Identification of two novel mutations in RASGRP2 affecting platelet CalDAG-GEFI expression and function in patients with bleeding diathesis
Identification of two novel mutations in RASGRP2 affecting platelet CalDAG-GEFI expression and function in patients with bleeding diathesis
复制标题
鉴定影响出血素质患者血小板 CalDAG-GEFI 表达和功能的 RASGRP2 两种新突变
作者：
T. Sevivas;J. Bastida;David S. Paul;E. Caparrós;V. Palma;M. Coucelo;D. Marques;F. Ferrer;J. González;V. Vicente;J. Hernández;S. Watson;M. Lozano;W. Bergmeier;J. Rivera
RASGRP 2基因编码钙离子和DAG调节的鸟嘌呤核苷酸交换因子I（CalDAG-GEFI），它在血小板和中性粒细胞的整合素活化中起关键作用。我们在这里报告了两个新的RASGRP 2变异与血小板功能障碍和出血患者。纯合子患者的血小板和中性粒细胞计数和形态正常。血小板表型分析显示：PFA-100闭合时间延长;主要糖蛋白受体表达正常;血小板对ADP和胶原蛋白的聚集反应严重降低（2例患者）; 1例患者对PAR 1和花生四烯酸的聚集反应明显受损; PMA诱导的聚集不受影响;血小板分泌、凝块收缩和扩散受到的影响最小。遗传分析鉴定了RASGRP 2中的两个新的纯合变体：c.706C>T（p.Q236X）和c.887G>A（p.C296Y）。在这两名患者中，在血小板裂解物中未检测到CalDAG-GEFI蛋白，通过纤维蛋白原结合评估的血小板αIIbβ3活化在对除PMA外的所有激动剂的反应中受到极大损害。患者中性粒细胞表现出正常的整合素表达，但受损Mn 2+诱导的纤维蛋白原结合。总之，我们已经确定了两个新的RASGRP 2突变，可以添加到这种快速增长的遗传性血小板功能障碍形式。
Abstract The RASGRP2 gene encodes the Ca2+ and DAG-regulated guanine nucleotide exchange factor I (CalDAG-GEFI), which plays a key role in integrin activation in platelets and neutrophils. We here report two new RASGRP2 variants associated with platelet dysfunction and bleeding in patients. The homozygous patients had normal platelet and neutrophil counts and morphology. Platelet phenotyping showed: prolonged PFA-100 closure times; normal expression of major glycoprotein receptors; severely reduced platelet aggregation response to ADP and collagen (both patients); aggregation response to PAR1 and arachidonic acid markedly impaired in one patient; PMA-induced aggregation unaffected; platelet secretion, clot retraction, and spreading minimally affected. Genetic analysis identified two new homozygous variants in RASGRP2: c.706C>T (p.Q236X) and c.887G>A (p.C296Y). In both patients, CalDAG-GEFI protein was not detectable in platelet lysates, and platelet αIIbβ3 activation, as assessed by fibrinogen binding, was greatly impaired in response to all agonists except PMA. Patient neutrophils showed normal integrin expression, but impaired Mn2+-induced fibrinogen binding. In summary, we have identified two new RASGRP2 mutations that can be added to this rapidly growing form of inherited platelet function disorder.