[Twenty-one cases of Sebastian platelet syndrome]

We report a Japanese family with Sebastian platelet syndrome. Twenty-one thrombocytopenic patients exhibited giant platelets and inclusion bodies in their granulocytes. They were thought to be related because they bore the same surname and lived within a localized area. None of them had additional clinical findings peculiar to Fechtner syndrome. Ultrastructural studies of the granulocytes were performed on four patients. The inclusion bodies in the granulocytes were different from those found in May-Hegglin anomaly, and consisted of ribosome clusters and rough endoplasmic reticula.