Airflow obstruction in COPD correlates with changes in mucin gene expression, increases in goblet-cell number and size (Innes et al., 2006), the occlusion of small airways with mucus (Sheehan et al., 1995), and expansion of the SMGs (Hogg, 2004; Hogg et al., 2004). This evidence concerns the gene MUC5AC and chronic obstructive pulmonary disease.