GP9-related Bernard-Soulier syndrome

Any Bernard-Soulier syndrome caused by the variation in the GP9 gene, marked by absent or markedly reduced GPIb-IX-V complex expression, resulting in impaired platelet adhesion and lifelong mucocutaneous bleeding. Platelets are large and functionally deficient, with severely reduced ristocetin-induced agglutination reflecting loss of functional GPIX within the receptor complex. Variants in GP9 disrupt synthesis or stability of the GPIX subunit, preventing proper assembly of the GPIb-IX-V complex and producing the characteristic bleeding phenotype.