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.

Study involvement will last for 48 weeks. There will be approximately 11 visits through week 48. Visits may take up to 2-3 hours to complete and occur every 4 weeks for the first 24 weeks, then every 12 weeks until week 48.

During each study visit, any or all of the following procedures may occur:

• List current medications and participant general health
• Obtain blood pressure, body weight, body temperature, respiratory rate and heart rate
• Measure Spleen by examination
• Obtain an abdominal MRI to evaluate spleen and any pre-existing or new blood clots
• Obtain blood samples for safety tests and to monitor kidney/liver function.
• Questionnaires for participant to complete regarding symptoms related to disease.
• Ruxolitinib dosing may be increased after 4 weeks if needed. The dose of the ruxolitinib may be reduced related to side effects.

Inclusion Criteria:

• Diagnosis of Chuvash polycythemia

Exclusion Criteria:

• Unable to comprehend or unwilling to sign an informed consent form.