Publication Date:
2016-09-02
Description:
In addition to mutations in ITG2B or ITGB3 genes that cause defective α IIb β 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 α IIb β 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 α IIb β 3 integrin activation and aggregation. In contrast, α- and -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.
Keywords:
Pediatric Hematology, Free Research Articles, Phagocytes, Granulocytes, and Myelopoiesis, Platelets and Thrombopoiesis
Print ISSN:
0006-4971
Electronic ISSN:
1528-0020
Topics:
Biology
,
Medicine
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