Quantitative assessment of JAK2 V617F and CALR mutations in Philadelphia negative myeloproliferative neoplasms

Abstract

Background: Philadelphia negative myeloproliferative neoplasms (MPNs) are characterized by frequent mutations of driver genes including JAK2, CALR and MPL. While the influence of JAK2 V617F mutant allele burden on the clinical phenotype of MPN patients is well-described, the impact of CALR mutant allele burden on clinical features needs further investigation.

Patients and methods: Quantitative assessment of JAK2 and CALR mutations was performed on diagnostic DNA samples from 425 essential thrombocythemia (ET) and 227 primary myelofibrosis patients using real-time quantitative PCR and fragment length analysis. Characterization of CALR mutations and detection of MPL mutations were performed by Sanger sequencing.

Results: Twelve novel CALR mutations have been identified. ET patients with CALR^mut load exceeding the median value exhibited lower hemoglobin values (12.0 vs. 13.6 g/dL), higher LDH levels (510 vs. 351 IU/L) and higher rate of myelofibrotic transformation (19% vs. 5%). The CALR^mut load was higher among ET patients presenting with splenomegaly compared to those without splenomegaly (50.0% vs. 43.5%).

Conclusion: Our study confirms the clinical significance of driver mutational status and JAK2^mut load in MPNs; in addition, unravels a novel clinical association between high CALR^mut load and a more proliferative phenotype in ET.

Keywords: CALR; JAK2 V617F; MPL; Mutant allele burden; Myeloproliferative neoplasm.