Discordant distribution of JAK2V617F mutation in siblings with familial myeloproliferative disorders

The recent identification of a somatically acquired, gain-of-function mutation in Janus kinase-2, JAK2 V617F (Tefferi and Gilliland11 and references therein) in varying proportions of patients with sporadic polycythemia vera (PV) (virtually 100%), idiopathic myelofibrosis (IMF) (50%), and