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Molecular genetic analysis of a variant Bernard–Soulier syndrome due to compound heterozygosity for two novel glycoprotein Ib β mutations
Author(s) -
Kunishima Shinji,
Sako Masahiro,
Yamazaki Tomio,
Hamaguchi Motohiro,
Saito Hidehiko
Publication year - 2006
Publication title -
european journal of haematology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.904
H-Index - 84
eISSN - 1600-0609
pISSN - 0902-4441
DOI - 10.1111/j.0902-4441.2006.t01-1-ejh2817.x
Subject(s) - bernard–soulier syndrome , platelet membrane glycoprotein , von willebrand factor , ristocetin , chinese hamster ovary cell , microbiology and biotechnology , platelet , glycoprotein ib , glycoprotein , chemistry , platelet glycoprotein gpib ix complex , biology , genetics , receptor , biochemistry , immunology
Bernard–Soulier syndrome (BSS) is a rare bleeding disorder characterized by giant platelets, thrombocytopenia, and prolonged bleeding time. It is caused by abnormalities in the glycoprotein (GP) Ib/IX/V complex, the receptor for von Willebrand factor (vWF). Most cases of BSS described so far involve quantitative rather than qualitative defects in the complex. In this study, we investigated the effects of two naturally occurring mutations in the GPIb β gene, C122S and 443delG, on the expression of the GPIb/IX complex identified in a variant type of BSS in which the platelets had severely reduced GPIb α (∼10%) and less markedly reduced GPIb β and GPIX (∼20%) expression. Immunoblot analysis showed the absence of non‐reduced GPIb (GPIb α /GPIb β ) in the patient's platelets. Transient transfection experiments in 293T cells revealed the expression of GPIb β Ser122 polypeptide and absence of GPIb β 443delG polypeptide. Although no disulfide‐linked association was observed between GPIb β Ser122 and GPIb α , GPIb β Ser122 was non‐covalently associated with both GPIb α and GPIX subunits on the cell surface when cotransfected with wild‐type GPIb α and GPIX. Chinese hamster ovary cells stably expressing GPIb α /Ib β Ser122/IX had the ability to bind soluble vWF and to aggregate in the presence of ristocetin. These results suggest that despite disruption of the disulfide linkage between GPIb α and GPIb β , GPIb/IX is formed, but its stability may be impaired, resulting in low levels of the complex on the platelet membranes.