COL4A1 and chronic rhinosinusitis with nasal polyps: We found a significant reduction in COL1A1, COL4A1, COL4A2, and COL5A1 gene mRNA expression in epithelial cells from patients with CRSwNP as compared with epithelial cells from controls, with a more profound reduction in eosinophilic CRSwNP than in noneosinophilic CRSwNP (Figure 8, A–D).