GALNT13 (polypeptide N-acetylgalactosaminyltransferase 13) is a Golgi-localized glycosyltransferase that catalyzes O-linked glycosylation by transferring N-acetylgalactosamine (GalNAc) to serine and threonine residues in mucin-type proteins 1. The enzyme can glycosylate both unmodified peptides and pre-glycosylated substrates, including MUC5AC, demonstrating sequential glycosylation capacity. GALNT13 is specifically expressed in pineal gland tissue, where a primate-specific long terminal repeat retrotransposon serves as its promoter 1. In disease contexts, GALNT13 dysregulation associates with multiple pathologies: damaging variants (R185C, L405Q) located in the substrate-binding site are linked to familial glioma susceptibility in a polygenic inheritance pattern 2. The gene is upregulated as a molecular marker of bone marrow dissemination in stage 4 neuroblastoma, with GALNT13 expression correlating strongly with poor clinical outcomes and minimal residual disease 3. Additionally, genome-wide association studies identified GALNT13 variants associated with melatonin secretion levels 4 and athletic performance 5. In silico analyses predict that missense mutations in GALNT13 cause significant functional impairment and disease susceptibility 6. GALNT13 deletion (2q23.3q24.1) contributes to neurological involvement in genomic disorders 7.