The natural history of patients treated for FGFR3-associated (Muenke-type) craniosynostosis

Mystery of the Muenke midface: spheno-occipital synchondrosis fusion and craniofacial skeletal patterns

PURPOSE

The spheno-occipital synchondrosis (SOS) is an important site of endochondral ossification in the cranial base that closes prematurely in Apert, Crouzon, and Pfeiffer syndromes, which contributes to varying degrees of midface hypoplasia. The facial dysmorphology of Muenke syndrome, in contrast, is less severe with low rates of midface hypoplasia. We thus evaluated the timing of SOS fusion and cephalometric landmarks in patients with Muenke syndrome compared to normal controls.

METHODS

Patients with Muenke syndrome who had at least one fine-cut head computed tomography scan performed from 2000 to 2020 were retrospectively reviewed. A case-control study was performed of patient scans and age- and sex-matched control scans. SOS fusion status was evaluated as open, partially closed, or closed.

RESULTS

We included 28 patients and compared 77 patient scans with 77 control scans. Kaplan-Meier analysis demonstrated an insignificantly earlier timeline of SOS fusion in Muenke syndrome (p = 0.300). Mean sella-orbitale (SO) distance was shorter (44.0 ± 6.6 vs. 47.7 ± 6.7 mm, p < 0.001) and mean sella-nasion-Frankfort horizontal (SN-FH) angle was greater (12.1° ± 3.8° vs. 10.1° ± 3.2°, p < 0.001) in the Muenke group, whereas mean sella-nasion-A point (SNA) angle was similar and normal (81.1° ± 5.7° vs. 81.4° ± 4.7°, p = 0.762).

CONCLUSION

Muenke syndrome is characterized by mild and often absent midfacial hypoplasia, with the exception of slight retropositioning of the infraorbital rim. Interestingly, SOS fusion patterns in these patients are not significantly different from age- and sex-matched controls despite an increased odds of fusion. It is possible that differences in timing of SOS fusion may manifest phenotypically at the infraorbital rim rather than at the maxilla.

Infigratinib, a selective FGFR1-3 tyrosine kinase inhibitor, alters dentoalveolar development at high doses

BACKGROUND

Fibroblast growth factor receptor-3 (FGFR3) gain-of-function mutations are linked to achondroplasia. Infigratinib, a FGFR1-3 tyrosine kinase inhibitor, improves skeletal growth in an achondroplasia mouse model. FGFs and their receptors have critical roles in developing teeth, yet effects of infigratinib on tooth development have not been assessed. Dentoalveolar and craniofacial phenotype of Wistar rats dosed with low (0.1 mg/kg) and high (1.0 mg/kg) dose infigratinib were evaluated using micro-computed tomography, histology, and immunohistochemistry.

RESULTS

Mandibular third molars were reduced in size and exhibited aberrant crown and root morphology in 100% of female rats and 80% of male rats at high doses. FGFR3 and FGF18 immunolocalization and extracellular matrix protein expression were unaffected, but cathepsin K (CTSK) was altered by infigratinib. Cranial vault bones exhibited alterations in dimension, volume, and density that were more pronounced in females. In both sexes, interfrontal sutures were significantly more patent with high dose vs vehicle.

CONCLUSIONS

High dose infigratinib administered to rats during early stages affects dental and craniofacial development. Changes in CTSK from infigratinib in female rats suggest FGFR roles in bone homeostasis. While dental and craniofacial disruptions are not expected at therapeutic doses, our findings confirm the importance of dental monitoring in clinical studies.

Syndromic Craniosynostosis: Cranial Vault Expansion in Infancy

Syndromic craniosynostosis (CS) represents a relatively uncommon disease process that poses significant reconstructive challenges for the craniofacial surgeon. Although there is considerable overlap in clinical features associated with various forms of syndromic CS, key extracranial features and close examination of the extremities help to distinguish the subtypes. While Virchow's law can easily guide the diagnosis of single suture, nonsyndromic CS, syndromic CS traditionally results in atypical presentations inherent to multiple suture fusion. Coronal ring involvement in isolation or associated with additional suture fusion is the most common pattern in syndromic CS often resulting in turribrachycephaly.

Surgical Result and Identification of FGFR2 Variants Using Whole-Exome Sequencing in a Chinese Family With Crouzon Syndrome

ABSTRACT

Crouzon syndrome is considered as one of the most common craniosynostosis syndromes with a prevalence of 1 in 65,000 individuals, and has a close relationship with variants in fibroblast growth factor receptor 2. Here the authors described a Crouzon syndrome case, which was asked for surgery treatment for the symptom of multisuture craniosynostosis. Mild midfacial retrusion, larger head circumference, proptosis, pseudo-prognathism, and dental malposition could also be found obviously. Then fronto-orbital advancement and cranial cavity expansion were performed to the child. After whole-exome sequencing (WES) and Sanger sequencing, gene variants in the exons 2 and 3 of FGFR2 were detected. And protein tyrosine 105 replaced by cysteine in the extracellular region of FGFR2 was also detected. After operation, she presented a satisfactory anterior plagiocephaly and scaphocephaly correction, and the result was satisfied by surgeons and her parents. Variants detected using WES have further research prospect.

