Immunoblot analysis of platelet glycoprotein IIb in patients with Glanzmann thrombasthenia in Israel

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.

Glanzmann's thrombasthenia due to a point mutation within intron 10 results in aberrant splicing of the beta3 gene

Glanzmann's thrombasthenia (GT) is an hereditary bleeding disorder caused by a quantitative or qualitative defect in the integrin alphaIIbbeta3. We attempted to identify genetic defects responsible for a case of GT in Korea. The patient was a 6-year-old boy who had suffered from hemorrhage and purpura. The cDNAs of alphaIIb and beta3 were amplified by reverse transcription (RT)-PCR and were sequenced. RT-PCR of COS7 cells transfected with Exontrap vectors containing the beta3 genomic DNA fragments were performed to verify an aberrant splicing. Transient expression of alphaIIbbeta3 on transfected-COS7 cells was determined by flow cytometry, and the presence of alphaIIbbeta3 was confirmed by immunoprecipitation. We discovered an abnormality with the insertion of 38 bp between exon 10 and exon 11, including a stop codon, in beta3 cDNA. Sequence analysis of genomic DNA showed a point mutation, G-->T, at the position 29 107 of intron 10. RT-PCR analyses of COS7 cells transfected with Exontrap vector containing the mutant beta3 gene revealed that the point mutation at the position 29 107 of intron 10, G-->T, was responsible for an aberrant splicing in the beta3 gene. The transfection experiments and immunoprecipitation revealed the absence of alphaIIbbeta3 in the COS7 cells transfected with mutant gene. The mutation at the position 29 107 of intron 10, G-->T, in the beta3 genomic DNA was found to induce an aberrant splicing and to be responsible for GT in this patient.

Dynamics of GPIIb/IIIa-mediated platelet-platelet interactions in platelet adhesion/thrombus formation on collagen in vitro as revealed by videomicroscopy

The conventional description of platelet interactions with collagen-coated surfaces in vitro, based on serial static measurements, is that platelets first adhere and spread to form a monolayer and then recruit additional layers of platelets. To obtain dynamic information, we studied gravity-driven platelet deposition in vitro on purified type 1 collagen by video phase-contrast microscopy at 22 degrees C. With untreated human and wild-type mouse platelets, soon after the initial adhesion of a small number of "vanguard" platelets, "follower" platelets attached to the spread-out vanguard platelets. Follower platelets then adhered to and spread onto nearby collagen or over the vanguard platelets. Thus, thrombi formed as a concerted process rather than as sequential processes. Treatment of human platelets with monoclonal antibody (mAb) 7E3 (anti-GPIIb/IIIa (alphaIIbbeta3) + alphaVbeta3) or tirofiban (anti-GPIIb/IIIa) did not prevent platelet adhesion but nearly eliminated the deposition of follower platelets onto vanguard platelets and platelet thrombi. Similar results were obtained with Glanzmann thrombasthenia platelets. Wild-type mouse platelets in the presence of mAb 1B5 (anti-GPIIb/IIIa) and platelets from beta3-null mice behaved like human platelets in the presence of 7E3 or tirofiban. Deposition patterns of untreated human and wild-type mouse platelets were consistent with random distributions under a Poisson model, but those obtained with 7E3- and tirofiban-treated human platelets, 1B5-treated mouse platelets, or beta3-null platelets demonstrated a more uniform deposition than predicted. Thus, in this model system, absence or blockade of GPIIb/IIIa receptors interferes with thrombus formation and alters the pattern of platelet deposition.

Glycoprotein IIb Leu214Pro Mutation Produces Glanzmann Thrombasthenia With Both Quantitative and Qualitative Abnormalities in GPIIb/IIIa

