The Wiskott-Aldrich syndrome: studies of platelets, basophils and polymorphonuclear leucocytes

Effects of eltrombopag on platelet count and platelet activation in Wiskott-Aldrich syndrome/X-linked thrombocytopenia

Because Wiskott-Aldrich syndrome (WAS) and X-linked thrombocytopenia (XLT) patients have microthrombocytopenia, hemorrhage is a major problem. We asked whether eltrombopag, a thrombopoietic agent, would increase platelet counts, improve platelet activation, and/or reduce bleeding in WAS/XLT patients. In 9 WAS/XLT patients and 8 age-matched healthy controls, platelet activation was assessed by whole blood flow cytometry. Agonist-induced platelet surface activated glycoprotein (GP) IIb-IIIa and P-selectin in WAS/XLT patients were proportional to platelet size and therefore decreased compared with controls. In contrast, annexin V binding showed no differences between WAS/XLT and controls. Eltrombopag treatment resulted in an increased platelet count in 5 out of 8 patients. Among responders to eltrombopag, immature platelet fraction in 3 WAS/XLT patients was significantly less increased compared with 7 pediatric chronic immune thrombocytopenia (ITP) patients. Platelet activation did not improve in 3 WAS/XLT patients whose platelet count improved on eltrombopag.

IN CONCLUSION

(1) the reduced platelet activation observed in WAS/XLT is primarily due to the microthrombocytopenia; and (2) although the eltrombopag-induced increase in platelet production in WAS/XLT is less than in ITP, eltrombopag has beneficial effects on platelet count but not platelet activation in the majority of WAS/XLT patients. This trial was registered at www.clinicaltrials.gov as #NCT00909363.

Platelets: still a therapeutical target for haemostatic disorders

Platelets are cytoplasmatic fragments from bone marrow megakaryocytes present in blood. In this work, we review the basis of platelet mechanisms, their participation in syndromes and in arterial thrombosis, and their potential as a target for designing new antithrombotic agents. The option of new biotechnological sources is also explored.

Thrombocytopenia in the Intensive Care Unit

Thrombocytopenia is a common laboratory finding in critically ill patients admitted to the intensive care unit. Potential etiologies of thrombocytopenia are myriad, ranging from acute disease processes and concomitant conditions to exposures and drugs. The mechanism of decreased platelet counts can also be varied: laboratory measurement may be spurious, platelet production may be decreased, or platelet destruction or sequestration may be increased. In addition to evaluation for the cause of thrombocytopenia, the clinician must also guard against spontaneous bleeding due to thrombocytopenia, prophylax against bleeding resulting from an invasive procedure performed in the setting of thrombocytopenia, and treat active bleeding related to thrombocytopenia.

The thrombocytopenia of WAS: a familial form of ITP?

In the first report of the concurrent immunodeficiency, thrombocytopenia, and eczema that we now call the Wiskott-Aldrich Syndrome (WAS), Alfred Wiskott asked whether it could be a familial form of Werlhof's disease (now called ITP). This review summarizes what is known about platelet production, consumption, and function in clinical and murine WAS. Both platelet production and consumption are affected by WASP deficiency. Likely molecular mechanisms have been identified for the former process, but remain problematic for the latter. Recent data in a murine model suggest that WASP deficiency could increase both the incidence of antiplatelet antibodies and susceptibility to their enhancement of platelet consumption. Wiskott's original speculation about the relationship between WAS and ITP may need to be reconsidered.

The laboratory diagnosis of platelet disorders

OBJECTIVE

To provide both a detailed description of the laboratory tests available in the diagnosis of platelet disorders and a testing algorithm, based on platelet count, that can be used to direct the evaluation of platelet disorders.

DATA SOURCES

A literature search was conducted using the National Library of Medicine database.

STUDY SELECTION

The literature on laboratory testing of platelet function was reviewed.

DATA EXTRACTION AND DATA SYNTHESIS

Based on the literature review, an algorithm for platelet testing was developed.

