Because Tie2 is also expressed in hematopoietic cells and a number of hematopoietic defects (e.g., anemia and splenomegaly) were apparent in Id cDKO mice4, the question arises as to whether hematopoietic Id contributes to the dilated cardiomyopathy observed in Id cDKO mice. The gene discussed is ID1; the disease is Splenomegaly.