What is the major cause of polycythemia?

Polycythemia vera, a bone marrow disorder causing abnormal increase in the number of blood cells, is related to a gene defect called JAK2V617F, according to MedlinePlus. The underlying cause of the gene defect is unknown.

Symptoms of polycythemia vera include dizziness, excess bleeding, red skin coloring and shortness of breath, says MedlinePlus. Other symptoms include an enlarged spleen and phlebitis, or inflamed veins. Physicians utilize a treatment known as phlebotomy for polycythemia. This treatment involves removing one unit of blood per week until the number of red blood cells drops to a normal level. Possible complications of polycythemia include gout, heart failure, thrombosis and acute myelogenous leukemia.