The molecular genetic basis of Glanzmann thrombasthenia in the Iraqi-Jewish and Arab populations in Israel

Pregnancy and childbirth in patients with Glanzmann Thrombasthenia

Glanzmann thrombasthenia (GT) is a rare inherited platelet bleeding disorder caused by a quantitative and/or qualitative defect of the αIIbβ3 integrin. Pregnancy and delivery pose special challenges as they entail increased risks of both maternal and foetal bleeding that may be life-threatening. Multidisciplinary management throughout the preconception, intrapartum and peripartum periods is vital to optimize pregnancy outcomes. This Nutshell review focuses on the challenging management of pregnancy and childbirth in patients with GT.

Hemorrhage of Upper Digestive and Respiratory Tracts in a Child with Glanzmann Thrombasthenia

Glanzmann thrombasthenia (GT) is an autosomal recessive platelet disorder that could cause mild to severe bleeding episodes. The incidence is approximately 1 per 1,000,000 births. Patients with GT frequently have mucocutaneous bleeding with absent platelet aggregation in response to all physiologic stimuli, but a normal platelet count and morphology. Specifically, the glycoprotein IIb/IIIa (GP IIb/IIIa) complex is either inadequate or dysfunctional. This case reports a 3.5-year-old boy with Glanzmann thrombasthenia who had two episodes with uncontrolled hemorrhage from upper digestive and respiratory tracts, the first with the bleeding point found in the left tonsil and the second in the adenoids.

A Novel Homozygous Frameshift Mutation in ITGB3 Causes Glanzmann's Thrombasthenia

The objective of this study was to elucidate the molecular characteristics of a Chinese family with Glanzmann's thrombasthenia (GT). The proband was diagnosed with GT based on clinical manifestations, platelet aggregation, and the expression of CD41 and CD61 in platelets. Whole-exome and Sanger sequencing were used to detect genetic defects related to GT in the proband and the family of the pedigree. Whole-exome sequencing showed a c.1784-1802delinsGTCACA, p. S595Cfs*70 homozygous mutation in exon 11 of the ITGB3 gene in the proband. Heterozygous mutations were found in the proband's parents, grandmother, uncle, aunt, and younger brother. This novel p. S595Cfs*70 ITGB3 gene mutation is not present in the 1000 Genomes and ExAC databases.

New αIIbβ3 variants in 28 Turkish Glanzmann patients; Structural hypothesis for complex activation by residues variations in I-EGF domains

Glanzmann thrombasthenia (GT) is a rare autosomal recessive bleeding disorder characterized by impaired platelet aggregation due to defects in integrin αIIbβ3, a fibrinogen receptor. Platelet phenotypes and allelic variations in 28 Turkish GT patients are reported. Platelets αIIbβ3 expression was evaluated by flow cytometry. Sequence analyzes of ITGA2B and ITGB3 genes allowed identifying nine variants. Non-sense variation effect on αIIbβ3 expression was studied by using transfected cell lines. 3D molecular dynamics (MDs) simulations allowed characterizing structural alterations. Five new alleles were described. αIIb:p.Gly423Asp, p.Asp560Ala and p.Tyr784Cys substitutions impaired αIIbβ3 expression. The αIIb:p.Gly128Val substitution allowed normal expression; however, the corresponding NM_000419.3:c.476G>T variation would create a cryptic donor splicing site altering mRNA processing. The β3:p.Gly540Asp substitution allowed αIIbβ3 expression in HEK-293 cells but induced its constitutive activation likely by impairing αIIb and β3 legs interaction. The substitution alters the β3 I-EGF-3 domain flexibility as shown by MDs simulations. GT variations are mostly unique although the NM_000419.3:c.1752 + 2 T > C and NM_000212.2:c.1697 G > A variations identified in 4 and 8 families, respectively, might be a current cause of GT in Turkey. MD simulations suggested how some subtle structural variations in the β3 I-EGF domains might induce constitutive activation of αIIbβ3 without altering the global domain structure.

Profiling the Genetic and Molecular Characteristics of Glanzmann Thrombasthenia: Can It Guide Current and Future Therapies?

Glanzmann thrombasthenia (GT) is the most widely studied inherited disease of platelet function. Platelets fail to aggregate due to a defect in platelet-to-platelet attachment. The hemostatic plug fails to form and a moderate to severe bleeding diathesis results. Classically of autosomal recessive inheritance, GT is caused by defects within the ITGA2B and ITGB3 genes that encode the αIIbβ3 integrin expressed at high density on the platelet surface and also in intracellular pools. Activated αIIbβ3 acts as a receptor for fibrinogen and other adhesive proteins that hold platelets together in a thrombus. Over 50 years of careful clinical and biological investigation have provided important advances that have improved not only the quality of life of the patients but which have also contributed to an understanding of how αIIbβ3 functions. Despite major improvements in our knowledge of GT and its genetic causes, extensive biological and clinical variability with respect to the severity and intensity of bleeding remains poorly understood. I now scan the repertoire of ITGA2B and ITGB3 gene defects and highlight the wide genetic and biological heterogeneity within the type II and variant subgroups especially with regard to bleeding, clot retraction, the internal platelet Fg storage pool and the nature of the mutations causing the disease. I underline the continued importance of gene profiling and biological studies and emphasize the multifactorial etiology of the clinical expression of the disease. This is done in a manner to provide guidelines for future studies and future treatments of a disease that has not only aided research on rare diseases but also contributed to advances in antithrombotic therapy.

Pathogenic and likely pathogenic variants in at least five genes account for approximately 3% of mild isolated nonsyndromic thrombocytopenia

BACKGROUND

Thrombocytopenia has a variety of different etiologies, both acquired and hereditary. Inherited thrombocytopenia may be associated with other symptoms (syndromic forms) or may be strictly isolated. To date, only about half of all the familial forms of thrombocytopenia have been accounted for in terms of well-defined genetic abnormalities. However, data are limited on the nature and frequency of the underlying causative genetic variants in individuals with mild isolated nonsyndromic thrombocytopenia.

STUDY DESIGN AND METHODS

Thirteen known or candidate genes for isolated thrombocytopenia were included in a gene panel analysis in which targeted next-generation sequencing was performed on 448 French blood donors with mild isolated nonsyndromic thrombocytopenia.

