Mutations in JAK2 are primarily associated with three diseases: essential thrombocythemia, polycythemia vera and primary myelofibrosis, according to Genetics Home Reference, a service of the National Institutes of Health. These diseases are all caused by misregulated cell production; JAK2 is a protein that regulates cell growth and proliferation.
GHR states that essential thrombocythemia is caused by an overproduction of platelets, which leads to abnormal blood clotting. Polycythemia vera is characterized by the overproduction of blood cells; this creates abnormal blood clots and thicker blood, which travels more slowly and does not deliver enough oxygen to the organs, states GHR. Primary myelofibrosis causes bone marrow to be converted to scar tissue due to the overproduction of megakaryocytes, which stimulate collagen production, according to GHR.