CONCLUSIONS

A history of mucocutaneous bleeding often indicates abnormal platelet function that can be associated with a normal, increased, or decreased platelet count. Multiple laboratory procedures can now be used to determine the underlying pathologic condition of platelet dysfunction when other deficiencies or defects of the coagulation cascade or fibrinolysis are ruled out. Simple procedures, such as platelet count, peripheral blood smear, and a platelet function screening test, will often lead the investigator to more specific analyses. Although platelet function testing is often limited to larger medical centers with highly trained technologists, newer technologies are being developed to simplify current procedures and make platelet function testing more accessible. This review provides an algorithm for platelet testing that may be of benefit to pathologists and physicians who deal with hemostatic disorders.

Regulation and Function of WASp in Platelets by the Collagen Receptor, Glycoprotein VI

Wiskott Aldrich syndrome (WAS) is an X-linked recessive disorder associated with abnormalities in platelets and lymphocytes giving rise to thrombocytopenia and immunodeficiency. WAS is caused by a mutation in the gene encoding the cytoskeletal protein (WASp). Despite its importance, the role of WASp in platelet function is not established. WASp was recently shown to undergo tyrosine phosphorylation in platelets after activation by collagen, suggesting that it may play a selective role in activation by the adhesion molecule. In the present study, we show that WASp is heavily tyrosine phosphorylated by a collagen-related peptide (CRP) that binds to the collagen receptor glycoprotein (GP) VI, but not to the integrin 2β1. Tyrosine phosphorylation of WASp was blocked by Src family kinase inhibitors and reduced by treatment with wortmannin and in patients with X-linked agammaglobulinemia (XLA), a condition caused by a lack of functional expression of Btk. This indicates that Src kinases, phosphatidylinositol 3-kinase (PI 3-kinase), and Btk all contribute to the regulation of tyrosine phosphorylation of WASp. The functional importance of WASp was investigated in 2 WAS brothers who show no detectable expression of WASp. Platelet aggregation and secretion from dense granules induced by CRP and thrombin was slightly enhanced in the WAS platelets relative to controls. Furthermore, there was no apparent difference in morphology in WAS platelets after stimulation by these agonists. These observations suggest that WASp does not play a critical role in intracellular signaling downstream of tyrosine kinase-linked and G protein-coupled receptors in platelets.

Regulation and Function of WASp in Platelets by the Collagen Receptor, Glycoprotein VI

Wiskott Aldrich syndrome (WAS) is an X-linked recessive disorder associated with abnormalities in platelets and lymphocytes giving rise to thrombocytopenia and immunodeficiency. WAS is caused by a mutation in the gene encoding the cytoskeletal protein (WASp). Despite its importance, the role of WASp in platelet function is not established. WASp was recently shown to undergo tyrosine phosphorylation in platelets after activation by collagen, suggesting that it may play a selective role in activation by the adhesion molecule. In the present study, we show that WASp is heavily tyrosine phosphorylated by a collagen-related peptide (CRP) that binds to the collagen receptor glycoprotein (GP) VI, but not to the integrin 2β1. Tyrosine phosphorylation of WASp was blocked by Src family kinase inhibitors and reduced by treatment with wortmannin and in patients with X-linked agammaglobulinemia (XLA), a condition caused by a lack of functional expression of Btk. This indicates that Src kinases, phosphatidylinositol 3-kinase (PI 3-kinase), and Btk all contribute to the regulation of tyrosine phosphorylation of WASp. The functional importance of WASp was investigated in 2 WAS brothers who show no detectable expression of WASp. Platelet aggregation and secretion from dense granules induced by CRP and thrombin was slightly enhanced in the WAS platelets relative to controls. Furthermore, there was no apparent difference in morphology in WAS platelets after stimulation by these agonists. These observations suggest that WASp does not play a critical role in intracellular signaling downstream of tyrosine kinase-linked and G protein-coupled receptors in platelets.

