Growth of the normal skull vault and its alteration in craniosynostosis: insights from human genetics and experimental studies

The Intertwined Evolution and Development of Sutures and Cranial Morphology

Phenotypic variation across mammals is extensive and reflects their ecological diversification into a remarkable range of habitats on every continent and in every ocean. The skull performs many functions to enable each species to thrive within its unique ecological niche, from prey acquisition, feeding, sensory capture (supporting vision and hearing) to brain protection. Diversity of skull function is reflected by its complex and highly variable morphology. Cranial morphology can be quantified using geometric morphometric techniques to offer invaluable insights into evolutionary patterns, ecomorphology, development, taxonomy, and phylogenetics. Therefore, the skull is one of the best suited skeletal elements for developmental and evolutionary analyses. In contrast, less attention is dedicated to the fibrous sutural joints separating the cranial bones. Throughout postnatal craniofacial development, sutures function as sites of bone growth, accommodating expansion of a growing brain. As growth frontiers, cranial sutures are actively responsible for the size and shape of the cranial bones, with overall skull shape being altered by changes to both the level and time period of activity of a given cranial suture. In keeping with this, pathological premature closure of sutures postnatally causes profound misshaping of the skull (craniosynostosis). Beyond this crucial role, sutures also function postnatally to provide locomotive shock absorption, allow joint mobility during feeding, and, in later postnatal stages, suture fusion acts to protect the developed brain. All these sutural functions have a clear impact on overall cranial function, development and morphology, and highlight the importance that patterns of suture development have in shaping the diversity of cranial morphology across taxa. Here we focus on the mammalian cranial system and review the intrinsic relationship between suture development and morphology and cranial shape from an evolutionary developmental biology perspective, with a view to understanding the influence of sutures on evolutionary diversity. Future work integrating suture development into a comparative evolutionary framework will be instrumental to understanding how developmental mechanisms shaping sutures ultimately influence evolutionary diversity.

Craniofacial Development: Neural Crest in Molecular Embryology

Craniofacial development, one of the most complex sequences of developmental events in embryology, features a uniquely transient, pluripotent stem cell-like population known as the neural crest (NC). Neural crest cells (NCCs) originate from the dorsal aspect of the neural tube and migrate along pre-determined routes into the developing branchial arches and frontonasal plate. The exceptional rates of proliferation and migration of NCCs enable their diverse contribution to a wide variety of craniofacial structures. Subsequent differentiation of these cells gives rise to cartilage, bones, and a number of mesenchymally-derived tissues. Deficiencies in any stage of differentiation can result in facial clefts and abnormalities associated with craniofacial syndromes. A small number of conserved signaling pathways are involved in controlling NC differentiation and craniofacial development. They are used in a reiterated fashion to help define precise temporospatial cell and tissue formation. Although many aspects of their cellular and molecular control have yet to be described, it is clear that together they form intricately integrated signaling networks required for spatial orientation and developmental stability and plasticity, which are hallmarks of craniofacial development. Mutations that affect the functions of these signaling pathways are often directly or indirectly identified in congenital syndromes. Clinical applications of NC-derived mesenchymal stem/progenitor cells, persistent into adulthood, hold great promise for tissue repair and regeneration. Realization of NCC potential for regenerative therapies motivates understanding of the intricacies of cell communication and differentiation that underlie the complexities of NC-derived tissues.

Cranial Suture Regeneration Mitigates Skull and Neurocognitive Defects in Craniosynostosis

Craniosynostosis results from premature fusion of the cranial suture(s), which contain mesenchymal stem cells (MSCs) that are crucial for calvarial expansion in coordination with brain growth. Infants with craniosynostosis have skull dysmorphology, increased intracranial pressure, and complications such as neurocognitive impairment that compromise quality of life. Animal models recapitulating these phenotypes are lacking, hampering development of urgently needed innovative therapies. Here, we show that Twist1+/- mice with craniosynostosis have increased intracranial pressure and neurocognitive behavioral abnormalities, recapitulating features of human Saethre-Chotzen syndrome. Using a biodegradable material combined with MSCs, we successfully regenerated a functional cranial suture that corrects skull deformity, normalizes intracranial pressure, and rescues neurocognitive behavior deficits. The regenerated suture creates a niche into which endogenous MSCs migrated, sustaining calvarial bone homeostasis and repair. MSC-based cranial suture regeneration offers a paradigm shift in treatment to reverse skull and neurocognitive abnormalities in this devastating disease.

Major skull manifestations of skeletal dysplasias - pictorial essay

Skeletal dysplasias are a large group of rare conditions with widely heterogeneous manifestations and a reputation for being diagnostically difficult. Involvement of the brain and craniovertebral junction are features familiar to the paediatric neuroradiologist. Involvement of the skull itself represents an area of overlap between the domains of the neuroradiologist and the skeletal dysplasia radiologist. In this pictorial essay, we review the principal skull manifestations of skeletal dysplasias as they present to the neuroradiologist.

Genetic background dependent modifiers of craniosynostosis severity

Craniosynostosis severity varies in patients with identical genetic mutations. To understand causes of this phenotypic variation, we backcrossed the FGFR2^+/C342Y mouse model of Crouzon syndrome onto congenic C57BL/6 and BALB/c backgrounds. Coronal suture fusion was observed in C57BL/6 (88% incidence, p < .001 between genotypes) but not in BALB/c FGFR2^+/C342Y mutant mice at 3 weeks after birth, establishing that that the two models differ in phenotype severity. To begin identifying pre-existing modifiers of craniosynostosis severity, we compared transcriptome signatures of cranial tissues from C57BL/6 vs. BALB/c FGFR2^+/+ mice. We separately analyzed frontal bone with coronal suture tissue from parietal bone with sagittal suture tissues because the coronal suture but not the sagittal suture fuses in FGFR2^+/C342Y mice. The craniosynostosis associated Twist and En1 transcription factors were down-regulated, while Runx2 was up-regulated, in C57BL/6 compared to BALB/c tissues, which could predispose to craniosynostosis. Transcriptome analyses under the GO term MAPK cascade revealed that genes associated with calcium ion channels, angiogenesis, protein quality control and cell stress response were central to transcriptome differences associated with genetic background. FGFR2 and HSPA2 protein levels plus ERK1/2 activity were higher in cells isolated from C57BL/6 than BALB/c cranial tissues. Notably, the HSPA2 protein chaperone is central to craniofacial genetic epistasis, and we find that FGFR2 protein is abnormally processed in primary cells from FGFR2^+/C342Y but not FGFR2^+/+ mice. Therefore, we propose that differences in protein quality control responses may contribute to genetic background influences on craniosynostosis phenotype severity.

Nonsyndromic Craniosynostosis Is Associated with Increased Risk for Psychiatric Disorders

BACKGROUND

Craniosynostosis is one of the most common craniofacial malformations demanding surgical treatment in infancy. Data on overall psychiatric morbidity among children with nonsyndromic craniosynostosis remain limited. This study investigated the risk of psychiatric disorders in nonsyndromic craniosynostosis.

