Glanzmann's thrombasthenia: updated

Glanzmann's thrombasthenia is an autosomal recessive disorder, rare in a global context, but a relatively more common platelet function defect in communities where consanguineous marriages are more frequent. On clinical grounds alone, it cannot be distinguished from other congenital platelet function defects. Epistaxis, gum bleeding, menorrhagia are the common clinical manifestations, whereas large muscle hematoma or hemarthrosis seldom occur in these patients. Essential diagnostic features are a normal platelet count and morphology, a greatly prolonged bleeding time, absence of platelet aggregation in response to ADP, collagen, epinephrine, thrombin and to all aggregating agents which ultimately depend on fibrinogen binding to platelets for this effect, flow cytometry, studies of GPIIb-IIIa receptors on the platelet membrane surface using monoclonal antibodies. The present review describes some of the uncommon features of the disorders and the currently available options which the treating physicians should be aware of during the management of these patients. Although by definition all patients with Glanzmann's thrombasthenia have a virtually complete failure of platelet aggregation, a number of variant forms of GT have been described in which the glycoproteins are present in normal or near normal amounts but are functionally defective. Understanding the pathophysiology of the disorder by the treating physicians is of utmost importance. Presence of high affinity platelet receptors resulting in thrombasthennia-like phenotype may require an antagonistic treatment atypical of classical GT management. It has now been established that different genetic mutations of either GPIIb or IIIa genes results in such a heterogeneity of thrombasthenia phenotype. Glanzmann's thrombasthenia is a paradigm for treating coronary artery disease patients with GPIIb-IIIa antibody and inhibitors. By using these medicines we create a temporary GT-like situation. Hence, understanding this disease is of utmost importance to the practicing cardiologist. As mutations for different variant forms of GT become known, our understanding of how GPIIb-IIIa molecules can be activated to act as a receptor for fibrinogen molecules will be increased. Such understanding undoubtedly will help us to devise better drugs with GPIIb-IIIa inhibitors. Molecular biology techniques have enabled us to equivocally detect heterozygote carriers who are clinically asymptomatic. However, there may be several laboratories in the developing world, which have no access to molecular biology techniques. Development of more robust techniques of quantitation of platelet receptors has enabled an accurate diagnosis of heterozygote carriers or an unborn fetus in the second trimester. The importance of the GPIIb-IIIa polymorphisms in carrier and prenatal diagnosis has not been properly studied. Nowadays the less direct method of PLA1 typing (determination of the levels of platelet antigen) of the foetal platelets as early as 16 weeks of intrauterine life can be used for prenatal diagnosis of GT.     

Glanzmann's thrombasthenia: updated

Glanzmann's thrombasthenia is an autosomal recessive disorder, rare in a global context, but a relatively more common platelet function defect in communities where consanguineous marriages are more frequent. On clinical grounds alone, it cannot be distinguished from other congenital platelet function defects. Epistaxis, gum bleeding, menorrhagia are the common clinical manifestations, whereas large muscle hematoma or hemarthrosis seldom occur in these patients. Essential diagnostic features are a normal platelet count and morphology, a greatly prolonged bleeding time, absence of platelet aggregation in response to ADP, collagen, epinephrine, thrombin and to all aggregating agents which ultimately depend on fibrinogen binding to platelets for this effect, flow cytometry, studies of GPIIb-IIIa receptors on the platelet membrane surface using monoclonal antibodies. The present review describes some of the uncommon features of the disorders and the currently available options which the treating physicians should be aware of during the management of these patients. Although by definition all patients with Glanzmann's thrombasthenia have a virtually complete failure of platelet aggregation, a number of variant forms of GT have been described in which the glycoproteins are present in normal or near normal amounts but are functionally defective. Understanding the pathophysiology of the disorder by the treating physicians is of utmost importance. Presence of high affinity platelet receptors resulting in thrombasthennia-like phenotype may require an antagonistic treatment atypical of classical GT management. It has now been established that different genetic mutations of either GPIIb or IIIa genes results in such a heterogeneity of thrombasthenia phenotype. Glanzmann's thrombasthenia is a paradigm for treating coronary artery disease patients with GPIIb-IIIa antibody and inhibitors. By using these medicines we create a temporary GT-like situation. Hence, understanding this disease is of utmost importance to the practicing cardiologist. As mutations for different variant forms of GT become known, our understanding of how GPIIb-IIIa molecules can be activated to act as a receptor for fibrinogen molecules will be increased. Such understanding undoubtedly will help us to devise better drugs with GPIIb-IIIa inhibitors. Molecular biology techniques have enabled us to equivocally detect heterozygote carriers who are clinically asymptomatic. However, there may be several laboratories in the developing world, which have no access to molecular biology techniques. Development of more robust techniques of quantitation of platelet receptors has enabled an accurate diagnosis of heterozygote carriers or an unborn fetus in the second trimester. The importance of the GPIIb-IIIa polymorphisms in carrier and prenatal diagnosis has not been properly studied. Nowadays the less direct method of PLA1 typing (determination of the levels of platelet antigen) of the foetal platelets as early as 16 weeks of intrauterine life can be used for prenatal diagnosis of GT.     

Family screening for a Glanzmann's thrombasthenia mutation using PCR-SSCP

Genetic counselling is often requested in Glanzmann's thrombasthenia, but measurements of GPIIb-IIIa density on platelets are often too inconclusive to allow a precise assessment of whether prospective parents are obligate heterozygotes for this disease by this measure alone. The recent application of PCR technology to Glanzmann's thrombasthenia has resulted in the identification of a large number of mutations, i.e. insertions/ deletions, splicing defects, in the genes for both GPIIb and GPIIIa. Among the reported abnormalities is an intronic G-->A substitution at the splice donor site of intron 15 in the GPIIb gene of a European gypsy tribe. This gives rise to an abnormal splicing, of an 8-bp deletion located at the 3' end of exon 15, a reading-frame shift and a premature stop codon in the mRNA for GPIIb. In applying PCR-SSCP to the elucidation of the genetic defects of a series of Glanzmann's patients, we have found the above-cited abnormality in three more gypsy families in France. The presence of the mutation was initially established by sequencing the amplified fragment, and its presence in family members was confirmed by both PCR-SSCP and HphI restriction analysis. Evaluation of the intronic G-->A mutation enabled genetic counselling to prospective parents within these families.     