RESULTS

A total of 68 rare variants, including missense, splice site, frameshift, nonsense, and in-frame variants (all heterozygous) were identified in 11 of the 13 genes screened. Twenty-nine percent (N = 20) of the variants detected were absent from both the French Exome Project and gnomAD exome databases. Using stringent criteria and an unbiased approach, we classified seven predicted loss-of-function variants (three in ITGA2B and four in TUBB1) and four missense variants (one in GP1BA, two in ITGB3 and one in ACTN1) as being pathogenic or likely pathogenic. Altogether, they were found in 13 members (approx. 3%) of our studied cohort.

CONCLUSION

We present the results of gene panel sequencing of known and candidate thrombocytopenia genes in mild isolated nonsyndromic thrombocytopenia. Pathogenic and likely pathogenic variants in five known thrombocytopenia genes were identified, accounting for approximately 3% of individuals with the condition.

Novel Pure αVβ3 Integrin Antagonists That Do Not Induce Receptor Extension, Prime the Receptor, or Enhance Angiogenesis at Low Concentrations

The integrin αVβ3 receptor has been implicated in several important diseases, but no antagonists are approved for human therapy. One possible limitation of current small-molecule antagonists is their ability to induce a major conformational change in the receptor that induces it to adopt a high-affinity ligand-binding state. In response, we used structural inferences from a pure peptide antagonist to design the small-molecule pure antagonists TDI-4161 and TDI-3761. Both compounds inhibit αVβ3-mediated cell adhesion to αVβ3 ligands, but do not induce the conformational change as judged by antibody binding, electron microscopy, X-ray crystallography, and receptor priming studies. Both compounds demonstrated the favorable property of inhibiting bone resorption in vitro, supporting potential value in treating osteoporosis. Neither, however, had the unfavorable property of the αVβ3 antagonist cilengitide of paradoxically enhancing aortic sprout angiogenesis at concentrations below its IC50, which correlates with cilengitide's enhancement of tumor growth in vivo.

Glanzmann Thrombasthenia in Children: Experience From a Tertiary Care Center in Southern India

BACKGROUND

Glanzmann thrombasthenia (GT) is a globally rare inherited disorder of hemostasis.

OBJECTIVES

To describe the clinical profile of GT in a tertiary care center in Southern India.

METHODS

A retrospective chart review of all children with GT was performed between January 2005 and August 2017 in the Department of Paediatrics.

RESULTS

A total of 48 patients (representing 43 families) were included. Median age at diagnosis was 2.75 years (interquartile range: 1.5 to 6.75). Two thirds had an onset of bleeding within the first 2 years of life. Sixty-seven percent were born out of consanguineous marriage. The common symptoms were epistaxis, gingival bleeding, and ecchymoses. Neonatal onset of bleeding manifested as purpura, epistaxis, and intracranial hemorrhage. Postsurgical bleeding and menorrhagia were unique presentations in adolescence. About 25% had life-threatening hemorrhage while 50% had growth retardation due to chronic anemia.

CONCLUSIONS

GT is relatively more common in areas of Southern India due to the higher prevalence of consanguinity. Chronic anemia can contribute to growth stunting in these patients.

Acquired Antibodies to αIIbβ3 in Glanzmann Thrombasthenia: From Transfusion and Pregnancy to Bone Marrow Transplants and Beyond

Patients with the inherited bleeding disorder Glanzmann thrombasthenia (GT) possess platelets that lack αIIbβ3 integrin and fail to aggregate, and have moderate to severe mucocutaneous bleeding. Many become refractory to platelet transfusions due to the formation of isoantibodies to αIIbβ3 with the rapid elimination of donor platelets and/or a block of function. Epitope characterization has shown isoantibodies to be polyclonal and to recognize different epitopes on the integrin with β3 a major site and αvβ3 on endothelial and vascular cells a newly recognized target. Pregnancy in GT can also lead to isoantibody formation when fetal cells with β3 integrins pass into the circulation of a mother lacking them; a consequence is neonatal thrombocytopenia and a high risk of mortality. Antibody removal prior to donor transfusions can provide transient relief, but all evidence points to recombinant FVIIa as the first choice for GT patients either to stop bleeding or as prophylaxis. Promoting thrombin generation by rFVIIa favors GT platelet interaction with fibrin, and the risk of deep vein thrombosis also associated with prolonged immobilization and catheter use requires surveillance. Although having a high risk, allogeneic bone marrow transplantation associated with different stem cell sources and conditioning regimens has proved successful in many cases of severe GT with antibodies, and often, the associated conditioning and immunosuppressive therapy leads to loss of isoantibody production. Animal models of gene therapy for GT show promising results, but isoantibody production can be stimulated and CRISPR/Cas9 technology has yet to be applied. Up-to-date consensus protocols for dealing with isoantibodies in GT are urgently required, and networks providing patient care should be expanded.

Immunisation against αIIbβ3 and αvβ3 in a type 1 variant of Glanzmann’s thrombasthenia caused by a missense mutation Gly540Asp on β3

Treatment of bleeding in patients with Glanzmann’s thrombasthenia (GT) can be hampered by iso-antibodies against the αIIbβ3 integrin, which cause rapid clearance of transfused donor platelets. Type 1 GT patients with a total absence of αIIbβ3 from the platelet surface are known to be susceptible to form such isoantibodies. In this study, we describe a type 1 GT patient with a missense mutation (Gly540Asn) located in the EGF3 domain of the β3 integrin subunit. Cotransfection analysis in CHO cells demonstrates total absence of αIIbβ3 from the surface, based on inappropriate αIIb maturation. The patient’s serum was reactive with αIIbβ3 and αvβ3 integrins in a capture assay, when platelets and endothelial cells were used. Two specificities could be isolated from the patient’s serum, anti-αIIbβ3 and anti-αvβ3 isoantibodies. Both specificities did not interfere with platelet aggregation. In contrast, isoantibodies against αvβ3, but not against αIIbβ3, were able to disturb endothelial cell adhesion onto vitronectin, triggered endothelial cell apoptosis and interfered with endothelial tube formation. This intriguing finding may explain more recently observed features of fetal/neonatal iso-immune thrombocytopenia in children from type 1 GT mothers with intracranial haemorrhage, which could be related to anti-endothelial activity of the maternal antibodies. In conclusion, we give evidence that two isoantibody entities exist in type 1 GT patients, which are unequivocally different, both in an immunological and functional sense. Further research on the clinical consequences of immunisation against αvβ3 is required, predominantly in GT patients of childbearing age.

