The low frequency of JAK2 clones among matched controls without blood count abnormalities was in agreement with three Danish population-based studies.24,44,45 The severity of thrombocytosis correlated with the clone size of MPN-associated genes in our cohort and JAK2 mutant cases were likely to have persistent thrombocytosis (78.6%). This evidence concerns the gene JAK2 and myeloproliferative disorder.