**3.2 IL-13 gene**

There exist several SNPs on the *IL13* gene. Thus far, two of them (Arg110Gln, also referred to as Arg130Gln or G4257A; and -1055C/T, also referred to as -1111C/T or -1024C/T) are reported to be associated with atopy or AD. We and other groups reported the genetic association of Arg110Gln with bronchial asthma (27), serum IgE levels (28, 29), and AD (29). This SNP causes exchange of arginine at the 110 (130) amino acid for glutamine. Several functional differences between the arginine type and the glutamine type have been demonstrated (30-32): (1) The glutamine type has lower affinity with the IL-13R α2 chain, a decoy receptor for IL-13, than the arginine type. (2) The glutamine type has enhanced stability over the arginine type (3). The glutamine type transduces a stronger signal via IL-13Rα1, a functional receptor for IL-13, than the arginine type. All of these results suggest that the glutamine type acts more potently *in vivo* than the arginine type. It has been reproducibly demonstrated that this SNP is genetically associated with serum total IgE levels (33-35), specific anti-allergen IgE (33, 35), or AD (36).

