Involved in the synthesis of the Sd(a) antigen (Sia-alpha2,3-[GalNAc-beta1,4]Gal-beta1,4-GlcNAc), a carbohydrate determinant expressed on erythrocytes, the colonic mucosa and other tissues. Transfers a beta-1,4-linked GalNAc to the galactose residue of an alpha-2,3-sialylated chain. Protein modification; protein glycosylation. Widely expressed. Highly expressed in colon and to a lesser extent in kidney, stomach, ileum and rectum. The Sd(a) antigen on red blood cells defines the SID blood group system. There is considerable variability in the strength of antigen expression, ranging from ordinary Sd(a+) to strong Sd(a++) expression [MIM:615018]. Lack of Sd(a) antigen results in the Sd(a-) phenotype, due to genetic variants in B4GALNT2. The gene represented in this entry is involved in disease pathogenesis. Belongs to the glycosyltransferase 2 family. Beta-1,4 N-acetylgalactosaminyltransferase 2