Multiple studies have demonstrated that TNF-α inhibits erythropoiesis and causes anemia in human.34, 38, 39, 40, 41 Moreover, TNF-α can induce cell death of erythroid cells via caspase-mediated cleavage of the master regulator of erythropoiesis, GATA1.9, 15, 42, 43, 44 Our finding that Stk40 deletion in the fetal liver causes aberrant activation of TNF-α signaling supports the idea that Stk40 plays an important role in repressing TNF-α signaling activation. Here, TNF is linked to anemia.