[An infant with premature closure of cranial sutures due to variant of ERF gene and a literature review].

OBJECTIVE: To analyze the clinical and genetic characteristics of an infant with craniosynostosis. METHODS: An infant who was admitted to Wuhan Children's Hospital Affiliated to Tongji Medical College of Huazhong University of Science and Technology in April 2021 due to widening of the lateral ventricles for over a month was selected as the study subject. Clinical data of the patient was collected. Peripheral blood samples were collected from the infant and her parents for chromosomal karyotyping and whole exome sequencing. Candidate variant was verified by Sanger sequencing and bioinformatic analysis. Relevant literature was retrieved from the PubMed, Wanfang and CNKI databases (up to December 2021) by using key words including ERF gene, craniosynostosis, ERF mutation, craniosynostosis and ERF-related craniosynostosis. RESULTS: The infant, a 1-month-and-16-day-old female, was found to have sagittal synostosis by cranial X-ray radiography. Genetic testing revealed that she has harbored a heterozygous c.787C>T (p.Q263*) variant of the ERF gene, which was not found in either parent. Based on the guidelines from the American College of Medical Genetics and Genomics (ACMG), the variant was predicted as pathogenic (PVS1+PS2+PM2_Supporting). In total 63 relevant cases were retrieved from the database, and a total of 64 individuals were analyzed by genetic testing. Most of the cases were sporadic and males. Multiple cranial sutures (including at least two of the sagittal suture, coronal suture, lambdoid suture, and frontal suture) were involved in 45.45% of the cases, and those with sagittal suture closure only have accounted for 20.00%. The main clinical manifestations have included hypertelorism, exophthalmos, development delay, malar dysplasia, etc. Chiari type 1 malformation may present in some patients. Variants of the ERF gene have mainly included splicing and deletional variants, and there was a strong genetic heterogeneity among the infants and their pedigrees. CONCLUSION: The c.787C>T (p.Q263*) variant of the ERF gene probably underlay the craniosynostosis of this infant. Above finding has enriched the phenotype ~ genotype spectrum of the ERF gene.

Pathogenic variants in the paired-related homeobox 1 gene (PRRX1) cause craniosynostosis with incomplete penetrance.

PURPOSE: Studies have previously implicated PRRX1 in craniofacial development, including demonstration of murine Prrx1 expression in the preosteogenic cells of the cranial sutures. We investigated the role of heterozygous missense and loss-of-function (LoF) variants in PRRX1 associated with craniosynostosis. METHODS: Trio-based genome, exome, or targeted sequencing were used to screen PRRX1 in patients with craniosynostosis; immunofluorescence analyses were used to assess nuclear localization of wild-type and mutant proteins. RESULTS: Genome sequencing identified 2 of 9 sporadically affected individuals with syndromic/multisuture craniosynostosis, who were heterozygous for rare/undescribed variants in PRRX1. Exome or targeted sequencing of PRRX1 revealed a further 9 of 1449 patients with craniosynostosis harboring deletions or rare heterozygous variants within the homeodomain. By collaboration, 7 additional individuals (4 families) were identified with putatively pathogenic PRRX1 variants. Immunofluorescence analyses showed that missense variants within the PRRX1 homeodomain cause abnormal nuclear localization. Of patients with variants considered likely pathogenic, bicoronal or other multisuture synostosis was present in 11 of 17 cases (65%). Pathogenic variants were inherited from unaffected relatives in many instances, yielding a 12.5% penetrance estimate for craniosynostosis. CONCLUSION: This work supports a key role for PRRX1 in cranial suture development and shows that haploinsufficiency of PRRX1 is a relatively frequent cause of craniosynostosis.

Histopathologic and Spectrometric Evaluation of Bony Components of Synostotic Suture and Parietal Bone in Children with Sagittal Synostosis.

