Somatic variant p.Val617Phe and variants in exon 12 of the JAK2 gene are the reason for the development of somatic erythrocytosis also termed polycythemia vera (PV) (OMIM ID: 263300) in 98% of erythrocytosis cases (Baxter et al., 2005; Scott et al., 2007; Bento, 2018). The gene discussed is JAK2; the disease is primary familial polycythemia due to EPO receptor mutation.