METHODS

The authors reviewed a register-based cohort of all individuals born with nonsyndromic craniosynostosis in Sweden between 1973 to 1986 and 1997 to 2012 (n = 1238). The nonsyndromic craniosynostosis cohort was compared with a matched community cohort (n = 12,380) and with unaffected full siblings (n = 1485). The authors investigated the risk of psychiatric disorders, suicide attempts, and suicides by using Cox regression adjusted for perinatal and somatic factors, season and birth year, sex, parental socioeconomic factors, and parental psychiatric disorders.

RESULTS

Children with nonsyndromic craniosynostosis had a higher risk of any psychiatric disorder (adjusted Cox-derived hazard ratio, 1.70; 95 percent CI, 1.43 to 2.02), including intellectual disability (adjusted Cox-derived hazard ratio, 4.96; 95 percent CI, 3.20 to 7.70), language disorders (adjusted Cox-derived hazard ratio, 2.36; 95 percent CI, 1.57 to 3.54), neurodevelopmental disorders (adjusted Cox-derived hazard ratio, 1.30; 95 percent CI, 1.01 to 1.69), and other psychiatric disorders (adjusted Cox-derived hazard ratio, 1.43; 95 percent CI, 1.11 to 1.85). Full siblings with nonsyndromic craniosynostosis were more likely, in the crude analyses, to be diagnosed with any psychiatric disorder, including intellectual disability, language disorders, and neurodevelopmental disorders compared with nonaffected siblings. The higher risk for any psychiatric disorder and intellectual disability remained after adjusting for confounders.

CONCLUSIONS

Children with nonsyndromic craniosynostosis demonstrated higher risks of any psychiatric disorder compared with children without nonsyndromic craniosynostosis. This risk cannot fully be explained by familial influences (i.e., genetic or environmental factors).

CLINICAL QUESTION/LEVEL OF EVIDENCE

Risk, III.

Cellular and developmental basis of orofacial clefts

During craniofacial development, defective growth and fusion of the upper lip and/or palate can cause orofacial clefts (OFCs), which are among the most common structural birth defects in humans. The developmental basis of OFCs includes morphogenesis of the upper lip, primary palate, secondary palate, and other orofacial structures, each consisting of diverse cell types originating from all three germ layers: the ectoderm, mesoderm, and endoderm. Cranial neural crest cells and orofacial epithelial cells are two major cell types that interact with various cell lineages and play key roles in orofacial development. The cellular basis of OFCs involves defective execution in any one or several of the following processes: neural crest induction, epithelial-mesenchymal transition, migration, proliferation, differentiation, apoptosis, primary cilia formation and its signaling transduction, epithelial seam formation and disappearance, periderm formation and peeling, convergence and extrusion of palatal epithelial seam cells, cell adhesion, cytoskeleton dynamics, and extracellular matrix function. The latest cellular and developmental findings may provide a basis for better understanding of the underlying genetic, epigenetic, environmental, and molecular mechanisms of OFCs.

Integrated Transcriptome and Network Analysis Reveals Spatiotemporal Dynamics of Calvarial Suturogenesis

Craniofacial abnormalities often involve sutures, the growth centers of the skull. To characterize the organization and processes governing their development, we profile the murine frontal suture, a model for sutural growth and fusion, at the tissue- and single-cell level on embryonic days (E)16.5 and E18.5. For the wild-type suture, bulk RNA sequencing (RNA-seq) analysis identifies mesenchyme-, osteogenic front-, and stage-enriched genes and biological processes, as well as alternative splicing events modifying the extracellular matrix. Single-cell RNA-seq analysis distinguishes multiple subpopulations, of which five define a mesenchyme-osteoblast differentiation trajectory and show variation along the anteroposterior axis. Similar analyses of in vivo mouse models of impaired frontal suturogenesis in Saethre-Chotzen and Apert syndromes, Twist1+/- and Fgfr2+/S252W, demonstrate distinct transcriptional changes involving angiogenesis and ribogenesis, respectively. Co-expression network analysis reveals gene expression modules from which we validate key driver genes regulating osteoblast differentiation. Our study provides a global approach to gain insights into suturogenesis.

Compound craniosynostosis, intellectual disability, and Noonan-like facial dysmorphism associated with 7q32.3-q35 deletion

OBJECTIVE

Craniosynostosis (CS) is the premature fusion of the cranial sutures, occurring either in isolated or syndromic form. Syndromic CS, which was described in over 180 genetic syndromes, accounts for 15-30% of all CS cases and usually originates from mutations within the FGFR1, FGFR2, FGFR3, and TWIST1 genes. However, causative alterations in other genes, or rarely copy number variations (CNVs) were also reported. In this article, we describe a patient with Noonan-like facial dysmorphism accompanied by intellectual disability and compound CS, involving coronal, sagittal, and squamous sutures.

METHODS

We applied karyotyping, copy number variations analysis using array comparative genomic hybridization, and microarray-based genes expresion analysis.

RESULTS

We have shown that the index carried a large and rare heterozygous deletion, which encompassed 12.782 Mb and mapped to a chromosomal region of 7q32.3-q35 (HG38 - chr7:131837067-144607071). The aberration comprised 109 protein-coding genes, including BRAF, that encodes serine/threonine-protein kinase B-Raf, being a part of the RAS/MAPK signaling pathway.

DISCUSSION

The RAS/MAPK pathway plays an essential role in human development; hence, its dysregulation not surprisingly results in severe congenital anomalies, such as phenotypically overlapping syndromes termed RASopathies. To our best knowledge, we report here the first CNV causing haploinsufficiency of BRAF, resulting in dysregulation of the RAS/MAPK cascade, and consequently, in the phenotype observed in our patient. To conclude, with this report, we have pointed to the involvement of the RAS/MAPK signaling pathway in CS development. Moreover, we have shown that the molecular analysis based on both DNA and RNA profiling, undoubtedly constitutes a comprehensive diagnostic and research strategy for elucidating a cause of genetic diseases.

Craniometric and Volumetric Analyses of Cranial Base and Cranial Vault Differences in Patients With Nonsyndromic Single-Suture Sagittal Craniosynostosis

PURPOSE

How different from "normal" are the cranial base and vault of infants with nonsyndromic, single-suture sagittal synostosis (NSSS)? This study quantitatively addresses this question utilizing computed tomography (CT) analytic technology.

METHOD

Head CT scans of infants with NSSS and normocephalic controls were analyzed using Mimics to calculate craniometric angles, distances, and segmented volumes. Craniometric measurements and asymmetry indices were compared between NSSS and control groups using linear regressions controlling for age. Ratios of anterior-, middle-, and posterior-to-total cranial vault volume were compared between groups using beta regressions controlling for age.

RESULTS

Seventeen patients with NSSS and 19 controls were identified. Cranial index and interoccipital angle were significantly smaller in NSSS compared with controls (P = 0.003 and <0.001, respectively). Right-but not left-external acoustic meatus angle and internal acoustic meatus-to-midline distance were significantly greater in NSSS than in controls (P = 0.021 and 0.016, respectively). NSSS patients and controls did not significantly differ in any asymmetry indices, except for the articular fossa angle asymmetry index (P = 0.016). Anterior vault volume proportion was greater in NSSS relative to controls (proportion ratio = 1.63, P < 0.001). NSSS trended toward a smaller posterior vault volume proportion (P = 0.068) yet did not differ in middle vault volume proportion compared with controls.