WASP is involved in proliferation and differentiation of human haemopoietic progenitors in vitro

The Wiskott-Aldrich syndrome (WAS) is an X-linked recessive disorder characterized by thrombocytopenia, immunodeficiency and eczema. X-linked thrombocytopenia (XLT) is a mild form of WAS with isolated thrombocytopenia. Both phenotypes are caused by mutation of the Wiskott-Aldrich syndrome protein (WASP) gene. In this study we investigated the role of WASP in the differentiation of CD34-positive (CD34+) cells isolated from the bone marrow of patients with WAS (n = 5) or with XLT (n = 4). Megakaryocyte colony formation was significantly decreased in patients with WAS when compared with normal controls. The formation of granulocyte-macrophage colonies and erythroid bursts were also decreased in WAS patinets. In contrast, in XLT patients, formation of all these colonies was normal. However, in vitro proplatelet formation of megakaryocytes induced by thrombopoietin was markedly decreased in both XLT and WAS. Electron microscopic examination revealed that megakaryocytes obtained from WAS or XLT patients grown in vitro had abnormal morphologic features, which seemed to be caused by defective actin cytoskeletal organization, including labyrinth-like structures of the demarcation membrane system and deviated distribution of the alpha-granules and demarcation membrane system. These observations indicate that WASP is involved in the proliferation and differentiation of CD34+ haemopoietic progenitor cells probably by its participation in signal transduction and in the regulation of the cytoskeleton.

Antigen receptor-induced activation and cytoskeletal rearrangement are impaired in Wiskott-Aldrich syndrome protein-deficient lymphocytes

The Wiskott-Aldrich syndrome protein (WASp) has been implicated in modulation of lymphocyte activation and cytoskeletal reorganization. To address the mechanisms whereby WASp subserves such functions, we have examined WASp roles in lymphocyte development and activation using mice carrying a WAS null allele (WAS(-)(/)(-)). Enumeration of hemopoietic cells in these animals revealed total numbers of thymocytes, peripheral B and T lymphocytes, and platelets to be significantly diminished relative to wild-type mice. In the thymus, this abnormality was associated with impaired progression from the CD44(-)CD25(+) to the CD44(-)CD25(-) stage of differentiation. WASp-deficient thymocytes and T cells also exhibited impaired proliferation and interleukin (IL)-2 production in response to T cell antigen receptor (TCR) stimulation, but proliferated normally in response to phorbol ester/ionomycin. This defect in TCR signaling was associated with a reduction in TCR-evoked upregulation of the early activation marker CD69 and in TCR-triggered apoptosis. While induction of TCR-zeta, ZAP70, and total protein tyrosine phosphorylation as well as mitogen-activated protein kinase (MAPK) and stress-activated protein/c-Jun NH(2)-terminal kinase (SAPK/JNK) activation appeared normal in TCR-stimulated WAS(-)(/)(-) cells, TCR-evoked increases in intracellular calcium concentration were decreased in WASp-deficient relative to wild-type cells. WAS(-)(/)(-) lymphocytes also manifested a marked reduction in actin polymerization and both antigen receptor capping and endocytosis after TCR stimulation, whereas WAS(-)(/)(-) neutrophils exhibited reduced phagocytic activity. Together, these results provide evidence of roles for WASp in driving lymphocyte development, as well as in the translation of antigen receptor stimulation to proliferative or apoptotic responses, cytokine production, and cytoskeletal rearrangement. The data also reveal a role for WASp in modulating endocytosis and phagocytosis and, accordingly, suggest that the immune deficit conferred by WASp deficiency reflects the disruption of a broad range of cellular behaviors.

The Wiskott-Aldrich syndrome protein (WASP): roles in signaling and cytoskeletal organization

The Wiskott-Aldrich Syndrome (WAS) is a rare X-linked primary immunodeficiency that is characterized by recurrent infections, hematopoietic malignancies, eczema, and thrombocytopenia. A variety of hematopoietic cells are affected by the genetic defect, including lymphocytes, neutrophils, monocytes, and platelets. Early studies noted both signaling and cytoskeletal abnormalities in lymphocytes from WAS patients. Following the identification of WASP, the gene mutated in patients with this syndrome, and the more generally expressed WASP homologue N-WASP, studies have demonstrated that WASP-family molecules associate with numerous signaling molecules known to alter the actin cytoskeleton. WASP/N-WASP may depolymerize actin directly and/or serve as an adaptor or scaffold for these signaling molecules in a complex cascade that regulates the cytoskeleton.

