Ser252Trp mutation in fibroblast growth factor receptor 2 promotes branching morphogenesis in mouse salivary glands.

OBJECTIVES: The purpose of this study was to perform morphological and immunohistochemical (IHC) analysis of the submandibular glands (SMGs) in early development in Apert syndrome model mice (Ap mice). METHODS: ACTB-Cre homozygous mice were mated with fibroblast growth factor receptor 2 (Fgfr2+/Neo-S252W) mice; ACTB-Cre heterozygous mice (ACTB-Cre mice) at embryonic day (E) 13.5 served as the control group, and Fgfr2+/S252W mice (Ap mice) served as the experimental group. Hematoxylin and eosin (H&E) staining was performed on SMGs; Total SMG area and epithelial area were determined, and the epithelial occupancy ratio was calculated. Immunostaining was performed to assess the localization of FGF signaling-related proteins. Next, bromodeoxyuridine (BrdU)-positive cells were evaluated to assess cell proliferation. Finally, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining was performed to assess apoptosis in SMGs. RESULTS: The epithelial occupancy ratio was significantly higher in SMGs of Ap mice compared with that in SMGs of controls. FGF7 and bone morphogenetic protein 4 (BMP4) exhibited different localizations in SMGs of Ap mice compared with SMGs of controls. Cell proliferation was higher in SMGs of Ap mice compared with that of controls; however, apoptosis did not different significantly between the two groups. CONCLUSION: Our results suggest that enhanced FGF signaling conferred by missense mutations in FGFR2 promotes branching morphogenesis in SMGs of Ap mice.

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-siRNAFgfr2S252W) to silence the Fgfr2S252W 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 (Fgfr2S252W/+) 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-siRNAFgfr2S252W, followed by western blot and real-time reverse transcription polymerase chain reaction analyses. RESULTS: After 24 h of Ex-siRNAFgfr2S252W 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-siRNAFgfr2S252W transfection but did not affect Wt-Ob. CONCLUSIONS: These results indicate that exosome-mediated delivery of siRNA targeting Fgfr2S252W is a potential non-invasive treatment for aberrant FGF/FGFR signaling.

A Twist-Box domain of the C. elegans Twist homolog, HLH-8, plays a complex role in transcriptional regulation.

TWIST1 is a basic helix-loop-helix (bHLH) transcription factor in humans that functions in mesoderm differentiation. TWIST1 primarily regulates genes as a transcriptional repressor often through TWIST-Box domain-mediated protein-protein interactions. The TWIST-Box also can function as an activation domain requiring 3 conserved, equidistant amino acids (LXXXFXXXR). Autosomal dominant mutations in TWIST1, including 2 reported in these conserved amino acids (F187L and R191M), lead to craniofacial defects in Saethre-Chotzen syndrome (SCS). Caenorhabditis elegans has a single TWIST1 homolog, HLH-8, that functions in the differentiation of the muscles responsible for egg laying and defecation. Null alleles in hlh-8 lead to severely egg-laying defective and constipated animals due to defects in the corresponding muscles. TWIST1 and HLH-8 share sequence identity in their bHLH regions; however, the domain responsible for the transcriptional activity of HLH-8 is unknown. Sequence alignment suggests that HLH-8 has a TWIST-Box LXXXFXXXR motif; however, its function also is unknown. CRISPR/Cas9 genome editing was utilized to generate a domain deletion and several missense mutations, including those analogous to SCS patients, in the 3 conserved HLH-8 amino acids to investigate their functional role. The TWIST-Box alleles did not phenocopy hlh-8 null mutants. The strongest phenotype detected was a retentive (Ret) phenotype with late-stage embryos in the hermaphrodite uterus. Further, GFP reporters of HLH-8 downstream target genes (arg-1::gfp and egl-15::gfp) revealed tissue-specific, target-specific, and allele-specific defects. Overall, the TWIST-Box in HLH-8 is partially required for the protein's transcriptional activity, and the conserved amino acids contribute unequally to the domain's function.

Molecular Scalpels: The Future of Pediatric Craniofacial Surgery?

SUMMARY: CRISPR-Cas genome editing tools are among the most substantial advances in the life sciences in modern history. Single-dose gene therapies to correct pathogenic mutations have moved quickly from bench to bedside, with several therapeutics designed by CRISPR pioneers entering various stages of clinical investigation. Applications of these genetic technologies are poised to reshape the practice of both medicine and surgery. Many of the most morbid conditions treated by craniofacial surgeons are syndromic craniosynostoses caused by mutations in fibroblast growth factor receptor genes, including Apert, Pfeiffer, Crouzon, and Muenke syndromes. The fact that pathogenic mutations in these genes are recurrent in the majority of affected families presents a unique opportunity to develop "off-the-shelf" gene editing therapies to correct these mutations in affected children. The therapeutic potential of these interventions could reshape pediatric craniofacial surgery, potentially first eliminating the need for midface advancement procedures in affected children.

