UGT1A1 and chronic obstructive pulmonary disease: For the first ranked candidate gene, UGT1A1, its low expression was found to play a protective role in COPD since several studies has found that the enzyme uridine diphosphate glucuronosyltransferase polypeptide 1A1, encoded by gene UGT1A1, was responsible for clearing bilirubin from the blood, whereas higher bilirubin concentrations were associated with a lower risk of acute exacerbations of COPD [21–23].