EFNB1 and craniosynostosis: Other forms of craniosynostosis are genetic syndromes caused by genetic mutations in fibroblast growth factor receptors (FGFRs), TWIST1, EFNB1, TCF12, MSX2, or ERF. 3 Syndromic craniosynostosis is characterized by complex craniofacial deformities with or without malformation of the extremities and neurocognitive defects3.