Achondroplasia (MIM 100800) is the most common non-lethal skeletal dysplasia. Its
incidence is between one in 10 000 and one in 30 000. The phenotype is characterized by
rhizomelic disproportionate short stature, enlarged head, midface hypoplasia, short hands
and lordotic lumbar spine, associated with normal cognitive development. This autosomal-
dominant disorder is caused by a gain-of-function mutation in the gene encoding the type 3
receptor for fibroblast growth factor (FGFR3); in more than 95% of cases, the mutation is …