ADRB2 and asthma: Two polymorphisms of beta2-adrenergic receptor (β2-AR) gene, namely the substitution from arginine (Arg) to glycine (Gly) at codon 16 and from glutamine (Gln) to glutamic (Glu) at codon 27, are linked with functional changes in the β2-AR in the respiratory system even though they are not deemed to be susceptibility genes for asthma per se.