PTHLH and achondroplasia: Proliferation of chondrocytes in the growth plate is upregulated by Indian hedgehog (IHH), which stimulates PTH-related protein (PTHrP), and specific bone morphogenic protein (BMP) and is repressed by the fibroblast growth factor (FGF)—FGFR3 receptor pathway (overactivation of FGFR3 results in achondroplasia).