Comprehensive Analysis of JAK2 Mutations: A Single Center Experience

Mutations in Janus kinase 2 (JAK2) genes are the genetic hallmark of BCR-ABL1-negative myeloproliferative neoplasms (MPN). In 2005 several groups described a point mutation in codon 617 of the protein tyrosine kinase (JAK2 gene) in BCR-ABL1-negative MPN. The mutation was found in a vast majority of patients with polycythemia vera (PV), in approximately half of patients with essential thrombocythaemia (ET) and in myelofibrosis (MF). In 2007, an additional exon 12 mutation were found in a small percentage of PV patients. The 2008 World Health Organization classification of haematopoietic neoplasms includes JAK2 mutations as one of the strongest diagnostic criteria for PV and together with the MPLmutations for ET and PMF.

In this study, we describe the JAK2 mutation profile in a series of 1811 samples collected over the period of 48-months (2010-2013). The samples were submitted from patients h thrombosis or clinically suspected for having MPN to the Molecular laboratory at King Faisal specialist Hospital & Research center, Riyadh, Saudi Arabia. A comprehensive analysis of exons 12-15 was carried using Sanger sequencing method. Of the 1811 samples, 1706 samples were available for analysis. JAK2 mutations was identified in 271 (16%) of the samples. We evaluated the positive cases for the following: age, gender, type of JAK2mutation, if the patients are evaluated for other genetic mutations and diagnosis.

Of these 271 positive cases; 148 (54.6%) were females and 123 (45.4%) males. 103 (38%) cases were from inside the hospital while 168 (62%) cases were from different referring institutions in which the diagnosis was not available. Their age varied between 4 months and 97 years with a median of 54 years. A total of 262 (96.7%) patients were positive for JAK2 V617F; In the remaining 9 (3.3%) samples non V617F mutation were detected, in which 5 (1.8%) cases with JAK2 G571S, 1 case (0.3%) with JAK2 p.E543_D544del, 1 (0.3%) case with JAK2 p.Y570Y, 1 (0.3%) with JAK2 exon 12 deletion (p.R541_E543>K) and 1 (0.3%) with JAK2 del (540I - 542N), ins M. of the 271, 13 (5%) cases were associated with other cytogenetic or DNA Sequence abnormalities together with the JAK2mutation. Of the 13, 4 cases (1.4%) presented with Abnormal karyotype, 5 (1.8%) with a heterozygous Methylenetetrahydrofolate reductase (MTHFR) polymorphism, 3 (1.1%) cases with BCR/ABL1 and 1 case has a missense mutation p.V726A, in exon 10 of the MEFV gene.

The positive in-house cases tested for JAK2mutation were 103 (38%). Clinical diagnosis included: 87 (84.4%) MPN cases of which 35 (40.2%) PV, 22 (25.3%) ET, 11 (12.6%) MF, 17 (19.5%) unclassifiable MPN, 2 (2.3%) CML. Moreover, 9 (8.7%) Budd-Chiari syndrome, 6 (5.8%) thrombosis (including DVT, PE and portal thrombosis) and 1 (0.9%) squamous cell carcinoma.

In our study 1811 sample were tested in 4 years which means almost 1 sample is submitted daily for JAK2 testing in our institute. The Majority of the in-house patients tested were MPN patients with small percentage having thrombosis which could progress later to full MPN clone. Over 50 different non-V617F mutations have been identified in the literature and were presented by a small portion of our patients cohort. It was shown to have biologic effects similar to those caused by the V617F mutation; however, more research in this area is ongoing.