Supplementary Material to this article is available online at www.thrombosis-online.com.

Should studies on Glanzmann thrombasthenia not be telling us more about cardiovascular disease and other major illnesses?

Glanzmann thrombasthenia (GT) is a rare inherited bleeding disorder caused by loss of αIIbβ3 integrin function in platelets. Most genetic variants of β3 also affect the widely expressed αvβ3 integrin. With brief mention of mouse models, I now look at the consequences of disease-causing ITGA2B and ITGB3 mutations on the non-hemostatic functions of platelets and other cells. Reports of arterial thrombosis in GT patients are rare, but other aspects of cardiovascular disease do occur including deep vein thrombosis and congenital heart defects. Thrombophilic and other risk factors for thrombosis and lessons from heterozygotes and variant forms of GT are discussed. Assessed for GT patients are reports of leukemia and cancer, loss of fertility, bone pathology, inflammation and wound repair, infections, kidney disease, autism and respiratory disease. This survey shows an urgent need for a concerted international effort to better determine how loss of αIIbβ3 and αvβ3 influences health and disease.

Clinical, Biochemical, and Molecular Aspects of Glanzmann's Thrombasthenia in Humans and Dogs

Glanzmann's thrombasthenia (GT) is an inherited, intrinsic platelet function defect that involves the platelet glycoprotein complex IIb–IIIa, also known as the fibrinogen receptor and the integrin αIIbβ3. The defect was originally described by Dr. Glanzmann in humans in 1918 as a bleeding disorder that differed clinically from other known coagulopathies. Over the decades that followed, researchers determined the biochemical and molecular basis for the disease in humans. Otterhounds with thrombasthenic thrombopathia, described in the 1960s, were the only animal model that closely resembled the disease described in humans until 1996. At that time, a Great Pyrenees dog was identified with unequivocal clinical and biochemical features of Type I GT. The cDNA encoding for glycoproteins IIb and IIIa were sequenced in normal dogs in 1999, allowing for identification of specific mutations causing Type I GT in both Otterhounds and Great Pyrenees dogs. Knowing the molecular basis for Type I GT in dogs as well as the cDNA sequences in normal dogs should enhance the understanding of structure/function relationships of the αIIbβ3 integrin and provide an excellent animal model for studies aimed at correction of GT in humans. The following review focuses on the structure and function of this platelet receptor and reviews the molecular, biochemical, and clinical aspects of Glanzmann's thrombasthenia in humans and dogs.

Inherited platelet disorders: toward DNA-based diagnosis

Variations in platelet number, volume, and function are largely genetically controlled, and many loci associated with platelet traits have been identified by genome-wide association studies (GWASs).(1) The genome also contains a large number of rare variants, of which a tiny fraction underlies the inherited diseases of humans. Research over the last 3 decades has led to the discovery of 51 genes harboring variants responsible for inherited platelet disorders (IPDs). However, the majority of patients with an IPD still do not receive a molecular diagnosis. Alongside the scientific interest, molecular or genetic diagnosis is important for patients. There is increasing recognition that a number of IPDs are associated with severe pathologies, including an increased risk of malignancy, and a definitive diagnosis can inform prognosis and care. In this review, we give an overview of these disorders grouped according to their effect on platelet biology and their clinical characteristics. We also discuss the challenge of identifying candidate genes and causal variants therein, how IPDs have been historically diagnosed, and how this is changing with the introduction of high-throughput sequencing. Finally, we describe how integration of large genomic, epigenomic, and phenotypic datasets, including whole genome sequencing data, GWASs, epigenomic profiling, protein-protein interaction networks, and standardized clinical phenotype coding, will drive the discovery of novel mechanisms of disease in the near future to improve patient diagnosis and management.

Glanzmann thrombasthenia: state of the art and future directions

Glanzmann thrombasthenia (GT) is the principal inherited disease of platelets and the most commonly encountered disorder of an integrin. GT is characterized by spontaneous mucocutaneous bleeding and an exaggerated response to trauma caused by platelets that fail to aggregate when stimulated by physiologic agonists. GT is caused by quantitative or qualitative deficiencies of αIIbβ3, an integrin coded by the ITGA2B and ITGB3 genes and which by binding fibrinogen and other adhesive proteins joins platelets together in the aggregate. Widespread genotyping has revealed that mutations spread across both genes, yet the reason for the extensive variation in both the severity and intensity of bleeding between affected individuals remains poorly understood. Furthermore, although genetic defects of ITGB3 affect other tissues with β3 present as αvβ3 (the vitronectin receptor), the bleeding phenotype continues to dominate. Here, we look in detail at mutations that affect (i) the β-propeller region of the αIIb head domain and (ii) the membrane proximal disulfide-rich epidermal growth factor (EGF) domains of β3 and which often result in spontaneous integrin activation. We also examine deep vein thrombosis as an unexpected complication of GT and look at curative procedures for the diseases, including allogeneic stem cell transfer and the potential for gene therapy.

Novel and recurrent mutations of ITGA2B and ITGB3 genes in Korean patients with Glanzmann thrombasthenia

Glanzmann thrombasthenia (GT) is an autosomal recessive bleeding disorder caused by defective glycoprotein, αIIb and β3, encoded by ITGA2B and ITGB3 genes, respectively. We herein describe four unrelated Korean patients with genetically confirmed GT. Two patients were homozygous for c.1913+5G>T (IVS11+5G>T) mutation of ITGB3 with a signature of founder effect. The other two patients were compound heterozygous for two mutations of ITGA2B: c.[2333A>C];[2975delA] (p.[Q778P];[E992Gfs*30]) and c.[1750C>T];[2333A>C] (p.[R584X];[Q778P]). The c.2975delA mutation was a novel frameshift mutation of ITGA2B. Although from a limited number of patients, these results suggests c.1913+5G>T of ITGB3 is a recurrent mutation in Korean patients with GT.

Lessons learned from phagocytic function studies in a large cohort of patients with recurrent infections

BACKGROUND

There is a paucity of data on the relationship between demographic characteristics, specific clinical manifestations, and neutrophil dysfunction, guiding physicians to decide which clinical signs and symptoms are a code for an underlying phagocytic disorder.

