The most common JAK2 activating mutation, the JAK2 V617F mutation, has been reported in several diagnostic subtypes of MPN [115], which can explain its high incidence (about 11%) in SM-AHN patients [29,50,51,81,88] as compared to other diagnostic subtypes of SM [10,12,29,51,88] (Table 3 and Table S3). The gene discussed is JAK2; the disease is systemic mastocytosis.