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.

The developing mouse coronal suture at single-cell resolution.

Sutures separate the flat bones of the skull and enable coordinated growth of the brain and overlying cranium. The coronal suture is most commonly fused in monogenic craniosynostosis, yet the unique aspects of its development remain incompletely understood. To uncover the cellular diversity within the murine embryonic coronal suture, we generated single-cell transcriptomes and performed extensive expression validation. We find distinct pre-osteoblast signatures between the bone fronts and periosteum, a ligament-like population above the suture that persists into adulthood, and a chondrogenic-like population in the dura mater underlying the suture. Lineage tracing reveals an embryonic Six2+ osteoprogenitor population that contributes to the postnatal suture mesenchyme, with these progenitors being preferentially affected in a Twist1+/-; Tcf12+/- mouse model of Saethre-Chotzen Syndrome. This single-cell atlas provides a resource for understanding the development of the coronal suture and the mechanisms for its loss in craniosynostosis.

The limits of clinical findings in similar phenotypes, from Carpenter to ATRX syndrome using a whole exome sequencing approach: a case review.

BACKGROUND: The diagnostic process for uncommon disorders with similar manifestations is complicated and requires newer technology, like gene sequencing for a correct diagnosis. MAIN BODY: We described two brothers clinically diagnosed with Carpenter syndrome, which is a condition characterized by the premature fusion of certain skull bones (craniosynostosis), abnormalities of the fingers and toes, and other developmental problems, for which they underwent craniotomies. However, whole exome sequencing analysis concluded a novel pathological variation in the ATRX chromatin remodeler gene and protein remodeling demonstrated structural variations that decreased the function, giving a completely different diagnosis to these patients. CONCLUSION: Our study focuses on the importance of using newer technologies, such as whole exome sequencing analysis, in patients with ambiguous phenotypes.

Autopsy Case of Pfeiffer Syndrome Type 2, a Phenotype of Fibroblast Growth Factor Receptor-Associated Craniosynostosis Syndromes, with Tracheal Cartilage Sleeve and Abnormal Hyperplasia of Bronchial Cartilages.

BACKGROUND Pfeiffer syndrome (PS) is a fibroblast growth factor receptor (FGFR)-associated craniosynostosis syndrome, characterized by abnormally broad and medially deviated thumbs and great toes. Tracheal cartilage sleeve (TCS) is associated with several FGFR-associated craniosynostosis syndromes, including PS. TCS is an airway malformation in which the tracheal cartilage rings fuse with each other to form a sleeve of cartilage. CASE REPORT The patient was a 4-year-old girl with PS, TCS, and abnormal hyperplasia of non-fused intrapulmonary cartilages. The patient showed cranial dysplasia on prenatal ultrasonography. At birth, a cloverleaf skull in association with hydrocephalus and digital malformations was apparent. These findings were consistent with PS type 2. The diagnosis of PS type 2 was confirmed from a genetic test detecting a FGFR2 mutation (Y340C). During the clinical course, she underwent several surgeries, including ventriculoperitoneal shunts, sequential cranioplasty surgeries, and tracheotomy due to upper airway abnormalities. At 4 years old, she died of multiple organ failure following aspiration pneumonia. The autopsy revealed that the tracheal cartilages had fused with each other, resulting in a condition called TCS, in which the cartilage rings and tracheal ligaments were absent. The lungs were poorly aerated, and the dilated bronchi had thickened walls surrounded by many cartilage fragments, mainly at the hilum. These cartilages tended to overlap at both ends, did not fuse, and were greatly altered in size and shape. CONCLUSIONS We report the results of autopsy for PS with the first histopathological findings for the lungs and other visceral organs.

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.

Novel GLI3 pathogenic variants in complex pre- and postaxial polysyndactyly and Greig cephalopolysyndactyly syndrome.

