New TET2 gene mutations in patients with myeloproliferative neoplasms and splanchnic vein thrombosis.

Abstract

The pathogenesis of venous thrombosis is multifactorial and generally involves both acquired and genetic factors. Very recently, acquired somatic mutations in TET2 have been found in patients with a spectrum of myeloid malignancies that are characterized by dysplasia, myeloproliferation, and acute leukemia [1-4]. TET2 mutations have been identified in a high proportion of patients with JAK2 V617F-positive and JAK2 V617F-negative myeloproliferative neoplasms (MPNs), suggesting that the occurrence of TET2 mutations may represent an early event in the pathogenesis of the disease [5]. MPN, whether overt or latent, represents a major intrinsic factor for the development of thrombosis in the portal, mesenteric or hepatic vasculature [6, 7]. Venous thrombosis significantly affects the morbidity and mortality of MPN patients, and is associated with severe organ damage and a high mortality rate [8]. We have investigated the TET2 gene locus for mutations in 23 unrelated non-cirrhotic patients with the JAK2 V617F mutation who presented with a splanchnic venous thrombosis diagnosed and followed up at the Gastroenterology Unit of the ‘A. Cardarelli’ Hospital, Naples. In three of these patients, a previously unreported TET2 mutation was found. The patients included an 85-year-old man with a mesenteric venous thrombosis (no. 1), an 80-year-old man with both portal and mesenteric venous thromboses (no. 2), and a 50-year-old man with splenic venous thrombosis (no. 3; Table 1). After approval of the local Ethics Committee had been obtained, the study was performed according to the Principles of the Declaration of Helsinki; informed consent was obtained. Venous thromboses were diagnosed by Doppler ultrasonography, spiral computed tomography, or magnetic resonance imaging, as required during the routine diagnostic work-up. MPNs were diagnosed according to established criteria [9]. DNA was extracted from peripheral blood leukocytes according to standard protocols, and amplification of all coding regions of TET2 and intron–exon boundaries was achieved using sense and antisense oligonucleotides designed and numbered on the basis of the known sequence of the TET2 gene locus (GenBank accession number NM_001127208). Amplified DNA fragments were subjected to direct cycle sequence analysis using an ABI PRISM 3100 Genetic Analyzer sequencer (PE Biosystems, Foster City, CA, USA). Gene sequencing of the TET2 gene locus showed previously unreported heterozygous deletions, in exon 3 [F572fsX7 (c.2102delT; no. 1) and Q642fsX57 (c.2311delA; no. 2)] and in exon 11 [E1555fsX22 (c.5050delAG; no. 3]. No other acquired or genetic thrombophilic risk factors or cytogenetic abnormalities were identified in these patients. The types of mutation that we identified support the contention that TET2 is a tumor suppressor gene, and supports the concept of haploinsufficiency exerted by dominant-negative mutant TET2. Only patient no. 3 exhibited overt MPN; the others developed MPN years after their venous thrombosis (Table 1). These findings confirm that MPN is a complex multifactorial disease. Both TET2 and JAK2 mutations are observed in a range of patients with phenotypically different diseases, the former being an early event and the latter a subsequent acquisition in MPN. Our findings do not exclude the possibility that an additional genetic ‘hit’ is necessary for the development of overt MPN. In keeping with this, because some of the patients who presented with splanchnic venous thrombosis did not suffer from an overt myeloproliferative disorder [10], our data suggest that, independently of the JAK2 V617F mutation, screening for TET2 mutations may be useful for identifying patients who should be carefully monitored for the subsequent development of an overt disease.