METHODS

The data over a 21-year period of all adult and pediatric patients referred to our Laboratory for Leukocyte Functions with recurrent pyogenic infections were analyzed. Neutrophil function studies included chemotaxis, superoxide production (SOP), bactericidal activity (BA), and specific studies in case of suspected primary phagocytic disorder (PPD).

RESULTS

Neutrophil dysfunction was found in 33.6% of 998 patients; chemotaxis in 16.6%, SOP in 6%, and BA in 24.5%. The younger the patient and the more organ systems involved, the greater the probability of finding phagocytic impairment. Impaired chemotaxis correlated with recurrent aphthous stomatitis, infections associated with elevated IgE, and purulent upper respiratory tract infections. Impaired SOP and BA correlated with deep-seated abscesses, recurrent lymphadenitis, sepsis, and bone and joint and central nervous system infections. PPDs were identified in 5.7%, chronic granulomatous disease in 4.8%, neutrophil glucose-6-phosphate dehydrogenase deficiency in 0.3%, leukocyte adhesion deficiency type 1 in 0.4%, and myeloperoxidase deficiency in 0.2%. Phagocytic evaluation contributed to the diagnosis of hyperimmunoglobulin-E syndrome (n = 21) and Chediak-Higashi syndrome (n = 3).

CONCLUSIONS

PPDs are identified in 5.7% of patients with recurrent pyogenic infections; in the remainder, phagocytic dysfunction may be related to deleterious effects of persistent infection, drug consumption, or disorders not yet established.

Glanzmann thrombasthenia: a review of ITGA2B and ITGB3 defects with emphasis on variants, phenotypic variability, and mouse models

Characterized by mucocutaneous bleeding arising from a lack of platelet aggregation to physiologic stimuli, Glanzmann thrombasthenia (GT) is the archetype-inherited disorder of platelets. Transmitted by autosomal recessive inheritance, platelets in GT have quantitative or qualitative deficiencies of the fibrinogen receptor, αIIbβ3, an integrin coded by the ITGA2B and ITGB3 genes. Despite advances in our understanding of the disease, extensive phenotypic variability with respect to severity and intensity of bleeding remains poorly understood. Importantly, genetic defects of ITGB3 also potentially affect other tissues, for β3 has a wide tissue distribution when present as αvβ3 (the vitronectin receptor). We now look at the repertoire of ITGA2B and ITGB3 gene defects, reexamine the relationship between phenotype and genotype, and review integrin structure in the many variant forms. Evidence for modifications in platelet production is assessed, as is the multifactorial etiology of the clinical expression of the disease. Reports of cardiovascular disease and deep vein thrombosis, cancer, brain disease, bone disorders, and pregnancy defects in GT are discussed in the context of the results obtained for mouse models where nonhemostatic defects of β3-deficiency or nonfunction are being increasingly described.

Platelet gene therapy improves hemostatic function for integrin alphaIIbbeta3-deficient dogs

Activated blood platelets mediate the primary response to vascular injury. Although molecular abnormalities of platelet proteins occur infrequently, taken collectively, an inherited platelet defect accounts for a bleeding diathesis in ≈1:20,000 individuals. One rare example of a platelet disorder, Glanzmann thrombasthenia (GT), is characterized by life-long morbidity and mortality due to molecular abnormalities in a major platelet adhesion receptor, integrin αIIbβ3. Transfusion therapy is frequently inadequate because patients often generate antibodies to αIIbβ3, leading to immune-mediated destruction of healthy platelets. In the most severe cases allogeneic bone marrow transplantation has been used, yet because of the risk of the procedure it has been limited to few patients. Thus, hematopoietic stem cell gene transfer was explored as a strategy to improve platelet function within a canine model for GT. Bleeding complications necessitated the use of a mild pretransplant conditioning regimen; therefore, in vivo drug selection was used to improve engraftment of autologously transplanted cells. Approximately 5,000 αIIbβ3 receptors formed on 10% of platelets. These modest levels allowed platelets to adhere to αIIbβ3's major ligand (fibrinogen), form aggregates, and mediate retraction of a fibrin clot. Remarkably, improved hemostatic function was evident, with ≤135-fold reduced blood loss, and improved buccal bleeding times decreased to 4 min for up to 5 y after transplant. One of four transplanted dogs developed a significant antibody response to αIIbβ3 that was attenuated effectively with transient immune suppression. These results indicate that gene therapy could become a practical approach for treating inherited platelet defects.

Are bone defects in rare patients with Glanzmann's thrombasthenia associated with ITGB3 or ITGA2B mutations?

The question as to whether Glanzmann thrombasthenia patients with ITGB3 defects and deficiencies of both αIIbβ3 and αvβ3 show phenotypic differences to those with abnormalities exclusive to αIIbβ3 is unresolved. Studies on β3-deficient mice have shown an increased bone mass. Here we review the literature on bone defects in thrombasthenia patients and report the molecular analysis of a patient associating a lifelong thrombasthenia-like syndrome with skeletal defects. We show that the patient is compound heterozygote for Arg327His and Gly391Arg mutations in αIIb, with one mutation inherited from each parent. Modelling strongly suggested that both mutations act by destabilizing the αIIb beta propeller. So it appears likely that this patient has a combination of co-expressed genetic defects.

Do cell junction protein mutations cause an airway phenotype in mice or humans?

Cell junction proteins connect epithelial cells to each other and to the basement membrane. Genetic mutations of these proteins can cause alterations in some epithelia leading to varied phenotypes such as deafness, renal disease, skin disorders, and cancer. This review examines if genetic mutations in these proteins affect the function of lung airway epithelia. We review cell junction proteins with examples of disease mutation phenotypes in humans and in mouse knockout models. We also review which of these genes are expressed in airway epithelium by microarray expression profiling and immunocytochemistry. Last, we present a comprehensive literature review to find the lung phenotype when cell junction and adhesion genes are mutated or subject to targeted deletion. We found that in murine models, targeted deletion of cell junction and adhesion genes rarely result in a lung phenotype. Moreover, mutations in these genes in humans have no obvious lung phenotype. Our research suggests that simply because a cell junction or adhesion protein is expressed in an organ does not imply that it will exhibit a drastic phenotype when mutated. One explanation is that because a functioning lung is critical to survival, redundancy in the system is expected. Therefore mutations in a single gene might be compensated by a related function of a similar gene product. Further studies in human and animal models will help us understand the overlap in the function of cell junction gene products. Finally, it is possible that the human lung phenotype is subtle and has not yet been described.

