High Rates of Anti-αIIbß3 Antibodies Produced by a Glanzmann Thrombasthenia Patient after First and Unique Red Blood Cells Administration.

Immunization against the platelet αIIbß3 glycoprotein due to blood transfusion represents one of the most severe complications in Glanzmann thrombasthenia (GT) disease. Anti-αIIbß3 isoantibodies development may lead to ineffective platelet transfusion and can, in case of pregnancy, cross the placenta leading to fetal thrombocytopenia. We describe here the case of a girl with type I GT who developed high rates of anti-αIIbß3 isoantibodies after first and unique blood transfusion. Surprisingly, this patient had only received red blood cell concentrates and immunization was presumably stimulated by the residual presence of platelets in concentrates. This study emphasizes the need for regular anti-αIIbß3 antibodies screening in GT, even though patients have never been previously transfused with platelet concentrates.

Glanzmann thrombasthenia: an uncommon cause of acute upper gastrointestinal bleeding.

The major function of platelets is to contribute to hemostasis. If an impairment in their production and/or function occurs, abnormal bleeding can develop. An 18-year-old male presented to our hospital after four episodes of hematemesis. His medical history was relevant for Glanzmann thrombasthenia diagnosed during early childhood. On initial examination, he appeared pale and with normal blood pressure. His complete blood count included a hemoglobin concentration of 11.0 g/dL, additional laboratory tests were within the normal ranges. The initial approach consisted of a high dose of proton pump inhibitors. Hours later, esophagogastroduodenoscopy revealed diffuse oozing bleeding from gastric mucosa with no other visible lesions such as peptic ulcers or varices.

Mutations in RASGRP2 gene identified in patients misdiagnosed as Glanzmann thrombasthenia patients.

INTRODUCTION: Glanzmann thrombasthenia (GT) is a severe inherited platelet function disorder (IPFD), presenting with bleeding diathesis and impaired platelet aggregation, is caused by mutations in the genes ITGA2B or ITGB3. AIM: We aimed to study the genetic cause of IPFD mimicking GT. METHODS: During 2017-2019, 16 patients were referred to our tertiary center with bleeding symptoms, impaired platelet aggregation and normal platelet count and size. RESULTS: Using flow cytometry, 13/16 patients were diagnosed with GT, yet three patients displayed normal surface expression of the integrins αIIbß3 and αvß3, as well as normal integrin αIIbß3 activation following incubation with the activating monoclonal antibody anti-LIBS6, while platelet activation following ADP or epinephrine was impaired. Whole exome sequencing detected 2 variants in RASGRP2 gene in all 3 patients. DISCUSSION: Both RASGRP2 mutations predicted frameshift, premature stop codon (p. I427Mfs*92 and p. R494Afs*54, respectively) and truncated calcium-sensing guanine nucleotide exchange factor [CalDAG-GEFI]- the major signaling molecule that regulates integrin-mediated aggregation and granule secretion, causing IPFD-18. CONCLUSION: Patients who suffer from bleeding diathesis without immune dysregulation, may be mistakenly diagnosed as GT. Further studies are required to confirm the diagnosis of specific IPFD.

Inherited platelet diseases with normal platelet count: phenotypes, genotypes and diagnostic strategy.

Inherited platelet disorders resulting from platelet function defects and a normal platelet count cause a moderate or severe bleeding diathesis. Since the description of Glanzmann thrombasthenia resulting from defects of ITGA2B and ITGB3, new inherited platelet disorders have been discovered, facilitated by the use of high throughput sequencing and genomic analyses. Defects of RASGRP2 and FERMT3 responsible for severe bleeding syndromes and integrin activation have illustrated the critical role of signaling molecules. Important are mutations of P2RY12 encoding the major ADP receptor causal for an inherited platelet disorder with inheritance characteristics that depend on the variant identified. Interestingly, variants of GP6 encoding the major subunit of the collagen receptor GPVI/FcRγ associate only with mild bleeding. The numbers of genes involved in dense granule defects including Hermansky-Pudlak and Chediak Higashi syndromes continue to progress and are updated. The ANO6 gene encoding a Ca2+-activated ion channel required for phospholipid scrambling is responsible for the rare Scott syndrome and decreased procoagulant activity. A novel EPHB2 defect in a familial bleeding syndrome demonstrates a role for this tyrosine kinase receptor independent of the classical model of its interaction with ephrins. Such advances highlight the large diversity of variants affecting platelet function but not their production, despite the difficulties in establishing a clear phenotype when few families are affected. They have provided insights into essential pathways of platelet function and have been at the origin of new and improved therapies for ischemic disease. Nevertheless, many patients remain without a diagnosis and requiring new strategies that are now discussed.