Glanzmann thrombasthenia is an inherited bleeding disorder due to a functional reduction or absence of platelet GPIIb/IIIa (αIIbβ3) integrin receptors. Based on a prolonged bleeding time and absence of platelet aggregation in response to physiologic agonists, a 55-year-old white man was diagnosed as having Glanzmann thrombasthenia. The patient's platelet fibrinogen level was ≈5% of normal. As judged by complex-dependent monoclonal antibody (MoAb) binding, surface expression of platelet GPIIb/IIIa receptors was less than 5.5% of normal, whereas the binding of an anti-GPIIIa specific MoAb (7H2) was ≈12% of normal. Immunoblot analysis of the patient's platelet lysates showed ≈35% of normal levels of GPIIIa, ≈30% of normal levels of GPIIb, and an abnormally migrating fragment of GPIIb. Biotinylation of the surface proteins on the patient's platelets followed by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed only GPIIb and GPIIIa subunits of normal size. Surface expression of platelet αvβ3 receptors was 192% of normal, suggesting that the patient's' defect was in GPIIb. Sequence analysis of the patient's GPIIb cDNA identified a T to C transition at nucleotide 643, predicting a Leu214Pro substitution. Direct sequencing of GPIIb exon 6 indicated that the patient is homozygous for the mutation. The nature of the Leu214Pro mutation was analyzed by expression in Chinese hamster ovary (CHO) cells. As judged by subunit-specific MoAb binding, surface expression of mutant receptors was ≈60% of normal, but these receptors were not recognized by the complex-dependent monoclonal antibodies, 10E5 and 7E3. In addition, mutant receptors pretreated with the ligand-induced binding site MoAb AP5 were not recognized by the activation-dependent MoAb PAC-1 and mutant expressing CHO cells did not adhere to immobilized fibrinogen. These data suggest that the Leu214Pro mutation in GPIIb disrupts the structural conformation, and either directly or indirectly, the ligand binding properties of the heterodimeric complex. This is in accord with studies from other integrins that have implicated a β-turn in a homologous region as important in ligand binding. Thus, the Leu214Pro mutation appears to produce the Glanzmann thrombasthenia phenotype by both qualitative and quantitative abnormalities. In addition, the mutation appears to confer susceptibility of the GPIIb subunit to proteolysis.

Glycoprotein IIb Leu214Pro Mutation Produces Glanzmann Thrombasthenia With Both Quantitative and Qualitative Abnormalities in GPIIb/IIIa

Glanzmann thrombasthenia is an inherited bleeding disorder due to a functional reduction or absence of platelet GPIIb/IIIa (αIIbβ3) integrin receptors. Based on a prolonged bleeding time and absence of platelet aggregation in response to physiologic agonists, a 55-year-old white man was diagnosed as having Glanzmann thrombasthenia. The patient's platelet fibrinogen level was ≈5% of normal. As judged by complex-dependent monoclonal antibody (MoAb) binding, surface expression of platelet GPIIb/IIIa receptors was less than 5.5% of normal, whereas the binding of an anti-GPIIIa specific MoAb (7H2) was ≈12% of normal. Immunoblot analysis of the patient's platelet lysates showed ≈35% of normal levels of GPIIIa, ≈30% of normal levels of GPIIb, and an abnormally migrating fragment of GPIIb. Biotinylation of the surface proteins on the patient's platelets followed by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed only GPIIb and GPIIIa subunits of normal size. Surface expression of platelet αvβ3 receptors was 192% of normal, suggesting that the patient's' defect was in GPIIb. Sequence analysis of the patient's GPIIb cDNA identified a T to C transition at nucleotide 643, predicting a Leu214Pro substitution. Direct sequencing of GPIIb exon 6 indicated that the patient is homozygous for the mutation. The nature of the Leu214Pro mutation was analyzed by expression in Chinese hamster ovary (CHO) cells. As judged by subunit-specific MoAb binding, surface expression of mutant receptors was ≈60% of normal, but these receptors were not recognized by the complex-dependent monoclonal antibodies, 10E5 and 7E3. In addition, mutant receptors pretreated with the ligand-induced binding site MoAb AP5 were not recognized by the activation-dependent MoAb PAC-1 and mutant expressing CHO cells did not adhere to immobilized fibrinogen. These data suggest that the Leu214Pro mutation in GPIIb disrupts the structural conformation, and either directly or indirectly, the ligand binding properties of the heterodimeric complex. This is in accord with studies from other integrins that have implicated a β-turn in a homologous region as important in ligand binding. Thus, the Leu214Pro mutation appears to produce the Glanzmann thrombasthenia phenotype by both qualitative and quantitative abnormalities. In addition, the mutation appears to confer susceptibility of the GPIIb subunit to proteolysis.

