The frequency of the JAK2 haplotypeGGCC_46/1 in the healthy population is about 24%, whereas it was found in 40–80% of JAK2 V617F positive MPN [7,8,12,13,14,15], in about 64% of cases bearing JAK2 exon 12 mutations [10], and in approximately 36% of MPN cases bearing MPL mutations [16]. The gene discussed is JAK2; the disease is myeloproliferative neoplasm.