Apert syndrome (OMIM 101200) is characterized by premature closing of the sutures between the bones of the skull (craniosynostosis) due to gain of function mutations in the receptor tyrosine kinase fibroblast growth factor receptor 2 gene (FGFR2), one of four such receptors (FGFR1-4). Here, FGFR1 is linked to craniosynostosis.