GPIb[alpha], GPIb[beta] and GPIX, encoded by the GPIBA
, GP1BB and GP9 genes, are all required for efficient expression of the complex on the platelet surface, while absence of GPV does not appear to affect receptor expression or VWF binding.
A1 and A3 domains are mainly involved in thrombosis: A1 binds to GpIba
on the platelet surface and microfibrillar collagen (type VI); A3 binds to fibrillar collagens (types I and III) .
Some experts have demonstrated that genetic polymorphisms of platelet membrane glycoproteins (GPI1, GPIba, GPIIIa, and GPIV) may influence the efficacy of aspirin or platelet responsiveness, and genetic polymorphisms of the thromboxane A2 receptor (TBXA2R), platelet-activating factor acetylhydrolase, and coagulation factor XIII were associated with platelet aggregation.
GPIba, GPIX, and GPV form a complex that binds Von Willebrand factor, and thus plays an important role in the initial process of platelet aggregation.
PT-VWD can be diagnosed only by specialized testing (ristocetin-induced platelet aggregation mixing studies) and genetic testing of GPIBA
(glycoprotein Ib (platelet), alpha polypeptide).
Recombinant human GPIba (RandD) was used as the antigen in assay detecting B cells producing IgG anti-GPIb antibodies.
Relative efficacy of steroid therapy in immune thrombocytopenia mediated by anti-platelet GPIIbIIIa versus GPIba antibodies.
* Part of the GPIba receptors may be occupied by soluble vWF and unable to interact with vWF immobilized on the tissues exposed at the sites of injury.
Thrombocytopenia may be present due to enhanced ability of vWFto bind platelet receptor GPIbA, causing removal of the platelet/vWF complex.
Platelet treatment with mocarhagin, a cobra venom metalloproteinase that cleaves GpIba
, significantly reduced aggregation induced by 5 mM without affecting the response to other agonists such as adenosine diphosphate (ADP).
Most of the genetic defects are due to mutations of the GPIba
gene, but may also be due to defects of the GPIbI3 or GPIX genes.