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A variety of mutations have been discovered in patients with essential thrombocythemia (ET). These include JAK2 (V617F), JAK2 exon 12, MPL exon 10, and most recently the gene encoding calreticulin (CALR), exon 9 (NEJM JW Oncol Hematol Jan 7 2014). Calreticulin controls protein folding and calcium signaling, but how the mutated gene induces megakaryocyte and platelet proliferation is unknown.
Two recent papers present the clinical features associated with CALR and JAK2 mutations in more than 1200 patients with ET. Those with the CALR mutation were predominantly male, younger, and had lower levels of white blood cells (median × 109/L, 8 vs. 9; P<0.001) and hemoglobin (median g/dL, 13.8 vs. 14.4; P<0.001), but higher platelet counts (median × 1…