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

作者：Luisa Lozano Maria; Cook Aaron; Maria Bastida Jose; Paul David S; Iruin Gemma; Rosa Cid Ana; Adan Pedroso Rosa; Ramon Gonzalez Porras Jose; Maria Hernandez Rivas Jesus; Fletcher Sarah J; Johnson Ben; Morgan Neil; Ferrer Marin Francisca; Vicente Vicente; Sondek John; Watson Steve P; Bergmeier Wolfgang; Rivera Jose

来源：Blood, 2016, 128(9): 1282-1289.

DOI：10.1182/blood-2015-11-683102

In addition to mutations in ITG2B or ITGB3 genes that cause defective alpha(IIb)beta(3) 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 alpha(IIb)beta(3). 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 alpha(IIb)beta(3) integrin activation and aggregation. In contrast, alpha- and beta-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.

• 出版日期2016-9-1