FUT3 is a fucosyltransferase that catalyzes the transfer of L-fucose to both type 1 and type 2 oligosaccharide chains, with preferential activity on type 1 substrates. Through this catalytic activity, FUT3 synthesizes Lewis blood group antigens (Le(a), Le(b), Le(x), and Le(y)) and related sialylated structures such as sialyl Lewis a and sialyl Lewis x, which regulate cell surface adhesion properties and E-selectin binding. Lewis-positive individuals express active FUT3, while Lewis-negative individuals carry inactive variants. In disease contexts, FUT3 polymorphisms associate with susceptibility to gastrointestinal infections: specific variants correlate with Helicobacter pylori infection in Han Chinese populations 1, and FUT3 SNPs influence lesion location in Crohn's disease 2. In gastric cancer, FUT3 promotes cell migration and invasion by synthesizing Lewis a antigens on ITGA6 and GLG1, affecting focal adhesion and intracellular vesicle distribution 3. In pancreatic ductal adenocarcinoma, FUT3 interacts with B3GNT3 to activate NF-κB signaling and autophagy, driving chemoresistance and poor survival 4. Breast cancer studies show divergent FUT3 regulation under hypoxia depending on cell type 5, and FUT3 absence associates with invasive ductal carcinoma 6. Beyond malignancy, FUT3 variants influence human milk oligosaccharide composition and infant microbiota establishment 7, and FUT3 enhances bacterial diarrhea susceptibility by activating glycosphingolipid biosynthesis and innate immune pathways 8.