Some studies have identified DNA as the main macromolecular constituent of CF sputum, and suggested that it may play a more significant role in defining its biophysical properties.38, 39 Moreover, it has been reported that mucin levels in CF sputum are decreased compared with those of healthy individuals.40 However, these early reports were based on sputum from patients chronically infected with P. aeruginosa. The gene discussed is MUC5AC; the disease is cystic fibrosis.