Polydactyly is a limb malformation and can occur as nonsyndromic polydactyly, syndromic polydactyly, or along with other limb defects. A few genes have been identified that cause various forms of syndromic and nonsyndromic polydactyly, of which GLI3 has been extensively explored. In the present study, GLI3 gene was screened by direct resequencing in 15 polydactyly cases with or without other anomalies. GLI3 screening revealed two novel pathogenic variants, NM_000168.6:c.3414delC [p.(H1138Qfs*68)] and NM_000168.6:c.1862C>T [p.(P621L)], found in two unrelated cases of familial complex pre- and postaxial polysyndactyly and sporadic Greig cephalopolysyndactyly syndrome (GCPS), respectively. The first pathogenic GLI3 variant, NM_000168.6:c.3414delC, causes premature protein truncation at the C-terminal domain of GLI3. Alternatively, the second pathogenic variant, NM_000168.6:c.1862C>T, lies in the DNA binding domain of GLI3 protein and may affect its hydrophobic interaction with DNA. Both pathogenic GLI3 variants had reduced transcriptional activity in HEK293 cells that likely had led to haploinsufficiency and, consequently, the clinical phenotypes. Overall, the present study reports a novel familial case of complex pre- and postaxial polysyndactyly and the underlying novel pathogenic GLI3 variant expanding the clinical criteria for GLI3 mutational spectrum to complex pre- and postaxial polysyndactyly. Furthermore, this study also reports a novel GLI3 pathogenic variant linked to GCPS, highlighting the known genotype-phenotype correlation.

Saethre-Chotzen syndrome: long-term outcome of a syndrome-specific management protocol.

AIM: To assess the long-term outcomes of our management protocol for Saethre-Chotzen syndrome, which includes one-stage fronto-orbital advancement. METHOD: All patients born with Saethre-Chotzen syndrome between January 1992 and March 2017 were included. Evaluated parameters included occipital frontal head circumference (OFC), fundoscopy, neuroimaging (ventricular size, tonsillar position, and the presence of collaterals/an abnormal transverse sinus), polysomnography, and ophthalmological outcomes. The relationship between papilledema and its associated risk factors was evaluated with Fisher's exact test. RESULTS: Thirty-two patients (21 females, 11 males) were included. Median (SD) age at first surgery was 9.6 months (3.1mo) for patients who were primarily referred to our center (range: 3.6-13.0mo), the median (SD) age at last follow-up was 13 years (5y 7mo; range: 3-25y). Seven patients had papilledema preoperatively, which recurred in two. Two patients had papilledema solely after first surgery. Second cranial vault expansion was indicated in 20%. Thirteen patients had an OFC deflection, indicating restricted skull growth, one patient had ventriculomegaly, and none developed hydrocephalus. Eleven patients had emissary veins, while the transverse sinus was aberrant unilaterally in 13 (hypoplastic n=10 and absent n=3). Four patients had mild tonsillar descent, one of which was a Chiari type I malformation. Four patients had obstructive sleep apnoea (two mild, one moderate, and one severe). An aberrant transverse sinus was associated with papilledema (p=0.01). INTERPRETATION: Single one-stage fronto-orbital advancement was sufficient to prevent intracranial hypertension for 80% of our patients with Saethre-Chotzen syndrome. Follow-up should focus on OFC deflection and venous anomalies.

A novel FGFR2 (S137W) mutation resulting in Apert syndrome: A case report.

RATIONALE: Apert syndrome (AS) is an autosomal dominant inheritance pattern of the most severe craniosynostosis syndrome. AS is characterized by synostosis of cranial sutures and acrocephaly, including brachycephaly, midfacial hypoplasia, and syndactyly of the hands and feet. Patients with AS often present with craniosynostosis, severe syndactyly, and skin, skeletal, brain, and visceral abnormalities. PATIENT CONCERNS: A pregnant Chinese woman presented with a fetus at 23 + 5 weeks of gestation with suspected AS in a prenatal ultrasound examination. Following ultrasound, the pregnancy underwent spontaneous abortion. Gene sequencing was performed on the back skin of the dead fetus. DIAGNOSIS: The diagnosis of AS was confirmed on the basis of clinical manifestations of the fetus, and a de novo mutation in the fibroblast growth factor receptor 2 (FGFR2) gene was identified. INTERVENTIONS: The couple finally chose to terminate the pregnancy based on the ultrasonic malformations and the risk of the parents having a neonate with AS in the future is small. However, any future pregnancy must be assessed by prenatal diagnosis. OUTCOMES: The dead fetus presented with bilateral skull deformation. Additionally, there were bilateral changes to the temporal bone caused by inwards movement leading to concave morphology, a "clover" sign, and syndactyly from the index finger/second toe to the little finger/little toe. AS was diagnosed by genetic testing, which showed a p.S137W (c.410C>G, chr10:123279677) mutation in the FGFR2 gene. LESSONS: Clinicians should be aware that there are a variety of ultrasound findings for AS. Therefore, genetic testing should be used when appropriate to confirm diagnosis of AS.

