Expanding the Mutation Spectrum Affecting αIIbß3 Integrin in Glanzmann Thrombasthenia: Screening of the ITGA2B and ITGB3 Genes in a Large International Cohort.

We report the largest international study on Glanzmann thrombasthenia (GT), an inherited bleeding disorder where defects of the ITGA2B and ITGB3 genes cause quantitative or qualitative defects of the αIIbß3 integrin, a key mediator of platelet aggregation. Sequencing of the coding regions and splice sites of both genes in members of 76 affected families identified 78 genetic variants (55 novel) suspected to cause GT. Four large deletions or duplications were found by quantitative real-time PCR. Families with mutations in either gene were indistinguishable in terms of bleeding severity that varied even among siblings. Families were grouped into type I and the rarer type II or variant forms with residual αIIbß3 expression. Variant forms helped identify genes encoding proteins mediating integrin activation. Splicing defects and stop codons were common for both ITGA2B and ITGB3 and essentially led to a reduced or absent αIIbß3 expression; included was a heterozygous c.1440-13_c.1440-1del in intron 14 of ITGA2B causing exon skipping in seven unrelated families. Molecular modeling revealed how many missense mutations induced subtle changes in αIIb and ß3 domain structure across both subunits, thereby interfering with integrin maturation and/or function. Our study extends knowledge of GT and the pathophysiology of an integrin.

Phenotype analysis and clinical management in a large family with a novel truncating mutation in RASGRP2, the CalDAG-GEFI encoding gene.

BACKGROUND: Genetic variants in the RASGRP2 gene encoding calcium and diacylglycerol-regulated guanine nucleotide exchange factor I (CalDAG-GEFI) represent a new inherited bleeding disorder linked to major defects of platelet aggregation and activation of αIIbß3 integrin. They are of major interest as CalDAG-GEFI is receiving attention as a potential target for antiplatelet therapy for prevention and treatment of cardiovascular disorders including arterial thrombosis and atherosclerosis. OBJECTIVES: To better understand the phenotypical and clinical profiles of patients with CalDAG-GEFI deficiency. PATIENTS: We report a five-generation family with a novel truncating CalDAG-GEFI mutation detailing clinical management and phenotypic variability. RESULTS: Patients IV.6 & IV.4 manifested with episodes of serious mucocutanous bleeding or bleeding after surgery not responding to platelet transfusion but responding well to recombinant Factor VIIa infusions. Their blood counts and coagulation parameters were normal but platelet aggregation to ADP and collagen was defective. Further work-up confirmed normal levels of αIIb and ß3 in their platelets but decreased αIIbß3 function. DNA analysis by whole exome sequencing within the BRIDGE-BPD consortium (Cambridge, UK), allowed us to highlight a homozygous c.1490delT predicted to give rise to a p.F497Sfs*22 truncating mutation near to the C-terminal domain of CalDAG-GEFI. Sanger sequencing confirmed that both patients were homozygous for the c.1490delT and 3 out of 4 close family members were heterozygous. CONCLUSIONS: A long-term prospective study is warranted for full clinical exploration of CalDAG-GEFI to understand the bleeding phenotyes and their management.