A case of Bernard-Soulier syndrome: study of platelet glycoprotein Ib in a kindred

Identification and characterisation of mutations associated with von Willebrand disease in a Turkish patient cohort

Several cohort studies have investigated the molecular basis of von Willebrand disease (VWD); however, these have mostly focused on European and North American populations. This study aimed to investigate mutation spectrum in 26 index cases (IC) from Turkey diagnosed with all three VWD types, the majority (73%) with parents who were knowingly related. IC were screened for mutations using multiplex ligation-dependent probe amplification and analysis of all von Willebrand factor gene (VWF) exons and exon/intron boundaries. Selected missense mutations were expressed in vitro. Candidate VWF mutations were identified in 25 of 26 IC and included propeptide missense mutations in four IC (two resulting in type 1 and two in recessive 2A), all influencing VWF expression in vitro. Four missense mutations, a nonsense mutation and a small in-frame insertion resulting in type 2A were also identified. Of 15 type 3 VWD IC, 13 were homozygous and two compound heterozygous for 14 candidate mutations predicted to result in lack of expression and two propeptide missense changes. Identification of intronic breakpoints of an exon 17-18 deletion suggested that the mutation resulted from non-homologous end joining. This study provides further insight into the pathogenesis of VWD in a population with a high degree of consanguineous partnerships.

Clinical benefit of recombinant factor VIIa in management of bleeds and surgery in two brothers suffering from the Bernard-Soulier syndrome

Bernard-Soulier syndrome (BSS) is a rare congenital bleeding disorder characterized by thrombocytopenia and giant platelets that display impaired or absent platelet agglutination with ristocetin. The disease is caused by mutations in genes controlling the expression of the platelet glycoprotein Ib-IX complex. The most severely affected patients suffer from profound muco-cutaneous bleeding tendency. Patients suffering from BSS may require platelet transfusion in prevention and management of severe bleeding. However, recent publications have suggested that recombinant factor VIIa (rFVIIa) infusion may support haemostasis in BSS. The present report describes two brothers who received treatment with rFVIIa together with tranexamic acid on a total of six occasions in management of haemostasis in minor surgery and for a serious spontaneous upper gastrointestinal tract bleed. Although platelet transfusion was omitted, haemostasis was regarded excellent in all of these treatment episodes.

A Fifty Percent Reduction of Platelet Surface Glycoprotein Ib Does Not Affect Platelet Adhesion Under Flow Conditions

Glycoprotein (GP) Ib is an adhesion receptor on the platelet surface that binds to von Willebrand Factor (vWF). vWF becomes attached to collagens and other adhesive proteins that become exposed when the vessel wall is damaged. Several investigators have shown that during cardiopulmonary bypass (CPB) surgery and also during platelet activation in vitro by thrombin or thrombin receptor activating peptide (TRAP) GPIb disappears from the platelet surface. Such a disappearance is presumed to lead to a decreased adhesive capacity. In the present study, we show that a 65% decrease in platelet surface expression of GPIb, due to stimulation of platelets in Orgaran anticoagulated whole blood with 15 μmol/L TRAP, had no effect on platelet adhesion to both collagen type III and the extracellular matrix (ECM) of human umbilical vein endothelial cells under flow conditions in a single-pass perfusion system. In contrast to adhesion, ristocetin-induced platelet agglutination was highly dependent on the presence of GPIb. Immunoelectron microscopic studies showed that GPIb almost immediately returned to the platelet surface once platelets had attached to collagen. In a subsequent series of experiments, we showed that when less than 50% of GPIb was blocked by an inhibitory monoclonal antibody against GPIb (6D1), platelet adhesion under flow conditions remained unaffected.

A Fifty Percent Reduction of Platelet Surface Glycoprotein Ib Does Not Affect Platelet Adhesion Under Flow Conditions

Glycoprotein (GP) Ib is an adhesion receptor on the platelet surface that binds to von Willebrand Factor (vWF). vWF becomes attached to collagens and other adhesive proteins that become exposed when the vessel wall is damaged. Several investigators have shown that during cardiopulmonary bypass (CPB) surgery and also during platelet activation in vitro by thrombin or thrombin receptor activating peptide (TRAP) GPIb disappears from the platelet surface. Such a disappearance is presumed to lead to a decreased adhesive capacity. In the present study, we show that a 65% decrease in platelet surface expression of GPIb, due to stimulation of platelets in Orgaran anticoagulated whole blood with 15 μmol/L TRAP, had no effect on platelet adhesion to both collagen type III and the extracellular matrix (ECM) of human umbilical vein endothelial cells under flow conditions in a single-pass perfusion system. In contrast to adhesion, ristocetin-induced platelet agglutination was highly dependent on the presence of GPIb. Immunoelectron microscopic studies showed that GPIb almost immediately returned to the platelet surface once platelets had attached to collagen. In a subsequent series of experiments, we showed that when less than 50% of GPIb was blocked by an inhibitory monoclonal antibody against GPIb (6D1), platelet adhesion under flow conditions remained unaffected.