Treatment and outcomes for epistaxis in children with Glanzmann's thrombasthenia

OBJECTIVES/HYPOTHESIS

:To understand Glanzmann's thrombasthenia and provide insight to the management of epistaxis in children with this disease.

STUDY DESIGN

Retrospective chart review.

METHODS

All children diagnosed with Glanzmann's thrombasthenia and treated for epistaxis at Children's Hospitals and Clinics of Minnesota were identified and a retrospective chart review was performed. Outpatient charts, hospitalization records, and operative reports were reviewed from 1999 up to 2009 and appropriate data were extracted. The episodes of epistaxis, therapy used, complications, and success rates for controlling hemorrhage were noted.

RESULTS

Five children with a total of 63 clinical encounters for epistaxis were identified. Forty-seven encounters required hospitalization, close to half of which necessitated medical care in the intensive care unit. Nearly all encounters required infusion of hemostatic therapy with either single or multiple agents. Seventy-one procedures for life-threatening hemorrhage were performed. The most common (n = 24) intervention was administration of bovine collagen matrix, which was successful only half of the time (50%). Anterior and posterior nasal packing with or without hemostatic material completely resolved hemorrhage in 35% of the procedures.

CONCLUSIONS

To date, no form of medical or surgical intervention in children with this condition has consistently demonstrated its ability resolve nasal hemorrhage. The role of the otolaryngologist is to control bleeding during major episodes of nasal hemorrhage that do not respond to medical management. These patients usually have remarkable improvement in the frequency and severity of epistaxis in adolescence and then require much less aggressive therapy.

An αIIb mutation in patients with Glanzmann thrombasthenia located in the N-terminus of blade 1 of the β-propeller (Asn2Asp) disrupts a calcium binding site in blade 6

BACKGROUND

Studies of Glanzmann thrombasthenia (GT)-causing mutations has generated invaluable information on the formation and function of integrin αIIbβ(3).

OBJECTIVE

To characterize the mutation in four siblings of an Israeli Arab family affected by GT, and to analyze the relationships between the mutant protein structure and its function using artificial mutations.

METHODS AND RESULTS

Sequencing disclosed a new A97G transversion in the αIIb gene predicting Asn2Asp substitution at blade 1 of the β-propeller. Alignment with other integrin α subunits revealed that Asn2 is highly conserved. No surface expression of αIIbβ(3) was found in patients' platelets and baby hamster kidney (BHK) cells transfected with mutated αIIb and WT β(3). Although the αIIbβ(3) was formed, the mutation impaired its intracellular trafficking. Molecular dynamics simulations and modeling of the αIIbβ(3) crystal indicated that the Asn2Asp mutation disrupts a hydrogen bond between Asn2 and Leu366 of a calcium binding domain in blade 6, thereby impairing calcium binding that is essential for intracellular trafficking of αIIbβ(3). Substitution of Asn2 to uncharged Ala or Gln partially decreased αIIbβ(3) surface expression, while substitution by negatively or positively charged residues completely abolished surface expression. Unlike αIIbβ(3), αVβ(3) harboring the Asn2Asp mutation was surface expressed by transfected BHK cells, which is consistent with the known lower sensitivity of αVβ(3) to calcium chelation compared with αIIbβ(3).

CONCLUSION

The new GT causing mutation highlights the importance of calcium binding domains in the β-propeller for intracellular trafficking of αIIbβ(3). The mechanism by which the mutation exerts its deleterious effect was elucidated by molecular dynamics.

A unique interaction between alphaIIb and beta3 in the head region is essential for outside-in signaling-related functions of alphaIIbbeta3 integrin

The main interface of the 2 subunits of platelet integrin alphaIIbbeta3 comprises the beta-propeller domain of alphaIIb and the betaA domain of beta3. In the center of the beta-propeller, several aromatic residues interact by cation-pi and hydrophobic bonds with Arg261 of betaA. In this study, we substituted alphaIIb-Trp110 or beta3-Arg261 by residues abundant in other alpha or beta subunits at corresponding locations and expressed them in baby hamster kidney cells along with normal beta3 or alphaIIb, respectively. These mutant cells displayed normal surface expression and fibrinogen binding but grossly impaired outside-in signaling-related functions: adhesion to immobilized fibrinogen, cell spreading, focal adhesion kinase phosphorylation, clot retraction, and reduced alphaIIbbeta3 stability in EDTA (ethylenediaminetetraacetic acid). Expression of mutants with substitutions of Arg261 in beta3 by alanine or lysine with normal alphav yielded normal surface expression of alphavbeta3 and soluble fibrinogen binding as well as normal outside-in signaling-related functions, contrasting findings for alphaIIbbeta3. Structural analysis of alphaIIbbeta3 and alphavbeta3 revealed that alphavbeta3 has several strong interactions between alphav and beta3 subunits that are missing in alphaIIbbeta3. Together, these findings indicate that the interaction between Trp110 of alphaIIb and Arg261 of beta3 is critical for alphaIIbbeta3 integrity and outside-in signaling-related functions.

Mutations in the β3 gene giving rise to type I Glanzmann thrombasthenia in two families in Portugal

Glazzmann thrombasthenia is an inherited bleeding syndrome in which an absence of platelet aggregation is associated with quantitative or qualitative deficiencies of the alphaIIbbeta3 integrin. We now describe biochemical and molecular studies on two Portuguese families where platelets lack both surface and intracellular pools of alphaIIbbeta3. DNA extraction was followed by PCR-SSCP analysis of all exons and intronic boundaries in the alphaIIb and beta3 genes. Migration abnormalities were found for PCR fragments encompassing exon 12 (family 1) and exon 10 (family 2). For patient 1, there was a homozygous G to T transition at position 1846 which resulted in a stop codon at codon 616 in the beta3 gene. For patient 2, direct sequencing revealed a homozygous 1347C insert which led to a stop codon at codon 444 in the beta3 gene. For both patients a single mutated allele was inherited from each parent. Evidence is accumulating that nonsense mutations leading to a truncated beta3 may be a frequent cause of type I Glanzmann thrombasthenia in the Iberian peninsula.

