A 13-bp deletion in α_IIb gene is a founder mutation that predominates in Palestinian-Arab patients with Glanzmann thrombasthenia

Glanzmann thrombasthenia (GT) is a rare autosomal recessive bleeding disorder caused by lack or dysfunction of α_IIbβ ₃ in platelets. GT is relatively frequent in highly inbred populations. We previously identified a 13-bp deletion in the α_IIb gene that causes in-frame deletion of six amino acids in three Palestinian GT patients. In this study, we determined the molecular basis of GT in all known Palestinian patients, examined whether Jordanian patients harbor the same mutations, analyzed whether there is a founder effect for the 13-bp deletion, and determined the mechanism by which the 13-bp deletion abolishes α_IIbβ₃ surface expression. Of 11 unrelated Palestinian patients, eight were homozygous for the 13-bp deletion that displayed common ancestry by haplotype analysis, and was estimated to have occurred 300-600 years ago. Expression studies in baby hamster kidney cells showed that substitution of Cys107 or Trp110 located within the deletion caused defective α_IIbβ₃ maturation. Substitution of Trp110, but not of Cys107, prevented fibrinogen binding. The other Palestinian patients harbored three novel mutations: G2374 deletion in α_IIb gene, TT1616-7 deletion in β₃ gene, and IVS14: -3C → G in β₃ gene. The latter mutation caused cryptic splicing predicting an extended cytoplasmic tail of β₃ and was expressed as dysfunctional α_IIbβ₃. None of 15 unrelated Jordanian patients carried any of the described mutations.