These clinical results are supported by experimental data demonstrating (A) that elastase causes lung tissue destruction and (B) that mice deficient in Mmp12 are resistant to CS-induced emphysema (Hautamaki et al., 1997; Selman et al., 2003; Morse and Rosas, 2014; Shibata et al., 2018). The gene discussed is MMP12; the disease is pulmonary emphysema.