AIM: To understand the characterization of the ossification process both in the synostotic suture, and the adjacent parietal bone. MATERIAL AND METHODS: The surgical procedure for the 28 patients diagnosed with sagittal synostosis consisted of removing the synostotic bone as a whole, if possible, "Barrel-Stave" relaxation osteotomies, and strip osteotomies to the parietal and temporal bones perpendicular to the synostotic suture. The synostotic (group I) and parietal (group II) bone segments are obtained during osteotomies. Atomic absorption spectrometry was used to determine the amount of calcium in both groups, which is an indicator of ossification. Scanning electron microscopy and immunohistochemistry were employed to assess trabecular bone formation, osteoblastic density, and osteopontin, which is one of the in vivo indicators of new bone formation. RESULTS: Histopathologically, trabecular bone formation scores did not indicate any significant difference between the groups. However, the osteoblastic density and calcium accumulation in group I were higher than those in group II, and the difference was significant. Osteopontin staining scores in cells showing membranous and cytoplasmic staining with osteopontin antibodies significantly increased in group II. CONCLUSION: In this study, we found reduced differentiation of osteoblasts despite their increase in number. Moreover, the osteoblastic maturation rate was low in synostotic sutures, bone resorption becomes slower than new bone formation, and the remodeling rate is low in sagittal synostosis.

The Simultaneous Use of Spring-Mediated Cranioplasty and Distraction Osteogenesis as a Safe Modality for Multi-Suture Craniosynostosis.

ABSTRACT: Craniosynostosis caused by premature fusion of the cranial sutures most commonly involves a single suture. Less commonly, multiple sutures may fuse prematurely resulting in complex craniosynostosis. The authors present 1 case of a patient with unilateral sagittal and unilateral lambdoid craniosynostosis treated safely simultaneous with spring-mediated cranioplasty and distraction osteogenesis.

Paediatric skull growth models: A systematic review of applications to normal skulls and craniosynostoses.

INTRODUCTION: Craniosynostoses affect 1/2000 births and their incidence is currently increasing. Without surgery, craniosynostosis can lead to neurological issues due to restrained brain growth and social stigma due to abnormal head shapes. Understanding growth patterns is essential to develop surgical planning approaches and predict short- and long-term post-operative results. Here we provide a systematic review of normal and pathological cranial vault growth models. MATERIAL AND METHODS: The systematic review of the literature identified descriptive and comprehensive skull growth models with the following criteria: full text articles dedicated to the skull vault of children under 2 years of age, without focus on molecular and cellular mechanisms. Models were analysed based on initial geometry, numerical method, age determination method and validation process. RESULTS: A total of 14 articles including 17 models was reviewed. Four descriptive models were assessed, including 3 models using statistical analyses and 1 based on deformational methods. Thirteen comprehensive models were assessed including 7 finite element models and 6 diffusion models. Results from the current literature showed that successful models combined analyses of cranial vault shape and suture bone formation. DISCUSSION: Growth modelling is central when assessing craniofacial architecture in young patients and will be a key factor in the development of future customized treatment strategies. Recurrent technical difficulties were encountered by most authors when generalizing a specific craniosynostosis model to all types of craniosynostoses, when assessing the role of the brain and when attempting to relate the age with different stages of growth.

Unexpected role of SIX1 variants in craniosynostosis: expanding the phenotype of SIX1-related disorders.

BACKGROUND: Pathogenic heterozygous SIX1 variants (predominantly missense) occur in branchio-otic syndrome (BOS), but an association with craniosynostosis has not been reported. METHODS: We investigated probands with craniosynostosis of unknown cause using whole exome/genome (n=628) or RNA (n=386) sequencing, and performed targeted resequencing of SIX1 in 615 additional patients. Expression of SIX1 protein in embryonic cranial sutures was examined in the Six1nLacZ/+ reporter mouse. RESULTS: From 1629 unrelated cases with craniosynostosis we identified seven different SIX1 variants (three missense, including two de novo mutations, and four nonsense, one of which was also present in an affected twin). Compared with population data, enrichment of SIX1 loss-of-function variants was highly significant (p=0.00003). All individuals with craniosynostosis had sagittal suture fusion; additionally four had bilambdoid synostosis. Associated BOS features were often attenuated; some carrier relatives appeared non-penetrant. SIX1 is expressed in a layer basal to the calvaria, likely corresponding to the dura mater, and in the mid-sagittal mesenchyme. CONCLUSION: Craniosynostosis is associated with heterozygous SIX1 variants, with possible enrichment of loss-of-function variants compared with classical BOS. We recommend screening of SIX1 in craniosynostosis, particularly when sagittal±lambdoid synostosis and/or any BOS phenotypes are present. These findings highlight the role of SIX1 in cranial suture homeostasis.

