Highly Significant Bleeding Diathesis in Patients with Platelet Dysfunction due to a Novel Mutation in RASGRP2, Encoding CalDAGGEFI (p.Gly305Asp)

ALBERTO MF; SÁNCHEZ LUCEROS A; BERMEJO EI; NURDEN P; BERGMEIER W; DAVID P; NURDEN AT

Berlin

Congreso; 26th Congress of ISTH & 63rd Annual Scientific and Standardization Committee (SSC) Meeting; 2017

International Society on Thrombosis and Haemostasis

Background: Mutations affecting RASGRP2, the gene encoding theRap GTPase activator, CalDAG-GEFI, give rise to a novel, and rare,group of platelet signal transduction abnormalities. We here reportplatelet studies of a novel variant, CalDAG-GEFI(p.Gly305Asp), previouslyidentified in an Argentinian pedigree.Aims: To fully characterize the platelet function defect and to describethe therapeutic approach for the treatment of hemorrhage in the twosiblings (P1, P2) affected in this consanguineous family.Methods: Flow cytometry was used to quantify platelet adhesion receptorexpression, and to measure integrin activation (fibrinogen binding)and granule secretion (surface expression of CD62P and CD63) inthe patients? and control platelets activated or not with classic agonistsand PMA. Platelet aggregation was measured by lumi-aggregometry.Thromboelastometry (ROTEM®) and Thromboelastogram [TEG®]were used to measure platelet procoagulant activity. Western blottingprocedures were used to detect CalDAG-GEFI.Results: Two brothers (P1 and P2) have a lifelong history of bleedingwith severe epistaxis successfully treated with rFVIIa. Other bleedingsinclude hemorrhage from minor wounds. Platelet counts werenormal, as was αIIbβ3 and GPIb expression. Fibrinogen binding, granulerelease, and the platelet aggregation response were significantlyimpaired with ADP or collagen but not PMA-activated platelets.ROTEM and TEG were normal, suggesting intact plasma coagulation,residual αIIbβ3 outside-in signaling and platelet pro-coagulant activity.CalDAG-GEFI protein expression was markedly reduced but notabsent. Homology modeling places the Gly305Asp substitution at theGEF-Rap1 interface, suggesting that the mutant protein has very limitedcatalytic activity.Conclusions: We characterize a new loss-of-function mutation inRASGRP2 causing impaired platelet adhesive function and highly significant bleeding in humans. Reach the World Travel Grant