Recently, investigators have shown that genetic factors have important influences on a patient's response to β2-AR agonists. Single nucleotide polymorphisms (SNP) at amino acid position 16 of the β2-AR gene are thought to be the most functionally relevant. A change at base 46 from adenine to guanine results in the amino acid sequence of the β2-AR containing a glycine (Gly), rather than an arginine (Arg), at amino acid position 16. Patients homozygous for Gly at this position (Gly/Gly) have been shown to have improved response to β2-AR agonist therapy when compared to children homozygous for Arginine (Arg/Arg) or heterozygous (Arg/Gly). The next most common polymorphism of the β2-AR gene, glutamine to glutamic acid at position 27 (Glu27Gln), may be associated with the development of asthma and airway hyperresponsiveness, but these relationships are less clear.