• mast cells
• proteases
• chymase
• severe aplastic anaemia
• systemic mastocytosis
• myelodysplastic

We read the article by Horny et al describing bone marrow mast cell (MC) specific protease expression patterns in cases of systemic mastocytosis and myelodysplastic syndromes (MDS) with great interest.¹ An increase in bone marrow MCs is a known feature of various haematological diseases, including myeloproliferative disorders and acquired severe aplastic anaemia (SAA). Although the MC increase is clonal in mastocytosis and benign in acquired SAA, its nature is not fully understood in myeloproliferative and myelodysplastic disorders.

Acquired SAA and hypoplastic MDS share several clinical and bone marrow features, and are often difficult to distinguish. Both conditions respond to immunosuppressive treatments. Is the increase in numbers of MCs in these conditions simply an innocent consequence of haemopoietic cell injury sparing MCs or, alternatively, does it contribute to the development of severe bone marrow hypoplasia/aplasia in …