Several human skeletal dysplasias are caused by gain-of-function mutations in FGFR1, FGFR2 and FGFR3. Activating mutations located in the extracellular ligand binding domain were found in FGFR1 and FGFR2 associated with Pfeiffer, Crouzon, Jackson-Weiss and Apert syndromes and in the FGFR2 kinase domain associated with Pfeiffer and Crouzon syndromes. This evidence concerns the gene FGFR3 and Crouzon disease.