Does the Mutation Type Affect the Response to Cranial Vault Expansion in Children With Apert Syndrome?

LEVEL OF EVIDENCE: III.

Postnatal Progressive Craniosynostosis in Syndromic Conditions: Two Patients With Saethre-Chotzen Due to TWIST1 Gene Deletions and Review of the Literature.

Saethre-Chotzen syndrome (SCS) is a known craniosynostosis syndrome with a variable presentation of craniofacial and somatic involvement. Congenital coronal craniosynostosis is most commonly observed in SCS; however, progressive postnatal craniosynostosis of other sutures has been reported. The authors present 2 infants with progressive postnatal craniosynostosis and SCS caused by chromosome 7p deletions including the TWIST1 gene. The evolution of their clinical features and a literature review of patients with syndromic, postnatal progressive craniosynostosis illustrate the importance of longitudinal observation and management of these patients.

Cranial Morphology Associated With Syndromic Craniosynostosis: A Potential Detection of Abnormality in Patient's Cranial Growth Using Angular Statistics.

INTRODUCTION: Apert, Crouzon, and Pfeiffer syndromes are common genetic syndromes related to syndromic craniosynostosis (SC), whereby it is a congenital defect that occurs when the cranial growth is distorted. Identifying cranial angles associated with these 3 syndromes may assist the surgical team to focus on a specific cranial part during the intervention planning, thus optimizing surgical outcomes and reducing potential morbidity. OBJECTIVE: The aim of this study is to identify the cranial angles, which are associated with Apert, Crouzon, and Pfeiffer syndromes. METHODS: The cranial computed tomography scan images of 17 patients with SC and 22 control groups aged 0 to 12 years who were treated in the University Malaya Medical Centre were obtained, while 12 angular measurements were attained using the Mimics software. The angular data were then divided into 2 groups (patients aged 0 to 24 months and >24 months). This work proposes a 95% confidence interval (CI) for angular mean to detect the abnormality in patient's cranial growth for the SC syndromes. RESULTS: The 95% CI of angular mean for the control group was calculated and used as an indicator to confirm the abnormality in patient's cranial growth that is associated with the 3 syndromes. The results showed that there are different cranial angles associated with these 3 syndromes. CONCLUSIONS: All cranial angles of the patients with these syndromes lie outside the 95% CI of angular mean of control group, indicating the reliability of the proposed CI in the identification of abnormality in the patient's cranial growth.

Auricles Anomalies in Patients With a TCF12 Gene Mutation.

Craniostenosis is a morphological anomaly affecting about 0.5 of 1000 births and one third of the cases are of genetic origin. Among the syndromes responsible for craniostenosis, there is the Saethre-Chotzen syndrome due to a mutation of the TWIST 1 gene located on chromosome 7. This polymalformative syndrome classically includes a particular morphology of the auricles. The penetrance is variable and results in a phenotypic variability at the origin of "Saethre-Chotzen like" clinical pictures for which the TWIST 1 gene mutation is sometimes not found. Recently, the TCF 12 gene has been implicated in some of these cases. Among the multiple facial malformations, we have carefully examined the particular morphology of the auricle of these patients. The authors found several abnormalities in patients with a TCF 12 gene mutation, namely a thickened and hammered upper pole of the helix, a narrow concha without crux cymbae and a thickened lobe. These morphological features may guide the diagnosis and allow an earlier search for a TCF 12 gene mutation.

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

Syndromic craniosynostosis (CS) patients exhibit early, bony fusion of calvarial sutures and cranial synchondroses, resulting in craniofacial dysmorphology. In this study, we chronologically evaluated skull morphology change after abnormal fusion of the sutures and synchondroses in mouse models of syndromic CS for further understanding of the disease. We found fusion of the inter-sphenoid synchondrosis (ISS) in Apert syndrome model mice (Fgfr2S252W/+ ) around 3 weeks old as seen in Crouzon syndrome model mice (Fgfr2cC342Y/+ ). We then examined ontogenic trajectories of CS mouse models after 3 weeks of age using geometric morphometrics analyses. Antero-ventral growth of the face was affected in Fgfr2S252W/+ and Fgfr2cC342Y/+ mice, while Saethre-Chotzen syndrome model mice (Twist1+/- ) did not show the ISS fusion and exhibited a similar growth pattern to that of control littermates. Further analysis revealed that the coronal suture synostosis in the CS mouse models induces only the brachycephalic phenotype as a shared morphological feature. Although previous studies suggest that the fusion of the facial sutures during neonatal period is associated with midface hypoplasia, the present study suggests that the progressive postnatal fusion of the cranial synchondrosis also contributes to craniofacial dysmorphology in mouse models of syndromic CS. These morphological trajectories increase our understanding of the progression of syndromic CS skull growth.

