EXT1 is a glycosyltransferase that functions as part of a heterodimeric heparan sulfate polymerase complex with EXT2 1. Within this complex, EXT1 catalyzes the transfer of N-acetylglucosamine and glucuronic acid residues to elongate the heparan sulfate glycan backbone 1. Specifically, EXT1 bears N-acetylglucosaminyl-proteoglycan 4-beta-glucuronosyltransferase activity while EXT2 carries complementary activity, with both enzymes required for full polymerase function 1. Heparan sulfate proteoglycans are ubiquitous extracellular matrix components essential for tissue homeostasis and signaling 2. EXT1 mutations are associated with hereditary multiple exostoses, a skeletal disorder, and chondrosarcoma development. Beyond orthopedic disease, EXT1 and EXT2 have emerged as novel target antigens in membranous nephropathy, an autoimmune kidney disease causing nephrotic syndrome 3. In approximately 5-15% of PLA2R-negative membranous nephropathy cases, EXT1/EXT2 accumulate along the glomerular basement membrane as immune complex targets, often associated with lupus and other autoimmune features 34. Additionally, EXT1 participates in heparan sulfate biosynthesis pathways critical for cellular processes including viral entry mechanisms 5.