Type 2B von Willebrand disease associated with the release of platelet agglutinates from megakaryocytes in the bone marrow.

We report a child with thrombocytopenia since birth, circulating platelet agglutinates, and a tendency to bleed. A bone marrow aspirate revealed large platelet clumps within the bone marrow and megakaryocyte nuclei surrounded by halos of clumped platelets. Laboratory evaluation revealed type 2B von Willebrand disease. Gene sequencing revealed a G to C mutation at base 3923 of the VWF gene. This mutation was previously described in a family with circulating platelet clumps and abnormal megakaryopoiesis with release of clumped platelets in culture. This same mutation was previously described in a family with circulating platelet aggregates and abnormalities of platelet release from megakaryocytes in vitro. Presence of megakaryocytes with halos of clumped platelets in our patient suggests that platelet agglutinate occurs in the bone marrow in some type 2B von Willebrand disease patients.