Cranial Fossa Volume and Morphology Development in Apert Syndrome.

BACKGROUND: Apert syndrome causes normal or enlarged intracranial volume overall as patients grow. This study aimed to trace the segmental anterior, middle, and posterior cranial fossae volume and structural morphology in these patients, to help discern a more focused and individualized surgical treatment plan for patients with Apert syndrome. METHODS: This study included 82 preoperative computed tomographic scans (Apert, n = 32; control, n = 50) divided into five age-related subgroups. The scans were measured using image processing and three-dimensional modeling software. RESULTS: The middle cranial fossa volume was increased and was the earliest change noted. It was increased by 45 percent (p = 0.023) compared with controls before 6 months of age and remained increased into adulthood (161 percent, p = 0.016), with gradually increasing severity. The anterior and posterior cranial fossae volumes also increased, by 35 percent (p = 0.032) and 39 percent (p = 0.007), respectively. Increased depth of cranial fossae contributed most to the increase in volumes of patients with Apert syndrome, with correlation coefficients of 0.799, 0.908, and 0.888 for anterior, middle, and posterior cranial fossa, respectively. The intracranial volume was increased 12 percent (p = 0.098) across the entire test age range (0 to 26 years old), but only had statistical significance during the age range of 6 to 18 years (22 percent, p = 0.001). CONCLUSIONS: Malformation of the middle cranial fossa is an early, perhaps the initial, pivotal cranial morphologic change in Apert syndrome. Increased cranial fossae depth is an inherent characteristic of the maldevelopment. Normalization of cranial volume and circumference overall may not achieve a normal skull structure, as it does not correct regional craniocerebral disproportion.

Síndrome de Apert. Reporte de caso / Apert syndrome. Case report

Introducción: El síndrome de Apert, o acrocefalosindactilia tipo I, es un síndrome caracte­rizado por craneosinostosis, acompañada de sindactilia simétrica en las cuatro extremidades, alteraciones maxilofaciales, cutáneas y retardo mental variable. Este síndrome se debe a una mutación en el gen del receptor 2 del factor del crecimiento fibroblástico (FGFR2), el cual se expresa de manera autosómica dominante (AD) Caso clínico: Se presenta caso de adolescente masculino de 24 años de edad, con las características fenotípicas clásicas de este síndrome como la acrocefalia y la sindactilia en manos y pies. Discusión: El síndrome de Apert hace parte de lo que hoy se denomina un espectro de enfermedades causadas por la mutación en el gen FGFR2 que se caracterizan por anorma­lidades en el cráneo y las extremidades. Este gen es necesario para la osificación normal y también está implicado en la diferenciación neural. Sus mutaciones producen un receptor anormal que funciona aun sin la unión de su ligando "ganancia de función", lo que se traduce en una osificación temprana de los huesos, en grados variables, dependiendo del sitio exacto de la mutación.

Introduction: Apert's syndrome or acrocefalosindactyly tipe I, is a syndrome character­ized by craniosynostosis, symmetric syndactylia in hands and feet's, maxillofacial and cutaneous disorders, and variable mental retardation. This syndrome is due to a mutation in the gene that encode the fibroblast growth factor Receptor 2 (FGFR2), which has an autosomal dominant inheritance (AD). Case report: We report a male24 yearsoldteen, with the classical phenotypic characteristics of this syndrome, as acrocefalia and syndactyly of hands and feet. Discussion: Apert's syndrome is part of what today is called a spectrum of disease caused by a mutation in the FGFR2 gene, which is characterized by abnormalities in the skull and extremities. This gene is required for normal ossification and is also involved in neural differentiation. Mutations cause an abnormal receptor that functions even without the binding of its ligand "gain of function", which translates into an early ossification of the bones, in varying degrees, depending on the exact site of the mutation.

Apert syndrome: prenatal diagnosis challenge.

