Signaling Mechanisms Underlying Genetic Pathophysiology of Craniosynostosis

Joint multi-ancestry and admixed GWAS reveals the complex genetics behind human cranial vault shape

The cranial vault in humans is highly variable, clinically relevant, and heritable, yet its genetic architecture remains poorly understood. Here, we conduct a joint multi-ancestry and admixed multivariate genome-wide association study on 3D cranial vault shape extracted from magnetic resonance images of 6772 children from the ABCD study cohort yielding 30 genome-wide significant loci. Follow-up analyses indicate that these loci overlap with genomic risk loci for sagittal craniosynostosis, show elevated activity cranial neural crest cells, are enriched for processes related to skeletal development, and are shared with the face and brain. We present supporting evidence of regional localization for several of the identified genes based on expression patterns in the cranial vault bones of E15.5 mice. Overall, our study provides a comprehensive overview of the genetics underlying normal-range cranial vault shape and its relevance for understanding modern human craniofacial diversity and the etiology of congenital malformations.

Association of gut microbiota composition and craniosynostosis

Background

Gut microbiota has been reported to be associated with a series of metabolic diseases including metabolic bone disease. However, study about gut microbiota and craniosynostosis (CS) is very rare. We aim to investigate the gut microbiota composition in CS patients and assess the possible relationship.

Methods

A total of 30 infants with CS and 30 infants with non-CS treated in Children's Hospital of Nanjing Medical University of Jiangsu Province from June 2021 to March 2022 were finally included in this study. All processing and analysis are carried out using 16S ribosomal RNA (rRNA) high-throughput gene sequencing.

Results

The CS group have significantly lower levels of family, genus, and species than non-CS group (all P<0.05). Furthermore, Staphylococcales and Lactobacillales at the order level, Enterococcaceae and Staphylococcaceae at the family level, and Enterococcus and Staphylococcus at the genus level were significantly enriched in the CS group (all P<0.05). Additionally, functional prediction showed that six metabolic pathways significantly differed between the two groups (all P<0.05). Of those, pathways involving polycyclic aromatic hydrocarbon degradation (P=0.030) and penicillin and cephalosporin biosynthesis (P=0.027) were more abundant in CS group than in non-CS group.

Conclusions

Gut microbiota was statistically associated with the development of CS, and several taxa and specific functional pathways with significantly altered abundance have been identified in CS patients. These findings can provide clues for the study on the mechanism and early diagnosis of CS.

Exosome-mediated small interfering RNA delivery inhibits aberrant osteoblast differentiation in Apert syndrome model mice

OBJECTIVE

Apert syndrome, an autosomal dominant congenital disorder characterized by craniosynostosis, is caused by a missense mutation (S252W or P253R) in fibroblast growth factor receptor 2 (FGFR2). Exosomes are naturally occurring carriers that deliver nucleic acids, including small interfering RNA (siRNA), to induce gene silencing. This study aimed to develop siRNA-loaded exosomes (Ex-siRNA^Fgfr2S252W) to silence the Fgfr2^S252W gain-of-function mutation, thereby inhibiting the increased osteoblastic differentiation caused by the constitutive activation of FGFR2 signaling in calvarial osteoblastic cells isolated from Apert syndrome model mice.

DESIGN

Primary calvarial osteoblast-like cells were isolated from the embryonic calvarial sutures of the Apert syndrome model (Fgfr2^S252W/+) and littermate wild-type mice (Ap-Ob and Wt-Ob, respectively). Exosomes were extracted from the serum of wild-type mice, validated using biomarkers, and used to encapsulate siRNAs. After exosome-mediated siRNA transfection, cells were analyzed under a fluorescence microscope to validate the delivery of Ex-siRNA^Fgfr2S252W, followed by western blot and real-time reverse transcription polymerase chain reaction analyses.

RESULTS

After 24 h of Ex-siRNA^Fgfr2S252W delivery in both Ap-Ob and Wt-Ob, siRNA-loaded exosome delivery was validated. Moreover, p44/42 mitogen-activated protein kinase (MAPK) phosphorylation, runt-related transcription factor 2 (Runx2), and collagen type 1 alpha 1 (Col1a1) mRNA expression, and alkaline phosphatase (ALP) activity were significantly increased in Ap-Ob. The levels of phospho-p44/42 protein, Runx2, Col1a1, and ALP were significantly decreased after Ex-siRNA^Fgfr2S252W transfection but did not affect Wt-Ob.

