Since the acquired somatic mutation, JAK2 V617F, was discovered as a first molecular marker of myeloproliferative neoplasms (MPN), and it has been detected variably in each MPN subtypes. However, JAK2 V617F does not found in all of MPN cases and not necessarily specific to a particular clinicpathologic entity. Recently, mutation of the putative tumor suppressor gene, Ten-Eleven-Translocation-2(TET2), has been identified in MPN patients. However, the frequency of TET2 mutation or its relationship with JAK2 V617F mutation or pathologic function in MPN has not been concluded, yet. The aim of our study was to evaluate the frequency of TET2 in MPN patients, and whether there is any correlation of TET2 mutation with JAK2V617F mutation or the clinicohematologic parameters.
Total 99 adult MPN patients (18 PV, 62 ET, 11 PMF and 8 MPN unclassified) whose bone marrow cells had been stored from 2007 to 2010 at point of first diagnosis were included in this study. Hematological diagnoses and subtyping were reconfirmed according to the 2008 WHO classification and clinicohematologic datas were collected from patient records. Direct sequencing for TET2(exon3–11) and JAK2 (exons 12 and 14) were performed using an ABI 3730XL DNA analyzer. The JAK2V617F allele burdens were determined by pyrosequencing for samples available and MPL was analyzed by allele-specific PCR.
The overall TET2 mutational frequency was 12.1%, and disease-specific mutational frequencies were 22.2% in PV, 9.7% in ET and 18.2% in PMF. The found mutations included 11 mutations, 7 frame-shift (p.Lys95AsnfsX18, p.Gln967AsnfsX40, p.Lys1022GlufsX4, p.Asp1314MetfsX49, p.Gln1534AlafsX43, p.Tyr1618LeufsX4, p.Leu1609GlufsX45), 1 nonsense (p.Gly1735X), 1 missense (Q599R) and 2 splicing mutations (c.3409+1G>T, c.4044+2insT). Those mutations most frequently involved exon 3(four mutations) and exon 11(four mutaions), and rarely intron 3, intron 8 and exon 7. None of the mutations were associated with a karyotypically apparent 4q24 rearrangement. All patients were also screened for JAK2 V617F, and the overall JAK2 V617F positive rate was 68%(94.4% in PV, 69.4% in ET, 45.5% in PMF and 37.5% in MPN, unclassified). All TET2 mutations occurred in JAK2 V617F positive cases. JAK2 exon12 mutation was not found in all patients. MPL W515L was found in one ET patient who also carried JAK2V617F, but not TET2 mutation. Information on JAK2 V617F allele burden was available in 78 patients.
Considering all 99 patients, the patient age, hematologic indexes (leukocyte count, neutrophil fraction, lymphocyte fraction, monocyte fraction, Hb, Hct and platelet count), the frequency of organomegaly, marrow fibrosis or thrombotic/hemorrhagic complications were not different according to carrying TET2 mutation. However, TET2 mutation was more frequently found in JAK2 V617F carriers than non-carriers (P=0.008), but JAK2 V617F allele burden did not correlated with the presence of mutant TET2.
When analysis was performed for each PV, ET, and PMF (no TET2 mutation in MPN-unclassifiable patients), correlation between TET2 and JAK2 V617F mutational status was not found in each subtypes (P=0.078 in PV, P=0.099 in ET and P=0.182 in PMF). However, the JAK2 V617F allele burden was significantly higher in PMF harboring TET2 mutation than PMF patients did not (88.0 ± 4.3% vs 19.1 ± 28.7%, P=0.034). In statistical analysis for the correlations of clinicohematologic parameters with TET2 mutation in each PV, ET and PMF patients, only a few statistically significant results were identified. The presence of TET2 mutation was correlated with high Hct in PMF (47.4 ± 5.4 vs 25.5 ± 6.2, P=0.037), and TET2 positive ET patients showed relatively higher frequency of organomegaly compared to ET patients without TET2 mutation (50% vs 19.6%, P=0.018).
The overall and disease-specific frequencies of TET2 mutation in our study are similar with previous studies, and frame-shift mutation is the most frequent mutation type. There is no specific relationship between JAK2 V617F and TET2 mutation occurrence, but TET2 mutant PMF has higher JAK2 V617F allele burden than non-mutant. TET2 mutation is also associated with a higher Hct in PMF and higher frequency of organomegaly in ET. Larger scale studies involving more MPN patients are needed.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.