Craniosynostosis is the premature fusion of one or more cranial sutures in the developing skull. If left untreated, craniosynostosis can result in developmental delays, blindness, deafness, and other impairments resulting from an increase in the intracranial pressure. In many cases, the treatment consists of complex calvarial vault reconstruction with the hope of restoring a normal skull appearance and volume. Re-synostosis, the premature re-closure following surgery, occurs in up to 40% children who undergo surgery. If this occurs, a second surgery is needed to remove portions of the fused skull in an attempt to correct the deformities and/or relieve an increase in intracranial pressure. These subsequent surgeries are associated with an incredibly high incidence of life threatening complications. To address this unmet clinical need we have developed strategies to delay the post-operative bone growth in a clinically relevant murine model of re-synostosis. The overall objective of this thesis was to develop a hydrogel based therapy to delay rapid bone regeneration in a murine model of re-synostosis. The overall hypothesis was that delivery of key BMP inhibitors involved in regulating normal suture development and regeneration will delay the rapid bone growth that in seen in a pediatric murine model of re-synostosis. The overall approach is to use micro-computed tomography (µCT) to determine the time course of suture fusion and to identify genes associated with key developmental time points, to develop a pediatric specific mouse model that displays rapid re-synostosis, and lastly to develop a hydrogel based therapy to delay the re-synostosis of this cranial defect.

Metopic synostosis is a condition in which the metopic suture of the human cranium fuses prematurely and may be related to poor behavioral inhibition leading to behaviors commonly associated with Attention-Deficit Hyperactivity Disorder (ADHD). The purpose of this project was to examine the behavior patterns among children with a history of metopic synostosis. It was hypothesized that children with a history of metopic synostosis would exhibit many of the same behavioral patterns associated with ADHD. It was also hypothesized that children with a history of simple synostosis not involving the metopic suture would not evidence this type of behavioral pattern. In order to test these hypotheses, the behavior of three groups of children was compared including (1) children who had a history of metopic synostosis (M= 7.63 years, SD = 1.92 years), (2) children who had a history of simple craniosynostosis not involving the metopic suture (M= 7.54 years, SD = 1.88 years), and (3) a group of children diagnosed with ADHD (M=7.78 year, SD = 1.87 years). It was found using the Home and School versions of the Attention Deficit Disorders Evaluation Scale (ADDES) that children with a history of metopic synostosis demonstrate significantly more behavioral disturbances than children with a history of simple craniosynostosis not involving the metopic suture. Using the BASC Teacher Rating Form it was found that children with a history of metopic synostosis have a behavior pattern similar to children diagnosed with ADHD and a dissimilar behavior pattern compared to children who have a history of craniosynostosis not involving the metopic suture. Using the BASC Parent Rating Form it was found that children with a history of metopic synostosis have a behavior pattern dissimilar to children diagnosed with ADHD and a dissimilar behavior pattern compared to children who have a history of craniosynostosis not involving the metopic suture.

This thesis further delineates the molecular genetic basis of a relatively common craniofacial condition, coronal craniosynostosis. It used whole-exome sequencing to identify novel disease genes in patients with non-syndromic coronal synostosis and negative genetic testing. Initially, 2 patients were identified with damaging, frameshift mutations in a gene not previously linked with craniosynostosis – Transcription Factor 12 (TCF12). A further intronic mutation was identified in a third patient. This gene encodes a transcription factor that dimerises with TWIST1, mutations of which cause Saethre-Chotzen syndrome, also associated with coronal synostosis. Screening 344 undiagnosed patients identified 35 further mutations, all with coronal synostosis with 14 cases arising de novo. This work was published and testing for TCF12-related craniosynostosis was translated clinically. Significant non-penetrance (60%) was identified in mutation-positive relatives and the genetic background was investigated. Firstly, analysis of parental origins of de novo mutations identified 6 of paternal origin and helped refine haplotype assignment. Secondly, haplotype analysis of TCF12-mutation carriers revealed modest correlation with phenotypic status, but this was insufficient to be useful in clinical testing. Thirdly, TCF12 haplotypes were analysed for association with non-syndromic coronal synostosis, but no significant association was found. Further exome sequencing revealed a de novo frameshift mutation in Transcription Factor 20 (TCF20) in a patient with coronal synostosis and autism, although the mutation only correlated with the latter phenotype. Analysis of 5 trios revealed a novel variant in myosin heavy chain 4 (MYH4) in 1 family, although its role in suture development is uncertain. Reviewing pooled exome data from 19 mutation-negative patients revealed no further disease genes. In summary, this thesis describes novel gene discovery, defines a new clinical entity and investigates genetic background of penetrant and non-penetrant individuals. Further exome sequencing identified another disease gene, a de novo mutation and compiled lists of damaging variants to allow future work.