Glycoprotein-N-acetylgalactosamine 3-beta-galactosyltransferase 1 (C1GALT1) is a glycosyltransferase that generates the core 1 O-glycan Gal-beta1-3GalNAc-alpha1-Ser/Thr (T antigen), which is a precursor for many extended O-glycans in glycoproteins [, ].