Glanzmann Thrombasthenia Associated with a 21-Amino Acid Deletion (Leu817-Gln837) in Glycoprotein IIb due to Abnormal Splicing in Exon 25

Expanding the Mutation Spectrum Affecting αIIbβ3 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 αIIbβ3 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 αIIbβ3 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 αIIbβ3 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 β3 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.

Glanzmann Thrombasthenia with Acute Myeloid Leukemia Successfully Treated by Bone Marrow Transplantation

We report successful treatment by bone marrow transplantation (BMT) in an acute myeloid leukemia (AML) patient with Glanzmann thrombasthenia (GT). Genetic analysis revealed that a novel point mutation in exon 3 of the GPIIb gene led to abnormal splicing resulting in an amino acid substitution and an in-frame deletion of 3 amino acid residues. Expression studies suggested a rapid degradation of the uncomplexed protein within the cells. Induction therapy for AML was performed with frequent platelet transfusions because of the patient's severe hemorrhagic manifestations. In the second remission, the patient was successfully treated by BMT from an HLA-matched unrelated donor. Platelet function returned to normal, and the GT phenotype completely disappeared. Our experience suggests that BMT is a curative therapeutic strategy for GT. Furthermore, we believe this study is the first to demonstrate that engraftment after BMT for AML can be determined by monitoring the congenital genetic defect of GT.