TNF-α is known to inhibit erythropoiesis and cause anemia in human.34 Interestingly, human STK40 was reported as a suppressor of TNF-α-induced NF-κB activation.18 Therefore, we anticipated that deletion of Stk40 might lead to over-activation of TNF-α signaling in the mouse fetal liver and thus impair erythropoiesis. Here, TNF is linked to anemia (phenotype).