GP9 encodes glycoprotein IX (GPIX), a critical subunit of the platelet GPIb-V-IX complex that functions as the von Willebrand factor (vWF) receptor 1. This complex mediates vWF-dependent platelet adhesion to vascular subendothelium, an essential initiating event in hemostasis 1. GP9 appears to facilitate proper membrane insertion and orientation of GPIb within this multisubunit receptor complex 2. The GPIb-V-IX complex enables platelet aggregation in response to ristocetin and primary hemostatic responses at sites of vascular injury 2. Bernard-Soulier syndrome (BSS) type C results from biallelic or heterozygous GP9 mutations, causing deficiency or dysfunction of the GPIb-V-IX complex 34. This leads to macrothrombocytopenia (giant platelets), thrombocytopenia, and severe bleeding tendency with manifestations including purpura, epistaxis, and menorrhagia 1. GP9 mutations account for 44% of BSS cases among 211 characterized families 2. A zebrafish gp9 knockout model demonstrated that GP9 disruption causes thrombocytopenia, bleeding tendency, and abnormal progenitor cell expansion, validating GP9's conserved role in thrombopoiesis 3. Recent gene therapy approaches using lentiviral vectors successfully restored GPIX expression and corrected the BSS phenotype in patient-derived cells 5, suggesting potential therapeutic interventions for this rare bleeding disorder.