Craniosynostosis: Posterior Cranial Vault Remodeling

Posterior cranial vault distraction osteogenesis is a powerful, reliable, low-morbidity method to achieve intracranial expansion. It is particularly useful in treating turribrachycephaly seen in syndromic craniosynostosis, allowing for gradual expansion of the bone while stretching the soft tissues over several weeks allowing greater volumetric expansion than conventional techniques. Posterior cranial vault distraction osteogenesis constitutes a more gradual remodeling modality, with infrequent complications. As a first step in intracranial expansion, it preserves the frontal cranium for future frontofacial procedures. A drawback is the need for a second surgery to remove the device, and this must be taken into account during counseling.

Evolution of Cranioorbital Shape in Nonsyndromic, Muenke, and Saethre-Chotzen Bilateral Coronal Synostosis: A Case-Control Study of 2-Year Outcomes

BACKGROUND

The purpose of this study was to quantify change in cranioorbital morphology from presentation, after fronto-orbital advancement, and at 2-year follow-up.

METHODS

Volumetric, linear, and angular analyses were performed on computed tomographic scans of consecutive bilateral coronal synostosis patients. Comparisons were made across three time points, between syndromic and nonsyndromic cases, and against normal controls. Significance was set at p < 0.05.

RESULTS

Twenty-five patients were included: 11 were nonsyndromic, eight had Saethre-Chotzen syndrome, and six had Muenke syndrome. Total cranial volume was comparable to normal, age-matched control subjects before and 2 years after surgery despite an expansion during surgery. Axial and sagittal vector analyses showed advancement and widening of the lower forehead beyond control values with surgery and comparable anterior position, but increased width compared to controls at 2 years. Frontal bossing decreased with a drop in anterior cranial height and advanced lower forehead position. Middle vault height was not normalized and turricephaly persisted at follow-up. Posterior fossa volume remained lower at all three time points compared to control subjects. Supraorbital retrusion relative to anterior corneal position was overcorrected by surgery, with values comparable to those of control subjects at 2 years because of differential growth. There was no difference at 2 years between syndromic and nonsyndromic groups.

CONCLUSIONS

Open fronto-orbital advancement successfully remodels the anterior forehead but requires overcorrection to be comparable to normal at 2 years. Although there are differences in syndromic cases at presentation, they do not result in significant morphometric differences on follow-up. Posterior fossa volume remains lower at all time points.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Facial Asymmetry in Nonsyndromic and Muenke Syndrome-Associated Unicoronal Synostosis: A 3-Dimensional Study Based on Facial Surfaces Extracted From CT Scans

OBJECTIVE

To quantify soft tissue facial asymmetry (FA) in children with nonsyndromic and Muenke syndrome-associated unicoronal synostosis (NS-UCS and MS-UCS), hypothesizing that MS-UCS presents with significantly larger FA than NS-UCS.

DESIGN

Retrospective cohort study.

PATIENTS AND METHODS

Twenty-one children (mean age: 0.6 years; range: 0.1-1.4 years) were included in the study (NS-UCS = 14; MS-UCS = 7). From presurgical computed tomography scans, facial surfaces were constructed for analysis. A landmark guided atlas was deformed to match each patient's surface, obtaining spatially detailed left-right point correspondence. Facial asymmetry was calculated in each surface point across the face, as the length (mm) of an asymmetry vector, with its Cartesian components providing 3 directions. Mean FA was calculated for the full face, and the forehead, eye, nose, cheek, mouth, and chin regions.

RESULTS

For the full face, a significant difference of 2.4 mm (P = .001) was calculated between the 2 groups, predominately in the transverse direction (1.5 mm; P < .001). The forehead and chin regions presented with the largest significant difference, 3.5 mm (P = .002) and 3.2 mm (P < .001), respectively; followed by the eye (2.4 mm; P = .004), cheek (2.2 mm; P = .004), nose (1.7 mm; P = .001), and mouth (1.4 mm; P = .009) regions. The transverse direction presented with the largest significant difference in the forehead, chin, mouth, and nose regions, the sagittal direction in the cheek region, and the vertical direction in the eye region.

CONCLUSIONS

Muenke syndrome-associated unicoronal synostosis presented with significantly larger FA in all regions compared to NS-UCS. The largest significant differences were found in the forehead and chin regions, predominantly in the transverse direction.

