On the other hand, a reduced CFTR activity in the small airway was determined by transepithelial potential differences in smokers with or without COPD in comparison with healthy nonsmokers, and the difference was statistically significantly associated with symptoms of dyspnea and CB [20], although healthy cigarette smokers bearing no CFTR gene mutations also exhibited a marked decrease in CFTR function as determined by nasal potential difference (NPD) measurements [19]. The gene discussed is CFTR; the disease is chronic obstructive pulmonary disease.