Single-cell analysis identifies a key role for Hhip in murine coronal suture development.

Craniofacial development depends on formation and maintenance of sutures between bones of the skull. In sutures, growth occurs at osteogenic fronts along the edge of each bone, and suture mesenchyme separates adjacent bones. Here, we perform single-cell RNA-seq analysis of the embryonic, wild type murine coronal suture to define its population structure. Seven populations at E16.5 and nine at E18.5 comprise the suture mesenchyme, osteogenic cells, and associated populations. Expression of Hhip, an inhibitor of hedgehog signaling, marks a mesenchymal population distinct from those of other neurocranial sutures. Tracing of the neonatal Hhip-expressing population shows that descendant cells persist in the coronal suture and contribute to calvarial bone growth. In Hhip-/- coronal sutures at E18.5, the osteogenic fronts are closely apposed and the suture mesenchyme is depleted with increased hedgehog signaling compared to those of the wild type. Collectively, these data demonstrate that Hhip is required for normal coronal suture development.

Septal chondrocyte hypertrophy contributes to midface deformity in a mouse model of Apert syndrome.

Midface hypoplasia is a major manifestation of Apert syndrome. However, the tissue component responsible for midface hypoplasia has not been elucidated. We studied mice with a chondrocyte-specific Fgfr2S252W mutation (Col2a1-cre; Fgfr2S252W/+) to investigate the effect of cartilaginous components in midface hypoplasia of Apert syndrome. In Col2a1-cre; Fgfr2S252W/+ mice, skull shape was normal at birth, but hypoplastic phenotypes became evident with age. General dimensional changes of mutant mice were comparable with those of mice with mutations in EIIa-cre; Fgfr2S252W/+, a classic model of Apert syndrome in mice. Col2a1-cre; Fgfr2S252W/+ mice showed some unique facial phenotypes, such as elevated nasion, abnormal fusion of the suture between the premaxilla and the vomer, and decreased perpendicular plate of the ethmoid bone volume, which are related to the development of the nasal septal cartilage. Morphological and histological examination revealed that the presence of increased septal chondrocyte hypertrophy and abnormal thickening of nasal septum is causally related to midface deformities in nasal septum-associated structures. Our results suggest that careful examination and surgical correction of the nasal septal cartilage may improve the prognosis in the surgical treatment of midface hypoplasia and respiratory problems in patients with Apert syndrome.

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.

Intraosseous Hemangioma of Nasal Bone: Unusual Cause of Epiphora.

Intraosseous hemangioma is very rare, accounting for <1% of bone tumors. Nasal bone origin of it is even rarer. A 63-year-old female patient visited our clinic with a complaint of epiphora. On physical examination, about 2-cm-sized nontender and fixed mass was palpated along the left nasomaxillary suture area. Preoperative magnetic resonance imaging findings were consistent with intraosseous hemangioma originating from the nasal bone. Epiphora was thought to be developed due to the mass effect and a marginal resection of the mass was performed. The defect was reconstructed with a septal cartilage and porous polyethylene implant (Synpor). Postoperatively, epiphora subsided and there has been no sign of recurrence or facial deformity during 6 months of follow-up.

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 FGFR2C342Y/+ model of neonatal onset craniosynostosis or a BALB/c FGFR2C342Y/+ 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 FGFR2C342Y/+ 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 FGFR2C342Y/+ mice. These results indicate that postnatal recombinant TNAP enzyme therapy diminishes craniosynostosis severity in the C57BL/6 FGFR2C342Y/+ neonatal onset mouse model of Crouzon syndrome, and that effects of exogenous TNAP are genetic background dependent.

Acute-on-Chronic Vertex Epidural Hematoma with Diastasis of the Sagittal Suture in an Adult.