Apert syndrome is a rare genetic disorder that manifests as craniosynostosis, craniofacial and limb dysmorphic features. Mutations in fibroblast growth factor receptor 2 (FGFR2) gene account for almost all cases. Given the impact it can have throughout life, prenatal management becomes a challenge. A healthy 33-year-old woman, gravida 4, para 0, was referred to routine ultrasound at 22 weeks of gestation. Atypical cranial morphology with prominent forehead, ocular proptosis, hypertelorism and mitten hands were detected. Genetic investigation revealed an FGFR2 gene mutation (c.755C>G(p.Ser252Trp)), confirming the diagnosis. Magnetic resonance showed brachycephaly, turricephaly and cortical malformation. Following counselling, parents requested medical termination of pregnancy. Macroscopic features were consistent with ultrasound findings. This case emphasises the importance of early diagnosis to provide the best family counselling and prenatal management. A multidisciplinary team, consisting of an obstetrician with ultrasonography experience, a medical geneticist and a fetal pathologist, should conduct these cases.

Airway Analysis in Apert Syndrome.

BACKGROUND: Apert syndrome is frequently combined with respiratory insufficiency, because of the midfacial deformity which, in turn, is influenced by the malformation of the skull base. Respiratory impairment resulting from Apert syndrome is caused by multilevel limitations in airway space. Therefore, this study evaluated the segmented nasopharyngeal and laryngopharyngeal anatomy to clarify subcranial anatomy in children with Apert syndrome and its relevance to clinical management. METHODS: Twenty-seven patients (Apert syndrome, n = 10; control, n = 17) were included. All of the computed tomographic scans were obtained from the patients preoperatively, and no patient had confounding disease comorbidity. Computed tomographic scans were analyzed using Surgicase CMF. Craniometric data relating to the midface, airway, and subcranial structures were collected. Statistical significance was determined using t test analysis. RESULTS: Although all of the nasal measurements were consistent with those of the controls, the nasion-to-posterior nasal spine, sphenethmoid-to-posterior nasal spine, sella-to-posterior nasal spine, and basion-to-posterior nasal spine distances were decreased 20 (p < 0.001), 23 (p = 0.001), 29 (p < 0.001), and 22 percent (p < 0.001), respectively. The distance between bilateral gonions and condylions was decreased 17 (p = 0.017) and 18 percent (p = 0.004), respectively. The pharyngeal airway volume was reduced by 40 percent (p = 0.01). CONCLUSION: The airway compromise seen in patients with Apert syndrome is attributable more to the pharyngeal region than to the nasal cavity, with a gradually worsening trend from the anterior to the posterior airway, resulting in a significantly reduced volume in the hypopharynx.

Craniofacial abnormalities in a murine model of Saethre-Chotzen Syndrome.

BACKGROUND: Saethre-Chotzen Syndrome (SCS) is an autosomal dominant syndrome that occurs due to a mutation or deletion of the Twist1 gene at chromosome 7p21. Our aim was to conduct a morphometric analysis of the craniofacial features in the mouse associated with a Twist1+/- mutation. METHODS: Micro-computed imaging was conducted for the skulls of forty skeletally mature mice, equally distributed by sex (male and female) and two genotypes (Twist1+/- or murine model of SCS; and Twist1+/+ or wild-type). A morphometric analysis was carried out for eight parameters for the maxillary-zygomatico-temporal region, 10 parameters for the mandible and three parameters for teeth from three-dimensional reconstructions. RESULTS: Compared with wild-type, the murine model of SCS showed these trends: (1) maxillary-zygomatico-temporal region, significantly shorter length and width posteriorly (p<0.05), (2) mandible, significantly reduced height and width (p<0.05), and (3) teeth, significantly shorter height, shorter mesio-distal width but longer bucco-lingual width (p<0.05). In the murine model of SCS, the key morphological variations included incomplete ossification of the temporal bone and zygomatic arch, twisting and/or incomplete ossification of the palatal process of the maxilla, premaxilla and the ventral nasal concha, as well as bifid coronoid processes. CONCLUSIONS: The skeletal and dental alterations in the height, length and width provide a foundation for large-scale phenomics studies, which will improve existing knowledge of the Twist1 signalling cascade. This is relevant given the predicted shift towards minimally invasive molecular medical treatment for craniosynostosis.