CONCLUSION

In this small study, patients with nonsyndromic, single-suture sagittal craniosynostosis had relatively similar cranial base measurements, and larger anterior vault volumes, when compared with controls. Further work is needed to confirm the possibility of rightward asymmetry of the anterior cranial base.

Viral delivery of tissue nonspecific alkaline phosphatase diminishes craniosynostosis in one of two FGFR2C342Y/+ mouse models of Crouzon syndrome

Craniosynostosis is the premature fusion of cranial bones. The goal of this study was to determine if delivery of recombinant tissue nonspecific alkaline phosphatase (TNAP) could prevent or diminish the severity of craniosynostosis in a C57BL/6 FGFR2^C342Y/+ model of neonatal onset craniosynostosis or a BALB/c FGFR2^C342Y/+ model of postnatal onset craniosynostosis. Mice were injected with a lentivirus encoding a mineral targeted form of TNAP immediately after birth. Cranial bone fusion as well as cranial bone volume, mineral content and density were assessed by micro CT. Craniofacial shape was measured with calipers. Alkaline phosphatase, alanine amino transferase (ALT) and aspartate amino transferase (AST) activity levels were measured in serum. Neonatal delivery of TNAP diminished craniosynostosis severity from 94% suture obliteration in vehicle treated mice to 67% suture obliteration in treated mice, p<0.02) and the incidence of malocclusion from 82.4% to 34.7% (p<0.03), with no effect on cranial bone in C57BL/6 FGFR2^C342Y/+ mice. In contrast, treatment with TNAP increased cranial bone volume (p< 0.01), density (p< 0.01) and mineral content (p< 0.01) as compared to vehicle treated controls, but had no effect on craniosynostosis or malocclusion in BALB/c FGFR2^C342Y/+ mice. These results indicate that postnatal recombinant TNAP enzyme therapy diminishes craniosynostosis severity in the C57BL/6 FGFR2^C342Y/+ neonatal onset mouse model of Crouzon syndrome, and that effects of exogenous TNAP are genetic background dependent.

Glycosylation of DMP1 maintains cranial sutures in mice

Craniosynostosis, a severe craniofacial developmental disease, can only be treated with surgery currently. Recent studies have shown that proteoglycans are involved in the suture development. For the bone matrix protein, dentin matrix protein 1 (DMP1), glycosylation on the N-terminal of it could generate a functional proteoglycan form of DMP1 during osteogenesis. We identified that the proteoglycan form of DMP1 (DMP1-PG) is highly expressed in mineralisation front of suture. But, the potential role of DMP1-PG in suture fusion remain unclear. To investigate the role of DMP1-PG in cranial suture fusion and craniofacial bone development. By using a DMP1 glycosylation site mutation mouse model, DMP1-S89G mice, we compared the suture development in it with control mice. We compared the suture phenotypes, bone formation rate, expression levels of bone formation markers in vivo between DMP1-S89G mice and wild-type mice. Meanwhile, cell culture and organ culture were performed to detect the differences in cell differentiation and suture fusion in vitro. Finally, chondroitin sulphate (CHS), as functional component of DMP1-PG, was employed to test whether it could delay the premature suture fusion and the abnormal differentiation of bone mesenchymal stem cells (BMSCs) of DMP1-PG mice. DMP1-S89G mice had premature closure of suture and shorter skull size. Lack of DMP1-PG accelerated bone formation in cranial suture. DMP1-PG maintained the essential stemness of BMSCs in suture through blocking the premature differentiation of BMSCs to osteoblasts. Finally, chondroitin sulphate, a major component of DMP1-PG, successfully delayed the premature suture fusion by organ culture of skull in vitro. DMP1-PG could inhibit premature fusion of cranial suture and maintain the suture through regulating the osteogenic differentiation of BMSCs.

Cranial CT scan evaluation of morphological variations and location of pterion in Pakistani male population for lateral neurosurgical approach

Objective

To determine the morphological variations and location of pterion in Pakistani male population.

Methods

This retrospective observational study was carried out in the Department of Radiology, Shifa International Hospital from December 2018 to June 2019. The sample size was calculated by Open Epi web-based calculator. Fifty-three cranial CT scans with slice thickness of 0.5mm; consecutive scans of males were randomly selected. The patients with no craniofacial fracture and ages from 25 to 45 years were included. The dataset was obtained from Toshiba Aquilion One, 360-slice MDCT. The images were imported into the imaging software PACS (WFM), and analyzed in maximum intensity projection mode with three dimensional multiplanar reconstruction viewers. Measurements were taken in lateral projections of skull in Frankfurt plane, as horizontal and vertical distance from the posterolateral margin of frontozygomatic suture to center of pterion. Vertical distance from the superior border of zygomaticotemporal arch to the center of pterion. The morphological types were also recognized.

Results

The type of pterion on right side was 94.3% sphenoparietal 5.6% epipteric whereas left side was (90.5%) sphenoparietal (3.7%) epipteric, (3.7%) stellate type, (1.8%) frontotemporal type. The mean horizontal and vertical frontozygomatic measurements on right side were 2.23 ± 0.22cm and 1.25±0.219 cm respectively. The same measurements on the left side were 2.27-±0.25 cm and 1.226-±0.22 cm respectively. The mean zygomaticotemporal measurements on the right and left sides were 3.45 ±0.29cm and 3.44 ±0.25 cm respectively. The mean distance on right and left side of skull was statistically insignificant.

Conclusion

The study provides useful data for position and location of pterion for safe neurosurgical procedures via pterion. Moreover, the knowledge about different morphological types of pterion help the radiologist to differentiate between a fracture line and normal morphological variety.

Clinical and aesthetic outcome analysis of a case series of trigonocephaly patients after early fronto-orbital advancement

The timing of operation for trigonocephaly is recommended before the age of 1 year. To evaluate the outcome of a consecutive series operated in a single centre, the current study was performed. The study cohort comprised a retrospective single-centre series of 20 patients with trigonocephaly operated before the age of 12 months. Intra- and postoperative clinical data, as well as aesthetic outcome measured by two-dimensional asymmetry index (2D AI) and correction of the curvature on lateral and pictures from above were evaluated. Furthermore, to evaluate postoperative aesthetic outcome, a new classification (Grades I-IV) was proposed. The mean age of the cohort was 7.9 months. 2D AI changed from 0.049 pre- to 0.03 postoperatively (P=0.165). The correction of the curvature in lateral pictures yielded a significant change on postoperative pictures (P=0.002) as well as on pictures from above. Using the proposed classification, 16/20 (80%) patients had a postoperative outcome of Grade I, 4/20 (20%) Grade II. In patients operated before the age of 12 months an excellent (Grade I, AI <0.03) or good aesthetic (Grade II, adequate parents' or surgeon's opinion) result could be reached in all patients.

