GALNT1 (polypeptide N-acetylgalactosaminyltransferase 1) catalyzes the initial transfer of N-acetyl-D-galactosamine to serine or threonine residues on protein substrates, initiating O-linked oligosaccharide biosynthesis 12. The enzyme exhibits broad substrate specificity, including mucin-derived peptides 2, and localizes to the Golgi apparatus and endoplasmic reticulum [GO annotations]. GALNT1 is frequently upregulated in multiple human cancers. In hepatocellular carcinoma, elevated GALNT1 promotes cell migration and invasion through EGFR O-glycosylation and activation, with poor survival correlation 3. Similarly, GALNT1 overexpression in gastric cancer enhances malignancy via aberrant CD44 O-glycosylation, activating Wnt/β-catenin signaling 4. In bladder cancer, GALNT1-mediated SHH glycosylation maintains cancer stem cell self-renewal and tumor-initiating capacity 5. GALNT1 expression is modulated by the LAMTOR5/c-Jun/c-Src axis in breast cancer metastasis 6. Beyond oncology, GALNT1 is essential for normal heart valve development; Galnt1-null mice exhibit congenital valve defects and compromised cardiac function due to aberrant extracellular matrix remodeling 7. Additionally, let-7i-5p-mediated GALNT1 suppression aggravates renal fibrosis and inflammation 8, and elevated plasma GALNT1 predicts visuospatial cognitive decline 9.