GP1BB encodes the beta subunit of glycoprotein Ib (GPIb), a critical platelet surface receptor that forms part of the GPIb-IX-V complex essential for hemostasis 1. The primary function of GP1BB is to participate in platelet plug formation by enabling platelet adhesion to von Willebrand factor (VWF) bound to the subendothelium 1. The mechanism involves the GPIb-IX-V complex serving as a platelet receptor for VWF, allowing platelets to adhere to vascular subendothelium and aggregate in response to ristocetin 1. GP1BB is located on chromosome 22, and variants in this region can influence phenotypes through haploinsufficiency effects 2. Disease relevance includes Bernard-Soulier syndrome (BSS), where biallelic mutations in GP1BB cause severe bleeding disorder with macrothrombocytopenia and platelet dysfunction 13. Interestingly, rare monoallelic variants in GP1BB can cause autosomal dominant macrothrombocytopenia with milder bleeding phenotypes 4. Clinical significance extends beyond bleeding disorders, as GP1BB variants have been identified in chr22 immune thrombocytopenia patients, where genetic testing can guide treatment decisions and avoid inappropriate immunosuppression 5. The gene shows evidence of founder effects in certain geographical populations 1.