In 2007, four additional gain-of-function somatic mutations in the exon 12 of JAK2 were detected in 3% of patients with PV [84,85]: p.N542-E543del (30%), p.K539L (14%), p.E543-D544del (12%), and p.F537-K539delinsL (10%). The gene discussed is JAK2; the disease is acquired polycythemia vera.