HS2ST1 (heparan sulfate 2-O-sulfotransferase 1) catalyzes the transfer of sulfate groups from PAPS to iduronic acid or glucuronic acid residues within heparan sulfate chains, a critical step in heparan sulfate proteoglycan biosynthesis 1. This 2-O-sulfation is essential for heparan sulfate-mediated signaling, particularly in kidney development where it facilitates communication between the ureteric bud and metanephric mesenchyme. Bi-allelic HS2ST1 mutations cause a recognizable syndrome characterized by developmental delay, corpus callosum abnormalities, skeletal dysplasia, and renal agenesis, with affected fibroblasts showing impaired FGF-2-mediated MAPK signaling 1. In cancer contexts, HS2ST1 dysregulation has complex, disease-specific effects. High HS2ST1 expression predicts poor prognosis in osteosarcoma, hepatocellular carcinoma, and breast cancer, correlating with enhanced glycolytic and invasive phenotypes 23. In breast cancer, HS2ST1 modulates cell invasiveness through altered E-cadherin and EGFR expression, reducing MAPK signaling responses to FGF-2 4. HS2ST1 also regulates tumor angiogenesis; cancer-derived exosomal miR-421 promotes angiogenesis by suppressing HS2ST1 in endothelial cells 5. Additionally, HS2ST1 expression correlates with vascular inflammation under high-salt conditions 6, highlighting its broader role in inflammatory signaling pathways.