Muenke syndrome: Medical and surgical comorbidities and long-term management

Muenke syndrome (MIM #602849), the most common syndromic craniosynostosis, results from the recurrent pathogenic p.P250R variant in FGFR3. Affected patients exhibit wide phenotypic variability. Common features include coronal craniosynostosis, hearing loss, carpal and tarsal anomalies, and developmental/behavioral issues. Our study examined the phenotypic findings, medical management, and surgical outcomes in a cohort of 26 probands with Muenke syndrome identified at the Children's Hospital of Philadelphia. All probands had craniosynostosis; 69.7% had bicoronal synostosis only, or bicoronal and additional suture synostosis. Three male patients had autism spectrum disorder. Recurrent ear infections were the most common comorbidity, and myringotomy tube placement the most common extracranial surgical procedure. Most patients (76%) required only one fronto-orbital advancement. de novo mutations were confirmed in 33% of the families in which proband and both parents were genetically tested, while in the remaining 66% one of the parents was a mutation carrier. In affected parents, 40% had craniosynostosis, including 71% of mothers and 13% of fathers. We additionally analyzed the medical resource utilization of probands with Muenke syndrome. To our knowledge, these data represent the first comprehensive examination of long-term management in a large cohort of patients with Muenke syndrome. Our study adds valuable information regarding neuropsychiatric and medical comorbidities, and highlights findings in affected relatives.

Deviating dental arch morphology in mild coronal craniosynostosis syndromes

Objectives

To determine whether the intramaxillary relationship of patients with Muenke syndrome and Saethre-Chotzen syndrome or TCF12-related craniosynostosis are systematically different than those of a control group.

Material and methods

Forty-eight patients (34 patients with Muenke syndrome, 8 patients with Saethre-Chotzen syndrome, and 6 patients with TCF12-related craniosynostosis) born between 1982 and 2010 (age range 4.84 to 16.83 years) that were treated at the Department of Oral Maxillofacial Surgery, Special Dental Care and Orthodontics, Children’s Hospital Erasmus University Medical Center, Sophia, Rotterdam, the Netherlands, were included. Forty-seven syndromic patients had undergone one craniofacial surgery according to the craniofacial team protocol. The dental arch measurements intercanine width (ICW), intermolar width (IMW), arch depth (AD), and arch length (AL) were calculated. The control group existed of 329 nonsyndromic children.

Results

All dental arch dimensions in Muenke (ICW, IMW, AL, p < 0.001, ADmax, p = 0.008; ADman, p = 0.002), Saethre-Chotzen syndrome, or TCF12-related craniosynostosis patients (ICWmax, p = 0.005; ICWman, IMWmax, AL, p < 0.001) were statistically significantly smaller than those of the control group.

Conclusions

In this study, we showed that the dental arches of the maxilla and the mandible of patients with Muenke syndrome and Saethre-Chotzen syndrome or TCF12-related craniosynostosis are smaller compared to those of a control group.

Clinical relevance

To gain better understanding of the sutural involvement in the midface and support treatment capabilities of medical and dental specialists in these patients, we suggest the concentration of patients with Muenke and Saethre-Chotzen syndromes or TCF12-related craniosynostosis in specialized teams for a multi-disciplinary approach and treatment.

What's New in Syndromic Craniosynostosis Surgery?

LEARNING OBJECTIVES

After studying this article, the participant should be able to: 1. Understand the role of prenatal screening and counseling of parents of unborn children with syndromic craniosynostosis. 2. Recognize the genetic abnormalities, craniofacial phenotype, associated anomalies, and challenges associated with each of the five major forms of syndromic craniosynostosis. 3. Identify the pros and cons associated with timing and types of cranial vault remodeling techniques in this patient population. 4. Understand the risks and benefits associated with midface advancement with Le Fort III, Le Fort II plus zygomatic repositioning, monobloc, and facial bipartition. 5. Understand the important role of psychological counseling throughout childhood in this at-risk group.

SUMMARY

Crouzon, Apert, Pfeiffer, Muenke, and Saethre-Chotzen syndromes are the five most common forms of syndromic craniosynostosis. Although each has different genetic underpinnings and associated anomalies, their hallmark finding is turribrachycephaly most often associated with bicoronal craniosynostosis. The role of prenatal screening and counseling is growing, with caregivers becoming involved before birth. Multidisciplinary care from birth onward involves craniofacial plastic surgeons, neurosurgeons, otolaryngologists, ophthalmologists, orthodontists, anesthesiologists, psychologists, speech therapists, and geneticists. Early partial, or regional, craniectomy may be urgently indicated in multisuture cases with signs of increased intracranial pressure. Others may be managed successfully with posterior cranial vault distraction, middle vault expansion, or fronto-orbital advancement. Some authors have advocated early monobloc advancement for those patients who require acute airway intervention and globe protection, although the risks of these procedures are high. Many patients will require midfacial advancement with a Le Fort III, Le Fort II plus zygomatic repositioning, monobloc, or facial bipartition. The indications, risks, and benefits for each midfacial procedure must be considered, as this step in the treatment algorithm may carry the greatest functional and aesthetic benefits but also the potential for the greatest morbidity. At the culmination of facial growth, it is not uncommon for patients to require conventional orthognathic surgery and other bony contouring and soft-tissue procedures. Finally, an understanding of the psychological aspects of craniofacial difference, both in affected individuals and in their families, is essential to a successful, holistic approach.

Assessing the midface in Muenke syndrome: A cephalometric analysis and review of the literature

BACKGROUND

Max Muenke included midface hypoplasia as part of the clinical syndrome caused by the Pro250Arg FGFR3 mutation that now bears his name. Murine models have demonstrated midface hypoplasia in homozygous recessive mice only, with heterozygotes having normal midfaces; as the majority of humans with the syndrome are heterozygotes, we investigated the incidence of midface hypoplasia in our institution's clinical cohort.