Heterogeneity of membrane surface proteins in Glanzmann's thrombasthenia

Studies in several laboratories have suggested that platelets from patients with Glanzmann's thrombasthenia are deficient in two major membrane glycoproteins and that this membrane defect is uniform from patient to patient. We have used an improved electrophoretic technique to study further the surface composition of normal and thrombasthenic platelets. Platelets from three unrelated thrombasthenic patients were labeled by either lactoperoxidase-catalyzed iodination or the neuraminidase-galactose oxidase-[3H]NaBH4 technique and the labeled proteins were separated by two dimensional isoelectric focusing SDS polyacrylamide gel electrophoresis. With both techniques, the major radiolabeled proteins were clearly separated from each other and were present as a horizontal collection of discrete spots that suggest charge heterogeneity. Most of the labeled proteins had an acidic isoelectric point. Compared to normal platelets, platelets from patients with Glanzmann's disease contained no electrophoretically identifiable fibrinogen. In two patients with thrombasthenia, there was total absence of surface glycoproteins GPIIb and GPIII, while a third patient with thrombasthenia, who was clinically indistinguishable from the previous two patients, had decreased, but detectable, amounts of GPIIb and GPIII. These studies suggest that there are at least two phenotypic patterns of membrane abnormalities in Glanzmann's thrombasthenia involving GPIIb and GPIII and may indicate genetic heterogeneity in this disease.     

Biochemical and molecular basis of Glanzmann's thrombasthenia.

Glanzmann's thrombasthenia is a rare autosomal recessive bleeding disorder characterized by a quantitative deficiency or a functional abnormality of the major platelet membrane integrin receptor: the glycoprotein (GP) IIb/IIIa complex. The GPIIb/IIIa complex functions as a platelet receptor for fibrinogen, von Willebrand factor, fibronectin and vitronectin; therefore it plays an important role in platelet adhesion and aggregation. Thrombasthenic platelets are severely deficient in GPIIb/IIIa content or function, and fail to aggregate and form the hemostatic plug at the site of vessel injury. On the other hand, heterozygous subjects (having about half the number of normal GPIIb/IIIa complexes) do not show bleeding problems. It has been demonstrated that a molecular defect affecting one of the two GP coding genes is sufficient to determine a contemporary deficit of both GPIIb and GPIIIa, and hence the thrombasthenic phenotype. Up to now, few molecular abnormalities giving rise to Glanzmann's thrombasthenia have been characterized. Large rearrangements within the GPIIb or GPIIIa coding genes appear to be unusual, whereas small modifications in the nucleotide sequence of the coding regions occur with higher frequency.     

Bone marrow transplantation in severe Glanzmann's thrombasthenia with antiplatelet alloimmunization

Glanzmann's thrombasthenia is an autosomal recessive disorder characterized by a lack of platelet aggregation due to the absence of platelet glycoprotein IIb and IIIa. Usually, the disease leads to mild hemorrhage but sometimes bleeding is severe enough to be life-threatening. We report the case of a 16-year-old girl, presenting with very severe type 1 Glanzmann's thrombasthenia, successfully treated with an HLA-identical sibling bone marrow transplant (BMT). We also update the clinical and laboratory data of her brother, who had received a BMT 16 years ago for the same disease. In the light of these two cases and two others published in the literature, we discuss the indications for BMT from HLA-identical sibling donors in Glanzmann's thrombasthenia. Alloimmunization against the missing platelet GPIIb/IIIa complex and severity of bleeding episodes may constitute sufficient criteria for allogeneic BMT after careful assessment of the risk-benefit of such a procedure, although this remains exceptional in this disease. Bone Marrow Transplantation (2000) 25, 327-330.     

Flow cytometric analysis of platelets in patients with Glanzmann's thrombasthenia

Platelets from 10 patients with Glanzmann's thrombasthenia (7 patients with type I and 3 with type II) and their 18 family members (11 parents, 6 siblings and one daughter) were analyzed by flow cytometry using 3 different commercially available FITC-labeled monoclonal antibodies. The amount of platelet GPIIbIIIa was calculated by using the ratio of the fluorescence intensity of the mean channel in comparison to normal platelets. The amount of platelet GPIIbIIIa was lower than 19% in 6 patients with type I and one patient with type II thrombasthenia. One type I patient had a 46.5% GPIIbIIIa amount as assessed using the monoclonal antibody TP80 (Nichirei Corp. Japan) which recognized GPIIb, although the other 2 antibodies showed an amount of less than 5%. One type II patient showed the following results: 30.9% (TP80), 28.2% (P2 antibody, Immunotech, France), and 3.9% (PLT1, Coulter Immunology, USA). The remaining type II patient consistently showed a normal amount of platelet GPIIbIIIa using all antibodies, appeared to be a variant form of thrombasthenia. The parents of type I patients had a significantly lower amount of platelet GPIIbIIIa compared to normal and 2 siblings of type I patients were diagnosed as heterozygotes. These findings suggest that Glanzmann's thrombasthenia is more heterogeneous than we have previously suspected, and that flow cytometric analysis using different monoclonal antibodies is a useful tool for identifying those heterogeneities and for the detection of type I carriers.