Integrin ß3 Deficiency Results in Hypertriglyceridemia via Disrupting LPL (Lipoprotein Lipase) Secretion.

OBJECTIVE: Integrin ß3 is implicated in numerous biological processes such as its relevance to blood triglyceride, yet whether ß3 deficiency affects this metabolic process remains unknown. Approach and Results: We showed that the Chinese patients with ß3-deficient Glanzmann thrombasthenia had a 2-fold higher serum triglyceride level together with a lower serum LPL (lipoprotein lipase) level than those with an αIIb deficiency or healthy subjects. The ß3 knockout mice recapitulated these phenotypic features. The elevated plasma triglyceride level was due to impaired LPL-mediated triglyceride clearance caused by a disrupted LPL secretion. Further analysis revealed that ß3 directly bound LPL via a juxtamembrane TIH (threonine isoleucine histidine)720-722 motif in its cytoplasmic domain and functioned as an adaptor protein by interacting with LPL and PKD (protein kinase D) to form the PKD/ß3/LPL complex that is required for ß3-mediated LPL secretion. Furthermore, the impaired triglyceride clearance in ß3 knockout mice could be corrected by adeno-associated virus serotype 9 (AAV9)-mediated delivery of wild-type but not TIH720-722-mutated ß3 genes. CONCLUSIONS: This study reveals a hypertriglyceridemia in both ß3-deficient Chinese patients and mice and provides novel insights into the molecular mechanisms of the significant roles of ß3 in LPL secretion and triglyceride metabolism, drawing attention to the metabolic consequences in patients with ß3-deficient Glanzmann thrombasthenia.

Flow cytometric analysis of platelet surface glycoproteins in the diagnosis of thirty-two Turkish patients with Glanzmann thrombasthenia: a multicenter experience

Background/aim: Glanzmann thrombasthenia (GT) is a rare autosomal recessively inherited bleeding disorder characterized by the quantitative (type 1 and type 2) or qualitative (type 3) deficiency in platelet membrane glycoprotein (GP) IIb/IIIa (CD41a/CD61) fibrinogen receptors. In type 1, 2, and 3, CD41a/CD61 expression is 5%, 5%­20% and above 20%, respectively. In this study, diagnosis of GT was confirmed and subgroups were identified in 32 Turkish patients by flow cytometry analysis. Materials and methods: CD41a/CD61 expression levels in platelet-rich plasma (PRP) obtained from peripheral venous EDTA blood samples were analyzed with a BD FACSCanto II flow cytometer (Becton Dickinson, Franklin Lakes, NJ, USA). GT subgroup analysis was performed by counting 50,000 events in the BD FACSDiva Software v6.1.3 program of the instrument. Results: In the present study, in blood samples of 32 patients from 23 families with GT and 22 healthy controls, co-expression levels of CD41a and CD61 in PRP was analyzed. 12 out of 23 families were consistent with type 1 GT (52.2%), 4 were consistent with type 2 GT (17.4%), and 7 were consistent with type 3 GT (30.4%). Conclusion: Especially due to consanguineous marriages, GT with various glycoprotein levels may be detected. As a result of the flow cytometry analysis of the present study with the highest GT patient population in Turkey, type 1 GT patients were the most common subgroup. In the determination of the GT subgroups; especially in the detection of type 3 GT, flow cytometry is the most sensitive glycoprotein analysis method. In addition to light transmission aggregometry, CD41a/CD61 study by flow cytometer confirms diagnosis when mutation analysis cannot be performed.