Collagen Induces Tyrosine Phosphorylation of Wiskott-Aldrich Syndrome Protein in Human Platelets

Wiskott-Aldrich syndrome (WAS) and X-linked thrombocytopenia (XLT) are caused by mutations of the WAS protein (WASP) gene. All hematopoietic stem cell-derived lineages, including platelets, express WASP. Platelets from WAS patients are smaller than their normal counterparts and defects in platelet aggregation and actin polymerization have been reported. To determine if WASP is important for normal platelet function, we examined its role in signal transduction. We found that collagen but not thrombopoietin or thrombin induces a rapid and robust increase in tyrosine phosphorylation of platelet-associated WASP. Collagen-induced tyrosine phosphorylation of WASP was inhibited by cytochalasin D and wortmannin, respectively, suggesting that actin polymerization and phosphatidylinositol 3-kinase (PI3-kinase) play a role in the induction of tyrosine phosphorylation of WASP. Binding of glutathion S-transferase (GST)-Grb2 to WASP was seen in the lysate of resting platelets. The binding was reduced when lysates from collagen-stimulated platelets were incubated with GST-Grb2, suggesting that tyrosine phosphorylation of WASP may directly or indirectly modulate the adapter function of WASP. Although thrombin- and thrombopoietin-induced increase in tyrosine phosphorylation of WASP is negligible or marginal, WASP from thrombin-activated platelets became incorporated into the Triton X-100–insoluble 10,000gsedimentable residue in an aggregation-dependent manner, suggesting that it may have a regulatory role in platelet cytoskeletal processes during aggregation. Lastly, we found that WASP is cleaved in response to activation of calpain, a protease that may have a role in postaggregation signaling processes. Our data suggest that collagen specifically induces an increase in tyrosine phosphorylation of WASP and that WASP is involved in signaling during thrombin-induced aggregation by its redistribution to the cytoskeleton and its cleavage during aggregation.

© 1998 by The American Society of Hematology.

Collagen Induces Tyrosine Phosphorylation of Wiskott-Aldrich Syndrome Protein in Human Platelets

Wiskott-Aldrich syndrome (WAS) and X-linked thrombocytopenia (XLT) are caused by mutations of the WAS protein (WASP) gene. All hematopoietic stem cell-derived lineages, including platelets, express WASP. Platelets from WAS patients are smaller than their normal counterparts and defects in platelet aggregation and actin polymerization have been reported. To determine if WASP is important for normal platelet function, we examined its role in signal transduction. We found that collagen but not thrombopoietin or thrombin induces a rapid and robust increase in tyrosine phosphorylation of platelet-associated WASP. Collagen-induced tyrosine phosphorylation of WASP was inhibited by cytochalasin D and wortmannin, respectively, suggesting that actin polymerization and phosphatidylinositol 3-kinase (PI3-kinase) play a role in the induction of tyrosine phosphorylation of WASP. Binding of glutathion S-transferase (GST)-Grb2 to WASP was seen in the lysate of resting platelets. The binding was reduced when lysates from collagen-stimulated platelets were incubated with GST-Grb2, suggesting that tyrosine phosphorylation of WASP may directly or indirectly modulate the adapter function of WASP. Although thrombin- and thrombopoietin-induced increase in tyrosine phosphorylation of WASP is negligible or marginal, WASP from thrombin-activated platelets became incorporated into the Triton X-100–insoluble 10,000gsedimentable residue in an aggregation-dependent manner, suggesting that it may have a regulatory role in platelet cytoskeletal processes during aggregation. Lastly, we found that WASP is cleaved in response to activation of calpain, a protease that may have a role in postaggregation signaling processes. Our data suggest that collagen specifically induces an increase in tyrosine phosphorylation of WASP and that WASP is involved in signaling during thrombin-induced aggregation by its redistribution to the cytoskeleton and its cleavage during aggregation.

© 1998 by The American Society of Hematology.

Intravenous immunoglobulin, splenectomy, and antibiotic prophylaxis in Wiskott-Aldrich syndrome

AIM

To assess the results of supportive treatment with intravenous immunoglobulin (IVIG) and antibiotic prophylaxis in combination with splenectomy in patients with Wiskott-Aldrich syndrome.

