B4GALNT2 encodes a glycosyltransferase that catalyzes the addition of N-acetylgalactosamine to galactose residues, synthesizing the Sd(a) histo-blood group antigen. This enzyme transfers its substrate in a beta-1,4-linkage onto sialic acid-carrying glycans present in O- and N-linked proteins and glycolipids throughout the body, including on erythrocytes, uromodulin in renal fluids, and colonic mucins. The Sd(a) antigen confers protection against influenza A virus strains by modifying host cell receptors and preventing viral entry 1. In colon cancer, B4GALNT2 expression is down-regulated and high expression correlates with improved survival 2. At the tissue level, B4GALNT2 suppresses the cancer-associated sialyl Lewis X antigens involved in metastasis 3. By contrast, in triple negative breast cancer, B4GALNT2 promotes cell proliferation, migration, and invasiveness through interaction with HLA-B protein 4. B4GALNT2 also regulates susceptibility to gastrointestinal pathogens through its effects on intestinal glycosylation and the microbiota 5, and participates in embryo implantation by facilitating blastocyst attachment to the endometrium 6. The gene produces at least two protein isoforms differing in their cytoplasmic tail length, with distinct subcellular localizations and roles in Sd(a) synthesis.