B3GNT4 (UDP-GlcNAc:betaGal beta-1,3-N-acetylglucosaminyltransferase 4) is a Golgi-localized glycosyltransferase that catalyzes beta-1,3-N-acetylglucosamine transfer to galactose residues, playing a central role in poly-N-acetyllactosamine and keratan sulfate proteoglycan biosynthesis 1. The enzyme functions in glycosphingolipid biosynthesis, a pathway critical for generating cell membrane glycoconjugates that serve as cellular receptors and signaling molecules 2. B3GNT4 pathogenic variants cause severe clinical disease. A homozygous c.478G>T (p.G160W) mutation in B3GNT4 produces an atypical glycosylation disorder manifesting as late-onset, progressive brain atrophy and muscular dystrophy, representing the first documented disease associated with B3GNT4 among the seven B3GNT galactosyltransferases 1. The gene is upregulated during norovirus infection in oysters, suggesting involvement in HBGA-like molecule synthesis that facilitates viral concentration 2. B3GNT4 variants associate with serum urate concentrations and gout susceptibility, highlighting metabolic roles beyond structural glycosylation 3. In cancer contexts, B3GNT4 participates in glyco-risk models predicting immunotherapy response in colorectal cancer and genomic instability in both lung and colon adenocarcinomas 4, 5. A B3GNT4 polymorphism (rs7136356) showed significant association with age-related cataract in Korean populations 6.