Glycosyltransferase required for the biosynthesis of heparan-sulfate. The EXT1/EXT2 complex possesses substantially higher glycosyltransferase activity than EXT1 or EXT2 alone. Appears to be a tumor suppressor. Defects in EXT2 are a cause of hereditary multiple exostoses type 2 (EXT2). EXT is a genetically heterogeneous bone disorder caused by genes segregating on human chromosomes 8, 11, and 19 and designated EXT1, EXT2 and EXT3 respectively. EXT is a dominantly inherited skeletal disorder primarily affecting endochondral bone during growth. The disease is characterized by formation of numerous cartilage-capped, benign bone tumors (osteocartilaginous exostoses or osteochondromas) that are often accompanied by skeletal deformities and short stature. In a small percentage of cases exostoses have exhibited malignant transformation resulting in an osteosarcoma or chondrosarcoma. Osteochondromas development can also occur as a sporadic event. Defects in EXT2 are a cause of Potocki-Shaffer syndrome (POSHS). It is a contiguous gene syndrome due to proximal deletion of chromosome 11p11.2, including EXT2 and ALX4. Belongs to the glycosyltransferase 47 family. 2 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.