MUC4 and chronic bronchitis: The most relevant links are found in cluster 1, and it involves mucins; the diseases associated include lung and intestinal adenocarcinomas (MUC, MUC1, MUC2, MUC4, MUC5AC/B), diverticulosis (MUC1, MUC3, MUC4, MUC6), cystic fibrosis (MUC, MUC7), chronic bronchitis, breast cancer (MUC1), and Kartagener’s syndrome (bronchiectasis) (MUC).