Apert syndrome without craniosynostosis.

BACKGROUND: Apert syndrome is a rare form of syndromic craniosynostosis, also known as acrocephalosyndactyly, which is a disorder characterized by a unique set of craniofacial, hand, and foot abnormalities. Diagnosis is made through a genetic analysis, where the mutation of FGFR2, Ser252Trp, and Pro253Arg confirms the diagnosis. CASE PRESENTATION: Although craniosynostosis is the most common characteristic in clinical presentation, we present an atypical case of a one-and-a-half-year-old girl with Apert syndrome confirmed by genetic testing but without craniosynostosis.

The turricephaly index: A validated method for recording turricephaly and its natural history in Apert syndrome.

INTRODUCTION: We present the CT scan-derived turricephaly index (TI) as a quotient of the maximal occipito-frontal length of the skull to the distance from the centre of the sella to the highest point on the vertex as a validated tool for assessing turricephaly and evaluating surgical techniques aimed at reducing it. MATERIALS AND METHODS: Measurements taken from CTs of non-operated children with Apert syndrome and age-matched controls were analysed using Centricity PACS system (from the lateral scout image) and the thick-sliced Osirix tool. CTs from non-operated children with Apert syndrome were used to investigate the natural history of their turricephaly both as a group and individually. RESULTS: There was statistically significant agreement between measurements taken from the CT scout and Osirix for 42 control children (R2 = 0.97) and 42 children with Apert syndrome (R2 = 0.98) and between two separate observers. There was a statistically significant difference (p < 0.001) between CT scout-derived TI value between controls (1.73 ± 0.12, range 1.46-1.99) and Apert children (1.42 ± 0.15, range 1.13-1.73). Analysis of 113 CTs of 65 non-operated children with Apert syndrome showed a decrease in turricephaly with age (positive spearman correlation: r = 0.50, p < 0.001). Analysis of 37 CTs of those with multiple (>2) CT's showed a similar decrease in turricephaly in the individual child (p < 0.001). CONCLUSIONS: TI derived from the CT scout view provides a simple, objective and validated method for assessing turricephaly. We recommend it for monitoring and for the prospective evaluation of reconstructive techniques in children with complex/syndromic craniosynostosis.

Temporal Evaluation of Craniofacial Relationships in Apert Syndrome.

Complicated craniofacial malformations interfacing with multiple intracellular regulatory mechanisms, lead to ambiguous growth patterns in Apert syndrome. This study aims to explore the chronology and pathogenesis of the development of craniofacial anatomic relationships and to verify the positional correlates between skull and facial structures in Apert syndrome. Fifty-four computed tomography scans (Apert, n = 18; control, n = 36) were included and divided into 3 age subgroups. Craniofacial 3-dimensional cephalometries were analyzed by Materialize software. The angle between sella-nasion plane and maxillary plane widens 7.74° (P = 0.003) prior to 6 months of age; thereafter, this widening increases by 10.36° (P < 0.001) in 6 months to 2 years of age, and remains increased by 8.9° (P = 0.046) throughout childhood. The angle between Frankfort horizontal plane and maxillary plane widens 5.17° (P = 0.022) before 6 months. Angles SNA, SNB, and ANB showed decreases, averaging 12.23° (P < 0.001), 5.19° (P = 0.004), and 6.72° (P = 0.001), respectively. The linear measurements showed synchronicity and continuing deformity into adulthood. Between 6 months to 2 years of age, the distance from sella to nasion (S-N), anterior nasal spine (S-ANS), and posterior nasal spine (S-PNS) decreased 8% (P = 0.006), 16% (P < 0.001), and 19% (P = 0.002), respectively, and remained shortened into adulthood. The angulation changes occur earlier in development than linear distance reduction in Apert syndrome patients compared with controls. Angular adjustments were not sufficient to maintain normal cranial base length. Facial deformity of Apert syndrome temporally begins with the midface, and affects orbit and mandible later in life.

Normal angulation of skull base in Apert syndrome.

