Although specific EPAS1 germline mutations (c.1603A>G, c.1609G>A, c.1609G>T) and somatic mutations (c.1595A>G, c.1586T>C) lead to polycythemia and not tumorigenesis, the onset of polycythemia might itself be a precursor to multiple diseases such as Pacak–Zhuang syndrome, for example [68,173,175,176]. The gene discussed is EPAS1; the disease is polycythemia.