[Hereditary hypogranular thrombocytopathic thrombocytopenia. Ultrastructural study of a megakaryocytopathy (author's transl)].

The ultrastructure of megakaryocytes and blood platelets has been studied in 3 members of a Swiss family, in which a haemorrhagic diathesis of varying degree occurred in at least three generations. Blood platelets show an extremely low number of dense granules, slightly increased mean diameter and irregular distribution of glycogen in unusually large clusters. The number of megakaryocytes in bone marrow is normal. Electron microscopy shows asynchronous development of their structural components: a severe defect in maturation of specific granules is followed by retardation and irregularity in the demarcation of the "platelet prospective fields", Golgi membranes have few vesicles, glycogen occurs partly in huge clusters and megakaryocytes with mature platelet fields are very rare. The ultrastructural picture of platelet formation in megakaryocytes indicates that this haemorrhagic syndrome may be understood as a megakaryocytopathy. The results of functional and biochemical analyses performed on blood platelets show a defect in both phases of aggregation and in PF 3 availability, normal survival, decreased total sialic acid content, and absence of the heaviest platelet population ("D") isolated by discontinuous sucrose gradient. The autosomal dominant transmission of this together with its concomitance with blood group O suggest its relationship with the familial thrombopathic thrombocytopenia described in 1968 by Kurstjens and al. in a Dutch family [13].