Study of JAK2 V617F allele Burden By Droplet Digital PCR in BCR-ABL1 Negative Myeloproliferative Neoplasms and Its Implications on Disease Phenotype

JAK2V617F mutation is the most common mutation seen among the BCR-ABL1 negative myeloproliferative neoplasms, the incidence of which is 90-95% in PV, 50-70% in ET and 40-50% in PMF. The discovery of the association of JAK2 V617F mutation with all the above mentioned myeloproliferative neoplasms and MPN-U boggled the minds of many scientists on how a single gene mutation can cause different disorders, and it was later reported that the allele burden determines the clinical phenotype of the disease. With the advent of droplet digital polymerase chain reaction(ddPCR), even a small quantity of JAK2 V617F allele burden could be detected and measured, facilitating an earlier definitive diagnosis and hence early treatment. In addition, with the rise in use of JAK2 inhibitors such as Ruxolitinib for treating high risk patients, the quantification of allele burden could probably play a role in defining treatment guidelines for usage of these drugs.

Method: After examination of bone marrow aspirate smears and biopsies in clinically suspected cases of MPN, molecular testing and allele burden quantification of JAK2 V617F mutation was done using ddPCR. The objectives of our study was to correlate the allele burden with the clinical phenotype, it's implication on the symptom burden and hematological parameters and it's correlation with the prognosis of patients. The symptom burden was measured using MPNTEN Score, whereas the prognosis for PV and ET was done based on Prognostic risk score for thrombosis. Prognostication of PMF was done using IPSS and DIPSS.

Results: In our study, among 50 patients, 50% (n=25) were diagnosed as PV, 30% (n=15) were diagnosed as Primary myelofibrosis, 16 % as ET (n=8) and 4% (n=2) as MPN-U. The mean allele burden of PV was highest (64.5%), closely followed by PMF at 61.65% and lowest in ET (31.17%). The allele burden showed significant (p<0.05) positive correlation with the symptom burden in patients. It was also found that a significant association between presence of para trabecular megakaryocyte localization and allele burden exists (p value of 0.02). It was observed that a significant correlation exists between previous history of thrombosis with increased allele burden at presentation (p<0.05). However, the allele burden quantification at presentation and prognostic scores of PV, ET and PMF did not show significant correlation.

Conclusion: To conclude, our study reports that the allele burden varies according to the clinical phenotype, has a bearing on the symptom burden of patients, has morphological implications and has a strong correlation with prior thrombotic episodes. Follow up of these patients based on remission criteria for PV, ET and PMF are being done and will be presented.

No relevant conflicts of interest to declare.