Glanzmann Thrombasthenia Caused by an 11.2-kb Deletion in the Glycoprotein IIIa (β3 ) Is a Second Mutation in Iraqi Jews That Stemmed From a Distinct Founder

Glanzmann thrombasthenia (GT) is a rare bleeding disorder resulting from mutations in either glycoprotein (GP) IIb or GPIIIa genes. The disease is relatively frequent in highly inbred populations such as Iraqi Jews. The molecular basis of GT in 6 unrelated Iraqi-Jewish patients was previously identified as an 11-bp deletion in exon 12 of the GPIIIa gene. We now describe a second mutation found in 3 unrelated Iraqi-Jewish families that consists of an 11.2-kb deletion between an Alu repeat in intron 9 and exon 13 of the GPIIIa gene. The mutant DNA is transcribed into mRNA in which exons 10 through 13 are absent. Splicing of exon 9 directly to exon 14 leads to a shift in the reading frame resulting in a stop codon. The predicted protein is truncated in the middle of the third cysteine-rich domain before the transmembrane domain. Simple DNA-based methods were devised for identification of both mutations in Iraqi Jews for the purpose of carrier detection and prenatal diagnosis enabling prevention of GT. A survey of the general Iraqi-Jewish population for the first 11-bp deletion and the second 11.2-kb deletion disclosed that the allele frequency of the first mutation was 0.0043, whereas none of 700 individuals examined bore the second mutation (allele frequency <0.0007). Among 40 GT patients of Iraqi-Jewish origin 31 were homozygous for the first mutation, 4 were compound heterozygotes for the first and second mutations, and 2 were homozygous for the second mutation. Haplotype analyses using 4 polymorphic markers in the GPIIIa gene showed that each mutation originated in a distinct founder.

Glanzmann Thrombasthenia Caused by an 11.2-kb Deletion in the Glycoprotein IIIa (β3 ) Is a Second Mutation in Iraqi Jews That Stemmed From a Distinct Founder

Glanzmann thrombasthenia (GT) is a rare bleeding disorder resulting from mutations in either glycoprotein (GP) IIb or GPIIIa genes. The disease is relatively frequent in highly inbred populations such as Iraqi Jews. The molecular basis of GT in 6 unrelated Iraqi-Jewish patients was previously identified as an 11-bp deletion in exon 12 of the GPIIIa gene. We now describe a second mutation found in 3 unrelated Iraqi-Jewish families that consists of an 11.2-kb deletion between an Alu repeat in intron 9 and exon 13 of the GPIIIa gene. The mutant DNA is transcribed into mRNA in which exons 10 through 13 are absent. Splicing of exon 9 directly to exon 14 leads to a shift in the reading frame resulting in a stop codon. The predicted protein is truncated in the middle of the third cysteine-rich domain before the transmembrane domain. Simple DNA-based methods were devised for identification of both mutations in Iraqi Jews for the purpose of carrier detection and prenatal diagnosis enabling prevention of GT. A survey of the general Iraqi-Jewish population for the first 11-bp deletion and the second 11.2-kb deletion disclosed that the allele frequency of the first mutation was 0.0043, whereas none of 700 individuals examined bore the second mutation (allele frequency <0.0007). Among 40 GT patients of Iraqi-Jewish origin 31 were homozygous for the first mutation, 4 were compound heterozygotes for the first and second mutations, and 2 were homozygous for the second mutation. Haplotype analyses using 4 polymorphic markers in the GPIIIa gene showed that each mutation originated in a distinct founder.

