JAK2 and primary myelofibrosis: In some reports, higher mutated JAK2 allele burden was associated with increased blood counts and hemoglobin26,27 but this was not confirmed by others.28,29,30 Thrombotic risk was elevated in patients with ET.26,31 Also, higher mutant allele burden together with histology classification was associated with disease progression to primary myelofibrosis.32