A knock-in mouse model by inserting an internal tandem duplication mutation into the JM domain of murine FLT3 developed the myeloproliferative disease (characterized by splenomegaly and leukocytosis with myeloid lineage cell expansion) by inserting an ITD mutation into the JM domain of murine FLT3 [45]. The gene discussed is FLT3; the disease is Increased total leukocyte count.