Role of thyroid hormones in craniofacial development

The development of the craniofacial skeleton relies on complex temporospatial organization of diverse cell types by key signalling molecules. Even minor disruptions to these processes can result in deleterious consequences for the structure and function of the skull. Thyroid hormone deficiency causes delayed craniofacial and tooth development, dysplastic facial features and delayed development of the ossicles in the middle ear. Thyroid hormone excess, by contrast, accelerates development of the skull and, in severe cases, might lead to craniosynostosis with neurological sequelae and facial hypoplasia. The pathogenesis of these important abnormalities remains poorly understood and underinvestigated. The orchestration of craniofacial development and regulation of suture and synchondrosis growth is dependent on several critical signalling pathways. The underlying mechanisms by which these key pathways regulate craniofacial growth and maturation are largely unclear, but studies of single-gene disorders resulting in craniofacial malformations have identified a number of critical signalling molecules and receptors. The craniofacial consequences resulting from gain-of-function and loss-of-function mutations affecting insulin-like growth factor 1, fibroblast growth factor receptor and WNT signalling are similar to the effects of altered thyroid status and mutations affecting thyroid hormone action, suggesting that these critical pathways interact in the regulation of craniofacial development.

ROCK-TAZ signaling axis regulates mechanical tension-induced osteogenic differentiation of rat cranial sagittal suture mesenchymal stem cells

Mechanical force across sutures is able to promote suture osteogenesis. Orthodontic clinics often use this biological characteristic of sutures to treat congenital cranio-maxillofacial malformations. However, the underlying mechanisms still remain poorly understood. Craniofacial sutures provide a special growth source and support primary sites of osteogenesis. Here, we isolated rat sagittal suture cells (rSAGs), which had mesenchymal stem cell characteristics and differentiating abilities. Cells were then subjected to mechanical tension (5% elongation, 0.5 Hz; sinusoidal waveforms) showing that mechanical tension could enhance osteogenic differentiation but hardly affect proliferation of rSAGs. Besides, mechanical tension could increase Rho-associated kinase (ROCK) expression and enhance transcriptional coactivator with PDZ-binding motif (TAZ) nuclear translocation. Inhibiting ROCK expression could suppress tension-induced osteogenesis and block tension-induced upregulation of nuclear TAZ. In addition, our results indicated that TAZ had direct combination sites with runt-related transcription factor 2 (Runx2) in rSAGs, and knock-downed TAZ simultaneously decreased the expression of Runx2 no matter with or without mechanical tension. In summary, our findings demonstrated that the multipotency of rSAGs in vitro could give rise to early osteogenic differentiation under mechanical tension, which was mediated by ROCK-TAZ signal axis.

Predicting calvarial morphology in sagittal craniosynostosis

Early fusion of the sagittal suture is a clinical condition called, sagittal craniosynostosis. Calvarial reconstruction is the most common treatment option for this condition with a range of techniques being developed by different groups. Computer simulations have a huge potential to predict the calvarial growth and optimise the management of this condition. However, these models need to be validated. The aim of this study was to develop a validated patient-specific finite element model of a sagittal craniosynostosis. Here, the finite element method was used to predict the calvarial morphology of a patient based on its preoperative morphology and the planned surgical techniques. A series of sensitivity tests and hypothetical models were carried out and developed to understand the effect of various input parameters on the result. Sensitivity tests highlighted that the models are sensitive to the choice of input parameter. The hypothetical models highlighted the potential of the approach in testing different reconstruction techniques. The patient-specific model highlighted that a comparable pattern of calvarial morphology to the follow up CT data could be obtained. This study forms the foundation for further studies to use the approach described here to optimise the management of sagittal craniosynostosis.

What Do Animal Models Teach Us About Congenital Craniofacial Defects?

The formation of the head and face is a complex process which involves many different signaling cues regulating the migration, differentiation, and proliferation of the neural crest. This highly complex process is very error-prone, resulting in craniofacial defects in nearly 10,000 births in the United States annually. Due to the highly conserved mechanisms of craniofacial development, animal models are widely used to understand the pathogenesis of various human diseases and assist in the diagnosis and generation of preventative therapies and treatments. Here, we provide a brief background of craniofacial development and discuss several rare diseases affecting craniofacial bone development. We focus on rare congenital diseases of the cranial bone, facial jaw bones, and two classes of diseases, ciliopathies and RASopathies. Studying the animal models of these rare diseases sheds light not only on the etiology and pathology of each disease, but also provides meaningful insights towards the mechanisms which regulate normal development of the head and face.

Calvarial Versus Long Bone: Implications for Tailoring Skeletal Tissue Engineering

Tissue-engineered graft substitutes have shown great potential to treat large bone defects. While we usually assume that therapeutic approaches developed for appendicular bone healing could be similarly translated for application in craniofacial reconstruction and vice versa, this is not necessarily accurate. In addition to those more well-known healing-associated factors, such as age, lifestyle (e.g., nutrition and smoking), preexisting disease (e.g., diabetes), medication, and poor blood supply, the developmental origins and surrounding tissue of the wound sites can largely affect the fracture healing outcome as well as designed treatments. Therefore, the strategies developed for long bone fracture repair might not be suitable or directly applicable to skull bone repair. In this review, we discuss aspects of development, healing process, structure, and tissue engineering considerations between calvarial and long bones to assist in designing the tailored bone repair strategies. Impact Statement We summarized, in this review, the existing body of knowledge between long bone and calvarial bone with regard to their development and healing, tissue structure, and consideration of current tissue engineering strategies. By highlighting their similarities and differences, we propose that tailored tissue engineering strategies, such as scaffold features, growth factor usage, and the source of cells for tissue or region-specific bone repair, are necessary to ensure an optimized healing outcome.

Occipital hemi-bun development and shape covariation in a longitudinal extant human growth sample

OBJECTIVES

Although the homology of the Neanderthal occipital bun and anatomically modern human "hemi-bun" has long been debated, little is known about the developmental timing and patterning of these two patterns of prominent occipital squama convexity. In this study, occipital hemi-bun ontogeny and cranial shape covariation are assessed in a comparative extant human sample.

MATERIALS AND METHODS

Two-dimensional geometric morphometric methods were used to investigate hemi-bun development in a longitudinal sample of growth study cephalograms representing extant human subjects predominantly of European ancestry. Subjects were each measured at three distinct age points, ranging from 3.0 to 20.4 years, and two-block partial least squares analysis was used to assess patterns of covariation between midsagittal occipital bone morphology and other aspects of craniofacial shape.

RESULTS

Occipital hemi-bun morphology, when present, was found to develop early in ontogeny, in association with anteroposterior elongation of the frontal and parietal bones. No significant pattern of covariation was found between occipital hemi-bun shape and cranial/basicranial breadth, basicranial length, basicranial angle, or midfacial prognathism.

DISCUSSION

This study suggests that the occipital hemi-bun, at least in this extant human population, should not be considered an independent trait, as its development is closely linked to shape variation in the frontal and parietal bones. Importantly, these results suggest that occipital hemi-bun morphology is not significantly influenced by basicranial morphology during development, but instead covaries with changes in midsagittal neurocranial vault shape.

A review of the management of single-suture craniosynostosis, past, present, and future

BACKGROUND

Craniosynostosis is a condition in which 2 or more of the skull bones fuse prematurely. The spectrum of the disorder most commonly involves the closure of a single suture in the skull, but it can also involve syndromic diagnoses in which multiple skull bones and/or bones outside of the cranium are affected. Craniosynostosis can result in cosmetic deformity as well as potential limitations in brain growth and development, and the neurocognitive impact of the condition is just starting to be studied more thoroughly. Our knowledge regarding the genetics of this condition has also evolved substantially. In this review, the authors explore the medical and surgical advancements in understanding and treating this condition over the past century, with a focus on how the diagnosis and treatment have evolved.

