Pfeiffer syndrome (associated with mutations in the FGFR1 and 2 gene) is a syndromic form of craniosynostosis characterised by the association of craniosynostosis. Often pansynostosis. Severe midface hypoplasia. Broad and deviated thumbs and big toes, and partial syndactyly of the fingers and toes. Hydrocephaly may be found occasionally, along with severe ocular proptosis, ankylosed elbows.