MMP12 and pulmonary emphysema: Specifically, it was shown that elevated levels of MMP12 in the sputum are associated with emphysema severity in COPD [8, 12, 38] and that a functional variant in the MMP12 promoter (rs2276109) [25, 59] is associated with a beneficial effect on lung function in children with asthma, as well as a reduced risk for adult smokers to develop COPD [24].