has material basis in germline mutation in GP1BA autosomal recessive disease platelet-type von Willebrand disease Bernard-Soulier syndrome GP1BA-related Bernard-Soulier syndrome https://github.com/monarch-initiative/mondo/issues/9994 Bernard-Soulier syndrome, type A1 GP1BA-related Bernard-Soulier syndrome MONDO:1060238 Any Bernard-Soulier syndrome in which the cause of the disease is a variation in the GP1BA gene, characterized by macrothrombocytopenia, reduced or absent expression of the GPIb-IX-V complex, and lifelong mucocutaneous bleeding. Affected individuals have large platelets with defective ristocetin-induced agglutination, reflecting the absence or dysfunction of GPIbα on the platelet surface. Variants in GP1BA impair production, trafficking, or incorporation of GPIbα into the receptor complex, preventing normal surface assembly and leading to the classic BSS adhesion defect.