METHODS

In this review article, the authors, who are the leaders of a craniofacial team at a major academic pediatric hospital, focus on single-suture craniosynostosis (SSC) affecting the 6 major cranial sutures and discuss the evolution of the treatment of SSC from its early history in modern medicine through the current state of the art and future trends. This discussion is based on the authors' broad experience and a comprehensive review of the literature.

SUMMARY

The management of SSC has evolved substantially over the past 100 years. There have been major advances in technology and medical knowledge that have allowed for safer treatment of this condition through the use of newer techniques and technologies in the fields of surgery, anesthesia, and critical care. The use of less invasive surgical techniques along with other innovations has led to improved outcomes in SSC patients. The future of SSC treatment will likely be guided by elucidation of the causes of neurocognitive delay in these children and assessment of how the timing and type of surgery can mitigate adverse outcomes.

Pharmacological exposures may precipitate craniosynostosis through targeted stem cell depletion

The Centers for Disease Control and Prevention, National Birth Defects Study suggests that environmental exposures including maternal thyroid diseases, maternal nicotine use, and use of selective serotonin reuptake inhibitors (SSRIs) may exacerbate incidence and or severity of craniofacial abnormalities including craniosynostosis. Premature fusion of a suture(s) of the skull defines the birth defect craniosynostosis which occurs in 1:1800–2500 births. A proposed mechanism of craniosynostosis is the disruption of proliferation and differentiation of cells in the perisutural area. Here, we hypothesize that pharmacological exposures including excess thyroid hormone, nicotine, and SSRIs lead to an alteration of stem cells within the sutures resulting in premature fusion. In utero exposure to nicotine and citalopram (SSRI) increased the risk of premature suture fusion in a wild-type murine model. Gli1⁺ stem cells were reduced, stem cell populations were depleted, and homeostasis of the suture mesenchyme was altered with exposure. Thus, although these pharmacological exposures can deplete calvarial stem cell populations leading to craniosynostosis, depletion of stem cells is not a unifying mechanism for pharmacological exposure associated craniosynostosis.

Sensitivity and specificity of magnetic resonance imaging and computed tomography for the determination of the developmental state of cranial sutures and synchondroses in the dog

BACKGROUND

During skull ontogenesis, growth centers in the skull base and calvarial bones allow gradual expansion of the cranial vault. Premature growth termination of cranial base synchondroses and/or calvarial sutures can result in devastating skull dysmorphologies. There is evidence to believe that a premature closure in one or more cranial growth centers contribute to the brachycephalic skull morphology in dogs. To provide a proof of concept for the non-invasive investigation of ontogenetic changes in cranial sutures and synchondroses in living dogs, we compared magnet resonance imaging (MRI) and computed tomography (CT) with histologic findings. Our aim was to determine the in vitro sensitivity and specificity for conventional clinical imaging methods in the assessment of cranial suture closure and synchondroses ossification in dogs.

RESULTS

The evaluation of cranial base synchondroses in MRI had a sensitivity of up to 93.1% and a specificity of 72.7% dependent on the observer. The evaluation of cranial base synchondroses in CT had a sensitivity of 92.2% and a specificity of 86.4%. Suture assessment on MRI suture assessment had a sensitivity of 82.1% dependent on the observer and a specificity of 19.3%. CT suture assessment had a sensitivity of 85.1% and a specificity of 40.4% in dependence of the observer.

CONCLUSION

Conventional cross-sectional imaging techniques (MRI and CT) allow reliable assessment of the open or closed state of synchondroses within the cranial base. In contrast CT and MRI are not suitable for a reliable assessment of the cranial sutures in dogs.

New Insights on Properties and Spatial Distributions of Skeletal Stem Cells

Skeletal stem cells (SSCs) are postnatal self-renewing, multipotent, and skeletal lineage-committed progenitors that are capable of giving rise to cartilage, bone, and bone marrow stroma including marrow adipocytes and stromal cells in vitro and in an exogenous environment after transplantation in vivo. Identifying and isolating defined SSCs as well as illuminating their spatiotemporal properties contribute to our understating of skeletal biology and pathology. In this review, we revisit skeletal stem cells identified most recently and systematically discuss their origin and distributions.

PIN1 is a new therapeutic target of craniosynostosis

Gain-of-function mutations in fibroblast growth factor receptors (FGFRs) cause congenital skeletal anomalies, including craniosynostosis (CS), which is characterized by the premature closure of craniofacial sutures. Apert syndrome (AS) is one of the severest forms of CS, and the only treatment is surgical expansion of prematurely fused sutures in infants. Previously, we demonstrated that the prolyl isomerase peptidyl-prolyl cis-trans isomerase interacting 1 (PIN1) plays a critical role in mediating FGFR signaling and that Pin1+/- mice exhibit delayed closure of cranial sutures. In this study, using both genetic and pharmacological approaches, we tested whether PIN1 modulation could be used as a therapeutic regimen against AS. In the genetic approach, we crossbred Fgfr2S252W/+, a mouse model of AS, and Pin1+/- mice. Downregulation of Pin1 gene dosage attenuated premature cranial suture closure and other phenotypes of AS in Fgfr2S252W/+ mutant mice. In the pharmacological approach, we intraperitoneally administered juglone, a PIN1 enzyme inhibitor, to pregnant Fgfr2S252W/+ mutant mice and found that this treatment successfully interrupted fetal development of AS phenotypes. Primary cultured osteoblasts from Fgfr2S252W/+ mutant mice expressed high levels of FGFR2 downstream target genes, but this phenotype was attenuated by PIN1 inhibition. Post-translational stabilization and activation of Runt-related transcription factor 2 (RUNX2) in Fgfr2S252W/+ osteoblasts were also attenuated by PIN1 inhibition. Based on these observations, we conclude that PIN1 enzyme activity is important for FGFR2-induced RUNX2 activation and craniofacial suture morphogenesis. Moreover, these findings highlight that juglone or other PIN1 inhibitors represent viable alternatives to surgical intervention for treatment of CS and other hyperostotic diseases.

Craniofacial, orofacial and dental disorders: the role of the RAS/ERK pathway

Deviations from the precisely coordinated programme of human head development can lead to craniofacial and orofacial malformations often including a variety of dental abnormalities too. Although the aetiology is still unknown in many cases, during the last decades different intracellular signalling pathways have been genetically linked to specific disorders. Among these pathways, the RAS/extracellular signal-regulated kinase (ERK) signalling cascade is the focus of this review since it encompasses a large group of genes that when mutated cause some of the most common and severe developmental anomalies in humans. We present the components of the RAS/ERK pathway implicated in craniofacial and orodental disorders through a series of human and animal studies. We attempt to unravel the specific molecular targets downstream of ERK that act on particular cell types and regulate key steps in the associated developmental processes. Finally we point to ambiguities in our current knowledge that need to be clarified before RAS/ERK-targeting therapeutic approaches can be implemented.

