There is clear evidence for tobacco use to cause its repression [264], and in a cross-sectional study, decreased SCGB1A1 serum levels were associated with tobacco smoke induced chronic obstructive pulmonary disease [265] while smoking cessation for 3, 6 and 9 months restored SCGB1A1 level in BAL fluid [266]. This evidence concerns the gene SCGB1A1 and chronic obstructive pulmonary disease.