CONCLUSIONS

These results indicate that exosome-mediated delivery of siRNA targeting Fgfr2^S252W is a potential non-invasive treatment for aberrant FGF/FGFR signaling.

Molecular Mechanisms Involved in Craniosynostosis

Craniosynostosis refers to the early fusion of one or many cranial sutures, causing craniofacial abnormalities observed in 1:2,500 births worldwide. In most cases (85%), craniosynostosis is presented as sporadic anomaly (non-syndromic craniosynostosis), while in other cases (15%) as part of syndromes (syndromic craniosynostosis). Patients with syndromic disorder usually have more severe symptoms compared to those with single suture synostosis. Most common syndromes of craniosynostosis include Pfeiffer, Apert, Crouzon, Jackson-Weiss, Muenke and Boston type MSX2-related syndrome. The main gene mutations in craniosynostosis involve FGFR1, FGFR2, FGFR3, TWIST1 and MSX2, which encode key factors influencing cranial bone morphogenesis. The main therapeutic approaches are surgical as discussed in this review, and the type of therapy depends on the graveness of the incident.

Retroperitoneal liposarcoma and craniosynostosis: possible genomic relationship, case report, and literature review

Based on a case report, this review explores the genomic landscape for patients with liposarcomas and possible relationships with gene mutations related to craniosynostosis. We describe the case of a 40-year-old man, known for a surgical correction of craniosynostosis before the age of 1 year, who underwent a radical resection of a voluminous retroperitoneal liposarcoma; histopathological analysis revealed a low-grade well-differentiated, mostly sclerosing, liposarcoma. A genetic analysis searching for mutations in blood DNA was performed and did not detect any specific mutation. A literature review was also conducted. Several tumors related to syndromic and non-syndromic craniosynostosis are mentioned in the literature; no specific link with retroperitoneal liposarcoma is established but the FGFR3 mutation is detected in dedifferentiated liposarcomas. To date, no case has been reported in the literature demonstrating a genetic relationship between craniosynostosis and low-grade differentiated retroperitoneal liposarcoma. We conclude that further studies for gene complex mutations should be conducted to show a possible genetic relationship between retroperitoneal liposarcoma and craniosynostosis.

Response of Gli1+ Suture Stem Cells to Mechanical Force Upon Suture Expansion

Normal development of craniofacial sutures is crucial for cranial and facial growth in all three dimensions. These sutures provide a unique niche for suture stem cells (SuSCs), which are indispensable for homeostasis, damage repair, as well as stress balance. Expansion appliances are now routinely used to treat underdevelopment of the skull and maxilla, stimulating the craniofacial sutures through distraction osteogenesis. However, various treatment challenges exist due to a lack of full understanding of the mechanism through which mechanical forces stimulate suture and bone remodeling. To address this issue, we first identified crucial steps in the cycle of suture and bone remodeling based on the established standard suture expansion model. Observed spatiotemporal morphological changes revealed that the remodeling cycle is approximately 3 to 4 weeks, with collagen restoration proceeding more rapidly. Next, we traced the fate of the Gli1⁺ SuSCs lineage upon application of tensile force in three dimensions. SuSCs were rapidly activated and greatly contributed to bone remodeling within 1 month. Furthermore, we confirmed the presence of Wnt activity within Gli1⁺ SuSCs based on the high co-expression ratio of Gli1⁺ cells and Axin2⁺ cells, which also indicated the homogeneity and heterogeneity of two cell groups. Because Wnt signaling in the sutures is highly upregulated upon tensile force loading, conditional knockout of β-catenin largely restricted the activation of Gli1⁺ SuSCs and suppressed bone remodeling under physiological and expansion conditions. Thus, we concluded that Gli1⁺ SuSCs play essential roles in suture and bone remodeling stimulated by mechanical force and that Wnt signaling is crucial to this process. © 2022 American Society for Bone and Mineral Research (ASBMR).

