Localization of a lysosomal enzyme in platelets from patients with the White platelet syndrome

The White platelet syndrome (WPS) is an autosomal dominant platelet disorder. Platelet structural abnormalities include the presence of Golgi complexes in up to 13% of their cells, frequently accompanied by centrioles, deficient numbers or absent alpha granules in 30-40% of their platelets and masses of dense tubular system (DTS) channels often forming areas of cytoplasmic sequestration. The degradation of cytoplasm and organelles in the sequestered areas suggested the possibility that hydrolytic enzymes remained in the DTS and were being transferred to sequestration vacuoles. The present study has used ultrastructural cytochemistry to localize the sites of a lysosomal enzyme, aryl sulfatase, in normal and WPS platelets. Enzyme reaction product, lead sulfide, was localized to lysosomal organelles in normal platelets, and only in rare examples appeared in the DTS. Aryl sulfatase activity was found in the Golgi complexes, a few lysosomes, much of the DTS and areas of cytoplasmic sequestration in WPS platelets. The findings indicate that aryl sulfatase, and, most likely, proteins destined for alpha granules in WPS platelets are not completely transferred from the endoplasmic reticulum to Golgi complexes, then to Golgi vesicles and finally to lysosomal and alpha granules in the parent cell before the platelets are delivered to the circulation.