EXT2 is a glycosyltransferase that functions as part of the EXT1-EXT2 heterodimeric heparan sulfate polymerase complex 1. Within this complex, EXT2 carries glucuronosyl-N-acetylglucosaminyl-proteoglycan 4-alpha-N-acetylglucosaminyltransferase activity, catalyzing the alternating transfer of GlcA and GlcNAc residues to elongate the heparan sulfate glycan backbone 1. Both EXT1 and EXT2 are required for full polymerase activity 1. Heparan sulfate proteoglycans are essential extracellular matrix components regulating tissue homeostasis and signaling 23. EXT2 dysfunction is associated with hereditary multiple exostoses 2 and seizures-scoliosis-macrocephaly/microcephaly syndrome. Additionally, EXT2 has emerged as a disease-relevant antigen in membranous nephropathy (MN), an autoimmune kidney disease causing nephrotic syndrome 45. EXT1/EXT2-associated MN represents approximately 5-10% of primary MN cases in PLA2R-negative patients and shows distinct clinical features including frequent autoimmune disease associations 46. EXT2 also plays roles in heparan sulfate biosynthesis pathways critical for influenza A virus internalization 7. Recent discoveries of EXT2-targeted therapeutics and improved diagnostic methods via mass spectrometry have enhanced clinical relevance for EXT2-associated diseases.