BACKGROUND: Vertex epidural hematoma (VEDH) is a rare intracranial mass constituting roughly 2.5% of all epidural hematomas. Bleeding usually derives from the superior sagittal sinus, and presentation is often acute-seldom chronic. Fractures are common, but diastasis of the sagittal suture in adults is unique. We hereby present a case combining these rare features along with diagnostic pitfalls and management. CASE DESCRIPTION: A 43-year-old male with a history of hitting his head against the roll cage of the racing car 3 weeks before admission presented with unbearable headache of 9 Numeric Rating Scale intensity and decreased muscular strength in the right upper limb down to 4/5 of the Lovett scale. The initial Glasgow Outcome Scale was 4. His axial computed tomography scan mimicked convexity hyperostosis, meningioma, or lymphoma. Coronal reconstruction revealed a 102-mL large biconcave mass of mixed hyperdensity and hypodensity at the vertex. Bone window showed sagittal suture diastasis. Contrast-enhanced magnetic resonance imaging gave evidence of superior sagittal sinus detachment. Parietofrontal craniotomy crossing the midline was performed in order to evacuate the hematoma. On 2-week follow-up his pain decreased, his right arm strength recovered, and he had a Glasgow Outcome Scale score of 5. CONCLUSIONS: VEDH can present as an intensifying headache even weeks after purported trauma. Axial computed tomography scans can be tricky because of the blind spot. Even large VEDH may be seen only in the very last few axial slices and may mimic other entities. Coronal reconstructions or additional magnetic resonance imaging come in handy. One-piece parietofrontal craniotomy is an option to approach this hematoma.

Craniofacial Sutural Pattern and Surgical Management in Patients With Different Degrees of Trigonocephaly Severity.

The aim of this study was to identify quantitative tools to classify the severity of trigonocephaly to guide surgical management and predict outcome. METHODS: We reviewed high-resolution computed tomography images of 59 patients with metopic synostosis. We assessed the craniofacial sutural pattern as well as interfrontal and metopic angles, and we related the frontal angulation degree with the sutural pattern, the surgical management, and clinical outcome. RESULTS: We identified 3 groups according to the severity of trigonocephaly. No difference was found between the sutural pattern of nasion complex and severity, whereas the closure of zygomatic maxillary sutures increased with the severity degree (P < 0.05). The operative management was related to the severity degree (P < 0.001) and to the reduced age (P = 0.009). CONCLUSIONS: Interfrontal and metopic angles are complementary measurements to evaluate with high accuracy the degree of frontal angulation. In preoperative assessment, they may guide surgery decision in particular when the choice is not straightforward.

Posterior fossa horns; a new calvarial finding of mucopolysaccharidoses with well-known cranial MRI features

Background/aim: Mucopolysaccharidoses (MPS) are a group of hereditary metabolic diseases. The aim of this study was to share the previously unreported calvarial finding of internal hypertrophy of the occipitomastoid sutures (IHOMS) together with some other well-known cranial MRI findings in this patient series. Materials and methods: A retrospective evaluation was conducted of 80 cranial MRIs of patients who had been diagnosed and followed up with MPS from 2008 to 2019 in our center. Of these patients, 11 had Hurler, 14 had Hunter, 24 had Sanfilippo, 15 had Morquio, 14 had Maroteaux­Lamy, and 2 had Sly disease. The cranial MRIs were assessed in two main groups as parenchymal intradural cranial MRI findings and extradural calvarial findings. Results: The most common parenchymal intradural cranial MRI findings were white matter signal alterations (n = 51, 63%) and perivascular space enlargements (n = 39, 48%). The most common extradural calvarial findings were J-shaped sella (n = 45, 56%) and tympanic effusion (n = 44, 55%). Although IHOMS was defined in a relatively small number of the patients (n = 12, 15%), the prevalence rate was high in MPS type I (n = 6, 54%). Conclusion: The abnormal cranial MRI findings of the MPS patients, including the newly identified IHOMS, may provide diagnostic clues to differentiate the type of the disease in radiological imaging.

Differential Responsiveness to BMP9 between Patent and Fused Suture Progenitor Cells from Craniosynostosis Patients.

