ADRB2 and asthma: ADRB2 gene is a 1200 bp intron-free gene located in the 5q31-q32 asthma susceptibility fragment [1, 2], encoding beta-2-adrenergic receptor (β2-AR), a member of the G protein-coupled transmembrane receptor superfamily, which can specifically bind catecholamine and other endogenous ligands and be activated by their agonists to produce a series of biological effects [3, 4].