PHENOGENETICS OF SKULL AND BRAIN INTEGRATION IN CRANIOSYNOSTOSIS

DESCRIPTION (provided by applicant): Craniosynostosis, the premature fusion of one or more cranial sutures, is a common malformation occurring in 1 out of every 2500 live births and shows marked variation of phenotypes. The skull shape in craniosynostosis can not be explained simply by the premature fusion of sutures, but involves widespread abnormal development of the head. A number of mutations have now been identified that are associated with certain clinically defined craniosynostosis conditions. Eight of the craniosynostosis disorders including Crouzon, Apert and Pfeiffer syndromes are caused by mutations in fibroblast growth factor receptors (FGFR)-1, -2 or -3. FGFR tyrosine kinases and their ligands play fundamental and widespread roles in development and are known to play a crucial role in the control of cell migration, proliferation, differentiation and survival by activation of multiple pathways and interaction among signaling pathways. Importantly, FGFRs are involved in development of the skull, meninges, and the brain. We propose a unifying study of molecular and morphological research aimed at identifying the intermediate developmental steps in the genotype-phenotype continuum of craniosynostosis. Ours is a phenogenetic approach that attempts to connect biological phenotypes with their underlying genetic processes such as regional differentiation by activation of signaling. Through a study of archived MR and CT images of humans with isolated craniosynostosis we defined phenotypic correlations of traits on skull and brain in isolated and syndromic craniosynostosis. These correlations are indicative of strong developmental associations between brain and skull. These associations will be further tested using additional 3D data from CT and MR images of cases of coronal craniosynostosis and Apert, Crouzon and Pfeiffer syndromes and micro-CT and micro-MR of two Fgfr2 mouse models for these syndromes. Using anatomical sites identified by our investigations of human skull and brain covariation as a temporal and spatial guide, we will document patterns of abnormal proliferation, differentiation, apoptosis, and Fgf/Fgfr signaling in developing cranial tissues of Fgfr2+/S252W and FgfrcC342Y/+ mutant mice at three developmental stages. Our hypothesis is that the spatiotemporal map of abnormal Fgf/Fgfr signaling in formative skull and brain is the basis for a series of developmental events that result in anomalous cellular processes local to those sites and ultimately result in the abnormal head and brain shape in craniosynostosis. Our morphological analyses will inform our molecular investigations of how two particular mutations affect phenogenetic processes to produce developmental relationships that lead to craniosynostosis phenotypes. PUBLIC HEALTH RELEVANCE: Craniosynostosis is a common malformation which is defined by the premature fusion of skull bones, most commonly those of the calvaria. Our aims are to study the integrated nature of skull and brain development in craniosynostosis using data from human populations with nonsyndromic coronal craniosynostosis and Apert, Crouzon and Pfeiffer syndrome, as well as data from mouse models for Apert and Crouzon syndrome to understand the production of the entire head in these disorders and not just the closed suture.