Studies on a new variant of the Hermansky-Pudlak syndrome: Qualitative,ultrastructural, and functional abnormalities of the platelet-dense bodies associated with a phospholipase a defect

The structure and functions of platelets from a patient in whom albinism and hemorrhagic diathesis were associated have been investigated. Electron microscope studies showed a large reduction in the number of dense bodies and this was confirmed by an examination of fluorescent platelets loaded with mepacrine. The rare dense bodies were much bigger than normally observed; their density was diminished and was localized in a peripheral ring. Other platelet constituents were found to be normal. Platelet peroxidase activity was normal in the canaliculi of the dense tubular system; catalase-positive granules were also present. Serotonin uptake by the patient's platelets was much decreased and reserpine, a potent inhibitor of serotonin accumulation by normal human platelets, did not further decrease this incorporation. The uptake of free ¹⁴C-arachidonic acid by the platelets was greatly diminished, as was its thrombin-induced liberation from phosphatidylcholine and phosphatidyl inositol. Moreover, platelet phospholipase A₁ activity was much reduced and phospholipase A₂ activity was undetectable.