AHR and asthma: ARG1 and CHIL3 are well-recognized susceptibility genes closely associated with childhood asthma that increase AHR and weaken lung function; additionally, the polymorphic and epigenetic states of ARG1 are associated with childhood asthma progression (Li et al., 2006; Ober et al., 2008; Salam et al., 2009; Cunningham et al., 2011).