Immunohistochemical Evaluation of BARX1, DLX4, FOXE1, HOXB3, and MSX2 in Nonsyndromic Cleft Affected Tissue

Background

Nonsyndromic craniofacial clefts are relatively common congenital malformations which could create a significant negative effect on the health status and life quality of affected individuals within the pediatric population. Multiple cleft candidate genes and their coded proteins have been described with their possible involvement during cleft formation. Some of these proteins like Homeobox Protein BarH-like 1 (BARX1), Distal-Less Homeobox 4 (DLX4), Forkhead Box E1 (FOXE1), Homeobox Protein Hox-B3 (HOXB3), and Muscle Segment Homeobox 2 (MSX2) have been associated with the formation of craniofacial clefts. Understanding the pathogenetic mechanisms of nonsyndromic craniofacial cleft formation could provide a better knowledge in cleft management and could be a possible basis for development and improvement of cleft treatment options. This study investigates the presence of BARX1, DLX4, FOXE1, HOXB3, and MSX2 positive cells by using immunohistochemistry in different types of cleft-affected tissue while determining their possible connection with cleft pathogenesis process.

Materials and Methods

Craniofacial cleft tissue material was obtained during cleft-correcting surgery from patients with nonsyndromic craniofacial cleft diagnosis. Tissue material was gathered from patients who had unilateral cleft lip (n=36), bilateral cleft lip (n=13), and cleft palate (n=26). Control group (n=7) tissue material was received from individuals without any craniofacial clefts. The number of factor positive cells in the control group and patient group tissue was evaluated by using the semiquantitative counting method. Data was evaluated with the use of nonparametric statistical methods.

Results

Statistically significant differences were identified between the number of BARX1, FOXE1, HOXB3, and MSX2-containing cells in controls and cleft patient groups but no statistically significant difference was found for DLX4. Statistically significant correlations between the evaluated factors were also notified in cleft patient groups.

Conclusions

HOXB3 could be more associated with morphopathogenesis of unilateral cleft lip during postnatal course of the disorder. FOXE1 and BARX1 could be involved with both unilateral and bilateral cleft lip morphopathogenesis. The persistence of MSX2 in all evaluated cleft types could indicate its possible interaction within multiple cleft types. DLX4 most likely is not involved with postnatal cleft morphopathogenesis process.

Endoscopic treatment of sagittal suture synostosis - a critical analysis of current management strategies

While many centers nowadays offer minimally invasive techniques for the treatment of single suture synostosis, surgical techniques and patient management vary significantly. We provide an overview of how scaphocephaly treated with endoscopic techniques is managed in the reported series and analyze the crucial steps that need to be dealt with during the management process. We performed a review of the published literature including all articles that examined sagittal-suture synostosis treated with endoscopic techniques as part of single- or multicenter studies. Fourteen studies reporting results of 885 patients were included. We identified 5 key steps in the management of patients. A total of 188 patients were female and 537 male (sex was only specified in 10 articles, for 725 included patients, respectively). Median age at surgery was between 2.6 and 3.9 months with a total range from 1.5 to 7.0 months. Preoperative diagnostics included clinical and ophthalmologic examinations as well as neuropsychological and genetic consultations if needed. In 5 publications, a CT scan was routinely performed. Several groups used anthropometric measurements, mostly the cephalic index. All groups analyzed equally recommended to perform endoscopically assisted craniosynostosis surgery with postoperative helmet therapy in children < 3 months of age, at least for non-syndromic cases. There exist significant variations in surgical techniques and patient management for children treated endoscopically for single suture sagittal synostosis. This heterogeneity constitutes a major problem in terms of comparability between different strategies.

Whole-exome sequencing in syndromic craniosynostosis increases diagnostic yield and identifies candidate genes in osteogenic signaling pathways

Craniosynostosis (CS) is a common congenital anomaly defined by premature fusion of one or more cranial sutures. Syndromic CS involves additional organ anomalies or neurocognitive deficits and accounts for 25%-30% of the cases. In a recent population-based study by our group, 84% of the syndromic CS cases had a genetically verified diagnosis after targeted analyses. A number of different genetic causes were detected, confirming that syndromic CS is highly heterogeneous. In this study, we performed whole-exome sequencing of 10 children and parents from the same cohort where previous genetic results were negative. We detected pathogenic, or likely pathogenic, variants in four additional genes (NFIA, EXTL3, POLR2A, and FOXP2) associated with rare conditions. In two of these (POLR2A and FOXP2), CS has not previously been reported. We further detected a rare predicted damaging variant in SH3BP4, which has not previously been related to human disease. All findings were clustered in genes involved in the pathways of osteogenesis and suture patency. We conclude that whole-exome sequencing expands the list of genes associated with syndromic CS, and provides new candidate genes in osteogenic signaling pathways.