A point mutation in KINDLIN3 ablates activation of three integrin subfamilies in humans

Monogenic deficiency diseases provide unique opportunities to define the contributions of individual molecules to human physiology and to identify pathologies arising from their dysfunction. Here we describe a deficiency disease in two human siblings that presented with severe bleeding, frequent infections and osteopetrosis at an early age. These symptoms are consistent with but more severe than those reported for people with leukocyte adhesion deficiency III (LAD-III). Mechanistically, these symptoms arose from an inability to activate the integrins expressed on hematopoietic cells, including platelets and leukocytes. Immortalized lymphocyte cell lines isolated from the two individuals showed integrin activation defects. Several proteins previously implicated in integrin activation, including Ras-associated protein-1 (RAP1) and calcium and diacylglycerol-regulated guanine nucleotide exchange factor-1 (CALDAG-GEF1), were present and functional in these cell lines. The genetic basis for this disease was traced to a point mutation in the coding region of the KINDLIN3 (official gene symbol FERMT3) gene. When wild-type KINDLIN-3 was expressed in the immortalized lymphocytes, their integrins became responsive to activation signals. These results identify a genetic disease that severely compromises the health of the affected individuals and establish an essential role of KINDLIN-3 in integrin activation in humans. Furthermore, allogeneic bone marrow transplantation was shown to alleviate the symptoms of the disease.

Glanzmann's thrombasthenia: an overview

Glanzmann's thrombasthenia (GT) is an autosomal recessive inherited bleeding disorder due to a defect in platelet function. The hallmark of this disease is severely reduced/absent platelet aggregation in response to multiple physiological agonists. Bleeding signs in GT include epistaxis, bruising, gingival hemorrhage, gastrointestinal hemorrhage, hematuria, menorrhagia, and hemarthrosis. Homozygous or compound heterozygous mutations in the genes of GPIIb and GPIIIa lead to GT. A patient with GT, with no possible causative mutations in GPIIb and GPIIIa genes, may harbor defects in a regulatory element affecting the transcription of these 2 genes. GT occurs in high frequency in certain ethnic populations with an increased incidence of consanguinity such as in Indians, Iranians, Iraqi Jews, Palestinian and Jordanian Arabs, and French Gypsies. Carrier detection in GT is important to control the disorder in family members. Carrier detection can be done both by protein analysis and direct gene analysis.

The GPIIb/IIIa (integrin alphaIIbbeta3) odyssey: a technology-driven saga of a receptor with twists, turns, and even a bend

Starting 90 years ago with a clinical description by Glanzmann of a bleeding disorder associated with a defect in platelet function, technologic advances helped investigators identify the defect as a mutation(s) in the integrin family receptor, alphaIIbbeta3, which has the capacity to bind fibrinogen (and other ligands) and support platelet-platelet interactions (aggregation). The receptor's activation state was found to be under exquisite control, with activators, inhibitors, and elaborate inside-out signaling mechanisms controlling its conformation. Structural biology has produced high-resolution images defining the ligand binding site at the atomic level. Research on alphaIIbbeta3 has been bidirectional, with basic insights resulting in improved Glanzmann thrombasthenia carrier detection and prenatal diagnosis, assays to identify single nucleotide polymorphisms responsible for alloimmune neonatal thrombocytopenia, and the development of alphaIIbbeta3 antagonists, the first rationally designed antiplatelet agents, to prevent and treat thrombotic cardiovascular disease. The future looks equally bright, with the potential for improved drugs and the application of gene therapy and stem cell biology to address the genetic abnormalities. The alphaIIbbeta3 saga serves as a paradigm of rigorous science growing out of careful clinical observations of a rare disorder yielding both important new scientific information and improved diagnosis, therapy, and prevention of other disorders.

Inherited platelet function disorders versus other inherited bleeding disorders: an Indian overview

Inherited deficiencies of plasma proteins involved in blood coagulation generally lead to lifelong bleeding disorders, whose severity is directly proportional to the degree of factor deficiency. Platelet and other coagulation factors play an important role in the haemostasis mechanism. We attempted to study the prevalence of inherited platelet function disorders (PFDs) and correlate with other coagulation factor disorders in the Indian population. Patients with PFDs and other coagulation factor disorders who presented at our hospital during the 5 year period (from January, 2001 to December, 2005) were the subjects of the study. A total of 1576 patients were diagnosed to have congenital bleeding disorders including PFDs, von Willebrand disease, haemophilia A and B and rare coagulation disorder cases. Haemophilia A (HA) was the most common and was seen in 52.31% of the patients followed by total PFDs seen in 27.77% of the patients. Based on severity of the disease, the results of PFDs were highly significant when compared to haemophilia and von Willebrand disease (VWD) (p=0.000). Severity was found higher in HA (77.8%) followed by HB (69.6%) and was found lower for PF3 availability defect (9.0%). It has been concluded that the prevalence of PFDs is relatively low as compared to coagulation factors related disorder and also it has been established that type-1 VWD is relatively less frequent in India as compared to the West.

Congenital Platelet Disorders

Congenital platelet disorders represent a rare group of diseases classified by either a qualitative or quantitative platelet defect. This article outlines the historical, clinical, laboratory, and genetic features of various inherited platelet disorders with attention given to updated information on disease classification, diagnosis, and genotypes. A separate discussion regarding management addresses the difficulty in treatment strategies, particularly in patients who develop alloimmunization to platelets.

Excessive Gingival Bleeding in Two Patients With Glanzmann Thrombasthenia

BACKGROUND

Glanzmann thrombasthenia (GT) is an exceedingly rare but well-defined inherited disorder of platelet function caused by a defect in the glycoprotein IIb/IIIa complex. The association of GT with consanguinity has been noted, especially in geographic regions in which intermarriage is common. In most patients, GT is diagnosed during early infancy or before the age of 5 years. Common manifestations of this disorder are gingival hemorrhage, purpura, epistaxis, petechiae, and menorrhagia. Chronic, prolonged, untreated, or unsuccessfully treated bleeding may be life threatening.

