Myeloproliferative disorders form a range of haematological
malignant diseases, with three main members: polycythaemia vera,
essential thrombocythaemia, and idiopathic myelofibrosis. The
disorders are characterised by overactive production of blood
cells and can lead to thrombosis, haemorrhage or acute myeloid
leukaemia. The absence of a definitive diagnostic test and the
scarcity of randomised clinical trials make management of these
diseases especially challenging. Tony Green (Cambridge Institute
for Medical Research, UK) and colleagues analysed a candidate
gene called JAK2 in 140 patients with myeloproliferative
disorders from haematological clinics in the UK. They also took
control DNA samples from a population of patients with type 1
diabetes. A single point mutation was identified in the JAK2
gene in 71 (97%) of 73 patients with polycythaemia vera, 29
(57%) of 51 with essential thrombocythaemia, and eight (50%) of
16 with idiopathic myelofibrosis. The mutation was not detected
in any of the controls. Di