Finally, large-scale genome-wide association studies (GWAS) have demonstrated that genetic susceptibility to allergic asthma is also determined by complex interactions between genes involved in OS, such as glutamate cysteine ligase (GCLM), glutathione peroxidase (GPX1), catalase (CAT), myeloperoxidase (MPO), NADPH oxidase (CYBA, p22phox subunit), NAD(P)H, quinone oxidoreductase type 1 (NQO1), and microsomal epoxide hydrolase (EPHX1) [26] (Table 1). Here, MPO is linked to allergic asthma.