Glanzmann thrombasthenia: genetic basis and clinical correlates.

Glanzmann thrombasthenia (GT) is an autosomal recessive disorder of platelet aggregation caused by quantitative or qualitative defects in integrins αIIb and ß3. These integrins are encoded by the ITGA2B and ITGB3 genes and form platelet glycoprotein (GP)IIb/IIIa, which acts as the principal platelet receptor for fibrinogen. Although there is variability in the clinical phenotype, most patients present with severe mucocutaneous bleeding at an early age. A classic pattern of abnormal platelet aggregation, platelet glycoprotein expression and molecular studies confirm the diagnosis. Management of bleeding is based on a combination of hemostatic agents including recombinant activated factor VII with or without platelet transfusions and antifibrinolytic agents. Refractory bleeding and platelet alloimmunization are common complications. In addition, pregnant patients pose unique management challenges. This review highlights clinical and molecular aspects in the approach to patients with GT, with particular emphasis on the significance of multidisciplinary care.

Identification of one novel pathogenic ITGB3 mutation and two known mutations in two Chinese pedigrees with hereditary Glanzmann thrombasthenia.

Glanzmann thrombasthenia (GT) is an inherited disorder of platelet aggregation resulting from quantitative and/or qualitative abnormalities of the glycoprotein IIb/IIIa complex. We analyzed the expression of GPIIb/IIIa and the gene sequencing in two pedigrees with GT, so as to determine the type and the relationship between genotype and clinical phenotype. Platelet aggregation tests and flow cytometric studies were performed, along with gene sequencing. Both probands were classified as grade III of bleeding. Platelet aggregation was absent or defective upon stimulation with physiological stimuli like AA and ADP, but platelets agglutinated normally in response to ristocetin. MFI values were considerably reduced. Gene sequencing showed ITGB3 mutations p.Cys549Ser/p.Leu705CysfsTer4 in proband 1 and p.Cys549Ser/p.Gln254Lys in proband 2 and her sister. This study reports one novel ITGB3 mutant gene, p.Gln254Lys, of which we will explore the potential pathogenicity.

Missed at first Glanz: Glanzmann thrombasthenia initially misdiagnosed as Von Willebrand Disease.

Glanzmann thrombasthenia (GT) is an autosomal recessive bleeding disorder caused by a defect in platelet integrin αIIbß3. Given the rarity of the condition (1/1,000,000), assessment and diagnosis should be undertaken in a specialist centre. We report the case of a 34 year old woman with severe menorrhagia and a childhood diagnosis from another centre of Von Willebrand Disease. She had an extensive bleeding history, with epistaxis, menorrhagia and postoperative bleeding requiring multiple previous transfusions. Repeat haemostatic workup in our centre revealed normal Von Willebrand levels but abnormal platelet aggregation consistent with Glanzmann thrombasthenia. Antibody screening detected both anti-HLA and anti-αIIbß3 antibodies, complicating subsequent haemostatic management. This case highlights the importance of diagnostic accuracy, the potential negative sequelae of misdiagnosis and subsequent therapeutic interventions.

Novel mutations in Thai patients with glanzmann thrombasthenia.

OBJECTIVES: Glanzmann thrombasthenia (GT) is an autosomal recessive platelet disorder, caused by defects of the platelet integrin αIIbß3 (GPIIb/IIIa) resulting from pathogenic mutations in either ITGA2B or ITGB3. It is characterized by spontaneous mucocutaneous bleeding. The molecular features of GT in Thailand have not been identified. This study aimed to determine the clinical and molecular features of unrelated Thai patients with GT. METHODS: Four patients with clinically suspected GT were recruited at the Division of Pediatric Hematology/Oncology, King Chulalongkorn Memorial Hospital. The diagnosis was based on clinical and hematological parameters as well as genetic analysis. Whole exome sequencing (WES) was performed in all cases. RESULTS: Of the four patients studied, the median age at first suspicion of GT was 2.5 years. All presented with severe bleeding symptoms (WHO bleeding scale 3). Flow cytometry to assess the surface GPIIb/IIIa complex showed reduced expression. By WES, we successfully identified seven mutant alleles in ITGA2B. One alteration, the c.2915dup (p.Leu973Alafs*63), was detected in two unrelated families. One patient was homozygous for the c.617T>A (p.Val206Asp). Of the five different mutations, three have never been previously described. These include a missense, c.617T>A (p.Val206Asp), a deletion, c.1524_1533del (p.Gln508Hisfs*3), and a nonsense, c.2344C>T (p.Arg782Ter). CONCLUSION: This study reported three novel mutations expanding the genotypic spectrum of ITGA2B causing GT.

