Future studies providing a clearer understanding of how proteases regulate the expression of MUC5B will be important not only in muco-obstructive lung disease, due to its role in MCC [58], but also the wider field of CLD including in idiopathic pulmonary fibrosis where a MUC5B promoter polymorphism and impaired MCC are associated with disease development [72,73]. The gene discussed is MUC5B; the disease is congenital secretory chloride diarrhea 1.