PDE4D and childhood onset asthma: On the other hand, interleukin‐21 (IL‐21), Major Histocompatibility Complex class I polypeptide‐related sequence B (MICB), cAMP‐specific 3′,5′‐cyclic phosphodiesterase 4D (PDE4D), Rac GTPase‐activating protein 1 (RGAP1), Toll‐like receptor 4: Lymphocyte antigen 96 complex (TLR4), Ubiquitin carboxyl‐terminal hydrolase 25 (UBP25), and Carbonyl reductase [NADPH] 1 (CBR1) were associated with lower risk of childhood asthma.