METHODS

We report two female patients with GT who were referred by our hematology clinic to our periodontology department for the treatment of excessive gingival bleeding. The first patient was treated with a platelet transfusion and underwent periodontal therapy (scaling and root planing and dental polishing). The second patient, whose GT was undiagnosed at the time of her referral to our department, applied to our emergency service because of uncontrolled gingival bleeding that developed after scaling and root planing was performed by her dentist. Both patients had been called for regular dental visits.

RESULTS

All treated sites healed without complications. The first patient was monitored for 2 years, during which she practiced proper oral hygiene and experienced no periodontal complications. The other patient did not participate in follow-up.

CONCLUSIONS

Gingival bleeding is usually the first sign of most hematologic disorders, and dentists must be alert for the signs of unusual gingival bleeding. In such cases, collaboration with a hematologist is essential. Under the proper circumstances, periodontal treatment can be performed with an acceptable outcome. With proper oral hygiene, we believe that there will be no complications and no gingival bleeding.

Aberrant 3' splice sites in human disease genes: mutation pattern, nucleotide structure and comparison of computational tools that predict their utilization

The frequency distribution of mutation-induced aberrant 3' splice sites (3'ss) in exons and introns is more complex than for 5' splice sites, largely owing to sequence constraints upstream of intron/exon boundaries. As a result, prediction of their localization remains a challenging task. Here, nucleotide sequences of previously reported 218 aberrant 3'ss activated by disease-causing mutations in 131 human genes were compared with their authentic counterparts using currently available splice site prediction tools. Each tested algorithm distinguished authentic 3'ss from cryptic sites more effectively than from de novo sites. The best discrimination between aberrant and authentic 3'ss was achieved by the maximum entropy model. Almost one half of aberrant 3'ss was activated by AG-creating mutations and approximately 95% of the newly created AGs were selected in vivo. The overall nucleotide structure upstream of aberrant 3'ss was characterized by higher purine content than for authentic sites, particularly in position -3, that may be compensated by more stringent requirements for positive and negative nucleotide signatures centred around position -11. A newly developed online database of aberrant 3'ss will facilitate identification of splicing mutations in a gene or phenotype of interest and future optimization of splice site prediction tools.

Proteomic approaches to dissect platelet function: Half the story

Platelets play critical roles in diverse hemostatic and pathologic disorders and are broadly implicated in various biological processes that include inflammation, wound healing, and thrombosis. Recent progress in high-throughput mRNA and protein profiling techniques has advanced our understanding of the biological functions of platelets. Platelet proteomics has been adopted to decode the complex processes that underlie platelet function by identifying novel platelet-expressed proteins, dissecting mechanisms of signal or metabolic pathways, and analyzing functional changes of the platelet proteome in normal and pathologic states. The integration of transcriptomics and proteomics, coupled with progress in bioinformatics, provides novel tools for dissecting platelet biology. In this review, we focus on current advances in platelet proteomic studies, with emphasis on the importance of parallel transcriptomic studies to optimally dissect platelet function. Applications of these global profiling approaches to investigate platelet genetic diseases and platelet-related disorders are also addressed.

Glanzmann thrombasthenia

Glanzmann thrombasthenia (GT) is a rare autosomal recessive bleeding syndrome affecting the megakaryocyte lineage and characterized by lack of platelet aggregation. The molecular basis is linked to quantitative and/or qualitative abnormalities of alphaIIb beta3 integrin. This receptor mediates the binding of adhesive proteins that attach aggregating platelets and ensure thrombus formation at sites of injury in blood vessels. GT is associated with clinical variability: some patients have only minimal bruising while others have frequent, severe and potentially fatal hemorrhages. The site of bleeding in GT is clearly defined: purpura, epistaxis, gingival hemorrhage, and menorrhagia are nearly constant features; gastrointestinal bleeding and hematuria are less common. In most cases, bleeding symptoms manifest rapidly after birth, even if GT is occasionally only diagnosed in later life. Diagnosis should be suspected in patients with mucocutaneous bleeding with absent platelet aggregation in response to all physiologic stimuli, and a normal platelet count and morphology. Platelet alphaIIb beta3 deficiency or nonfunction should always be confirmed, for example by flow cytometry. In order to avoid platelet alloimmunisation, therapeutic management must include, if possible, local hemostatic procedures and/or desmopressin (DDAVP) administration. Transfusion of HLA-compatible platelet concentrates may be necessary if these measures are ineffective, or to prevent bleeding during surgery. Administration of recombinant factor VIIa is an increasingly used therapeutic alternative. GT can be a severe hemorrhagic disease, however the prognosis is excellent with careful supportive care.

Molecular diversity of Glanzmann thrombasthenia in southern India: new insights into mRNA splicing and structure-function correlations ofαIIbβ3 integrin (ITGA2B, ITGB3)

The molecular basis of Glanzmann thrombasthenia (GT) was studied in 40 families from southern India. Of 23 identified mutations (13 in the alphaIIb (ITGA2B) gene and 10 in the beta3 (ITGB3) gene), 20 were novel and three were described previously. Three mutations in the beta3 gene-p.Leu143Trp (Leu117Trp), p.Tyr307Stop (Tyr281Stop), and p.Arg119Gln (Arg93Gln)-were detected in 12, three, and two families, respectively, with definite founder effects observed for the first two mutations. Alternative splicing was predicted in silico for the normal variant and a missense variant of the beta3 gene, and for 10/11 frameshift or nonsense mutations in alphaIIb or beta3. The prediction was confirmed experimentally for a c.2898_2902dupCCCCT mutation in exon 28 of the alphaIIb gene that induced exon skipping. Seven out of nine missense mutations substituted highly conserved amino acids buried in the proteins' cores, predicting structural abnormalities. Among these, a beta3 substitution, p.Cys39Gly (Cys13Gly) was found to cause intracellular degradation of the beta3 subunit, in contrast to previous findings that mutations at Cys435, the partner of Cys13 in a disulfide bond, cause constitutive activation of alphaIIbbeta3. The two patients with a beta3 Arg93Gln mutation had normal clot retraction, consistent with a recent finding that this substitution is associated with normal surface expression of alphaIIbbeta3. In conclusion, this study demonstrates that a variety of mutations account for GT in southern Indian patients, provides new insights into mRNA splicing, and highlights the role of specific amino acids in structure-function correlations of alphaIIbbeta3.