Independent adjudicator assessments of platelet refractoriness and rFVIIa efficacy in bleeding episodes and surgeries from the multinational Glanzmann's thrombasthenia registry.

Glanzmann's thrombasthenia (GT) is a rare congenital bleeding disorder associated with decreased platelet aggregation due to qualitative/quantitative deficiencies of the fibrinogen receptor. Severe bleeding episodes and perioperative bleeding are typically managed with platelet transfusions, although patients can develop anti-platelet antibodies or experience clinical refractoriness. The GT Registry (GTR) was established to collect efficacy/safety data on hemostatic treatments for GT, including recombinant factor VIIa (rFVIIa). At the request of the United States Food and Drug Administration, three hematology experts evaluated platelet refractoriness, antibody status, and rFVIIa efficacy data on a case-by-case basis to support a potential indication for rFVIIa in GT. Adjudication included 195 patients with 810 events (619 severe bleeding episodes, 192 surgeries), and a consensus algorithm was developed to describe adjudicators' coding of refractoriness and antibody status based on treatment patterns over time. Most rFVIIa-treated events were in patients without refractoriness or antibodies. Adjudicators rated most rFVIIa-treated bleeding episodes as successful (251/266, 94.4%; rFVIIa only, 101/109, 92.7%; rFVIIa ± platelets ± other agents, 150/157, 95.5%); efficacy was consistent in patients with platelet refractoriness ± antibodies (75/79, 94.9%), antibodies only (10/10, 100.0%), and neither/unknown (166/177, 93.8%). Adjudicators also rated most rFVIIa-treated surgeries as successful (159/160, 99.4%; rFVIIa only, 65/66, 98.5%; rFVIIa ± platelets ± other agents, 94/94, 100.0%); efficacy was consistent in patients with platelet refractoriness ± antibodies (69/70, 98.6%), antibodies only (24/24, 100.0%), and neither/unknown (66/66, 100.0%). Unblinding the adjudicators to investigator efficacy ratings changed few assessments. Doses of rFVIIa were narrowly distributed, regardless of other hemostatic agents used.

Linkage disequilibrium amongst ITGA2B and ITGB3 gene variants in patients with Glanzmann thrombasthenia confirms that most disease-causing mutations are recent.

We recently reported mutation analysis of the largest cohort of Glanzmann thrombasthenia (GT) patients so far examined. Sanger sequencing of coding regions, splice sites, upstream and downstream regions of the ITGA2B and ITGB3 genes identified 78 causal genetic variants (55 novel); 4 large deletions or duplications were also detected. We have now analysed the expression of non-causal gene polymorphisms in the sequenced regions of both genes in selected members of this cohort. We identified 10 mostly silent variants in ITGA2B and 37 in ITGB3; all were present in control donor databases. Three non-synonymous single nucleotide polymorphisms present were human platelet alloantigen (HPA) variants. A series of haplogroups, often including HPA-3b in ITGA2B, repeated with little variation across unrelated families of wide geographical origins and with different GT-causing mutations whether in ITGA2B or ITGB3. In contrast, a deleterious heterozygous c.1440-13_c.1440-1del in intron 14 of ITGA2B shared a common ITGA2B haplogroup composed of at least five gene polymorphisms and re-occurred in seven European families with no known family relationships. Our results highlight the value of gene polymorphism analysis in GT and are consistent with the bulk of disease-causing mutations in GT being of recent origin.

