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 (delta-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 delta-SPD associated with
albinism.
Granulophysin levels in platelet homogenates of 30 patients with the
Hermansky-Pudlak syndrome form of delta-SPD were 1/4 to 1/5 of levels in controls or obligate heterozygotes. Two patients with the Chediak-Higashi form of delta-SPD syndrome also had markedly reduced levels of
granulophysin. Patients with other forms of delta-SPD had normal levels of
granulophysin. Two sisters with delta-SPD in one family had normal
granulophysin present in empty dense granule membrane vesicles. Three members of another family with delta-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 delta-SPD patients and may provide clues to the nature of defective granules in delta-SPD subtypes.