A new familial 'giant platelet syndrome' with structural, metabolic and functional abnormalities of platelets due to a primary megakaryocyte defect.

We have investigated platelet morphology, function and biochemistry in a family affected by dominantly inherited congenital thrombocytopenia with giant platelets. A defect of aggregation was defined with evidence of disturbed fatty acid distribution in platelet membrane phospholipids and impaired arachidonic acid mobilization. Release of 5-hydroxytryptamine was normal. Platelet ultrastructure was grossly abnormal and volume analysis revealed small as well as giant forms. Bone marrow megakaryocytes were morphologically abnormal and the distribution of mean nuclear ploidy atypical, suggesting the production of abnormal platelets due to a primary megakaryocyte disorder. The features of this condition are distinct from those previously described in familial thrombocytopenia and constitute a new "giant platelet syndrome". The qualitative and quantitative platelet defects may be secondary to a disturbance of megakaryocyte cytoplasmic fragmentation.