by distinctive bone marrow features at the beginning. The prominent abnormalities of megakaryopoiesis together with the granulocytic proliferation were extremely helpful to differentiate prefibrotic IMF with accompanying thrombocythemia from essential thrombocythemia (ET). Dynamics of fiber progression were calculated by regarding increase in density per time. Speed of progression during the first year of observation proved to be significantly higher in group II patients with prefibrotic IMF in comparison to full-blown cases (group I). In conclusion, with respect to prospective clinical trials, diagnostic criteria for IMF should be re-evaluated by also taking initial, prefibrotic stages into account.

Anemia, Refractory↗
PubMed2002

Acute myeloid leukemia (AML) having evolved from essential thrombocythemia (ET): distinctive chromosome abnormalities in patients treated with pipobroman or hydroxyurea.

ET is a chronic myeloproliferative disorder rarely evolving into AML, sometimes preceded by a myelodysplastic syndrome (MDS). Such transformations mostly occur in patients treated with radiophosphorous ((32)P) or alkylating agents, especially busulfan. Recently, concern has also arisen about the long-term safety of hydroxyurea (HU). Pipobroman (PI), a well tolerated and simple to use drug, constitutes a valid alternative to those cytoreductive treatments. The present study reports on 155 ET patients treated at our institution from 1985 to 1995, and monitored until December 2000. A good control of thrombocytosis was achieved with PI as the only treatment in 106 patients and with HU in 23 patients. Twenty-six patients received no treatment. After a median follow-up of 104 months, seven patients (four treated with HU, and three with PI) developed AML whereas one patient treated with PI developed MDS. A significant difference in progression-free survival was observed between HU- and PI-treated patients (P = 0.004). A short-arm deletion of chromosome 17 was most frequently detected in HU-treated patients, while a long-arm trisomy of chromosome 1 and a monosomy 7q were seen in PI-treated patients. No TP53 mutation was discovered in the six patients studied (two HU-treated and four PI-treated). We conclude that these cytogenetic abnormalities are not linked to the natural history of the disease, but rather that they might be induced by the cytoreductive treatment.

Acute Disease↗
PubMed2006

Frequency and risk factors for thrombosis in idiopathic myelofibrosis: analysis in a series of 155 patients from a single institution.

Thrombosis is a frequent complication of polycythemia vera and essential thrombocythemia, but its incidence and predisposing factors in idiopathic myelofibrosis (IM) are unknown. In 18 (11.6%) of 155 patients diagnosed with IM in a single institution, 31 thrombotic events (19 arterial, 12 venous) were registered after a mean follow-up of 4.2 (s.d.: 4.5) years. In six patients, the thrombosis was simultaneous to or appeared a few months before IM diagnosis and 14 had one or more thrombotic episodes. When compared with the general population, a significant increase was observed in the incidence of venous thrombosis (odds ratio 17.5, 95% confidence interval: 10.3-31.4). At multivariate analysis, the initial variables associated with an increased risk of thrombosis were thrombocytosis (platelets >450 x 10(9)/l, P=0.001), presence of one cardiovascular risk factor (arterial hypertension, smoking, hypercholesterolemia, or diabetes, P=0.003), cellular phase of myelofibrosis (P=0.005), and Hb >11 g/dl (P=0.02). Considering post-diagnosis events, the 5-year thrombosis-free survival probability was 90.4% in the series, 80.6% for patients with platelets >450 x 10(9)/l, 82.6% for patients with one cardiovascular risk factor, and 85.1% for those in cellular phase. These results indicate an increased thrombotic risk for IM patients with hyperproliferative features and/or coexistent cardiovascular risk factors.

Adolescent↗
PubMed1997

The production of tissue inhibitors of metalloproteinases (TIMPs) in megakaryopoiesis: possible role of platelet- and megakaryocyte-derived TIMPs in bone marrow fibrosis.

We quantified tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2 in serum and plasma in normal control subjects and patients with a low or high platelet count, using one-step sandwich enzyme immunoassays. The serum levels of TIMP-1 and TIMP-2 were 101.1 +/- 13.3 ng/ml, and 82.7 +/- 26.3 ng/ml, respectively, in normal subjects. In patients with an elevated platelet count, such as in essential thrombocytosis, polycythaemia vera, and myelofibrosis, serum levels of TIMP-1 and TIMP-2 were 351.6 +/- 200.9 ng/ml and 148.9 +/- 84.0 ng/ml, respectively. Serum levels of TIMP-1 and TIMP-2 in patients with a low platelet count, such as in aplastic anaemia and idiopathic thrombocytopenic purpura, were 57.2 +/- 25.8 ng/ml and 19.7 +/- 7.68 ng/ml, respectively. The serum level of TIMP-1 was significantly correlated with the platelet count in all subjects. The correlation between the serum level of TIMP-2 and the platelet count was not as strong. The level of TIMP-1 in platelet-depleted plasma was not correlated with the platelet count. Immunohistochemical staining using monoclonal antibodies against TIMP-1 and TIMP-2 showed that megakaryocytes and platelets were positive for both TIMP-1 and TIMP-2, confirming that they are rich sources of TIMPs. TIMP-1 and TIMP-2 stimulated the proliferation of bone marrow fibroblasts, although their effect was less potent than that of TGF-beta and PDGF. Erythroleukaemia and megakaryoblastic cell lines showed the highest secretion of TIMP-1 among the leukaemia cell lines examined. There was no lineage specificity for TIMP-2 secretion. These results suggest that TIMPs released from megakaryocytes or from local platelet coagulation may be important in the development of bone marrow fibrosis.

Blood Platelet Disorders↗
PubMed1997

Defective response to thrombopoietin and impaired expression of c-mpl mRNA of bone marrow cells in congenital amegakaryocytic thrombocytopenia.

Congenital amegakaryocytic thrombocytopenia (CAMT) is an uncommon disorder in newborns and infants, characterized by isolated thrombocytopenia and megakaryocytopenia in the first year without physical anomalies. The defect of thrombopoiesis is not well understood. Recently, thrombopoietin (TPO), the ligand for the c-mpl receptor, was cloned. Accumulating evidence from in vitro and in vivo studies indicate that TPO plays a key role in the regulation of megakaryocytopoiesis. In this study we examined the effect of TPO on megakaryocyte colony formation from a patient with CAMT using a plasma-containing methylcellulose clonal culture. The in vitro results demonstrated a defective response to TPO in megakaryocyte colony formation from bone marrow mononuclear cells (MNC) of the patient. although interleukin-3 (IL-3) but not stem cell factor (SCF) induced only a small number of megakaryocyte colonies. These findings indicated that thrombocytopenia in CAMT could not be corrected by administration of TPO in vitro. Additionally, clonal cultures containing SCF, IL-3, IL-6 and erythropoietin showed decreased numbers of erythroid and myelocytic progenitors in the bone marrow of the patient. The serum TPO level measured by enzyme-linked immunosorbent assay was significantly higher than that in healthy controls. By PCR, marrow MNC from healthy children and from a patient with essential thrombocytosis expressed c-mpl mRNA, whereas no c-mpl mRNA was detected in marrow MNC from the patient with CAMT. There was no difference in the CD34 expression and c-kit mRNA between the CAMT patient and healthy children. The results of this study suggest that the pathophysiology in CAMT may be a defective response to TPO in haemopoietic cells through impaired expression of c-mpl mRNA.

Bone Marrow↗