Clinical and Genetic Studies of the First Monozygotic Twins with Pfeiffer Syndrome.

Objective: To report the clinical and radiographic findings and molecular etiology of the first monozygotic twins affected with Pfeiffer syndrome. Methods: Clinical and radiographic examination and whole exome sequencing were performed on two monozygotic twins with Pfeiffer syndrome. Results: An acceptor splice site mutation in FGFR2 (c.940-2A>G) was detected in both twins. The father and both twins shared the same haplotype, indicating that the mutant allele was from their father's chromosome who suffered severe upper airway obstruction and subsequent obstructive sleep apnea. Hypertrophy of nasal turbinates appears to be a newly recognized finding of Pfeiffer syndrome. Increased intracranial pressure in both twins were corrected early by fronto-orbital advancement with skull expansion and open osteotomy, in order to prevent the more severe consequences of increased intracranial pressure, including hydrocephalus, the bulging of the anterior fontanelle, and the diastasis of suture. Conclusions: Both twins carried a FGFR2 mutation and were discordant for lambdoid synostosis. Midface hypoplasia, narrow nasal cavities, and hypertrophic nasal turbinates resulted in severe upper airway obstruction and subsequent obstructive sleep apnea in both twins. Hypertrophy of the nasal turbinates appears to be a newly recognized finding of Pfeiffer syndrome. Fronto-orbital advancement with skull expansion and open osteotomy was performed to treat increased intracranial pressure in both twins. This is the first report of monozygotic twins with Pfeiffer syndrome.

TWIST1, a gene associated with Saethre-Chotzen syndrome, regulates extraocular muscle organization in mouse.

Heterozygous loss of function mutations in TWIST1 cause Saethre-Chotzen syndrome, which is characterized by craniosynostosis, facial asymmetry, ptosis, strabismus, and distinctive ear appearance. Individuals with syndromic craniosynostosis have high rates of strabismus and ptosis, but the underlying pathology is unknown. Some individuals with syndromic craniosynostosis have been noted to have absence of individual extraocular muscles or abnormal insertions of the extraocular muscles on the globe. Using conditional knock-out alleles for Twist1 in cranial mesenchyme, we test the hypothesis that Twist1 is required for extraocular muscle organization and position, attachment to the globe, and/or innervation by the cranial nerves. We examined the extraocular muscles in conditional Twist1 knock-out animals using Twist2-cre and Pdgfrb-cre drivers. Both are expressed in cranial mesoderm and neural crest. Conditional inactivation of Twist1 using these drivers leads to disorganized extraocular muscles that cannot be reliably identified as specific muscles. Tendons do not form normally at the insertion and origin of these dysplastic muscles. Knock-out of Twist1 expression in tendon precursors, using scleraxis-cre, however, does not alter EOM organization. Furthermore, developing motor neurons, which do not express Twist1, display abnormal axonal trajectories in the orbit in the presence of dysplastic extraocular muscles. Strabismus in individuals with TWIST1 mutations may therefore be caused by abnormalities in extraocular muscle development and secondary abnormalities in innervation and tendon formation.

Mother and Daughter Carrying of the Same Pathogenic Variant in FGFR2 with Discordant Phenotype.

Craniosynostosis are a heterogeneous group of genetic conditions characterized by the premature fusion of the skull bones. The most common forms of craniosynostosis are Crouzon, Apert and Pfeiffer syndromes. They differ from each other in various additional clinical manifestations, e.g., syndactyly is typical of Apert and rare in Pfeiffer syndrome. Their inheritance is autosomal dominant with incomplete penetrance and one of the main genes responsible for these syndromes is FGFR2, mapped on chromosome 10, encoding fibroblast growth factor receptor 2. We report an FGFR2 gene variant in a mother and daughter who present with different clinical features of Crouzon syndrome. The daughter is more severely affected than her mother, as also verified by a careful study of the face and oral cavity. The c.1032G>A transition in exon 8, already reported as a synonymous p.Ala344 = variant in Crouzon patients, also activates a new donor splice site leading to the loss of 51 nucleotides and the in-frame removal of 17 amino acids. We observed lower FGFR2 transcriptional and translational levels in the daughter compared to the mother and healthy controls. A preliminary functional assay and a molecular modeling added further details to explain the discordant phenotype of the two patients.

