Quantification of a novel dense granule protein (granulophysin) in platelets of patients with dense granule storage pool deficiency

Abstract

An antigen-capture sandwich enzyme-linked immunosorbent assay (ELISA) was developed for a novel protein granulophysin, a constituent of the platelet dense granule (DG) membrane and used to characterize patients with dense granule storage pool deficiency (δ-SPD). The assay uses two monoclonal antibodies against the protein, one of which is conjugated to peroxidase. Purified DGs, an enriched source of the protein, were used for the standard curve. Granulophysin levels were only low in forms of δ-SPD associated with albinism. Granulophysin levels in platelet homogenates of 30 patients with the Hermansky-Pudlak syndrome form of δ-SPD were 1/4 to 1/5 of levels in controls or obligate heterozygotes. Two patients with the Chediak-Higashi form of δ-SPD syndrome also had markedly reduced levels of granulophysin. Patients with other forms of δ-SPD had normal levels of granulophysin. Two sisters with δ-SPD in one family had normal granulophysin present in empty dense granule membrane vesicles. Three members of another family with δ-SPD had low DG counts but normal granulophysin levels, indicating that in this group the level of granulophysin was maintained despite the reduction in granule formation. Thus, granulophysin quantitation facilitates characterization of δ-SPD patients and may provide clues to the nature of defective granules in δ-SPD subtypes. © 1992 by The American Society of Hematology.