CYP2E1 and chronic obstructive pulmonary disease: Apart from recognized deficiency of alpha1antitrypsin [9], genomics in COPD found that other gene alleles, such as IREB2[11], CYP2E1 and NAT2[12], CYP1A1, CYP1A2 and CYBA[13], TNF-α [14] were associated with COPD susceptibility.