Inherited giant platelet disorders

Giant platelet disorders (GPD) refer to rare, usually inherited states characterized by abnormally large platelets, thrombocytopenia and bleeding tendency of variable severity. This review summarizes major clinical and laboratory features of three GPDs (Bernard-Soulier syndrome, May-Hegglin anomaly and gray platelet syndrome). Differential diagnosis between immunological thrombocytopenia and GPDs is important. Although rare, giant platelet disorders should be borne in mind, since bleeding tendency in some individuals may be severe and knowledge of bleeding diathesis is of importance before delivery or surgical procedures also in less symptomatic individuals.

Bernard-Soulier syndrome in two Swedish families: effect of DDAVP on bleeding time

We present 2 patients with Bernard-Soulier syndrome from two different families. The parents of one of the patients were found to have had common ancestors in the 17th century. The platelet membrane content of glycoprotein (GP)Ib was measured in the patients and their first-degree relatives with an ELISA technique based on monoclonal antibodies. Both patients had very low levels of GPIb. In one of the families the heterozygotes had reduced expression of GPIb but in the other the obligate heterozygotes had normal values, suggesting that the molecular pathology differs between the two families. In both patients, bleeding time was shortened by infusion of DDAVP (1-deamino-8-D-arginine vasopressin), although it was not completely normalised. DDAVP may be of some therapeutic value in cases of Bernard-Soulier syndrome.

Nonsense mutation in the glycoprotein Ib alpha coding sequence associated with Bernard-Soulier syndrome

Three distinct gene products, the alpha and beta chains of glycoprotein (GP) Ib and GP IX, constitute the platelet membrane GP Ib-IX complex, a receptor for von Willebrand factor and thrombin involved in platelet adhesion and aggregation. Defective function of the GP Ib-IX complex is the hallmark of a rare congenital bleeding disorder of still undefined pathogenesis, the Bernard-Soulier syndrome. We have analyzed the molecular basis of this disease in one patient in whom immunoblotting of solubilized platelets demonstrated absence of normal GP Ib alpha but presence of a smaller immunoreactive species. The truncated polypeptide was also present, along with normal protein, in platelets from the patient's mother and two of his four children. Genetic characterization identified a nucleotide transition changing the Trp-343 codon (TGG) to a nonsense codon (TGA). Such a mutation explains the origin of the smaller GP Ib alpha, which by lacking half of the sequence on the carboxyl-terminal side, including the trans-membrane domain, cannot be properly inserted in the platelet membrane. Both normal and mutant codons were found in the patient, suggesting that he is a compound heterozygote with a still unidentified defect in the other GP Ib alpha allele. Nonsense mutation and truncated GP Ib alpha polypeptide were found to cosegregate in four individuals through three generations and were associated with either Bernard-Soulier syndrome or carrier state phenotype. The molecular abnormality demonstrated in this family provides evidence that defective synthesis of GP Ib alpha alters the membrane expression of the GP Ib-IX complex and may be responsible for Bernard-Soulier syndrome.

Differentiation between Bernard-Soulier syndrome and immune thrombocytopenia by immunostaining of peripheral blood

Peripheral blood smears from seven patients with Bernard-Soulier syndrome were examined by an immunocytochemical staining procedure using a monoclonal antibody specific for platelet glycoprotein Ib. No platelet staining was observed except for very slight staining of the large sized platelets from one of the patients. Application of the assay to blood smears from 12 patients with immune thrombocytopenia showed that their peripheral platelets stained normally, so the assay can be used to differentiate between immune thrombocytopenia and Bernard-Soulier syndrome and to confirm a diagnosis of the syndrome.

Bernard-Soulier syndrome: whole blood diagnostic assays of platelets

Diagnosing Bernard-Soulier syndrome (BSS), a congenital hemorrhagic disorder of blood platelets, is complicated by the difficulty of separating the giant platelets from other blood cells to allow studies of platelet function and structure. We report on the use of three whole blood assays for diagnosing BSS. Whole blood platelet aggregation responses studied with an electrical impedance aggregometer were equivalent to those more laboriously obtained by using platelet-rich plasma prepared by unit gravity sedimentation and studied with an optical light transmittance aggregometer. Platelet aggregation responses were normal with adenosine diphosphate or collagen stimulation but absent with ristocetin or bovine plasma stimulation. Whole blood radioimmunoassay of platelet glycoprotein (GP) expression was performed by using iodinated murine monoclonal antibodies HP1-1D (anti-GP IIb/IIIa) and 6D1 (anti-GP Ib). After incubation with citrated whole blood, centrifugation was used to separate cell-bound antibody that was quantitated with a gamma counter. The patient's whole blood had a normal level of cell-bound GP IIb/IIIa but a substantially reduced level of cell-bound GP Ib (5% of normal mean). Whole blood smear immunocytochemical staining with monoclonal antibodies and qualitative analysis by light microscopy revealed a considerable reduction of GP Ib expression by the patient's giant platelets, whereas GP IIb/IIIa expression was normal. These data helped establish the diagnosis of BSS. We conclude that these three relatively simple assays of platelets in whole blood should be of particular value in the clinical laboratory differential diagnosis of patients with congenital thrombocytopenias and giant platelet syndromes.