Synchondrosis fusion contributes to the progression of postnatal craniofacial dysmorphology in syndromic craniosynostosis.

Syndromic craniosynostosis (CS) patients exhibit early, bony fusion of calvarial sutures and cranial synchondroses, resulting in craniofacial dysmorphology. In this study, we chronologically evaluated skull morphology change after abnormal fusion of the sutures and synchondroses in mouse models of syndromic CS for further understanding of the disease. We found fusion of the inter-sphenoid synchondrosis (ISS) in Apert syndrome model mice (Fgfr2 ) around 3 weeks old as seen in Crouzon syndrome model mice (Fgfr2c ). We then examined ontogenic trajectories of CS mouse models after 3 weeks of age using geometric morphometrics analyses. Antero-ventral growth of the face was affected in Fgfr2 and Fgfr2c mice, while Saethre-Chotzen syndrome model mice (Twist1 ) did not show the ISS fusion and exhibited a similar growth pattern to that of control littermates. Further analysis revealed that the coronal suture synostosis in the CS mouse models induces only the brachycephalic phenotype as a shared morphological feature. Although previous studies suggest that the fusion of the facial sutures during neonatal period is associated with midface hypoplasia, the present study suggests that the progressive postnatal fusion of the cranial synchondrosis also contributes to craniofacial dysmorphology in mouse models of syndromic CS. These morphological trajectories increase our understanding of the progression of syndromic CS skull growth.