LNT; is a neutral, non-fucosylated human milk oligosaccharide. It is a tetrasaccharide formed of lacto-N-biose linked to lactose (Gal β1‑3 GlcNAc β1‑3 Gal β1‑4 Glc) (Kunz et al. 2000). Lacto-N-tetraose is always present in human milk at all stages, but concentrations are indirectly regulated by the secretor gene FUT2. This gene encodes the enzyme fucosyltransferase‑2 that adds fucose to glycans.
Women who have active Se genes (Se+) and functional fucosyltransferase‑2 are in the secretor milk groups. In these groups, average LNT concentrations are low (0.79 g/l (Thurl et al. 2017) and 0.94 g/l (Kunz et al. 2017)). This changes in the non‑secretor groups in which women do not have fucosyltransferase‑2. Here, LNT is one of the most abundant HMO isoforms with concentration of 2.92 g/l (Kunz et al. 2017). This is because fucose is not added to LNT, which would change the HMO isoform and its function to fucosylated human milk oligosaccharides.