[A case of Pfeiffer syndrome caused by FGFR2 gene variation].

A 29-month-old male child with FGFR2 heterozygous missense mutation at birth was diagnosed as Pfeiffer syndrome. He was treating for binocular exophthalmos and exposed keratitis in Beijing Tongren Hospital Affiliated to Capital Medical University. The child had skull fusion (clover head), obvious exophthalmos, deformity of fingers and toes, ankylosis of elbow joint or bony fusion, accompanied by neurological complications and growth retardation; FGFR2 (NM_001144916) gene c.679T>G (thymine>guanine) and p.c227gG(cysteine>glycine) heterozygous missense mutations were found in the the child, and his parents did not carry the same mutation. Pfeiffer syndrome type Ⅱ was diagnosed. Permanent adhesion of eyelid margin was performed under general anesthesia, and the postoperative condition was stable.

Processes and patterns: Insights on cranial covariation from an Apert syndrome mouse model.

BACKGROUND: Major cell-to-cell signaling pathways, such as the fibroblast growth factors and their four receptors (FGF/FGFR), are conserved across a variety of animal forms. FGF/FGFRs are necessary to produce several "vertebrate-specific" structures, including the vertebrate head. Here, we examine the effects of the FGFR2 S252W mutation associated with Apert syndrome on patterns of cranial integration. Our data comprise micro-computed tomography images of newborn mouse skulls, bred to express the Fgfr2 S252W mutation exclusively in either neural crest or mesoderm-derived tissues, and mice that express the Fgfr2 S252W mutation ubiquitously. RESULTS: Procrustes-based methods and partial least squares analysis were used to analyze craniofacial integration patterns. We found that deviations in the direction and degree of integrated shape change across the mouse models used in our study were potentially driven by the modular variation generated by differing expression of the Fgfr2 mutation in cranial tissues. CONCLUSIONS: Our overall results demonstrate that covariation patterns can be biased by the spatial distribution and magnitude of variation produced by underlying developmental-genetic mechanisms that often impact the phenotype in disproportionate ways.

Phenotypic variability of syndromic craniosynostosis caused by c.833G > T in FGFR2: Clinical and genetic evaluation of eight patients from a five-generation family.

OBJECTIVE: Craniosynostosis is the result of the early fusion of cranial sutures. Syndromic craniosynostosis includes but not limited by Crouzon syndrome and Pfeiffer syndrome. Considerable phenotypic overlap exists among these syndromes and mutations in FGFR2 may cause different syndromes. This study aims to investigate the explanation of the phenotypic variability via clinical and genetic evaluation for eight patients in a large pedigree. METHODS: For each patient, comprehensive physical examination, cranial plain CT scan with three-dimensional CT reconstruction (3D-CT), and eye examinations were conducted. Whole exome sequencing was applied for genetic diagnosis of the proband. Variants were analyzed and interpreted following the ACMG/AMP guidelines. Sanger sequencing was performed to reveal genotypes of all the family members. RESULTS: A pathogenic variant in the FGFR2 gene, c.833G > T (p.C278F), was identified and proved to be co-segregate with the disease. Some symptoms of head, hearing, vision, mouth, teeth expressed differently by affected individuals. Nonetheless, all the eight patients manifested core symptoms of Crouzon syndrome without abnormality in the limbs, which could exclude diagnosis of Pfeiffer syndrome. CONCLUSION: We have established clinical and genetic diagnosis of Crouzon syndrome for eight patients in a five-generation Chinese family. Variability of clinical features among these familial patients was slighter than that in previously reported sporadic cases.

Excessive osteoclast activation by osteoblast paracrine factor RANKL is a major cause of the abnormal long bone phenotype in Apert syndrome model mice.

The fibroblast growth factor (FGF)/FGF receptor (FGFR) signaling pathway plays important roles in the development and growth of the skeleton. Apert syndrome caused by gain-of-function mutations of FGFR2 results in aberrant phenotypes of the skull, midface, and limbs. Although short limbs are representative features in patients with Apert syndrome, the causative mechanism for this limb defect has not been elucidated. Here we quantitatively confirmed decreases in the bone length, bone mineral density, and bone thickness in the Apert syndrome model of gene knock-in Fgfr2S252W/+ (EIIA-Fgfr2S252W/+ ) mice. Interestingly, despite these bone defects, histological analysis showed that the endochondral ossification process in the mutant mice was similar to that in wild-type mice. Tartrate-resistant acid phosphatase staining revealed that trabecular bone loss in mutant mice was associated with excessive osteoclast activity despite accelerated osteogenic differentiation. We investigated the osteoblast-osteoclast interaction and found that the increase in osteoclast activity was due to an increase in the Rankl level of osteoblasts in mutant mice and not enhanced osteoclastogenesis driven by the activation of FGFR2 signaling in bone marrow-derived macrophages. Consistently, Col1a1-Fgfr2S252W/+ mice, which had osteoblast-specific expression of Fgfr2 S252W, showed significant bone loss with a reduction of the bone length and excessive activity of osteoclasts was observed in the mutant mice. Taken together, the present study demonstrates that the imbalance in osteoblast and osteoclast coupling by abnormally increased Rankl expression in Fgfr2S252W/+ mutant osteoblasts is a major causative mechanism for bone loss and short long bones in Fgfr2S252W/+ mice.