Apert syndrome is characterized by the severe craniofacial deformities. The subsequent process of skeletal maldevelopment is likely to be influenced by multiple interactions at several levels, at a given time. In this study, we aimed to explore the evolution of cranial basal dysmorphology and the chronology of these deformities in Apert syndrome, by objectively analyzing three-dimensional measurements. Fifty-four CT scans from unoperated patients (Apert, n = 18; control, n = 36) were included in this study, with age range from 3 days to 24 years. Before 6 months of age, Apert's anterior cranial base was widened 60%. Between 6 months and 2 years of age, the whole cranial base length, anterior cranial base length and posterior cranial base length decreased 8%, 8% and 14%, respectively. The greater sphenoid wing angle was wider by 26.0°, and continued into adulthood. The cranial base angles did not produce significant changes throughout life. The extra cranial distances synchronously and almost proportionally shortened after later infancy. The anterior and posterior cranial base length shortened at an almost proportional rate. The malformations of the skull vault are additive effects with cranial base fusion on skull length restriction, but the angulation of the skull base is virtually normal.

Altered bone growth dynamics prefigure craniosynostosis in a zebrafish model of Saethre-Chotzen syndrome.

Cranial sutures separate the skull bones and house stem cells for bone growth and repair. In Saethre-Chotzen syndrome, mutations in TCF12 or TWIST1 ablate a specific suture, the coronal. This suture forms at a neural-crest/mesoderm interface in mammals and a mesoderm/mesoderm interface in zebrafish. Despite this difference, we show that combinatorial loss of TCF12 and TWIST1 homologs in zebrafish also results in specific loss of the coronal suture. Sequential bone staining reveals an initial, directional acceleration of bone production in the mutant skull, with subsequent localized stalling of bone growth prefiguring coronal suture loss. Mouse genetics further reveal requirements for Twist1 and Tcf12 in both the frontal and parietal bones for suture patency, and to maintain putative progenitors in the coronal region. These findings reveal conservation of coronal suture formation despite evolutionary shifts in embryonic origins, and suggest that the coronal suture might be especially susceptible to imbalances in progenitor maintenance and osteoblast differentiation.

Quantification of gene expression patterns to reveal the origins of abnormal morphogenesis.

The earliest developmental origins of dysmorphologies are poorly understood in many congenital diseases. They often remain elusive because the first signs of genetic misregulation may initiate as subtle changes in gene expression, which are hard to detect and can be obscured later in development by secondary effects. Here, we develop a method to trace back the origins of phenotypic abnormalities by accurately quantifying the 3D spatial distribution of gene expression domains in developing organs. By applying Geometric Morphometrics to 3D gene expression data obtained by Optical Projection Tomography, we determined that our approach is sensitive enough to find regulatory abnormalities that have never been detected previously. We identified subtle but significant differences in the gene expression of a downstream target of a Fgfr2 mutation associated with Apert syndrome, demonstrating that these mouse models can further our understanding of limb defects in the human condition. Our method can be applied to different organ systems and models to investigate the etiology of malformations.

Midface and upper airway dysgenesis in FGFR2-related craniosynostosis involves multiple tissue-specific and cell cycle effects.

Midface dysgenesis is a feature of more than 200 genetic conditions in which upper airway anomalies frequently cause respiratory distress, but its etiology is poorly understood. Mouse models of Apert and Crouzon craniosynostosis syndromes exhibit midface dysgenesis similar to the human conditions. They carry activating mutations of Fgfr2, which is expressed in multiple craniofacial tissues during development. Magnetic resonance microscopy of three mouse models of Apert and Crouzon syndromes revealed decreased nasal passage volume in all models at birth. Histological analysis suggested overgrowth of the nasal cartilage in the two Apert syndrome mouse models. We used tissue-specific gene expression and transcriptome analysis to further dissect the structural, cellular and molecular alterations underlying midface and upper airway dysgenesis in Apert Fgfr2+/S252W mutants. Cartilage thickened progressively during embryogenesis because of increased chondrocyte proliferation in the presence of Fgf2 Oral epithelium expression of mutant Fgfr2, which resulted in a distinctive nasal septal fusion defect, and premature facial suture fusion contributed to the overall dysmorphology. Midface dysgenesis in Fgfr2-related craniosynostosis is a complex phenotype arising from the combined effects of aberrant signaling in multiple craniofacial tissues.