STUDY DESIGN

Retrospective review of case records of 21 patients from March 1984 to February 1996.

RESULTS

Thrombocytopenia was cured in 14 of 15 patients who had splenectomy, but it recurred intermittently in three. Mean platelet volume (MPV) was normal transiently in some patients, but all MPV values were subnormal 8-23 months after splenectomy. Antibiotic and IVIG prophylaxis may have contributed to the lack of a detectable increase in the number of severe acute bacterial infections in the 451 months after splenectomy. Four patients died in 2205 months of observation before and after splenectomy (median 82, range 16-248): two of cerebral B cell lymphoma, one of progressive multifocal leucoencephalopathy, and one with severe chronic chest disease of pneumonia.

CONCLUSION

Adequate supportive treatment with IVIG and antibiotic prophylaxis together with splenectomy enables good survival and quality of life in the short and medium term in patients with Wiskott-Aldrich syndrome. Persistence of infection, bleeding, and vasculitic and allergic symptoms in a significant minority and the risk of development of lymphoma, however, suggest that bone marrow transplantation may be indicated if an HLA identical donor is available.

Wiskott-Aldrich syndrome: new molecular and biochemical insights

The Wiskott-Aldrich syndrome is an uncommon X-linked recessive disease characterized by eczema, thrombocytopenia, and immunodeficiency. The clinical features begin early in life and include recurrent infections, bleeding, and severe eczema. Unless the condition is treated by bone marrow transplantation, the prognosis of Wiskott-Aldrich syndrome is grave, and premature death caused by sepsis, hemorrhage, or lymphoreticular malignancy is common. Although the biochemical defect responsible for the syndrome is not known, recent investigations with restriction fragment length polymorphisms have mapped the Wiskott-Aldrich syndrome locus to the proximal portion of the short arm of the human X chromosome (Xp11). The isolation of these DNA markers makes feasible both carrier detection and prenatal diagnosis of Wiskott-Aldrich syndrome and provides an important adjunct to the management of Wiskott-Aldrich syndrome for patients and their families. These genetic data, in conjunction with the recent identification of a specific O-glycosylation defect in lymphocytes from patients with Wiskott-Aldrich syndrome, present an opportunity for the eventual isolation of the Wiskott-Aldrich syndrome gene and identification of the underlying cellular defect. We review the clinical and laboratory features of this syndrome and summarize the new molecular and biochemical approaches that can be used in diagnosis, genetic counseling, and treatment.

Functional and biochemical evidence of a specific adenosine A2/Ra receptor on human platelets

5'-N-ethylcarboxamideadenosine (NECA) greater than 2-chloroadenosine greater than adenosine greater than (-)-N6-(R-phenyl-isopropyl)-adenosine [(-)-R-PIA] greater than (+)-N6-(S-phenyl-isopropyl)-adenosine [(+)-S-PIA] inhibited in vitro human platelet aggregation in a dose-dependent fashion. 6-nitrobenzylthioinosine and dipyridamole, which inhibit adenosine uptake, and erythro-9-(2-hydroxy-3-nonyl)-adenine, which blocks adenosine metabolism, did not impair the inhibition induced by NECA and adenosine. 8-phenyltheophylline and theophylline, two competitive antagonists of adenosine receptors, blocked the inhibition of platelet aggregation caused by NECA and adenosine. NECA greater than 2-chloroadenosine greater than adenosine greater than (-)-R-PIA greater than (+)-S-PIA increased platelet cyclic adenosine monophosphate (cAMP) levels in a dose-dependent fashion. A significant linear correlation (r = 0.70, p less than 0.001) was found between the increase of platelet cAMP and the inhibition of platelet aggregation induced by adenosine and its analogs. 8-phenyltheophylline, which is a competitive antagonist of adenosine in platelets, also blocked the cAMP accumulation caused by NECA. These data suggest that NECA and other adenosine analogs activate a specific cell surface adenylate cyclase-linked adenosine receptor whose properties are similar to those of an adenosine A2/Ra receptor.