Functional and molecular characterization of an inherited abnormal platelet function related to a new Cal- DAG-GEFI protein variant in an argentinean family.

SANCHEZ LUCEROS A; OUWEHAND WH; BERMEJO E; NURDEN AT; TURRO E; ALBERTO MF; SIMEONI I; NURDEN P

Montpellier

Encuentro; ISTH SSC 2016; 2016

Background: Signal transduction dysfunction is a cause of platelet related bleeding. Genetic variants affecting the function of CalDAGGEFI, essential for integrin activation, have only recently been identified and are ultra-rare.Aims: Characterization of a platelet function defect in a pedigree witha bleeding diathesis.Methods: The affected pedigree from Argentina consisted of two male siblings P1, P2 and their mother P3. Platelet aggregation was performed in a lumi-aggregometer. The agonist panel included:ADP,epinephrine( Epi), collagen(Col),TRAP,A23187,PMA,arachidonicacid (AA),ristocetin and thrombin(T). The monoclonal antibodies for flow cytometric (FACS) analysis were against CD42b, CD61 and CD41. The DNA samples were analysed using the ThromboGenomics highthroughput sequencing platform, which targets 113 genes. Results: P1 and P2 have a lifelong bleeding syndrome with severe epistaxis, and hematomas requiring transfusions on several occasions. P3 had epistaxis during childhood, and menorrhagia. All had a normal platelet count. Platelet function testing demonstrated a muchreduced maximal aggregation for P1 and P2 and a normal aggregation for P3 in response to ADP, Epi, A23187 and at low doses of TRAP and Col; whereas aggregation with AA, ristocetin, PMA, high-dose Col and T was normal or slightly diminished. ATP release was absent with ADP, Epi or A23187 for P1 and P2 and marginally decreased with Col and AA. Membrane receptors aIIbb3 and GPIb were present. Genetic analysis led to the identification of a novel homozygous c.914G>A transition in exon 9 of the RASGRP2 gene for P1 and P2 and P3 was a carrier. This variant gives rise to p.Gly305Asp in CalDAG-GEFI.Conclusions: We report a new variant p.Gly305Asp of CalDAG-GEFI identified in a pedigree with severe bleeding syndrome. The clinical phenotype resembled a Glanzmann?s thrombasthenia variant but with residual platelet aggregation with strong platelet agonists and with PMA, a characteristic for this gene.