MUC5AC and atrial fibrillation: The differentially expressed genes in persistent atrial fibrillation compared with normal atrial fibrillation mainly involved neuroactive ligand-receptor interactions, tight junctions, complement and coagulation cascades, mucin-type O-glycan biosynthesis, calcium signaling pathways, endocrine, and other factors regulating calcium reabsorption, glycosaminoglycan biosynthesis-heparan/heparin sulfate, amyotrophic lateral sclerosis (ALS), cGMP-PKG signaling pathway, and retinol metabolism (Figure 3D).