2. Academic Validation
  3. Novel mutations in RASGRP2, which encodes CalDAG-GEFI, abrogate Rap1 activation, causing platelet dysfunction

Novel mutations in RASGRP2, which encodes CalDAG-GEFI, abrogate Rap1 activation, causing platelet dysfunction

  • Blood. 2016 Sep 1;128(9):1282-9. doi: 10.1182/blood-2015-11-683102.
María Luisa Lozano 1,  Aaron Cook 2,  José María Bastida 3,  David S Paul 4,  Gemma Iruin 5,  Ana Rosa Cid 6,  Rosa Adan-Pedroso 5,  José Ramón González-Porras 3,  Jesús María Hernández-Rivas 3,  Sarah J Fletcher 7,  Ben Johnson 7,  Neil Morgan 7,  Francisca Ferrer-Marin 1,  Vicente Vicente 1,  John Sondek 8,  Steve P Watson 7,  Wolfgang Bergmeier 9,  José Rivera 1
Affiliations

Affiliations

  • 1 Servicio de Hematología y Oncología Médica, Hospital Universitario Morales Meseguer, Centro Regional de Hemodonación, Universidad de Murcia, Instituto Murciano de Investigaciones Biomédicas-Arrixaca, Murcia, Spain;
  • 2 Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC;
  • 3 Department of Hematology, Instituto de Investigación Biomédica de Salamanca-Hospital Universitario de Salamanca, Salamanca, Spain;
  • 4 McAllister Heart Institute, University of North Carolina at Chapel Hill, Chapel Hill, NC;
  • 5 Servicios de Hematología, Pediatría y Oncología Infantil, Hospital de Cruces, Bilbao, Spain;
  • 6 Unidad de Hemostasia y Trombosis, Servicio de Hematología y Hemostasia, Hospital Universitario Politécnico de la Fe, Valencia, Spain;
  • 7 Institute of Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham, United Kingdom; and.
  • 8 Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC.
  • 9 Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC; McAllister Heart Institute, University of North Carolina at Chapel Hill, Chapel Hill, NC;
PMID: 27235135 DOI: 10.1182/blood-2015-11-683102
Abstract

In addition to mutations in ITG2B or ITGB3 genes that cause defective αIIbβ3 expression and/or function in Glanzmann's thrombasthenia patients, platelet dysfunction can be a result of genetic variability in proteins that mediate inside-out activation of αIIbβ3 The RASGRP2 gene is strongly expressed in platelets and neutrophils, where its encoded protein CalDAG-GEFI facilitates the activation of Rap1 and subsequent activation of integrins. We used next-generation Sequencing (NGS) and whole-exome Sequencing (WES) to identify 2 novel function-disrupting mutations in RASGRP2 that account for bleeding diathesis and platelet dysfunction in 2 unrelated families. By using a panel of 71 genes, we identified a homozygous change (c.1142C>T) in exon 10 of RASGRP2 in a 9-year-old child of Chinese origin (family 1). This variant led to a p.Ser381Phe substitution in the CDC25 catalytic domain of CalDAG-GEFI. In 2 Spanish siblings from family 2, WES identified a nonsense homozygous variation (c.337C>T) (p.Arg113X) in exon 5 of RASGRP2 CalDAG-GEFI expression was markedly reduced in platelets from all patients, and by using a novel in vitro assay, we found that the nucleotide exchange activity was dramatically reduced in CalDAG-GEFI p.Ser381Phe. Platelets from homozygous patients exhibited agonist-specific defects in αIIbβ3 Integrin activation and aggregation. In contrast, α- and δ-granule secretion, platelet spreading, and clot retraction were not markedly affected. Integrin activation in the patients' neutrophils was also impaired. These patients are the first cases of a CalDAG-GEFI deficiency due to homozygous RASGRP2 mutations that are linked to defects in both leukocyte and platelet Integrin activation.

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