Achondroplasia is a single gene disorder caused by certain mutations in the gene on chromosome 4. The disease is described as dominant because only one copy of the gene need be mutated before symptoms develop.
The FGFR3 gene encodes the fibroblast growth factor receptor number 3. Growth factors are proteins that control cell growth and behaviour, but in order to work they must bind to receptors on the surface of responding cells. When the receptors are absent or not working properly, the growth factors cannot carry out their normal functions. The FGFR3 protein is concentrated in the cartilage and the central nervous system, so mutations in the FGFR3 gene predominantly affect these parts of the body.
Other mutations in the same gene cause more severe developmental disorders such as Crouzon syndrome, while mutations in other genes can also cause skeletal disorders – disorders such as multiple epiphyseal dysplasia and pseudoachondroplasia