A 'touch' of the White platelet syndrome

Investigations into structural defects in platelets from a large family with the White platelet syndrome (WPS) separated the members into three groups. The first group of 22 members was the subject of our first report (White JG, Key NS, King RA, Vercellotti GM. The white platelet syndrome: A new autosomal dominant platelet disorder. Platelets 2004;15:173-184). A third group of 13 members had no abnormalities of platelet ultrastructure. The second group of 17 members, the focus of the present study, had a 'touch' of the WPS. Platelet counts, mean platelet volumes (MPVs) and platelet responses to aggregating agents were normal in 'touch' patients in contrast to platelets of those with the full WPS in whom these parameters were abnormal. Up to 13% of the full WPS platelets contained large, fully developed Golgi complexes, up to seven in number, extruding innumerable vesicles from the trans-Golgi face and filling the cytoplasm of many platelets. Many Golgi complexes had centrioles associated with them. 'Touch' platelets had one or two Golgi complexes of intermediate size in 3-5% of their platelets. Golgi vesicles were uncommon and centrioles absent. Gray platelets and hypogranular cells were infrequent in patients with a 'touch' of the WPS, whereas up to 44% of the platelets from those with the WPS were gray or hypogranular. Elements of the dense tubular system were prominent in full WPS platelets, together with their formation into areas of cytoplasmic sequestration and autodigestion. These features were absent in 'touch' platelets. As commonly observed in full WPS platelets, mitochondria were larger and more numerous than alpha granules in some 'touch' cells. Both 'touch' and full WPS platelets frequently contained giant and rod-shaped granules. Dense bodies, however, were normal in size and number in 'touch' platelets, and half normal size in full WPS platelets. The separation of ultrastructural abnormalities in the two varieties of the WPS suggests that genetic defects involve more than a single gene and the genes are variable in their penetrance. Genetic studies to determine if this is the case are currently in progress.