HSPGs bind to and modulate the activity of Indian hedgehog (Ihh), which is expressed in prehypertrophic chondrocytes and regulates chondrocyte maturation, and the abnormal modulation of the tightly regulated Ihh/parathyroid hormone related peptide (PTHrP)-negative feedback loop has been proposed as a molecular model of osteochondroma formation in multiple hereditary exostoses [36]. Here, IHH is linked to exostosis.