It was established that several gains of function mutations (activation mutation) in JAK1, JAK2, and JAK3 are entirely responsible for hematopoietic disorders such as T and B cell acute lymphocytic leukemias, acute myeloid leukemia, polycythemia vera, essential thrombocytopenia, or Hodgkin Lymphoma [65]. The gene discussed is JAK2; the disease is acquired polycythemia vera.