BACKGROUND: Several studies have verified that bone morphogenetic proteins (BMPs) may be involved in the development of craniosynostosis; little attention has been focused on the role of BMP9 in cranial suture biology. The authors investigated the role of BMP9 in suture progenitor cells. METHODS: The authors isolated and cultured prematurely fused and internal control patent suture progenitor cells from patients with nonsyndromic craniosynostosis. Overexpression of BMP9 was mediated by adenoviral vectors. Osteoblast and osteoclast differentiation-related markers were evaluated by staining techniques and touchdown quantitative polymerase chain reaction analysis. In vivo analysis of BMP9-induced suture progenitor cell osteogenesis was performed in an ectopic bone formation model. RESULTS: The authors demonstrated that the prematurely fused sutures have a higher endogenous expression of the osteogenic differentiation-related genes than patent sutures, whereas the same pattern of gene expression exists between fused and patent suture progenitor cells. Importantly, both patent and fused suture progenitor cells undergo osteogenic differentiation and express multiple lineage regulators and NELL-1 on BMP9 stimulation, whereas fused suture progenitor cells have a higher basal osteogenic potential than patent suture progenitor cells. BMP9 regulates the expression of osteoclast differentiation-related genes in suture progenitor cells. Forced BMP9 expression enhances the mineralization and maturity of ectopic bone formation of suture progenitor cells implanted in vivo. CONCLUSIONS: The authors' findings suggest that fused suture progenitor cells have elevated osteogenic potential. BMP9 could regulate the expression of multiple osteoblast and osteoclast differentiation-related genes, and NELL-1, in both suture progenitor cells, indicating that BMP9 may play a role in craniosynostosis.

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.

Exome sequencing reveals a novel splice site variant in HUWE1 gene in patients with suspected Say-Meyer syndrome.

Say-Meyer syndrome is a rare and clinically heterogeneous syndrome characterized by trigonocephaly, short stature, developmental delay and hypotelorism. Nine patients with this syndrome have been reported thus far although no causative gene has yet been identified. Here, we report two siblings with clinical phenotypes of Say-Meyer syndrome with moderate to severe intellectual disability and autism spectrum disorder. Cytogenetics and array-based comparative genomic hybridization did not reveal any chromosome abnormalities or copy number alterations. Exome sequencing of the patients revealed a novel X-linked recessive splice acceptor site variant c.145-2A > G in intron 5 of HUWE1 gene in both affected siblings. RT-PCR and sequencing revealed the use of an alternate cryptic splice acceptor site downstream, which led to deletion of six nucleotides resulting loss of two amino acids p.(Cys49-Glu50del) in HUWE1 protein. Deletion of these two amino acids, which are located in a highly conserved region, is predicted to be deleterious and quite likely to affect the function of HUWE1 protein. This is the first report of a potential candidate gene mutation for Say-Meyer syndrome, which was initially described four decades ago.

NGS targeted screening of 100 Scandinavian patients with coronal synostosis.

Craniosynostosis (CS), the premature closure of one or more cranial sutures, occurs both as part of a syndrome or in isolation (nonsyndromic form). Here, we have studied the prevalence and spectrum of genetic alterations associated with coronal suture closure in 100 Scandinavian patients treated at a single craniofacial unit. All patients were phenotypically assessed and analyzed with a custom-designed 63 gene NGS-panel. Most cases (78%) were syndromic forms of CS. Pathogenic and likely pathogenic variants explaining the phenotype were found in 80% of the families with syndromic CS and in 14% of those with nonsyndromic CS. Sixty-five percent of the families had mutations in the CS core genes FGFR2, TWIST1, FGFR3, TCF12, EFNB1, FGFR1, and POR. Five novel pathogenic/likely pathogenic variants in TWIST1, TCF12, and EFNB1 were identified. We also found novel variants in SPECC1L, IGF1R, and CYP26B1 with a possible modulator phenotypic effect. Our findings demonstrate that NGS targeted sequencing is a powerful tool to detect pathogenic mutations in patients with coronal CS and further emphasize the importance of thorough assessment of the patient's phenotype for reliable interpretation of the molecular findings. This is particularly important in patients with complex phenotypes and rare forms of CS.