Glycosylation of proteins affects cell-cell interaction, interactions with the matrix, and the functions of intracellular molecules. ST6GALNAC1 transfers a sialic acid, N-acetylneuraminic acid (NeuAc), in an alpha-2,6 linkage to O-linked GalNAc residues. The cancer-associated sialyl-Tn (sTn) antigen is formed by ST6GALNAC1-catalyzed sialylation of GalNAc residues on mucins (Ikehara et al., 1999 [PubMed 10536037]; Sewell et al., 2006 [PubMed 16319059]).[supplied by OMIM, Mar 2008].