For example, genes in the 5q31-5q33 region code for Th2-type cytokines (IL-4, IL-13, which regulate B cell heavy-chain class-switching to IgE production) [10] and ADRB2 (which mediates airway smooth muscle relaxation and protects against bronchial hyperreactivity) [11,12]. Here, IL4 is linked to asthma.