A NEW LEU123 TO PRO MUTATION IN THE FIFTH LEUCINE-RICH REPEAT OF GLYCOPROTEIN IBALPHA IN A BERNARD-SOULIER PATIENT INDUCES DEFECTIVE SHEAR-DEPENDENT CELL ADHESION ON VON WILLEBRAND FACTOR
Abstract number: P-W-260
Proulle1 V., Strassel2 C., Perrault2 C., Ravanat2 C., Baas2 M., Nurden3 P., Dreyfus1 M., Lanza2 F., Crpp4 .
11Laboratoire d'Hématologie, Hôpital Bicêtre, université Paris Sud, AP-HP, Le Kremlin Bicêtre 22INSERM U311, EFS-Alsace, Strasbourg 33Laboratoire d'Hématologie, Hôpital Cardiologique 44Centre de Référence des Pathologies Plaquettaires, Hôpital Xavier Arnozan, Pessac, France
How-to-cite Proulle V, Strassel C, Perrault C, Ravanat C, Baas M, Nurden P, Dreyfus M, Lanza F, Crpp. A NEW LEU123 TO PRO MUTATION IN THE FIFTH LEUCINE-RICH REPEAT OF GLYCOPROTEIN IBALPHA IN A BERNARD-SOULIER PATIENT INDUCES DEFECTIVE SHEAR-DEPENDENT CELL ADHESION ON VON WILLEBRAND FACTOR. J Thromb Haemost 2007; 5 Supplement 2: P-W-260
Abstract
Introduction: Bernard Soulier syndrome (BSS), which diagnosis is often overlooked, is due to platelet glycoprotein (GP) Ib-IX-V abnormalities and is characterized by defective platelet adhesion to von Willebrand factor (VWF) under shear. We present a case of BSS with a novel mutation in the fifth leucine-rich repeat (LRR) of GPIbalpha resulting in defective shear-dependent adhesion in cells expressing the mutant GP.
Methods: A 5 year-old boy was misdiagnosed and treated for 3 years for immune thrombocytopenia. Classical platelet studies and gene sequencing were performed. The expression and function of mutated GPIb-IX were analyzed in transfected CHO cells.
Results: Platelet studies showed giant, spheroid platelets often with large vacuoles with defective ristocetin-induced agglutination. Binding of monoclonal antibodies (mAb) showed dramatic decrease in GPIbalpha levels (2-17%) whereas GPIbbeta, IX and V levels were only 40-50% decreased, suggesting a BSS variant. A homozygous Leu123 to Pro mutation was identified in the fifth LRR domain of GPIbalpha. As compared to CHO expressing normal GP, transfected CHO reproducing the mutation expressed 25-50% of GPIb-IX surface levels. As expected, mAb (6D1) directed against the fifth LRR was negative. Moreover, the mutant complex retained the capacity to bind soluble VWF in proportion with GPIbalpha expression but did not allow for efficient adhesion on immobilized VWF under flow conditions. Mutant cells were rolling at higher velocity at 150 s-1 and were less resistant to detachment at higher shear rates, going up to 6.000 s-1.
Conclusions: Our case underlines that an inherited origin has to be systematically searched for in chronic childhood thrombocytopenia, possibly bringing valuable information on platelet function. Indeed, identification and expression of this new Leu123 to Pro mutation, responsible for a BSS variant, highlights the role of the fifth LRR of GPIbalpha in shear-dependent cell adhesion.
