A Novel Mutation in GP1BB Reveals the Role of the Cytoplasmic Domain of GPIbβ in the Pathophysiology of Bernard-Soulier Syndrome and GPIb-IX Complex Assembly

Int J Mol Sci. 2021 Sep 22;22(19):10190. doi: 10.3390/ijms221910190.

Abstract

Bernard-Soulier syndrome (BSS) is an autosomal-recessive bleeding disorder caused by biallelic variants in the GP1BA, GP1BB, and GP9 genes encoding the subunits GPIbα, GPIbβ, and GPIX of the GPIb-IX complex. Pathogenic variants usually affect the extracellular or transmembrane domains of the receptor subunits. We investigated a family with BSS caused by the homozygous c.528_550del (p.Arg177Serfs*124) variant in GP1BB, which is the first mutation ever identified that affects the cytoplasmic domain of GPIbβ. The loss of the intracytoplasmic tail of GPIbβ results in a mild form of BSS, characterized by only a moderate reduction of the GPIb-IX complex expression and mild or absent bleeding tendency. The variant induces a decrease of the total platelet expression of GPIbβ; however, all of the mutant subunit expressed in platelets is correctly assembled into the GPIb-IX complex in the plasma membrane, indicating that the cytoplasmic domain of GPIbβ is not involved in assembly and trafficking of the GPIb-IX receptor. Finally, the c.528_550del mutation exerts a dominant effect and causes mild macrothrombocytopenia in heterozygous individuals, as also demonstrated by the investigation of a second unrelated pedigree. The study of this novel GP1BB variant provides new information on pathophysiology of BSS and the assembly mechanisms of the GPIb-IX receptor.

Keywords: Bernard-Soulier syndrome; GPIb-IX complex; inherited platelet disorders; inherited thrombocytopenia; vWF receptor.

Publication types

  • Case Reports

MeSH terms

  • Adult
  • Bernard-Soulier Syndrome / blood
  • Bernard-Soulier Syndrome / genetics*
  • Bernard-Soulier Syndrome / pathology
  • Blood Platelets / physiology
  • Female
  • Humans
  • Male
  • Middle Aged
  • Pedigree
  • Platelet Glycoprotein GPIb-IX Complex / genetics*
  • Platelet Glycoprotein GPIb-IX Complex / metabolism
  • Protein Domains / genetics
  • Thrombocytopenia / genetics*
  • Thrombocytopenia / pathology
  • von Willebrand Factor / metabolism

Substances

  • Platelet Glycoprotein GPIb-IX Complex
  • adhesion receptor
  • glycoprotein receptor GPIb-IX
  • von Willebrand Factor