The mucin genes encode epithelial glycoproteins, some of which are secreted and some membrane bound. Each of the genes contains at least one large domain of tandemly repeated sequence that encodes the peptide sequence rich in serine and/or threonine residues, which carries most of the O-linked glycosylation (Gendler and Spicer, 1995 [PubMed 7778880]).[supplied by OMIM, Aug 2008].