For example, IL-13 SNP rs20541 is a common coding SNP in exon 4, which is located at position 130 and resulted in a change from G to A. IL-13 SNP rs20541 has been reported to be associated with a decrease in the affinity of IL-13 for the IL-13 receptor and an increase in the expression of IL-13 in patients with asthma [11,12]. This evidence concerns the gene IL13 and asthma.