FGFR2 has two naturally occurring isoforms, FGFR2IIIb and FGFR2IIIc, created by splicing of the third immunoglobulin-like domain. FGFR2IIIb is predominantly found in ectoderm derived tissues and endothelial organ lining, i.e. skin and internal organs.[8] FGFR2IIIc is found in mesenchyme, which includes craniofacial bone and for this reason the mutations of this gene and isoform are associated with craniosynostosis.