FGF23 and its role in X-linked hypophosphatemia-related morbidity

Background

X-linked hypophosphatemia (XLH) is an inherited disease of phosphate metabolism in which inactivating mutations of the Phosphate Regulating Endopeptidase Homolog, X-Linked (PHEX) gene lead to local and systemic effects including impaired growth, rickets, osteomalacia, bone abnormalities, bone pain, spontaneous dental abscesses, hearing difficulties, enthesopathy, osteoarthritis, and muscular dysfunction. Patients with XLH present with elevated levels of fibroblast growth factor 23 (FGF23), which is thought to mediate many of the aforementioned manifestations of the disease. Elevated FGF23 has also been observed in many other diseases of hypophosphatemia, and a range of animal models have been developed to study these diseases, yet the role of FGF23 in the pathophysiology of XLH is incompletely understood.

Methods

The role of FGF23 in the pathophysiology of XLH is here reviewed by describing what is known about phenotypes associated with various PHEX mutations, animal models of XLH, and non-nutritional diseases of hypophosphatemia, and by presenting molecular pathways that have been proposed to contribute to manifestations of XLH.

Results

The pathophysiology of XLH is complex, involving a range of molecular pathways that variously contribute to different manifestations of the disease. Hypophosphatemia due to elevated FGF23 is the most obvious contributor, however localised fluctuations in tissue non-specific alkaline phosphatase (TNAP), pyrophosphate, calcitriol and direct effects of FGF23 have been observed to be associated with certain manifestations.

Conclusions

By describing what is known about these pathways, this review highlights key areas for future research that would contribute to the understanding and clinical treatment of non-nutritional diseases of hypophosphatemia, particularly XLH.

An Overview of Modelling Craniosynostosis Using the Finite Element Method

Craniosynostosis is a medical condition caused by the early fusion of the cranial joint. The finite element method (FEM) is a computational technique that can answer a variety of "what if" questions in relation to the biomechanics of this condition. The aim of this study was to review the current literature that has used FEM to investigate the biomechanics of any aspect of craniosynostosis, being its development or its reconstruction. This review highlights that a relatively small number of studies (n = 10) has used FEM to investigate the biomechanics of craniosynostosis. Current studies set a good foundation for the future to take advantage of this method and optimize reconstruction of various forms of craniosynostosis.

Characterizing and Modeling Bone Formation during Mouse Calvarial Development

The newborn mammalian cranial vault consists of five flat bones that are joined together along their edges by soft fibrous tissues called sutures. Early fusion of these sutures leads to a medical condition known as craniosynostosis. The mechanobiology of normal and craniosynostotic skull growth is not well understood. In a series of previous studies, we characterized and modeled radial expansion of normal and craniosynostotic (Crouzon) mice. Here, we describe a new modeling algorithm to simulate bone formation at the sutures in normal and craniosynostotic mice. Our results demonstrate that our modeling approach is capable of predicting the observed ex vivo pattern of bone formation at the sutures in the aforementioned mice. The same approach can be used to model different calvarial reconstruction in children with craniosynostosis to assist in the management of this complex condition.

A tale of two cities: The genetic mechanisms governing calvarial bone development

The skull bones must grow in a coordinated, three-dimensional manner to coalesce and form the head and face. Mammalian skull bones have a dual embryonic origin from cranial neural crest cells (CNCC) and paraxial mesoderm (PM) and ossify through intramembranous ossification. The calvarial bones, the bones of the cranium which cover the brain, are derived from the supraorbital arch (SOA) region mesenchyme. The SOA is the site of frontal and parietal bone morphogenesis and primary center of ossification. The objective of this review is to frame our current in vivo understanding of the morphogenesis of the calvarial bones and the gene networks regulating calvarial bone initiation in the SOA mesenchyme.

Rapamycin rescues BMP mediated midline craniosynostosis phenotype through reduction of mTOR signaling in a mouse model

Craniosynostosis is defined as congenital premature fusion of one or more cranial sutures. While the genetic basis for about 30% of cases is known, the causative genes for the diverse presentations of the remainder of cases are unknown. The recently discovered cranial suture stem cell population affords an opportunity to identify early signaling pathways that contribute to craniosynostosis. We previously demonstrated that enhanced BMP signaling in neural crest cells (caA3 mutants) leads to premature cranial suture fusion resulting in midline craniosynostosis. Since enhanced mTOR signaling in neural crest cells leads to craniofacial bone lesions, we investigated the extent to which mTOR signaling is involved in the pathogenesis of BMP-mediated craniosynostosis by affecting the suture stem cell population. Our results demonstrate a loss of suture stem cells in the caA3 mutant mice by the newborn stage. We have found increased activation of mTOR signaling in caA3 mutant mice during embryonic stages, but not at the newborn stage. Our study demonstrated that inhibition of mTOR signaling via rapamycin in a time specific manner partially rescued the loss of the suture stem cell population. This study provides insight into how enhanced BMP signaling regulates suture stem cells via mTOR activation.

A Road Map for Important Centers of Growth in the Pediatric Skeleton to Consider During Radiation Therapy and Associated Clinical Correlates of Radiation-Induced Growth Toxicity

With the increasing use of advanced radiation techniques such as intensity modulated radiation therapy, stereotactic radiation therapy, and proton therapy, radiation oncologists now have the tools to mitigate radiation-associated toxicities. This is of utmost importance in the treatment of a pediatric patient. To best use these advanced techniques to mitigate radiation-induced growth abnormalities, the radiation oncologist should be equipped with a nuanced understanding of the anatomy of centers of growth. This article aims to enable the radiation oncologist to better understand, predict, and minimize radiation-mediated toxicities on growth. We review the process of bone development and radiation-induced growth abnormalities and provide an atlas for contouring important growth plates to guide radiation treatment planning. A more detailed recognition of important centers of growth may improve future treatment outcomes in children receiving radiation therapy.

Like a hole in the head: Development, evolutionary implications and diseases of the cranial foramina

Cranial foramina are holes in the skull through which nerves and blood vessels pass to reach both deep and superficial tissues. They are often overlooked in the literature; however they are complex structures that form within the developing cranial bones during embryogenesis and then remain open throughout life, despite the bone surrounding them undergoing constant remodelling. They are invaluable in assigning phylogeny in the fossil record and their size has been used, by some, to imply function of the nerve and/or blood vessel that they contained. Despite this, there are very few studies investigating the development or normal function of the cranial foramina. In this review, we will discuss the development of the cranial foramina and their subsequent maintenance, highlighting key gaps in the knowledge. We consider whether functional interpretations can be made from fossil material given a lack of knowledge regarding their contents and maintenance. Finally, we examine the significant role of malformation of foramina in congenital diseases such as craniosynostosis.

Non-sutural basicranium-derived cells undergo a unique mineralization pathway via a cartilage intermediate in vitro

The basicranium serves as a key interface in the mammalian skull, interacting with the calvarium, facial skeleton and vertebral column. Despite its critical function, little is known about basicranial bone formation, particularly on a cellular level. The goal of this study was therefore to cultivate a better understanding of basicranial development by isolating and characterizing the osteogenic potential of cells from the neonatal murine cranial base. Osteoblast-like basicranial cells were isolated, seeded in multicellular aggregates (designated micromasses), and cultured in osteogenic medium in the presence or absence of bone morphogenetic protein-6 (BMP6). A minimal osteogenic response was observed in control osteogenic medium, while BMP6 treatment induced a chondrogenic response followed by up-regulation of osteogenic markers and extensive mineralization. This response appears to be distinct from prior analyses of the calvarium and long bones, as basicranial cells did not mineralize under standard osteogenic conditions, but rather required BMP6 to stimulate mineralization, which occurred via an endochondral-like process. These findings suggest that this site may be unique compared to other cranial elements as well as the limb skeleton, and we propose that the distinct characteristics of these cells may be a function of the distinct properties of the basicranium: endochondral ossification, dual embryology, and complex loading environment.

