However, in muco-obstructive disease [asthma, cystic fibrosis (CF) or chronic obstructive pulmonary disease (COPD)], the mucin content of mucus increases (3–9% [60]), which, coupled with a reduction in water content to ≥90%, results in impaired MCC [61–63]. This evidence concerns the gene MUC5AC and cystic fibrosis.