Transfers 1,4-N-acetylgalactosamine (GalNAc) from UDP-GalNAc to the non-reducing end of glucuronic acid (GlcUA). Required for addition of the first GalNAc to the core tetrasaccharide linker and for elongation of chondroitin chains. Important role in chondroitin chain biosynthesis in cartilage formation and subsequent endochondral ossification (PubMed:11788602, PubMed:12163485, PubMed:12446672, PubMed:17145758, PubMed:31705726). Moreover, is involved in the metabolism of aggrecan (By similarity). 3-O-(beta-D-GlcA-(1->3)-beta-D-Gal-(1->3)-beta-D-Gal-(1->4)-beta-D-Xyl)-L-seryl-[protein] + UDP-N-acetyl-alpha-D-galactosamine = 3-O-(beta-D-GalNAc-(1->4)-beta-D-GlcA-(1->3)-beta-D-Gal-(1->3)-beta-D-Gal-(1->4)-beta-D-Xyl)-L-seryl-[protein] + H(+) + UDP Ubiquitous, with the highest levels in placenta, thyroid, bladder, prostate and adrenal gland. Detected at low levels in the other tissues examined. N-glycosylated. The disease is caused by variants affecting the gene represented in this entry. Belongs to the chondroitin N-acetylgalactosaminyltransferase family. Chondroitin beta-1,4-N-acetylgalactosaminyltransferase 1