Heterogeneity of membrane surface proteins in Glanzmann's thrombasthenia

Studies in several laboratories have suggested that platelets from patients with Glanzmann's thrombasthenia are deficient in two major membrane glycoproteins and that this membrane defect is uniform from patient to patient. We have used an improved electrophoretic technique to study further the surface composition of normal and thrombasthenic platelets. Platelets from three unrelated thrombasthenic patients were labeled by either lactoperoxidase-catalyzed iodination or the neuraminidase-galactose oxidase-[3H]NaBH4 technique and the labeled proteins were separated by two dimensional isoelectric focusing SDS polyacrylamide gel electrophoresis. With both techniques, the major radiolabeled proteins were clearly separated from each other and were present as a horizontal collection of discrete spots that suggest charge heterogeneity. Most of the labeled proteins had an acidic isoelectric point. Compared to normal platelets, platelets from patients with Glanzmann's disease contained no electrophoretically identifiable fibrinogen. In two patients with thrombasthenia, there was total absence of surface glycoproteins GPIIb and GPIII, while a third patient with thrombasthenia, who was clinically indistinguishable from the previous two patients, had decreased, but detectable, amounts of GPIIb and GPIII. These studies suggest that there are at least two phenotypic patterns of membrane abnormalities in Glanzmann's thrombasthenia involving GPIIb and GPIII and may indicate genetic heterogeneity in this disease.