Moreover, according to source of controls, signficant association of MMP-9 -1562C/T with COPD risk was revealed in the subgroup with smoker-based controls in the additive (OR:1.71, 95% CI: 1.42–2.07; p<0.00001) (Figure 2A) and dominant (OR:1.92, 95% CI:1.34–2.76; p = 0.0004) (Figure 2B) genetic models, while there was no association between MMP-1 -1607G/GG and COPD risk. Here, MMP9 is linked to chronic obstructive pulmonary disease.