S100A9 and myeloproliferative disorder: In granulocytes of JAK2 positive MPN subjects a significant gene over-expression was determined for phosphoribosyl pyrophosphate synthetase-associated protein (PRPSAP2), myosin VIIB retinoblastoma-like 2 (RBL2), S100A9, and microRNA 424 genes (MIR424, S4 Table).