FGFR2 and syndromic craniosynostosis: However, two different diagnostic labs were unable to identify any pathogenic variants after DNA sequence analysis of the IIIa and IIIc exons of FGFR2. Further DNA sequence analysis of additional exons of FGFR2, and other genes in which mutations have been identified in craniosynostosis syndromes (FGFR1, FGFR3 and TWIST1) was also negative.