TET2 Mutations in a Cohort of Patients with Myeloproliferative Neoplasms Lacking a Molecular Marker.

The myeloproliferative neoplasms (MPNs) include different diseases presenting several mutations in variable frequency. The JAK2V617F mutation is present in 90-95% Polycythemia Vera (PV), 50-60% Essential Thrombocythemia (ET) and 50-60% Primary Myelofibrosis (PMF) patients. In addition, JAK2 exon 12 mutations are observed in 1-3% of PV patients and mutations in the thrombopoietin receptor gene (c-MPL) (S505N, W515K/L) are present in a 5-9% of PMF and in a 1-4% of ET patients.

Recently, acquired mutations of the Ten-Eleven Translocation (TET) 2 gene, have been reported in about 14% of sporadic MPNs. TET2 mutations may precede the acquisition of JAK2V617F predisposing to a MPN development. However, the incidence of TET2 mutations in patients lacking the JAK2V617F mutation has not been extensively studied.

To analyze the incidence of TET2 mutations in a cohort of MPN patients negative for JAK2V617F, JAK2 exon 12 mutations and c-MPL exon 10 mutations (S505N or W515K/L).

From a whole cohort of 241 patients with MPN (93 PV, 16 PMF and 132 ET) we excluded those patients positive for JAK2V617F (determined by quantitative allele-specific PCR), JAK2 exon 12 mutations or c-MPL exon 10 mutations (S505N or W515K/L) (analyzed by direct sequencing). We analyzed the TET2 gene in 5 PV, 5 PMF and 53 ET patients lacking any of the aforementioned molecular markers.

The mutational analysis of the coding sequence of TET2 was performed by direct sequencing using cDNA from granulocytes. In 13 patients, DNA from T lymphocytes was obtained to indentify the presence of single nucleotide polymorphisms (SNPs) in germline DNA.

Sixty-three patients were screened for mutations in the whole coding sequence of the TET2 gene. Only 3 ET patients (4.7%) presented deleterious mutations in the TET2 gene. The three distinct TET2 mutations were: Q706X, S1848X and V1395_R1400delinsR. In 48 out of 63 (76.1%) patients we observed a total of 13 different missense mutations and 2 silent mutations in the coding sequence of the gene. The most frequent missense mutation was the I1762V which was detected in 27 patients.

In 13 patients whose matched normal DNA was available, we analyzed the presence of missense mutations being all of them present in the control DNA suggesting that they were SNPs and not acquired mutations.

The two nonsense mutations (Q706X and S1848X), were not present in matched normal tissue indicating that these mutations were somatically acquired in myeloid cells.

TET2 pathogenic mutations are infrequent (<5%) in myeloproliferative neoplasms negative for JAKV617F, JAK2 exon 12 and c-MPL (S505, W515K/L) gene mutations.

The role and the biological significance of missense mutations in the coding sequence of TET2 has to be elucidated.

Fellowship FI2008 (AGAUR) to LMM-A, FIS EC07/90791

No relevant conflicts of interest to declare.