Background: The diagnosis of underlying myeloproliferative neoplasms (MPNs) is often problematic in patients with Budd Chiari syndrome (BCS). A clonal mutation in JAK2 tyrosine kinase (JAK2V617F) occurs in a high proportion of patients with MPNs and is of use in the characterization of occult MPNs in BCS. Aim of the work: Detection of JAK2 V617F mutation in patients with BCS and its value in detection of occult MPNs. Patients and Methods: This study was carried out on fifty seven newly diagnosed Budd Chiari syndrome patientswho were attending tropical department in Ain Shams University Hospitals during the period from July 2017 to July 2018.Detection of JAK2V617F mutation was done by real time polymerase chain reaction. Results: Out of the studied 57 BCS patients, JAK2 V617F mutation was detected in 12 patients (21.1%) {10 (83.3%) were heterozygous and 2(16.7%) were homozygous for mutation}, while 45 patients (78.9%) were negative.On comparing JAK2 V617F positive and negative groups, there was a highly statistically significant relation regarding MPNs diagnosis, where all JAK2 V617F positive patients were diagnosed as MPNs of whom 7 (58.3%) had overt
presentation and 5(41.7%) had occult presentation, while in JAK2 V617F negative patients only 2 were diagnosed overt MPNs (p=0.001). Conclusion: In conclusion the JAK2 V617F mutation is an acquired mutation that can be used for diagnosis of latent MPNs presenting with thrombotic events, thus it is recommended to include JAK2 V617F gene analysis in the research panel for BCS patients.