METHODS

We retrospectively reviewed all patients with a genetic and clinical diagnosis of Muenke syndrome from 1990 to 2014. Review of clinical records and photographs included skeletal Angle Class, dental occlusion, and incidence of orthognathic intervention. Cephalometric evaluation of our patients was compared to the Eastman Standard Values.

RESULTS

18 patients met inclusion criteria - 7 females and 11 males, with average follow-up of 11.2 years (1.0-23.1). Cephalometric analysis revealed an average sella-nasion-A point angle (SNA) of 82.5 (67.8-88.8) and an average sella-nasion-B point angle (SNB) of 77.9 (59.6-84.1). The SNA of our cohort was found to be significantly different from the Eastman Standards (p = 0.017); subgroup analysis revealed that this was due to the mixed dentition group which had a higher than average SNA. 12 patients were noted to be in Class I occlusion, 4 in Class II malocclusion, and 2 in Class III malocclusion. Only one patient (6%) underwent orthognathic surgery for Class III malocclusion.

CONCLUSIONS

While a part of the original description of Muenke syndrome, clinically significant midface hypoplasia is not a common feature. This data is important, as it allows more accurate counseling of patients and families.

LEVEL OF EVIDENCE

III.

Facial Asymmetry in Children with Unicoronal Synostosis who have Undergone Craniofacial Reconstruction in Infancy

Objective

Quantitatively assess 3D spatially detailed soft-tissue facial asymmetry in children who had undergone craniofacial reconstruction for Unicoronal Synostosis (UCS), and compare the facial asymmetry to control patients. It was hypothesized that there would be no significant differences in the facial asymmetry between the groups.

Design

Clinical, retrospective follow-up study. Methodological study.

Setting

Primary care center.

Patients/Participants

Twenty-two children with UCS were selected after review of records. Inclusion criteria: isolated UCS; surgically treated for UCS within the first 19 months of life, without secondary reconstruction; and DNA analysis for the Muenke mutation. An age- and sex-matched control group was employed.

Interventions

The UCS group had undergone bilateral craniotomy of the frontal bone with unilateral supraorbital rim advancement.

Main outcome Measure(s)

Using 3D surface scanning, a detailed map of 3D asymmetry presenting the amount of asymmetry in the sagittal, vertical, and transverse directions was calculated for six facial subregions.

Results

The facial asymmetry in the UCS group was significantly larger than in the control group for all regions, to the largest extent in the sagittal direction (level of significance: 5%). The regions with the most pronounced asymmetry were cheeks (mean: 5.45 mm; SD: 1.83 mm), forehead (mean: 5.00 mm; SD: 1.57 mm), and eyes (mean: 4.26 mm; SD: 1.44 mm).

Conclusions

Ninety percent of the UCS patients in the study had significant facial asymmetry throughout the facial area. The study demonstrates a methodology of facial asymmetry quantification well suited for soft-tissue surgical outcome evaluations and long-term follow-up studies in patients with craniofacial anomalies.

Muenke syndrome: An international multicenter natural history study

Muenke syndrome is an autosomal dominant disorder characterized by coronal suture craniosynostosis, hearing loss, developmental delay, carpal, and calcaneal fusions, and behavioral differences. Reduced penetrance and variable expressivity contribute to the wide spectrum of clinical findings. Muenke syndrome constitutes the most common syndromic form of craniosynostosis, with an incidence of 1 in 30,000 births and is defined by the presence of the p.Pro250Arg mutation in FGFR3. Participants were recruited from international craniofacial surgery and genetic clinics. Affected individuals, parents, and their siblings, if available, were enrolled in the study if they had a p.Pro250Arg mutation in FGFR3. One hundred and six patients from 71 families participated in this study. In 51 informative probands, 33 cases (64.7%) were inherited. Eighty-five percent of the participants had craniosynostosis (16 of 103 did not have craniosynostosis), with 47.5% having bilateral and 28.2% with unilateral synostosis. Females and males were similarly affected with bicoronal craniosynostosis, 50% versus 44.4% (P = 0.84), respectively. Clefting was rare (1.1%). Hearing loss was identified in 70.8%, developmental delay in 66.3%, intellectual disability in 35.6%, attention deficit/hyperactivity disorder in 23.7%, and seizures in 20.2%. In patients with complete skeletal surveys (upper and lower extremity x-rays), 75% of individuals were found to have at least a single abnormal radiographical finding in addition to skull findings. This is the largest study of the natural history of Muenke syndrome, adding valuable clinical information to the care of these individuals including behavioral and cognitive impairment data, vision changes, and hearing loss.

