Abstract

One of the major genetic insights into the pathogenesis of polycythaemia vera included the identification of the somatic point gain-of-function mutations in Janus kinase 2 gene—first JAK2V617F on exon 14, present in 95%–97% of the cases, and later on exon 12. In the literature, we can find some reported studies where different exon 12 mutations are identified. Unlike patients with JAK2V617F mutation in exon 14, the mutation at exon 12 is not usually associated with an increase in the three haematopoietic series (erythrocytosis, leucocytosis and thrombocytosis). It appears to be associated with a distinct syndrome, mostly characterised by isolated and more marked erythrocytosis, independently of the mutational variant. We report here the case of a patient who is JAK2exon 12 positive, presenting a novel mutation—c.1605G>T (p.Met535Ile)—associated with c.1612C>T (p.His538Tyr) mutation previously described, evidencing an atypical clinical phenotype.