Mucus accumulation is evident across this spectrum of chronic lung diseases, including COPD, CF, bronchiectasis, and asthma, and patients with any of these conditions can regularly cough up sputum.10, 11, 12 In CF, defects in ion transport caused by mutations in the CFTR (cystic fibrosis transmembrane conductance regulator) gene causes mucus dehydration.13 Here, CFTR is linked to chronic obstructive pulmonary disease.