[Cytogenetics and molecular genetics in myelofibrosis with myeloid metaplasia and polycythemia vera]

Myelofibrosis with myeloid metaplasia (MMM) is a rare myeloproliferative disorder (MPD) characterized by clonal proliferation of hematopoietic progenitors. 40-50% of karyotypes on blood (or more rarely on bone marrow) revealed at least one abnormality: 30% at diagnosis and 90% in blastic transformation phase. A minority of patients with newly diagnosed polycythemia vera (PV) presented chromosomal abnormalities in their myeloid cells. The most frequent visible alteration in MMM and PV is a 20q deletion, also characterized in other MPDs and myeloid malignancies. Among other chromosomal changes, deletion 13q is more common in MMM than in other MPDs, trisomy 9 and 9p alterations appear more frequent in PV. Cytogenetic studies have disclosed cryptic anomalies and pointed out the high frequency of 9p alterations. JAK2 (V617F) mutation was found in almost all PV patients and near half of MMM patients. This molecular abnormality takes an increased importance in the knowledge of the physiopathology of MPDs, particularly in PV and also in prognosis of MMM patients.