It is widely accepted that EPHX1 play a dual role in both the activation and the detoxification of PAHs and aromatic amines.[19] Variations of EPHX1 gene may alter enzymatic function,[20] leading to several diseases such as cancers and birth defects.[21–23] Such traits were mainly manifested in the presence of exogenous substance (such as tobacco smoke by-products) that cross the placenta,[24] but there is little evidence regarding whether maternal EPHX1 gene polymorphisms interact with PAHs exposure in susceptibility to CHDs. The gene discussed is EPHX1; the disease is cancer.