The Osteogenic Potential of the Neural Crest Lineage May Contribute to Craniosynostosis

The craniofacial skeleton is formed from the neural crest and mesodermal lineages, both of which contribute mesenchymal precursors during formation of the skull bones. The large majority of cranial sutures also includes a proportion of neural crest-derived mesenchyme. While some studies have addressed the relative healing abilities of neural crest and mesodermal bone, relatively little attention has been paid to differences in intrinsic osteogenic potential. Here, we use mouse models to compare neural crest osteoblasts (from frontal bones or dura mater) to mesodermal osteoblasts (from parietal bones). Using in vitro culture approaches, we find that neural crest-derived osteoblasts readily generate bony nodules, while mesodermal osteoblasts do so less efficiently. Furthermore, we find that co-culture of neural crest-derived osteoblasts with mesodermal osteoblasts is sufficient to nucleate ossification centres. Altogether, this suggests that the intrinsic osteogenic abilities of neural crest-derived mesenchyme may be a primary driver behind craniosynostosis.

Mid-facial developmental defects caused by the widely used LacZ reporter gene when expressed in neural crest-derived cells

Reporter genes play important roles in transgenic research. LacZ is a widely used reporter gene that encodes Escherichia coli β-galactosidase, an enzyme that is well known for its ability to hydrolyze X-gal into a blue product. It is unknown whether transgenic LacZ has any adverse effects. R26R reporter mice, containing a LacZ reporter gene, were generated to monitor the in vivo recombination activity of various transgenic Cre recombinase via X-gal staining. P0-Cre is expressed in neural crest-derived cells, which give rise to the majority of the craniofacial bones. Herein, we report that 12% of the R26R reporter mice harboring P0-Cre had unexpected mid-facial developmental defects manifested by the asymmetrical growth of some facial bones, thus resulting in tilted mid-facial structure, shorter skull length, and malocclusion. Histological examination showed a disorganization of the frontomaxillary suture, which may at least partly explain the morphological defect in affected transgenic mice. Our data calls for the consideration of the potential in vivo adverse effects caused by transgenic β-galactosidase.

Reduced Intracranial Volume in Fabry Disease: Evidence of Abnormal Neurodevelopment?

Introduction: Lysosomal storage disorders (LSD) are often characterized by abnormal brain development, reflected by a reduction of intracranial volume (ICV). The aim of our study was to perform a volumetric analysis of intracranial tissues in Fabry Disease (FD), investigating possible reductions of ICV as a potential expression of abnormal brain development in this condition.

Materials and Methods: Forty-two FD patients (15 males, mean age 43.3 ± 13.0 years) were enrolled along with 38 healthy controls (HC) of comparable age and sex. Volumetric MRI data were segmented using SPM12 to obtain intracranial tissue volumes, from which ICV values were derived.

Results: Mean ICV of FD patients was 8.1% smaller compared to the control group (p < 5·10⁻⁵). Unlike what typically happens in neurodegenerative disorders, no significant differences emerged when comparing between the two groups the fractional volumes of gray matter, white matter and CSF (i.e., normalized by ICV), consistent with a harmonious volumetric reduction of intracranial structures.

Discussion: The present results suggest that in FD patients an abnormality of brain development is present, expanding the current knowledge about central nervous system involvement in FD, further emphasizing the importance of an early diagnosis.

How does nonsyndromic craniosynostosis affect on bone width of nasal cavity in children? - Computed tomography study

Craniosynostosis is caused by premature fusion of one or more cranial sutures, restricting skull, brain and face growth. Nonsyndromic craniosynostosis could disturb the proportions of face. Although morphometric diameters of nasal cavity in healthy children are already known, they have not been established yet in children with nonsyndromic craniosynostosis. The aim our study was to check whether diameters of bone structures of nasal cavity in children with nonsyndromic craniosynostosis measured in CT are within normal range. 249 children aged 0–36 months (96 with clinical diagnosis of nonsyndromic craniosynostosis and 153 in control group) were included into the study. The following diameters were measured on head CT scans: anterior bony width (ABW), bony choanal aperture width (BCAW), right and left posterior bony width (between bone sidewall and nasal cavity septum—RPBW and LPBW). The study group has been divided into 4 categories, depending on child’s age. The dimensions measured between bone structures of nasal cavity were statistically significantly lower in comparison to the control group. They did not depend on the sex for ABW, nor on age in groups 7–12 months and < 2 years for BCAW, RPBW and LPBW. The measured dimensions increased with age. In children with nonsyndromic craniosynostosis the diameter of pyriform aperture and bony choanal aperture were lower than in controls, what may be described as fronto-orbital anomalies. Morphometric measurements of anthropometric indicators on CT scans could be used as standards in the clinical identification of craniosynostosis type and may help in planning surgical procedures, particularly in the facial skeleton in children.

Evaluation of anesthesia in endoscopic strip craniectomy: A review of 121 patients

OBJECTIVE

The aim of this study was to evaluate pre-, intra-, and postoperative anesthetic parameters in endoscopic strip craniectomy in order to improve anesthesiological care.

MATERIALS AND METHODS

This is a retrospective patient cohort study of our first 121 patients treated by endoscopic strip craniectomy. Preoperative as well as intra- and postoperative anesthesiological and neurological parameters were analyzed. Furthermore, the need for intensive care unit admission, blood loss, and blood transfusion rate were measured.

RESULTS

The mean age of patients was 3.9 months (standard deviation = 1) at a mean weight of 6.3 kg (standard deviation = 1.3). Comorbidity was registered in 13 (11%) patients of which 5 had syndrome-related comorbidities. Mean duration of anesthesia was 131 minutes (standard deviation = 32) . One hundred and sixteen patients were induced by mask induction with sevoflurane and 5 patients were induced intravenously. In 10 patients, mild intraoperative hypothermia (between 35 and 36 degrees Celsius) occurred. The mean estimated blood loss was 35.4 mL (standard deviation = 28.9) and blood transfusion rate was 21.5%. Brief and small intraoperative oxygen saturation drops were common during this study. No indication for venous air embolism was found based on endtidal CO₂ . Postoperative temperature above 38 degrees Celsius occurred 16 times and benign deviations in postoperative cardiopulmonary parameters occurred in 17 patients. Postoperative pain management was mainly established by paracetamol and low-dose morphine when necessary. No postoperative neurological symptoms were reported and no deaths occurred.

CONCLUSION

These patients had a relatively short intraoperative course with stable vital parameters during surgery. We report a low incidence of significant venous air embolism, a blood transfusion rate of 21% and only minor perioperative disturbances in vital parameters.

An audiological evaluation of syndromic and non-syndromic craniosynostosis in pre-school going children

OBJECTIVE

To study the audiological outcome and early screening of pre-school going children with craniosynostosis under follow-up at the University of Malaya Medical Center(UMMC), Kuala Lumpur, Malaysia over a 10 year period.

