LAUSR

A 60-year-old woman presented with anaemia (haemoglobin concentration 102 g/l) with MCV 97 6 fl, reticulocyte count 60 1 9 10/l, white blood cell count 5 3 9 10/l and 1% circulating blast cells. Other laboratory tests were unremarkable. A bone marrow (BM) aspirate was hypercellular with 0 5% blasts and trilineage dysplasia. Megakaryocytes were increased in number, with 50% being micromegakaryocytes. The most striking morphological feature was platelet phagocytosis by 2% of granulopoietic precursors, from promyelocytes to metamyelocytes (images). No platelet phagocytosis by mature neutrophils was observed. Platelets were contained within a phagosomal vacuole surrounded by a clear halo; more rarely there were two or more vacuoles per cell. The BM karyotype was 47,XX,+1,del(1)(p21)[15]/48,idem,+8[2]/46,XX[3] [correction added on 8 March 2017, after first online publication: this karyotype was corrected]. (see supplementary information). Fluorescence in situ hybridization confirmed trisomies 1q and 8 (see supplementary information). A diagnosis of myelodysplastic syndrome (MDS), unclassifiable, was made. The patient was initially observed without treatment. Four years after the initial diagnosis she developed profound pancytopenia. Hypoplastic MDS with grade 2/4 fibrosis and increased CD34 cells was detected on BM re-examination. Platelet phagocytosis by granulopoietic precursors is an uncommon phenomenon, although platelet phagocytosis by mature peripheral blood neutrophils has been reported in myocardial infarction and in myeloproliferative neoplasms. On activation, platelets express the P-selectin glycoprotein on the cell membrane. Platelet P-selectin interacts with its counter receptor on neutrophils, which initiates phagocytosis to remove activated platelets. The SELP gene, encoding P-selectin, is located on chromosome 1q24.2. It therefore appeared possible that the platelet phagocytosis was due to increased SELP transcription as a consequence of trisomy 1q. SELP expression was studied by real-time polymerase chain reaction with DDCt method. Although there was no significant overexpression in BM cultured cells or whole peripheral blood, there was a 32 3-fold increase (P < 0 01) in mRNA extracted from platelet-rich plasma. This case highlights the observation of platelet phagocytosis by granulopoietic precursors as a relevant finding in MDS. This rare phenomenon may be explained by SELP overexpression leading to dysfunctional platelet clearance.