Philadelphia-negative chronic myeloproliferative disorders in children

Philadelphia-negative chronic myeloproliferative disorders (Ph-MPDs) are clonal haematopoietic disorders typically found in medianadvanced age. The recently discovered acquired JAK2V617F mutation and other somatic mutations in JAK2, TPO, MPL and EPO-R in the myeloid cells of these patients are now considered specific biological markers, and their presence is considered a main diagnostic criterion of these diseases. Ph-MPD are extremely rare in children and need to be distinguished from other more common causes of thrombocytosis and erythrocytosis. Essential thrombocythaemia (ET) is the less rare Ph-MPD, while polycythaemia vera (PV) and primary myelofibrosis (PMF) are occasional findings in paediatrics. In this group of patients the incidence of haemorrhagic and thrombotic complications, as well as transformation into MF and acute leukaemia, seem to be rarer than in adults. Moreover, the biological markers found in adults with Ph-MPDs are not as common in paediatric cases, and familial forms are relatively frequent. Therefore, the tests used in adults are not exhaustive for most children. Because gene mutations are detectable in a minority of paediatric cases, new markers are needed to better understand such cases. Therapy is devoted to reducing symptoms, not improving collateral drug effects. New drugs targeting the JAK2 molecule are under development and open new possibilities in the treatment of these rare diseases.