A novel hereditary macrothrombocytopenia

A family is described in which macrothrombocytopenia and hearing loss are transmitted in an autosomal-dominant fashion. Several members of the family were studied extensively. Review of blood smears, coagulation studies, platelet function testing, and electron microscopy were performed. Platelet membrane glycoproteins were examined using flourescein-conjugated antibodies and flow cytometry. Platelet counts ranged from 50,000 to 123,000/microliters. Both mean platelet diameter and volume were increased. No leukocyte inclusions were noted by light or electron microscopy. Platelet aggregation was normal with adenosine diphosphate (ADP), collagen, and ristocetin but diminished with epinephrine and arachidonic acid. Flow cytometry showed normal platelet membrane glycoproteins and the unusual expression of glycophorin A on 40-60% of the giant platelets. This family's syndrome of macrothrombocytopenia and late-onset hearing loss appears to represent a novel giant platelet disorder. The expression of glycophorin A suggests disordered megakaryocytopoiesis with the early release of immature platelets.