A 13-bp deletion in alpha(IIb) gene is a founder mutation that predominates in Palestinian-Arab patients with Glanzmann thrombasthenia

Glanzmann thrombasthenia (GT) is a rare autosomal recessive bleeding disorder caused by lack or dysfunction of alpha(IIb)beta3 in platelets. GT is relatively frequent in highly inbred populations. We previously identified a 13-bp deletion in the alpha(IIb) gene that causes in-frame deletion of six amino acids in three Palestinian GT patients. In this study, we determined the molecular basis of GT in all known Palestinian patients, examined whether Jordanian patients harbor the same mutations, analyzed whether there is a founder effect for the 13-bp deletion, and determined the mechanism by which the 13-bp deletion abolishes alpha(IIb)beta3 surface expression. Of 11 unrelated Palestinian patients, eight were homozygous for the 13-bp deletion that displayed common ancestry by haplotype analysis, and was estimated to have occurred 300-600 years ago. Expression studies in baby hamster kidney cells showed that substitution of Cys107 or Trp110 located within the deletion caused defective alpha(IIb)beta3 maturation. Substitution of Trp110, but not of Cys107, prevented fibrinogen binding. The other Palestinian patients harbored three novel mutations: G2374 deletion in alpha(IIb) gene, TT1616-7 deletion in beta3 gene, and IVS14: -3C --> G in beta3 gene. The latter mutation caused cryptic splicing predicting an extended cytoplasmic tail of beta3 and was expressed as dysfunctional alpha(IIb)beta(3). None of 15 unrelated Jordanian patients carried any of the described mutations.

Biased exon/intron distribution of cryptic and de novo 3' splice sites

We compiled sequences of previously published aberrant 3′ splice sites (3′ss) that were generated by mutations in human disease genes. Cryptic 3′ss, defined here as those resulting from a mutation of the 3′YAG consensus, were more frequent in exons than in introns. They clustered in ∼20 nt region adjacent to authentic 3′ss, suggesting that their under-representation in introns is due to a depletion of AG dinucleotides in the polypyrimidine tract (PPT). In contrast, most aberrant 3′ss that were induced by mutations outside the 3′YAG consensus (designated ‘de novo’) were in introns. The activation of intronic de novo 3′ss was largely due to AG-creating mutations in the PPT. In contrast, exonic de novo 3′ss were more often induced by mutations improving the PPT, branchpoint sequence (BPS) or distant auxiliary signals, rather than by direct AG creation. The Shapiro–Senapathy matrix scores had a good prognostic value for cryptic, but not de novo 3′ss. Finally, AG-creating mutations in the PPT that produced aberrant 3′ss upstream of the predicted BPS in vivo shared a similar ‘BPS-new AG’ distance. Reduction of this distance and/or the strength of the new AG PPT in splicing reporter pre-mRNAs improved utilization of authentic 3′ss, suggesting that AG-creating mutations that are located closer to the BPS and are preceded by weaker PPT may result in less severe splicing defects.

Presentation and pattern of symptoms in 382 patients with Glanzmann thrombasthenia in Iran

Glanzmann thrombasthenia (GT) is a rare autosomal recessive disease characterized by prolonged bleeding time with normal platelet count and morphology. It is caused by the quantitative or qualitative deficiency of the platelet glycoprotein IIb-IIIa. In 382 Iranian patients with GT diagnosed at a single center during the period 1969-2001, consanguinity between parents was 86.6%, in accord with the high frequency of intrafamilial marriages in Iran. Almost all patients had had abnormal mucocutaneous bleeding (epistaxis and gum bleeding); at follow-up, 4/5 of the patients had been transfused at least once to control hemorrhagic episodes. As expected, almost all the patients had a normal platelet count while the leukocyte count was increased in 19.3%. Among women, an unexpected low rate of pregnancies was observed.

CalDAG-GEFI integrates signaling for platelet aggregation and thrombus formation

Signaling through the second messengers calcium and diacylglycerol (DAG) is a critical element in many biological systems. Integration of calcium and DAG signals has been suggested to occur primarily through protein kinase C family members, which bind both calcium and DAG. However, an alternative pathway may involve members of the CalDAG-GEF/RasGRP protein family, which have structural features (calcium-binding EF hands and DAG-binding C1 domains) that suggest they can function in calcium and DAG signal integration. To gain insight into the signaling systems that may be regulated by CalDAG-GEF/RasGRP family members, we have focused on CalDAG-GEFI, which is expressed preferentially in the brain and blood. Through genetic ablation in the mouse, we have found that CalDAG-GEFI is crucial for signal integration in platelets. Mouse platelets that lack CalDAG-GEFI are severely compromised in integrin-dependent aggregation as a consequence of their inability to signal through CalDAG-GEFI to its target, the small GTPase Rap1. These results suggest that analogous signaling defects are likely to occur in the central nervous system when CalDAG-GEFI is absent or compromised in function.

α5β1, αVβ3 and the platelet-associated integrin αIIbβ3 coordinately regulate adhesion and migration of differentiating mouse trophoblast cells

During blastocyst implantation, interaction between integrins on the apical surface of the trophoblast and extracellular matrix (ECM) in the endometrium anchors the embryo to the uterine wall. Strong adhesion of the blastocyst to fibronectin (FN) requires integrin signaling initiated by exogenous fibronectin. However, it is not known how integrin signaling enhances blastocyst adhesion. We present new evidence that the integrin, alphaIIbbeta3, plays a key role in trophoblast adhesion to fibronectin during mouse peri-implantation development. Trafficking of alphaIIb to the apical surface of the trophoblast increased dramatically after blastocysts were exposed to fibronectin, whereas other fibronectin-binding integrins, alpha5beta1 and alphaVbeta3, were resident at the apical surface before ligand exposure. Functional comparisons among the three integrins revealed that ligation of alpha5beta1 most efficiently strengthened blastocyst fibronectin-binding activity, while subsequent trophoblast cell migration was dependent primarily on the beta3-class integrins. In vivo, alphaIIb was highly expressed by invasive trophoblast cells in the ectoplacental cone and trophoblast giant cells of the parietal yolk sac. These data demonstrate that trafficking of alphaIIb regulates adhesion between trophoblast cells and fibronectin as invasion of the endometrium commences.