ADRB2 and asthma: In particular, variants of interleukin (IL)-4, IL-4RA, IL-13, β-adrenergic receptor (β-AR), tumor necrosis factor (TNF)-α, human leukocyte antigen (HLA)-DRB1, DQB1, the β-subunit of the high-affinity IgE receptor (FceRI), CD14, a disintegrin and a metalloproteinase 33 (ADAM33) genes have been consistently associated with asthma-related phenotypes in independent studies [22, 23].