Surprisingly, the phenotype of myeloproliferative disorders associated with CALR mutations includes growth factor independent activation of JAK2 (Klampfl et al., 2013; Nangalia et al., 2013), and these patients respond to treatment with JAK inhibitors, such as Ruxolitinib (Cervantes et al., 2013; Passamonti et al., 2014). This evidence concerns the gene JAK2 and myeloproliferative disorder.