Case report: A novel truncating variant of BCL11B associated with rare feature of craniosynostosis and global developmental delay

Craniosynostosis is a premature fusion of cranial sutures, resulting in abnormally shaped skull and brain development disorder. The description of craniosynostosis in patients with BCL11B mutations is rare. Here, we firstly report a 25-month-old Chinese boy with a novel frameshift variant in BCL11B gene. The patient was identified c.2346_2361del by whole-exome sequencing and was confirmed to be de novo by parental Sanger sequencing. This patient presented clinical phenotype of craniosynostosis as well as global developmental delay. He had a small mouth, thin upper lip, arched eyebrows, a long philtrum, midfacial hypoplasia and craniosynostosis. Brain MRI showed brain extracerebral interval and myelination changes, and brain CT with 3D reconstruction showed multi-craniosynostosis. Our study expands the clinical phenotypes of patients with BCL11B gene mutation, and our findings may help guide clinical treatment and family genetic counseling.

De novo ALX4 variant detected in child with non-syndromic craniosynostosis

Current understanding of the genetic factors contributing to the etiology of non-syndromic craniosynostosis (NSC) remains scarce. The present work investigated the presence of variants in ALX4, EFNA4, and TWIST1 genes in children with NSC to verify if variants within these genes may contribute to the occurrence of these abnormal phenotypes. A total of 101 children (aged 45.07±40.94 months) with NSC participated in this cross-sectional study. Parents and siblings of the probands were invited to participate. Medical and family history of craniosynostosis were documented. Biological samples were collected to obtain genomic DNA. Coding exons of human TWIST1, ALX4, and EFNA4 genes were amplified by polymerase chain reaction and Sanger sequenced. Five missense variants were identified in ALX4 in children with bilateral coronal, sagittal, and metopic synostosis. A de novo ALX4 variant, c.799G>A: p.Ala267Thr, was identified in a proband with sagittal synostosis. Three missense variants were identified in the EFNA4 gene in children with metopic and sagittal synostosis. A TWIST1 variant occurred in a child with unilateral coronal synostosis. Variants were predicted to be among the 0.1% (TWIST1, c.380C>A: p. Ala127Glu) and 1% (ALX4, c.769C>T: p.Arg257Cys, c.799G>A: p.Ala267Thr, c.929G>A: p.Gly310Asp; EFNA4, c.178C>T: p.His60Tyr, C.283A>G: p.Lys95Glu, c.349C>A: Pro117Thr) most deleterious variants in the human genome. With the exception of ALX4, c.799G>A: p.Ala267Thr, all other variants were present in at least one non-affected family member, suggesting incomplete penetrance. Thus, these variants may contribute to the development of craniosynostosis, and should not be discarded as potential candidate genes in the diagnosis of this condition.

Benefits of clinical criteria and high-throughput sequencing for diagnosing children with syndromic craniosynostosis

An accurate diagnosis of syndromic craniosynostosis (CS) is important for personalized treatment, surveillance, and genetic counselling. We describe detailed clinical criteria for syndromic CS and the distribution of genetic diagnoses within the cohort. The prospective registry of the Norwegian National Unit for Craniofacial Surgery was used to retrieve individuals with syndromic CS born between 1 January 2002 and 30 June 2019. All individuals were assessed by a clinical geneticist and classified using defined clinical criteria. A stepwise approach consisting of single-gene analysis, comparative genomic hybridization (aCGH), and exome-based high-throughput sequencing, first filtering for 72 genes associated with syndromic CS, followed by an extended trio-based panel of 1570 genes were offered to all syndromic CS cases. A total of 381 individuals were registered with CS, of whom 104 (27%) were clinically classified as syndromic CS. Using the single-gene analysis, aCGH, and custom-designed panel, a genetic diagnosis was confirmed in 73% of the individuals (n = 94). The diagnostic yield increased to 84% after adding the results from the extended trio-based panel. Common causes of syndromic CS were found in 53 individuals (56%), whereas 26 (28%) had other genetic syndromes, including 17 individuals with syndromes not commonly associated with CS. Only 15 individuals (16%) had negative genetic analyses. Using the defined combination of clinical criteria, we detected among the highest numbers of syndromic CS cases reported, confirmed by a high genetic diagnostic yield of 84%. The observed genetic heterogeneity encourages a broad genetic approach in diagnosing syndromic CS.

