What are MPNs?

Myeloproliferative neoplasms (MPN), known in the past as myeloproliferative disorders (MPDs), are classified as rare since less than 1 in 50,000 people develop them. They are chronic blood conditions which are more common in adults over the age of 60, but will sometimes also be found in children.

There are three major disorders which comprise the MPNs, these are;

  1. Essential thrombocythemia (ET)
  2. Polycythemia vera (PV)
  3. Primary myelofibrosis (MF)

These diseases are differentiated by the major blood cell types involved. For example in ET it is the platelets and in PV it is the erythrocytes or red cells. The three MPNs (ET, PV and MF) have many features in common including their molecular origins and symptoms.

Common symptoms such as fatigue, night sweats, fever, bone pain and itching, as well as an increased chance of developing thrombosis, bleeding, and leukaemia will be seen in all three diseases. Also the three MPNs may transform over time from one type to another; most often ET to PV or ET and PV to MF.

The molecular cause that MPNs have in common is the increase in activity of a cell signaling pathway known as the JAK/STATpathway, this causes enhanced cell division and therefore increases the number of blood cells. This cell signaling abnormality is due to over activity of JAK2 (Janus kinase 2), in most patients caused by a V617F mutation in the JAK2 gene. Very recently, a mutation in the CALR gene was found to be associated with JAK2-negative ET and MF.