SHAPE-CHANGING AGENTS PRODUCE ABNORMALLY LARGE PLATELETS IN A HEREDITARY GIANT PLATELETS SYNDROME (MPS)

Abstract

Geometries of platelets in citrated PRP [platelet-poor plasma] obtained from normal donors (17) and donors (5) with a hereditary dominant giant platelet syndrome, herein referred to as Montreal platelet syndrome (MPS), were compared. The measured geometric axial ration (rp = thickness/diameter) was used to classify platelet morphologies into 3 groups: discocytes (rp < 0.5), disco-echinocytes (rp = 0.5 to 0.9), sphero-echinocytes (rp > 0.9). MPS discocytes were normal sized. MPS sphero-echinocytes and disco-echinocytes had mean volumes approximately 2 times larger than normal. These larger-than-normal sized MPS platelets and be produced directly from MPS discocytes by treatment with agents known to induce platelet shape change (ADP, thrombin and incubation at 4.degree. C). Treatment of platelets obtained from normal donors which were resuspended in MPS PPP with ADP or incubation at 4.degree. C caused the formation of normal-sized disco-echinocytes and sphero-echinocytes. The diameters of MPS disco-echinocytes were identical to the diameters of MPS platelets observed on peripheral blood smear, whereas those of MPS sphero-echinocytes were .apprx. 20% lower. The appearance of abnormally large platelets in MPS may be related to a defect in the mechanism which regulated platelet size and shape during shape change.