Expansion of the phenotypic and mutational spectrum of Carpenter syndrome.

Carpenter syndrome 1 (CRPT1) is an acrocephalopolysyndactyly (ACPS) disorder characterized by craniosynostosis, polysyndactyly, obesity, and other malformations. It is caused by mutations in the gene RAB23. We are reporting on two patients from two unrelated consanguineous Egyptian families. Patient 1 presented with an atypical clinical presentation of Carpenter syndrome including overgrowth with advanced bone age, epileptogenic changes on electroencephalogram and autistic features. Patient 2 presented with typical clinical features suggestive of Carpenter syndrome. Therefore, Patient 1 was subjected to whole exome sequencing (WES) to find an explanation for his unusual features and Patient 2 was subjected to Sanger sequencing of the coding exons of theRAB23 gene to confirm the diagnosis. We identified a novel homozygous missense RAB23 variant (NM_001278668:c.T416C:p.Leu139Pro) in Patient 1 and a novel homozygous splicing variant (NM_016277.5:c.398+1G > A) in Patient 2. We suggest that the overgrowth with advanced bone age, electroencephalogram epileptogenic changes, and autistic features seen in Patient 1 are an expansion of the Carpenter phenotype and could be due to the novel missense RAB23 variant. Additionally, the novel identified RAB23 variants in Patient 1 and 2 broaden the spectrum of variants associated with Carpenter syndrome.

Quantitative Morphologic Analysis of Cranial Vault in Twist1+/- Mice: Implications in Craniosynostosis.

BACKGROUND: The haploinsufficiency in the TWIST1 gene encoding a basic helix-loop-helix transcription factor is a cause of one of the craniosynostosis syndromes, Saethre-Chotzen syndrome. Patients with craniosynostosis usually require operative release of affected sutures, which makes it difficult to observe the long-term consequence of suture fusion on craniofacial growth. METHODS: In this study, we performed quantitative analysis of morphologic changes of the skull in Twist1 heterozygously-deleted mice (Twist1+/-) with micro-computed tomographic images. RESULTS: In Twist1+/- mice, fusion of the coronal suture began before postnatal day 14 and progressed until postnatal day 56, during which morphologic changes occurred. The growth of the skull was not achieved by a constant increase in the measured distances in wild type mice; some distances in the top-basal axis were decreased during the observation period. In the Twist1+/- mouse, growth in the top-basal axis was accelerated and that of the frontal cranium was reduced. In the unicoronal suture fusion mouse, the length of the zygomatic arch of affected side was shorter in the Twist1+/- mouse. In one postnatal day 56 Twist1+/- mouse with bilateral coronal suture fusion, asymmetric zygomatic arch length was identified. CONCLUSION: The authors'results suggest that measuring the length of the left and right zygomatic arches may be useful for early diagnosis of coronal suture fusion and for estimation of the timing of synostosis, and that more detailed study on the growth pattern of the normal and the synostosed skull could provide prediction of the risk of resynostosis. CLINICAL RELEVANCE STATEMENT: The data from this study can be useful to better understand the cranial growth pattern in patients with craniosynostosis.

Familial Pfeiffer Syndrome: Variable Manifestations and Role of Multidisciplinary Team Care.

Pfeiffer syndrome is one of the autosomal dominant craniofacial syndromes. Classical clinical manifestations are coronal suture synostosis causing brachycephaly, midface retrusion, airway compromise, broad thumbs, and toes. Pfeiffer syndrome type I (classic type) is associated with FGFR1 mutation. However, wide range of clinical manifestations, with and without craniosynostosis, have been reported. Here, we present a family of Pfeiffer syndrome across 3 generations with identical FGFR1: c.755C>G (p.Pro252Arg) mutation. Where the members of the youngest generation have no cranial involvement. Lastly, we propose a guideline management for familial Pfeiffer syndrome management.