Novel point mutation in a leucine-rich repeat of the GPIbalpha chain of the platelet von Willebrand factor receptor, GPIb/IX/V, resulting in an inherited dominant form of Bernard-Soulier syndrome affecting two unrelated families: the N41H variant.
Platelet transfusions can fail to prevent bleeding in patients with inherited platelet function disorders (IPDs), such as Glanzmann's thrombasthenia (GT; integrin αIIbβ3 dysfunction), Bernard-Soulier syndrome [BSS; glycoprotein (GP) Ib/V/IX dysfunction], and the more recently identified nonsyndromic <i>RASGRP2</i> variants.
Several point mutations and deletions affecting the GPIb alpha gene have been identified as the cause of BSS, whilst in four BSS families a GPIX gene defect has been reported.
The laboratory parameters which are characteristically for BSS such as platelet count, platelet volume and the expression of CD42a (GPIX), CD42b (GPIbalpha) and CD41 (GPIIb) were measured for all 38 individuals.
These findings reveal a novel nonredundant regulatory role for platelets in hepatic TPO homeostasis, which improves our understanding of constitutive TPO regulation and has important implications in diseases related to GPIbα, such as BSS and auto- and alloimmune-mediated thrombocytopenias.
These results suggest that a signaling process through the GPIbα cytoplasmic tail required for full platelet activation is defective in BSS variant case II and a length polymorphism of GPIbα is associated with a modified level of RIPA heterozygous BSS case I.
We demonstrated that the novel deletion mutation resulted in complete defectiveness of the GPIbalpha protein and null expression of the entire GPIb/IX complex, and was responsible for the Bernard-Soulier syndrome phenotype in this patient.
We describe in a BSS patient the first case of homozygous four bases deletion (TGAG) in the gpIbalpha gene coding sequence, leading to a premature stop codon.