Demonstration of a marked reduction in the amount of GPIIb in most type II patients with Glanzmann's thrombasthenia

In this study employing a sensitive immunoblot assay, we have characterized GPIIb and GPIIIa in thrombasthenic platelets from seven type II and four type I patients from 10 unrelated families. The amounts of GPIIb and GPIIIa were both markedly reduced in all these patients, and abnormal molecular weight GPIIb or GPIIIa was not detected. In all of four type I patients the amount of GPIIb was much lower than that of GPIIIa. In this study, however, we found that the amount of GPIIb was also lower even in six out of seven type II patients. Immunodepletion of patients' platelets with AP2 (a monoclonal antibody specific for the GPIIb-IIIa complex), AP3 (specific for GPIIIa) or AMF7 (specific for alpha v) further confirmed that GPIIIa existed in excess, and demonstrated that excess GPIIIa were mostly in free form and not associated with GPIIb or alpha v. The reduction of GPIIb may represent an abnormality in GPIIb processing in these type II and type I thrombasthenic platelets. It remains unclear whether these two subgroups represent distinct categories.

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

Glanzmann thrombasthenia is an autosomal recessive bleeding disorder characterized by a decrease or absence of functional platelet glycoprotein (GP) IIb-IIIa (alpha IIb beta 3) integrin receptors. Although thrombasthenia is a rare disorder, its occurrence is increased in some regions of the world where intracommunity marriage and consanguinity are commonplace, resulting in increased expression of autosomal recessive traits. We have been studying two populations having an unusually high frequency of Glanzmann disease, Iraqi Jews and Arabs living in Israel, and were able to distinguish the populations on the basis of immunodetectable GPIIIa and platelet surface vitronectin receptor (alpha v beta 3) expression. In this article, we describe molecular genetic studies based on use of the PCR that have allowed us to characterize platelet mRNA sequences encoding GPIIb and GPIIIa from patients in these populations. In six of six Iraqi-Jewish families studied, cDNA sequence analysis identified an 11-base deletion within exon 12 of the GPIIIa gene. This mutation produces a frameshift leading to protein termination shortly before the transmembrane domain of GPIIIa. In contrast, a 13-base deletion encompassing the splice acceptor site of exon 4 of the GPIIb gene was found in three of five Arab kindreds studied. This deletion results in forced alternative splicing to a downstream AG acceptor, producing a 6-amino acid deletion in the GPIIb protein, including a single cysteine residue. These nucleotide sequence variations were exploited to design a rapid, PCR-based oligonucleotide dot-blot hybridization test for both pre- and postnatal diagnosis of Glanzmann disease. These studies demonstrate the heterogeneity of Glanzmann thrombasthenia in different populations, and its homogeneity within geographically restricted populations, and offer insight into the requirements for integrin surface expression.

Variant Bernard-Soulier syndrome type bolzano. A congenital bleeding disorder due to a structural and functional abnormality of the platelet glycoprotein Ib-IX complex

We have studied a patient with a congenital bleeding disorder and phenotypic manifestations typical of Bernard-Soulier syndrome, including giant platelets with absent ristocetin-induced von Willebrand factor binding. Two monoclonal antibodies reacting with distinct epitopes in the amino-terminal domain of the alpha-chain of glycoprotein (GP) Ib were used to estimate the number of GP Ib molecules on the platelet membrane. In the patient, binding of one antibody (LJ-Ib10) was approximately 50% of normal, while binding of the other (LJ-Ib1) was absent. Binding of both antibodies was reduced to approximately 50% of normal in the mother and one sister of the propositus, and their platelets exhibited approximately 70% of normal von Willebrand factor binding. Immunoblotting studies confirmed the presence of GP Ib alpha, as well as GP IX, in patient platelets. Antibody LJ-Ib10, but not LJ-Ib1, could immunoprecipitate the patient's GP Ib alpha from surface-labeled proteins. Thus, platelets from the propositus contained a structurally and functionally altered GP Ib-IX complex lacking a specific antibody epitope and the ability to bind von Willebrand factor. In contrast, the binding of human alpha-thrombin to the patient's platelets was normal, and three classes of binding sites with high, intermediate, and low affinity could be detected. These studies define a distinct variant form of Bernard-Soulier syndrome and provide evidence, based on a naturally occurring mutant molecule, that the amino-terminal region of GP Ib alpha contains a von Willebrand factor-binding domain distinct from the high affinity thrombin-binding site. Use of different monoclonal antibodies with distinct epitope specificities appears to be essential for a correct identification of variant Bernard-Soulier syndrome.