Grey platelet syndrome: studies on platelet alpha-granules, lysosomes and defective response to thrombin.

The platelets of a young man with the grey platelet syndrome were severely depleted of all seven alpha-granule proteins assayed as well as partially deficient in alpha-mannosidase and alpha-fucosidase; four other lysosomal enzymes were present in normal concentrations. Total platelet 5-hydroxytryptamine (5HT) and adenine nucleotides were normal, and 14C-5HT uptake reached normal levels only slightly more slowly than a control. Aggregation and dense body secretion occurred normally in response to ADP, adrenaline, collagen, PAF-acether, sodium arachidonate, A23187, Ionomycin, TPA and U44069, but were very delayed in response to thrombin. The increase in cytosolic free calcium in response to thrombin was very slow and much reduced in amplitude, whether in the presence or absence of extracellular Ca2+. These defects in response to thrombin were not corrected by the separate addition of purified alpha-granule proteins or by a whole releasate from normal platelets. It is suggested that these platelets, in addition to their alpha-granule deficiency, may have a specific defect of thrombin receptor-mediated activation of phospholipase C.