FGFR1 and Crouzon syndrome: Meanwhile, the mutation of FGF receptors can cause the fusion of cranial sutures associated with several types of craniosynostosis, such as Pfeiffer, Apert, and Crouzon syndromes.18,24 A recent study showed that nerve-derived FGF signaling is indispensable for stem cell maintenance in the mouse incisor.25 Loss of FGF ligand in nerves or FGFR1 in MSCs leads to abnormal dentin formation in the mouse incisor.