DEFB1 and chronic obstructive pulmonary disease: Moreover, genetic variations of DEFB1 identified in the 1654 G/A locus in the DEFB1 exon 2 coding for a valine to isoleucine substitution at position 38 (Val38Ile) and in the 668 C/G locus in 3′ flank of DEFB1 mRNA were found to be associated with COPD [5], [25].