Additional Glycoprotein Defects In Glanzmann’s Thrombasthenia Platelets

Glanzmann’s thrombasthenia (G.T.) platelets are deficient in 2 major membrane GP (IIb and IIIa). In order to investigate if these are the only defects in this disorder, platelets from G.T. patients and from healthy donors were isolated, washed and surface-labelled by techniques specific for protein or for sugars (sialic acid or penultimate galactose/N-acetylgalactosamine residues). Labelled or unlabelled platelets were solubilized in sodium dodecyl sulphate (SDS) and separated by 2-dimensional polyacrylamide gel electrophoresis, first according to isoelectric point and then according to molecular weight. Glycoproteins from unlabelled platelets separated by 2-dimensional electrophoresis were identified by binding of 125I-labelled Lens culinaris lectin (mannose, glucose specific) GPIIbA1 and IIIaA1 were absent in one G.T. patient while in others lower amounts of 2 GP were found in positions similar to these GP. Major membrane GP (IbA1, IbA2, IbB1 and IIIbA1) had more intensely labelled terminal sialic acid moieties in G.T. platelets than in normals. A major membrane GP designated Ic had an altered pi and its penultimate galactose/N-acetyl galactosamine residues labelled more intensely in G.T. platelets than in controls. One high M.Wt. GP and a number of lower M.Wt. GP (IVa, IVb and VII) normally found in platelets of healthy donors were absent in G.T. platelets. These results indicate strongly that there is a major perturbation of the platelet surface in G.T.