Fibroblast growth factor (FGF) signaling in development and skeletal diseases

Fibroblast growth factors (FGF) and their receptors serve many functions in both the developing and adult organism. Humans contain 18 FGF ligands and four FGF receptors (FGFR). FGF ligands are polypeptide growth factors that regulate several developmental processes including cellular proliferation, differentiation, and migration, morphogenesis, and patterning. FGF-FGFR signaling is also critical to the developing axial and craniofacial skeleton. In particular, the signaling cascade has been implicated in intramembranous ossification of cranial bones as well as cranial suture homeostasis. In the adult, FGFs and FGFRs are crucial for tissue repair. FGF signaling generally follows one of three transduction pathways: RAS/MAP kinase, PI3/AKT, or PLCγ. Each pathway likely regulates specific cellular behaviors. Inappropriate expression of FGF and improper activation of FGFRs are associated with various pathologic conditions, unregulated cell growth, and tumorigenesis. Additionally, aberrant signaling has been implicated in many skeletal abnormalities including achondroplasia and craniosynostosis. The biology and mechanisms of the FGF family have been the subject of significant research over the past 30 years. Recently, work has focused on the therapeutic targeting and potential of FGF ligands and their associated receptors. The majority of FGF-related therapy is aimed at age-related disorders. Increased understanding of FGF signaling and biology may reveal additional therapeutic roles, both in utero and postnatally. This review discusses the role of FGF signaling in general physiologic and pathologic embryogenesis and further explores it within the context of skeletal development.

Hearing loss in syndromic craniosynostoses: introduction and consideration of mechanisms

PURPOSE

There are a number of craniosynostosis syndromes with hearing loss-including Muenke, Apert, Pfeiffer, Crouzon, Beare-Stevenson, Crouzon with acanthosis nigricans, and Jackson-Weiss syndromes-that result from mutations in the fibroblast growth factor receptor (FGFR) genes. Studies of FGFRs and their ligands, fibroblast growth factors (FGFs), have revealed clues to the precise contribution of aberrant FGFR signaling to inner ear morphogenesis and the hearing loss encountered in craniosynostoses. The purpose of this article is to review basic studies of FGFRs with emphasis on their function and expression in the inner ear and surrounding structures.

METHOD

A Medline search was performed to find basic science articles regarding FGFR, their ligands, and their expression and relevant mouse models. Additional items searched included clinical descriptions and studies of individuals with FGFR-related craniosynostosis syndromes.

RESULTS

The FGF signaling pathway is essential for the morphogensis and proper function of the inner ear and auditory sensory epithelium.

CONCLUSION

The variable auditory phenotypes seen in individuals with Muenke syndrome may have a genetic basis, likely due to multiple interacting factors in the genetic environment or modifying factors. Further analysis and studies of mouse models of Muenke syndrome, in particular, may provide clues to the specific effects of the defining mutation in FGFR3 in the inner ear not only at birth but also into adulthood. In particular, investigations into these models may give insight into the variable expression and incomplete penetrance of this phenotype.

A familial case of Muenke syndrome. Diverse expressivity of the FGFR3 Pro252Arg mutation--case report and review of the literature

Muenke is a fibroblast growth factor receptor 3 (FGFR-3)-associated syndrome, which was first described in late 1990 s. Muenke syndrome is an autosomal dominant disorder characterized mainly by coronal suture craniosynostosis, hearing impairment and intellectual disability. The syndrome is defined molecularly by a unique point mutation c.749C > G in exon 7 of the FGFR3 gene which results to an amino acid substitution p.Pro250Arg of the protein product. Despite the fact that the mutation rate at this nucleotide is one of the most frequently described in human genome, few Muenke familial case reports are published in current literature. We describe individuals among three generations of a Greek family who are carriers of the same mutation. Medical record and physical examination of family members present a wide spectrum of clinical manifestations. In particular, a 38-year-old woman and her father appear milder clinical findings regarding craniofacial characteristics compared to her uncle and newborn female child. This familial case illustrates the variable expressivity of Muenke syndrome in association with an identical gene mutation.

Syndromic craniosynostosis

Although most cases of craniosynostosis are nonsyndromic, craniosynostosis is known to occur in conjunction with other anomalies in well-defined patterns that make up clinically recognized syndromes. Patients with syndromic craniosynostoses are much more complicated to care for, requiring a multidisciplinary approach to address all of their needs effectively. This review describes the most common craniosynostosis syndromes, their characteristic features and syndrome-specific functional issues, and new modalities utilized in their management. General principles including skull development, the risk of developing increased intracranial pressure in craniosynostosis syndromes, and techniques to measure intracranial pressure are discussed. Evolving techniques of the established operative management of craniosynostosis are discussed together with more recent techniques including spring cranioplasty and posterior cranial vault distraction osteogenesis.

Phenotype profile of a genetic mouse model for Muenke syndrome

PURPOSE

The Muenke syndrome mutation (FGFR3 (P250R)), which was discovered 15 years ago, represents the single most common craniosynostosis mutation. Muenke syndrome is characterized by coronal suture synostosis, midface hypoplasia, subtle limb anomalies, and hearing loss. However, the spectrum of clinical presentation continues to expand. To better understand the pathophysiology of the Muenke syndrome, we present collective findings from several recent studies that have characterized a genetically equivalent mouse model for Muenke syndrome (FgfR3 (P244R)) and compare them with human phenotypes.