Expanding the Mutation Spectrum Affecting αIIbß3 Integrin in Glanzmann Thrombasthenia: Screening of the ITGA2B and ITGB3 Genes in a Large International Cohort.

We report the largest international study on Glanzmann thrombasthenia (GT), an inherited bleeding disorder where defects of the ITGA2B and ITGB3 genes cause quantitative or qualitative defects of the αIIbß3 integrin, a key mediator of platelet aggregation. Sequencing of the coding regions and splice sites of both genes in members of 76 affected families identified 78 genetic variants (55 novel) suspected to cause GT. Four large deletions or duplications were found by quantitative real-time PCR. Families with mutations in either gene were indistinguishable in terms of bleeding severity that varied even among siblings. Families were grouped into type I and the rarer type II or variant forms with residual αIIbß3 expression. Variant forms helped identify genes encoding proteins mediating integrin activation. Splicing defects and stop codons were common for both ITGA2B and ITGB3 and essentially led to a reduced or absent αIIbß3 expression; included was a heterozygous c.1440-13_c.1440-1del in intron 14 of ITGA2B causing exon skipping in seven unrelated families. Molecular modeling revealed how many missense mutations induced subtle changes in αIIb and ß3 domain structure across both subunits, thereby interfering with integrin maturation and/or function. Our study extends knowledge of GT and the pathophysiology of an integrin.

A novel flow cytometry-based platelet aggregation assay.

The main function of platelets is to maintain normal hemostasis. Inefficient platelet production and/or defective platelet function results in bleeding disorders resulting from a wide range of genetic traits and acquired pathologies. Several platelet function tests have been developed for use in the clinic and in experimental animal models. In particular, platelet aggregation is routinely measured in an aggregometer, which requires normal platelet counts and significant blood sample volumes. For this reason, the analysis of thrombocytopenic patients, infants, and animal models is problematic. We have developed a novel flow cytometry test of platelet aggregation, in which 10- to 25-fold lower platelet counts or sample volumes can be used, either of platelet-rich plasma or whole blood from human subjects or mice. This setup can be applied to test in small assay volumes the influence of a variety of stimuli, drugs, and plasma factors, such as antibodies, on platelet aggregation. The presented principle stands as a novel promising tool, which allows analysis of platelet aggregation in thrombocytopenic patients or infants, and facilitates studies in platelets obtained from experimental animal models without the need of special devices but a flow cytometer.

The international, prospective Glanzmann Thrombasthenia Registry: treatment and outcomes in surgical intervention.

Standard treatment for Glanzmann thrombasthenia, a severe inherited bleeding disorder, is platelet transfusion. Recombinant factor VIIa is reported to be effective in Glanzmann thrombasthenia with platelet antibodies and/or refractoriness to platelet transfusions. We aimed to evaluate recombinant factor VIIa effectiveness and safety for the treatment and prevention of surgical bleeding in patients, with or without platelet antibodies and/or refractoriness, using data from the Glanzmann Thrombasthenia Registry, an international, multicenter, observational, post-marketing study of rFVIIa. Between 2007 and 2011, 96 patients were treated for 206 surgical procedures (minor 169, major 37). History of platelet antibodies was present in 43 patients, refractoriness in 23, antibodies+refractoriness in 17, while 47 had no confirmed antibodies/refractoriness. Treatments analyzed included antifibrinolytics, recombinant factor VIIa, recombinant factor VIIa+antifibrinolytics, platelets±antifibrinolytics and recombinant factor VIIa+platelets±antifibrinolytics. The most frequent treatment for minor procedures was recombinant factor VIIa+antifibrinolytics (n=65), and for major procedures, recombinant factor VIIa+platelets±antifibrinolytics (n=13). In patients without antibodies/refractoriness, recombinant factor VIIa, either alone or with antifibrinolytics, and platelets±antifibrinolytics were rated 100% effective for minor and major procedures. The effectiveness of treatment for minor procedures in patients with antibodies and refractoriness was 88.9% for recombinant factor VIIa, 100% for recombinant factor VIIa+antifibrinolytics, 66.7% for platelets±antifibrinolytics and 100% for recombinant factor VIIa+platelets±antifibrinolytics. One of four adverse events reported for surgery was considered recombinant factor VIIa-treatment-related (non-fatal thromboembolic event in an adult female receiving recombinant factor VIIa+platelets+antifibrinolytics). For all patients, regardless of platelet antibody or refractoriness status, recombinant factor VIIa, administered with or without platelets (±antifibrinolytics), provided effective hemostasis with a low frequency of adverse events in surgical procedures in Glanzmann thrombasthenia patients. This trial was registered at clinicaltrials.gov identifier: 01476423.

