In addition, MUC5AC expression in COPD patients correlated negatively with airway obstruction in terms of FEV1 and FEV1/FVC ratio (Fig. E3,A,B) (while β-tubulin IV in current and former smokers negatively correlated with pack years (Fig. E3,C). The gene discussed is MUC5AC; the disease is chronic obstructive pulmonary disease.