CONCLUSIONS

FgfR3 (P244R) mutant mice show premature fusion of facial sutures, premaxillary and/or zygomatic sutures, but rarely the coronal suture. The mice also lack the typical limb phenotype. On the other hand, the mutant mice display maxillary retrusion in association with a shortening of the anterior cranial base and a premature closure of intersphenoidal and spheno-occipital synchondroses, resembling human midface hypoplasia. In addition, sensorineural hearing loss is detected in all FgfR3 (P244R) mutant mice as in the majority of Muenke syndrome patients. It is caused by a defect in the mechanism of cell fate determination in the organ of Corti. The mice also express phenotypes that have not been previously described in humans, such as reduced cortical bone thickness, hypoplastic trabecular bone, and defective temporomandibular joint structure. Therefore, the FgfR3 (P244R) mouse provides an excellent opportunity to study disease mechanisms of some classical phenotypes of Muenke syndrome and to test novel therapeutic strategies. The mouse model can also be further explored to discover previously unreported yet potentially significant phenotypes of Muenke syndrome.

Impact of genetics on the diagnosis and clinical management of syndromic craniosynostoses

PURPOSE

More than 60 different mutations have been identified to be causal in syndromic forms of craniosynostosis. The majority of these mutations occur in the fibroblast growth factor receptor 2 gene (FGFR2). The clinical management of syndromic craniosynostosis varies based on the particular causal mutation. Additionally, the diagnosis of a patient with syndromic craniosynostosis is based on the clinical presentation, signs, and symptoms. The understanding of the hallmark features of particular syndromic forms of craniosynostosis leads to efficient diagnosis, management, and long-term prognosis of patients with syndromic craniosynostoses.

METHODS

A comprehensive literature review was done with respect to the major forms of syndromic craniosynostosis and additional less common FGFR-related forms of syndromic craniosynostosis. Additionally, information and data gathered from studies performed in our own investigative lab (lab of Dr. Muenke) were further analyzed and reviewed. A literature review was also performed with regard to the genetic workup and diagnosis of patients with craniosynostosis.

RESULTS

Patients with Apert syndrome (craniosynostosis syndrome due to mutations in FGFR2) are most severely affected in terms of intellectual disability, developmental delay, central nervous system anomalies, and limb anomalies. All patients with FGFR-related syndromic craniosynostosis have some degree of hearing loss that requires thorough initial evaluations and subsequent follow-up.

CONCLUSIONS

Patients with syndromic craniosynostosis require management and treatment of issues involving multiple organ systems which span beyond craniosynostosis. Thus, effective care of these patients requires a multidisciplinary approach.

The Muenke syndrome mutation (FgfR3P244R) causes cranial base shortening associated with growth plate dysfunction and premature perichondrial ossification in murine basicranial synchondroses

Muenke syndrome caused by the FGFR3(P250R) mutation is an autosomal dominant disorder mostly identified with coronal suture synostosis, but it also presents with other craniofacial phenotypes that include mild to moderate midface hypoplasia. The Muenke syndrome mutation is thought to dysregulate intramembranous ossification at the cranial suture without disturbing endochondral bone formation in the skull. We show in this study that knock-in mice harboring the mutation responsible for the Muenke syndrome (FgfR3(P244R)) display postnatal shortening of the cranial base along with synchondrosis growth plate dysfunction characterized by loss of resting, proliferating and hypertrophic chondrocyte zones and decreased Ihh expression. Furthermore, premature conversion of resting chondrocytes along the perichondrium into prehypertrophic chondrocytes leads to perichondrial bony bridge formation, effectively terminating the postnatal growth of the cranial base. Thus, we conclude that the Muenke syndrome mutation disturbs endochondral and perichondrial ossification in the cranial base, explaining the midface hypoplasia in patients.

Craniosynostosis genetics: The mystery unfolds

Craniosynsostosis syndromes exhibit considerable phenotypic and genetic heterogeneity. Sagittal synostosis is common form of isolated craniosynostosis. The sutures involved, the shape of the skull and associated malformations give a clue to the specific diagnosis. Crouzon syndrome is one of the most common of the craniosynostosis syndromes. Apert syndrome accounts for 4.5% of all craniosynostoses and is one of the most serious of these syndromes. Most syndromic craniosynostosis require multidisciplinary management. The following review provides a brief appraisal of the various genes involved in craniosynostosis syndromes, and an approach to diagnosis and genetic counseling.

Pediatric Craniofacial Surgery: A Review for the Multidisciplinary Team

Pediatric craniofacial surgery is a specialty that grew dramatically in the 20th century and continues to evolve today. Out of the efforts to correct facial deformities encountered during World War II, the techniques of modern craniofacial surgery developed. An analysis of the relevant literature allowed the authors to explore this historical progression.

Current advances in technology, tissue engineering, and molecular biology have further refined pediatric craniofacial surgery. The development of distraction osteogenesis and the progressive study of craniosynostosis provide remarkable examples of this momentum. The growing study of genetics, biotechnology, the influence of growth factors, and stem cell research provide additional avenues of innovation for the future. The following article is intended to reveal a greater understanding of pediatric craniofacial surgery by examining the past, present, and possible future direction. It is intended both for the surgeon, as well as for the nonsurgical individual specialists vital to the multidisciplinary craniofacial team.