METHODS

A retrospective descriptive cohort study on the audiological findings detected during the first hearing assessment done on a child with craniosynostosis using otoacoustic emissions, pure tone audiometry or auditory brainstem response examination. The main aim of this study was to evaluate the type and severity of hearing loss when compared between syndromic and non-sydromic craniosynostosis, and other associated contributory factors.

RESULTS

A total of 31 patients with 62 ears consisting of 14 male patients and 17 female patients were evaluated. Twenty two patients (71%) were syndromic and 9 (29%) were non-syndromic craniosynostosis. Amongst the syndromic craniosynostosis, 9 (41%) had Apert syndrome, 7 (32%) had Crouzon syndrome, 5 (23%) had Pfieffer syndrome and 1 (4%) had Shaethre Chotzen syndrome. Patients with syndromic craniosynostosis were more likely to present with all types and severity of hearing loss, including severe to profound sensorineural hearing loss while children with non-syndromic craniosynostosis were likely to present with normal hearing (p < 0.05). In addition, when the first hearing test was done at a later age, a hearing loss including sensorineural hearing loss is more likely to be present in a child with syndromic craniosynostosis (p < 0.05).

CONCLUSION

Our study suggested that children who are born with syndromic craniosynostosis were more likely to suffer from a hearing loss, including that of a severe to profound degree compared to children with non-syndromic craniosynostosis. In addition to that, hearing loss is more likely to be detected when the first hearing test is done at a later age, and this can be an irreversible sensorineural hearing loss. We would like to advocate the need for early audiological screening and follow up in children with syndromic craniosynostosis.

Novel 1q22-q23.1 duplication in a patient with lambdoid and metopic craniosynostosis, muscular hypotonia, and psychomotor retardation

Craniosynostosis (CS) refers to the group of craniofacial malformations characterized by the premature closure of one or more cranial sutures. The disorder is clinically and genetically heterogeneous and occurs usually as an isolated trait, but can also be syndromic. In 30-60% of patients, CS is caused by known genetic factors; however, in the rest of the cases, causative molecular lesions remain unknown. In this paper, we report on a sporadic male patient affected by complex CS (metopic and unilateral lambdoid synostosis), muscular hypotonia, psychomotor retardation, and facial dysmorphism. Since a subset of CS results from submicroscopic chromosomal aberrations, we performed array comparative genomic hybridization (array CGH) in order to identify possibly causative copy-number variation. Array CGH followed by breakpoint sequencing revealed a previously unreported de novo 1.26 Mb duplication at chromosome 1q22-q23.1 that encompassed two genes involved in osteoblast differentiation: BGLAP, encoding osteocalcin (OCN), and LMNA, encoding lamin A/C. OCN is a major component of bone extracellular matrix and a marker of osteogenesis, whereas mutations in LMNA cause several genetic disorders called laminopathies, including mandibuloacral dysostosis (MAD) that manifests with low bone mass, severe bone deformities, and delayed closure of the cranial sutures. Since LMNA and BGLAP overexpression promote osteoblast differentiation and calcification, phenotype of our patient may result from misexpression of the genes. Based on our findings, we hypothesize that both LMNA and BGLAP may be implicated in the pathogenesis of CS in humans. However, further studies are needed to establish the exact pathomechanism underlying development of this defect.

Anti-osteogenic function of a LIM-homeodomain transcription factor LMX1B is essential to early patterning of the calvaria

The calvaria (upper part of the skull) is made of plates of bone and fibrous joints (sutures and fontanelles), and the proper balance and organization of these components are crucial to normal development of the calvaria. In a mouse embryo, the calvaria develops from a layer of head mesenchyme that surrounds the brain from shortly after mid-gestation. The mesenchyme just above the eye (supra-orbital mesenchyme, SOM) generates ossification centers for the bones, which then grow toward the apex gradually. In contrast, the mesenchyme apical to SOM (early migrating mesenchyme, EMM), including the area at the vertex, does not generate an ossification center. As a result, the dorsal midline of the head is occupied by sutures and fontanelles at birth. To date, the molecular basis for this regional difference in developmental programs is unknown. The current study provides vital insights into the genetic regulation of calvarial patterning. First, we showed that osteogenic signals were active in both EMM and SOM during normal development, which suggested the presence of an anti-osteogenic factor in EMM to counter the effect of these signals. Subsequently, we identified Lmx1b as an anti-osteogenic gene that was expressed in EMM but not in SOM. Furthermore, head mesenchyme-specific deletion of Lmx1b resulted in heterotopic ossification from EMM at the vertex, and craniosynostosis affecting multiple sutures. Conversely, forced expression of Lmx1b in SOM was sufficient to inhibit osteogenic specification. Therefore, we conclude that Lmx1b plays a key role as an anti-osteogenic factor in patterning the head mesenchyme into areas with different osteogenic competence. In turn, this patterning event is crucial to generating the proper organization of the bones and soft tissue joints of the calvaria.

Craniosynostosis - Recognition, clinical characteristics, and treatment

Craniosynostosis is a developmental craniofacial anomaly, resulting in impairment of brain development and abnormally shaped skull. The main cause of craniosynostosis is premature closure of one or more cranial sutures. It usually occurs as an isolated condition, but may also be associated with other malformations as part of complex syndromes. When left untreated, craniosynostosis can cause serious complications, such as developmental delay, facial abnormality, sensory, respiratory and neurological dysfunction, anomalies affecting the eye, and psychological disturbances. Thus, early diagnosis, expert surgical techniques, postoperative care, and adequate follow-up are of vital importance in treating craniosynostosis.

BRCA1 and BRCA2 tumor suppressors in neural crest cells are essential for craniofacial bone development

Craniofacial abnormalities, including facial skeletal defects, comprise approximately one-third of all birth defects in humans. Since most bones in the face derive from cranial neural crest cells (CNCCs), which are multipotent stem cells, craniofacial bone disorders are largely attributed to defects in CNCCs. However, it remains unclear how the niche of CNCCs is coordinated by multiple gene regulatory networks essential for craniofacial bone development. Here we report that tumor suppressors breast cancer 1 (BRCA1) and breast cancer 2 (BRCA2) are required for craniofacial bone development in mice. Disruption of Brca1 in CNCC-derived mesenchymal cells, but not in epithelial-derived cells, resulted in craniofacial skeletal defects. Whereas osteogenic differentiation was normal, both osteogenic proliferation and survival were severely attenuated in Brca1 mutants. Brca1-deficient craniofacial skeletogenic precursors displayed increased DNA damage and enhanced cell apoptosis. Importantly, the craniofacial skeletal defects were sufficiently rescued by superimposing p53 null alleles in a neural crest-specific manner in vivo, indicating that BRCA1 deficiency induced DNA damage, cell apoptosis, and that the pathogenesis of craniofacial bone defects can be compensated by inactivation of p53. Mice lacking Brca2 in CNCCs, but not in epithelial-derived cells, also displayed abnormalities resembling the craniofacial skeletal malformations observed in Brca1 mutants. Our data shed light on the importance of BRCA1/BRCA2 function in CNCCs during craniofacial skeletal formation.