Use of allogeneic stem cell transplantation for moderate-severe Glanzmann thrombasthenia.

Glanzmann thrombasthenia (GT) is a rare, autosomal recessive coagulopathy characterized by either qualitative or quantitative abnormalities of the membrane glycoprotein αIIbß3 complex leading to bleeding tendencies, ranging from purpura to life-threatening hemorrhage. Although patients can be managed with supportive measures including platelet transfusions, complications such as alloimmunization are possible. Allogeneic stem cell transplantation (ASCT) can be indicated in severe cases of GT. We report the case of an eight-month-old girl diagnosed with moderate-severe GT, who was successfully treated with a reduced-intensity, human leukocyte antigen (HLA)-identical ASCT.

Novel mutations of integrin αIIb and ß3 genes in Turkish children with Glanzmann's thrombasthenia.

Glanzmann's thrombasthenia (GT) is an inherited disorder of platelet aggregation, characterized by qualitative and quantitative defect on platelet αIIbß3 integrin (GpIIb/IIIa), resulting in lifelong bleeding tendency due to defective platelet plug formation. The αIIb gene (ITGA2B) and ß3 gene (ITGB3) are closely located at chromosome 17q21.31-32. ITGA2B consist of 30 exons and encoding α chain, whereas ITGB3 has 15 exons and encoding ß chain. Until now, according to the Human Gene Mutation Database (HGMD), 138 mutations at ITGA2B gene and 101 mutations at ITGB3 gene have been identified. We aimed to determine whether there was any mutation in the ITGA2B and ITGB3 genes, and a correlation between clinical phenotype and genotype in Turkish GT patients. We examined 20 patients with GT followed at the Department of Pediatric Hematology, Meram Faculty of Medicine, for Clinical and Laboratory Findings and Molecular Genetic Analysis. Peripheral blood was collected from patients, and a written informed consent for genetic analysis was obtained from parents. DNA was isolated from by proteinase K and phenol/chloroform extraction. ITGA2B and ITGB3 genes were screened by polymerase chain reaction. There were 12 females and 8 males with a median age of 15.25 years. Major clinical presentations of these patients were mucocutaneous bleedings. The most common bleeding type was epistaxis (85%). Life-threatening bleedings were seen in five patients. Seven (35%) patients showed various mutations in the ITGA2B or ITGB3 genes. We detected four novel mutations in three different regions and two mutations defined previously within the ITGA2B gene. These changes are at exon 4; c.570 T > G alteration, at exon 13 c.1277 T > A, c.1291 T > G alterations, at exon 19 c.1921A > G alterations. And from the start point of exon 14, behind 107 bases, we detected a heterozygous alteration at Thymine to Guanine. According to PolyPhen Database Program and NCBI Multiple Alignment Tool Database, four transitions are conserved at evolutionary process, so we can say that these transitions are novel mutations. c. 468T > G alteration at exon 4 and c. 1378 T > A alteration at exon 13 were reported to HGMD previously. Screening the exons of the ITGB3 gene from the same patient groups, we reported a novel missense mutation at exon 5, at nucleotide 680. No correlation was found between clinical phenotype and genotype. These mutations were described for the first time in Turkish population, and all novel mutations are not defined previously. Furthermore, collaborative studies are needed for the population point of view.