Chuvash polycythemia (CP) is a rare form of congenital polycythemia caused by mutations in the VHL gene. Currently, there are no therapies that have proven effective for CP. Recent studies have demonstrated that VHL (von Hippel-Lindau tumor suppressor) regulates the activity of JAK2 (Janus kinase 2). In mouse models, inhibition of JAK2 reverses the CP phenotype. Therefore, the investigators hypothesize that JAK2 inhibition may have significant clinical benefits for CP patients.