Familial thrombocytosis in which the cause of the disease is a mutation in the JAK2 gene. The disease is thrombocythemia 3 (MONDO_0013794). Also known as: JAK2 familial thrombocytosis, familial thrombocytosis caused by mutation in JAK2, thrombocythemia 3, autosomal dominant, somatic mutation, thrombocythemia type 3.