Additional phenotypic features of Muenke syndrome in 2 Dutch families

In about 30% of the patients with syndromal craniosynostosis, a genetic mutation can be traced. For the purpose of adequate genetic counseling and treatment of these patients, the full spectrum of clinical findings for each specific mutation needs to be appreciated. The Pro250Arg mutation in the FGFR3 gene is found in patients with Muenke syndrome and is one of the most frequently encountered mutations in craniosynostosis syndromes. A number of studies on the relationship between genotype and phenotype concerning this specific mutation have been published. Two Dutch families with Muenke syndrome were screened for the reported characteristics of this syndrome and for additional features. New phenotypical findings were hypoplasia of the frontal sinus, ptosis of the upper eyelids, dysplastic elbow joints with restricted elbow motion, and mild cutaneous syndactyly. Incidentally, polydactyly, severe ankylosis of the elbow, fusion of cervical vertebrae, and epilepsy were found. Upper eyelid ptosis is thought to be pathognomonic for Saethre-Chotzen syndrome but was also observed in our series of patients with Muenke syndrome. Because Muenke and Saethre-Chotzen syndrome can have similar phenotypes, DNA analysis is needed to distinguish between these syndromes, even when a syndrome diagnosis is already made in a family member.

Craniofacial growth in patients with FGFR3Pro250Arg mutation after fronto-orbital advancement in infancy

BACKGROUND

The facial features of children with FGFR3Pro250Arg mutation (Muenke syndrome) differ from those with the other eponymous craniosynostotic disorders. We documented midfacial growth and position of the forehead after fronto-orbital advancement (FOA) in patients with the FGFR3 mutation.

METHODS

We retrospectively reviewed all patients who had an FGFR3Pro250Arg mutation and craniosynostosis. Only patients who had FOA in infancy or early childhood were included. The clinical records were evaluated for type of sutural fusion; midfacial hypoplasia and other clinical data, including age at operation; type of procedures and fixation (wire vs resorbable plate); frequency of frontal readvancement, forehead augmentation, midfacial advancement; and complications. Preoperative and postoperative sagittal orbital-globe relationship was measured by direct anthropometry. Outcome of FOA was graded according to the Whittaker classification as category I, no revision; category II, minor revisions, that is, foreheadplasty; category III, alternative bony work; category IV; redo of initial procedure (ie, secondary FOA). Midfacial position was determined by clinical examination and lateral cephalometry.

RESULTS

A total of 21 study patients with Muenke syndrome (8 males and 13 females) were analyzed. The types of craniosynostosis were bilateral coronal (n=15), of which 3 also had concurrent sagittal fusion, and unilateral coronal (n=5). Two patients had early endoscopic suturectomy, but later required FOA. Mean age at FOA was 22.9 months (range, 3-128 months). Secondary FOA was necessary in 40% of patients (n=8), and secondary foreheadplasty in 25% (n=5) of patients. No frontal revisions were needed in the remaining 35% of patients (n=7). Mean age at initial FOA was significantly younger in the group requiring repeat FOA or foreheadplasty compared with patients who did not require revision (P<0.05). Location of synostosis, type of fixation, and bone grafting did not significantly affect the need for revision. Only 30% (n=6) of patients developed midfacial retrusion.

CONCLUSIONS

The frequency of frontal revision in patients with Muenke syndrome who had FOA in infancy and early childhood is lower than previously reported. Age at forehead advancement inversely correlated with the incidence of relapse and need for secondary frontal procedures. Midfacial retrusion is relatively uncommon in FGFR3Pro250Arg patients.

Coronal synostosis syndrome (Muenke syndrome): the value of genetic testing versus clinical diagnosis

BACKGROUND

Muenke syndrome is a fibroblast growth factor receptor 3 (FGFR-3)-associated coronal craniosynostosis syndrome, which was first described in 1997.

CASE

We report an infant girl who was born to a 29-year-old primapara at 38 weeks' gestation. When evaluated at 3 days old, physical examination revealed a high forehead with frontal bossing, upturned nose, arched palate, shallow midface structures, and heavily ridged coronal sutures bilaterally. Clinically, the infant seemed to be neurologically normal. Skull radiographs and computed tomography confirmed the presence of bilateral coronal synostosis, with patency of all other sutures. Family history was remarkable, in that the infant's father, paternal grandmother, and a paternal cousin demonstrated subtle craniofacial features, which had not been previously identified. Mutation analysis of FGFR-3 revealed a missense mutation in exon 6, c.749 C>G, with a resultant amino acid change from proline to arginine at codon 250 (P250R), in keeping with Muenke syndrome (Am J Hum Genet 1997;60:555-564). The mutation was subsequently identified in her father, suggesting variable expression in this family, as he had only mild midfacial flattening. At 9 months of age, our patient underwent anterior cranial expansion, correction of orbital hypertelorism, intracranial orbital osteotomies, and advancement of the frontal bandeau. She tolerated the procedure well and has done well postoperatively.

