A somatic point mutation in the JAK2 gene, 1849G>T, which changes amino acid residue 617 of the kinase from valine to phenylalanine (termed JAK2 V617F), has been identified by various studies in a substantial number of Philadelphia chromosome-negative myeloproliferative neoplasm (Ph-MPN) patients (1). Here, JAK2 is linked to myeloproliferative disorder.