One of the genes involved in craniosynostosis syndromes is the fibroblast growth 
factor receptor 2 (FGFR2) gene, a tyrosine kinase receptor gene. Upon ligand 
binding the FGFR2 receptors dimerise, and this is followed by activation of the 
intracellular tyrosine kinase domains. This initiates a cascade of signals that 
influence cell division and differentiation. FGFR2 mutations have been found in 
the Apert, Crouzon and Pfeiffer craniosynostosis syndromes. Most mutations are 
gain of function mutations, inducing ligand-independent receptor activation or 
altered ligand binding. With the exception of Apert syndrome, there is no clear 
genotype-phenotype correlation. Many different mutations have been found in 
Pfeiffer and Crouzon syndrome, but all of the mutations occur in the same 
extracellular region of the receptor. Identical mutations have been found in 
Pfeiffer and Crouzon syndrome. So within one family, both Crouzon and Pfeiffer 
syndrome may occur. Mutations in other FGFR-genes have also been found in 
craniosynostosis syndromes.