CONCLUSIONS

We report the case of an infant with Muenke syndrome, with evidence of variable expressivity within the paternal family. The pertinent literature, in which only 2 prior Canadian cases were identified, is reviewed.

Prevalence and complications of single-gene and chromosomal disorders in craniosynostosis

OBJECTIVES

We describe the first cohort-based analysis of the impact of genetic disorders in craniosynostosis. We aimed to refine the understanding of prognoses and pathogenesis and to provide rational criteria for clinical genetic testing.

METHODS

We undertook targeted molecular genetic and cytogenetic testing for 326 children who required surgery because of craniosynostosis, were born in 1993-2002, presented to a single craniofacial unit, and were monitored until the end of 2007.

RESULTS

Eighty-four children (and 64 relatives) had pathologic genetic alterations (86% single-gene mutations and 14% chromosomal abnormalities). The FGFR3 P250R mutation was the single largest contributor (24%) to the genetic group. Genetic diagnoses accounted for 21% of all craniosynostosis cases and were associated with increased rates of many complications. Children with an initial clinical diagnosis of nonsyndromic craniosynostosis were more likely to have a causative mutation if the synostoses were unicoronal or bicoronal (10 of 48 cases) than if they were sagittal or metopic (0 of 55 cases; P = .0003). Repeat craniofacial surgery was required for 58% of children with single-gene mutations but only 17% of those with chromosomal abnormalities (P = .01).

CONCLUSIONS

Clinical genetic assessment is critical for the treatment of children with craniosynostosis. Genetic testing of nonsyndromic cases (at least for FGFR3 P250R and FGFR2 exons IIIa/c) should be targeted to patients with coronal or multisuture synostoses. Single-gene disorders that disrupt physiologic signaling in the cranial sutures often require reoperation, whereas chromosomal abnormalities follow a more-indolent course, which suggests a different, secondary origin of the associated craniosynostosis.

Hypodontia in Beare-Stevenson Syndrome: An Example of Dental Anomalies in FGFR-Related Craniosynostosis Syndromes

The authors report a new case of Beare-Stevenson syndrome (BSS) characterized by cutis gyrata, craniosynostosis, acanthosis nigricans, ear defects, a prominent umbilical stump, and midface hypoplasia. The patient had dental findings of natal teeth and hypodontia of the primary and permanent teeth. This is the second patient with BSS syndrome to be reported with hypodontia and natal teeth; the first patient was described by Beare in 1969. The authors review the current literature to investigate the relationship between dental anomalies and fibroblast growth factor receptor-related mutations in BSS and other craniosynostosis syndromes such as Apert, Crouzon, and Pfeiffer.

Skeletal analysis of the Fgfr3(P244R) mouse, a genetic model for the Muenke craniosynostosis syndrome

Muenke syndrome, defined by heterozygosity for a Pro250Arg substitution in fibroblast growth factor receptor 3 (FGFR3), is the most common genetic cause of craniosynostosis in humans. We have used gene targeting to introduce the Muenke syndrome mutation (equivalent to P244R) into the murine Fgfr3 gene. A rounded skull and shortened snout (often skewed) with dental malocclusion was observed in a minority of heterozygotes and many homozygotes. Development of this incompletely penetrant skull phenotype was dependent on genetic background and sex, with males more often affected. However, these cranial abnormalities were rarely attributable to craniosynostosis, which was only present in 2/364 mutants; more commonly, we found fusion of the premaxillary and/or zygomatic sutures. We also found decreased cortical thickness and bone mineral densities in long bones. We conclude that although both cranial and long bone development is variably affected by the murine Fgfr3(P244R) mutation, coronal craniosynostosis is not reliably reproduced.

Hearing loss in a mouse model of Muenke syndrome

The heterozygous Pro250Arg substitution mutation in fibroblast growth factor receptor 3 (FGFR3), which increases ligand-dependent signalling, is the most common genetic cause of craniosynostosis in humans and defines Muenke syndrome. Since FGF signalling plays dosage-sensitive roles in the differentiation of the auditory sensory epithelium, we evaluated hearing in a large group of Muenke syndrome subjects, as well as in the corresponding mouse model (Fgfr3^P244R). The Muenke syndrome cohort showed significant, but incompletely penetrant, predominantly low-frequency sensorineural hearing loss, and the Fgfr3^P244R mice showed dominant, fully penetrant hearing loss that was more severe than that in Muenke syndrome individuals, but had the same pattern of relative high-frequency sparing. The mouse hearing loss correlated with an alteration in the fate of supporting cells (Deiters'-to-pillar cells) along the entire length of the cochlear duct, with the most extreme abnormalities found at the apical or low-frequency end. In addition, there was excess outer hair cell development in the apical region. We conclude that low-frequency sensorineural hearing loss is a characteristic feature of Muenke syndrome and that the genetically equivalent mouse provides an excellent model that could be useful in testing hearing loss therapies aimed at manipulating the levels of FGF signalling in the inner ear.