Infrequent occurrence of this unique JAK2 mutation has been reported in chronic myelomonocytic leukemia (CMML), atypical or unclassified myeloproliferative disorder (MPD), myelodysplastic syndrome (MDS), systemic mastocytosis (SM), and chronic neutrophilic leukemia (CNL) [10–16]. The gene discussed is JAK2; the disease is chronic myelomonocytic leukemia.