Polycystin-1 modulates RUNX2 activation and osteocalcin gene expression via ERK signalling in a human craniosynostosis cell model

Craniosynostosis refers to the premature fusion of one or more cranial sutures leading to skull shape deformities and brain growth restriction. Among the many factors that contribute to abnormal suture fusion, mechanical forces seem to play a major role. Nevertheless, the underlying mechanobiology-related mechanisms of craniosynostosis still remain unknown. Understanding how aberrant mechanosensation and mechanotransduction drive premature suture fusion will offer important insights into the pathophysiology of craniosynostosis and result in the development of new therapies, which can be used to intervene at an early stage and prevent premature suture fusion. Herein, we provide evidence for the first time on the role of polycystin-1 (PC1), a key protein in cellular mechanosensitivity, in craniosynostosis, using primary cranial suture cells isolated from patients with trigonocephaly and dolichocephaly, two common types of craniosynostosis. Initially, we showed that PC1 is expressed at the mRNA and protein level in both trigonocephaly and dolichocephaly cranial suture cells. Followingly, by utilizing an antibody against the mechanosensing extracellular N-terminal domain of PC1, we demonstrated that PC1 regulates runt-related transcription factor 2 (RUNX2) activation and osteocalcin gene expression via extracellular signal-regulated kinase (ERK) signalling in our human craniosynostosis cell model. Altogether, our study reveals a novel mechanotransduction signalling axis, PC1-ERK-RUNX2, which affects osteoblastic differentiation in cranial suture cells from trigonocephaly and dolichocephaly patients.

FACEts of mechanical regulation in the morphogenesis of craniofacial structures

During embryonic development, organs undergo distinct and programmed morphological changes as they develop into their functional forms. While genetics and biochemical signals are well recognized regulators of morphogenesis, mechanical forces and the physical properties of tissues are now emerging as integral parts of this process as well. These physical factors drive coordinated cell movements and reorganizations, shape and size changes, proliferation and differentiation, as well as gene expression changes, and ultimately sculpt any developing structure by guiding correct cellular architectures and compositions. In this review we focus on several craniofacial structures, including the tooth, the mandible, the palate, and the cranium. We discuss the spatiotemporal regulation of different mechanical cues at both the cellular and tissue scales during craniofacial development and examine how tissue mechanics control various aspects of cell biology and signaling to shape a developing craniofacial organ.

A novel p.Pro871Leu missense mutation in SPECC1L gene causing craniosynostosis in a patient

INTRODUCTION

Craniosynostosis is one of the most common craniofacial abnormalities. It involves premature closure of one or more cranial sutures. Mutations in many genes have been and continue to be identified in patients.

SETTINGS AND SAMPLE POPULATION

Whole blood samples were collected from the patient and family members.

MATERIAL AND METHODS

Whole exome sequencing was performed to identify potential mutations in the patient. The results were verified by Sanger sequencing by comparing SPECC1L gene sequence of blood samples from 100 unrelated population-matched controls.

RESULTS

The patient presented with craniosynostosis with fusion of the bicoronal and sagittal sutures. A novel missense mutation (c.2612C>T, p.Pro871Leu) in the SPECC1L gene was identified. Gene analysis showed a missense mutation in exon1 of SPECC1L that led to an amino acid substitution in the region between coiled-coil domain 3 and calponin homology domain.

CONCLUSION

Our observations expand the molecular spectrum of gene mutations in craniosynostosis and emphasize the importance of gene testing in the diagnosis of craniosynostosis. The observations also reinforce the characteristics of SPECC1L-related cranial disorders.

The power of zebrafish models for understanding the co-occurrence of craniofacial and limb disorders

Craniofacial and limb defects are two of the most common congenital anomalies in the general population. Interestingly, these defects are not mutually exclusive. Many patients with craniofacial phenotypes, such as orofacial clefting and craniosynostosis, also present with limb defects, including polydactyly, syndactyly, brachydactyly, or ectrodactyly. The gene regulatory networks governing craniofacial and limb development initially seem distinct from one another, and yet these birth defects frequently occur together. Both developmental processes are highly conserved among vertebrates, and zebrafish have emerged as an advantageous model due to their high fecundity, relative ease of genetic manipulation, and transparency during development. Here we summarize studies that have used zebrafish models to study human syndromes that present with both craniofacial and limb phenotypes. We discuss the highly conserved processes of craniofacial and limb/fin development and describe recent zebrafish studies that have explored the function of genes associated with human syndromes with phenotypes in both structures. We attempt to identify commonalities between the two to help explain why craniofacial and limb anomalies often occur together.