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Summary. Investigations of the haemostatic functions in three patients with the Wiskott‐Aldrich syndrome are presented. All patients had severe thrombocytopenia and prolonged bleeding times. The platelets had abnormal morphology with reduced size and variations of shape. Electron microscopy revealed ultrastructural abnormalities with a reduced number of organelles, and many of the platelets contained large numbers of tubules. Platelet electrophoretic mobility in citrated plasma was not reduced by collagen, and platelet aggregation by collagen and ADP was deficient. Biochemical studies revealed a lack of the storage pool of adenine nucleotides. Platelet adhesiveness in vitro in whole blood was reduced. Platelet factor‐3 release by kaolin, ADP and freezing and thawing was normal in one and reduced in another of the patients. Platelet survival studies showed a normal survival time of normal donor platelets in one patient, while autologous platelets had a markedly reduced survival time in two of the patients. The bone marrow contained normal numbers of megakaryocytes. By electron microscopy of the bone marrow, blood platelets were found to be phagocytosed by macrophages and reticulum cells. The main cause of the thrombocytopenia is most probably incrcased peripheral destruction of platelets. It is suggested that the qualitatively defective platelets are recognized in the reticulo‐endothelial system as foreign particles and phagocytosed.

Cat, cattle, dog, horse, human, mink, pig, and rabbit platelets were separated from plasma by gel filtration. The gel-filtered platelets (GFP) were treated with thrombin to induce maximal granule secretion and the potential dense granule constituents ATP, ADP, serotonin (5-HT), Ca2+, and Mg2+ were measured in GFP and in the control and thrombin-treated platelets and in the respective supernatants. The amount of Ca2+, Mg2+, 5-HT, ATP, and ADP within the nonreleasable pool for all species varied between 3.1 and 10.0 mumol/10(11) platelets for Ca2+ and Mg2+ was less than 1.5 mumol/10(11) platelets for ADP and 5-HT and was between 2.0 and 5.0 mumol/10(11) platelets for ATP. Marked differences were observed in the releasable fraction. Human platelets were characterized by the largest releasable Ca2+ pool (greater than 10 mumol/10(11) platelets), the smallest secretable 5-HT and Mg2+ pool (less than 0.5 mumol/10(11) platelets), and the lowest ATP-to-ADP ratio (greater than 1.0). Pig platelets had the highest amount of releasable Mg2+ (approximately 8.0 mumol/10(11) platelets). Rabbits platelets released the most 5-HT (greater than 3.0 mumol/10(11)) and had the highest ATP/ADP (greater than 5.0). The releasable pool of Ca2+, Mg2+, ATP, and ADP in the remaining species varied in mumol/10(11) platelets from approximately 1.5-4.0, approximately 1.0-3.0, 0.5-3.5, and approximately 0.5-1.5, respectively.