Absence of Cytogenetic Abnormalities of PRV-1, TPO and C-MPL Genes Detected by Fluorescence In Situ Hybridization in Essential Thrombocythemia.

Introduction. Essential thrombocythemia (ET) is a chronic myeloproliferative disorder (CMPD) with heterogeneous features and no specific diagnostic markers. Consequently, its diagnosis is based on exclusion of other CMPD and secondary thrombocytosis. The role of PRV-1 (Polycythemia rubra vera-1), TPO (Thrombopoietin) and c-Mpl (Myeloproliferative leukemia virus oncogene) in ET pathogenesis has been studied in order to find new molecular targets which would help in ET diagnosis. PRV-1 gene is overexpressed in granulocytes from polycythemia vera (PV) and in some ET patients. TPO serum levels are not diagnostically useful and c-Mpl expression in megakaryocytes and platelets are generally decreased in ET. Mutations in TPO and c-MPL genes have been detected in familial thrombocythemia, but not in patients with acquired ET. The aim of the present study was to analyse PRV-1, TPO and c-MPL genes status by fluorescence in situ hybridization (FISH) technique in order to find new molecular markers in ET patients.

Patients and Methods. Thirty bone marrow samples of ET patients (7M/23F) diagnozed by PVSG criteria with a normal karyotype and 10 bone marrow samples of normal healthy donors were included in the study. All samples were studied by three locus-specific probes for PRV-1, TPO and c-MPL genes as follows: 1. PRV-1 gene (BAC RP11-160A19, 157 Kb, located at 19q13.12-2) labeled in red cohybridized with the 19p telomeric probe (D19S238E, Vysis) labeled in green. 2. TPO gene (BAC RP11-45NP16, 183 Kb, located at 3q27) labeled in green cohybridized with the centromeric probe for chromosome 3 (D3Z1, Vysis) labeled in red. 3. c-MPL gene (BAC RP11-297L5, 190 Kb, located at 1p34) labeled in green cohybridized with the centromeric probe for chromosome 1 (D1Z5, Vysis) labeled in orange. A minimum of 100 interphase nuclei were analyzed.

Results. FISH study showed no PRV-1, TPO and c-MPL cytogenetic abnormalities in any of the analyzed cases, except for one patient in which 21% of interphase nuclei presented a trisomy for the TPO gene region. The monosomy and trisomy thresholds were 6.1% and 4.7% for PRV-1, 4.9% and 3.4% for TPO, and 5.4% and 3.71% for c-MPL, respectively.

Conclusions. Our results suggest a lack of structural and numerical rearrangements of PRV-1, TPO and c-MPL genes in ET patients. The PRV-1 gene FISH results are in line with the previously reported by Najfeld et al (