Prevalence of Pro250Arg mutation of fibroblast growth factor receptor 3 in coronal 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.

Cerebral cortex maldevelopment in syndromic craniosynostosis

AIM

To assess the relationship of surface area of the cerebral cortex to intracranial volume (ICV) in syndromic craniosynostosis.

METHOD

Records of 140 patients (64 males, 76 females; mean age 8y 6mo [SD 5y 6mo], range 1y 2mo-24y 2mo) with syndromic craniosynostosis were reviewed to include clinical and imaging data. Two hundred and three total magnetic resonance imaging (MRI) scans were evaluated in this study (148 patients with fibroblast growth factor receptor [FGFR], 19 patients with TWIST1, and 36 controls). MRIs were processed via FreeSurfer pipeline to determine total ICV and cortical surface area (CSA). Scaling coefficients were calculated from log-transformed data via mixed regression to account for multiple measurements, sex, syndrome, and age. Educational outcomes were reported by syndrome.

RESULTS

Mean ICV was greater in patients with FGFR (1519cm³ , SD 269cm³ , p=0.016) than in patients with TWIST1 (1304cm³ , SD 145cm³ ) or controls (1405cm³ , SD 158cm³ ). CSA was related to ICV by a scaling law with an exponent of 0.68 (95% confidence interval [CI] 0.61-0.76) in patients with FGFR compared to 0.81 (95% CI 0.50-1.12) in patients with TWIST1 and 0.77 (95% CI 0.61-0.93) in controls. Lobar analysis revealed reduced scaling in the parietal (0.50, 95% CI 0.42-0.59) and occipital (0.67, 95% CI 0.54-0.80) lobes of patients with FGFR compared with controls. Modified learning environments were needed more often in patients with FGFR.

INTERPRETATION

Despite adequate ICV in FGFR-mediated craniosynostosis, CSA development is reduced, indicating maldevelopment, particularly in parietal and occipital lobes. Modified education is also more common in patients with FGFR.

Quantitative Craniofacial Analysis and Generation of Human Induced Pluripotent Stem Cells for Muenke Syndrome: A Case Report

In this case report, we focus on Muenke syndrome (MS), a disease caused by the p.Pro250Arg variant in fibroblast growth factor receptor 3 (FGFR3) and characterized by uni- or bilateral coronal suture synostosis, macrocephaly without craniosynostosis, dysmorphic craniofacial features, and dental malocclusion. The clinical findings of MS are further complicated by variable expression of phenotypic traits and incomplete penetrance. As such, unraveling the mechanisms behind MS will require a comprehensive and systematic way of phenotyping patients to precisely identify the impact of the mutation variant on craniofacial development. To establish this framework, we quantitatively delineated the craniofacial phenotype of an individual with MS and compared this to his unaffected parents using three-dimensional cephalometric analysis of cone beam computed tomography scans and geometric morphometric analysis, in addition to an extensive clinical evaluation. Secondly, given the utility of human induced pluripotent stem cells (hiPSCs) as a patient-specific investigative tool, we also generated the first hiPSCs derived from a family trio, the proband and his unaffected parents as controls, with detailed characterization of all cell lines. This report provides a starting point for evaluating the mechanistic underpinning of the craniofacial development in MS with the goal of linking specific clinical manifestations to molecular insights gained from hiPSC-based disease modeling.

Clinical study and some molecular features of Mexican patients with syndromic craniosynostosis

BACKGROUND

Craniosynostosis is one of the major genetic disorders affecting 1 in 2,100-2,500 live newborn children. Environmental and genetic factors are involved in the manifestation of this disease. The suggested genetic causes of craniosynostosis are pathogenic variants in FGFR1, FGFR2, FGFR3, and TWIST1 genes.

METHODS

In order to describe their major clinical characteristics and the presence of pathogenic variants, a sample of 36 Mexican patients with craniosynostosis diagnosed as: Crouzon (OMIM 123,500), Pfeiffer (OMIM 101,600), Apert (OMIM 101,200), Saethre-Chotzen (OMIM 101,400), and Muenke (OMIM 602,849) was analyzed.

RESULTS

In addition to craniosynostosis, most of the patients presented hypertelorism, midface hypoplasia, and abnormalities in hands and feet. To detect the pathogenic variants p.Pro252Arg FGFR1 (OMIM 136,350), p.Ser252Trp, p.Pro253Arg FGFR2 (OMIM 176,943), p.Pro250Arg, FGFR3 (OMIM 134,934), and p.Gln119Pro TWIST1 (OMIM 601,622), PCR amplification and restriction enzyme digestion were performed. Four and two patients with Apert presented the pathogenic variants p.Ser252Trp and p.Pro253Arg in FGFR2, respectively (with a frequency of 11.1% and 5.5%). The p.Pro250Arg pathogenic variant of FGFR3 was found in a patient with Muenke (with a frequency of 2.8%). The above percentages were calculated with the total number of patients.

CONCLUSION

The contribution of this work is discreet, since only 4 genes were analyzed and sample size is small. However, this strategy could be improved by sequencing the FGFR1, FGFR2, FGFR3, and TWIST1 genes, to determine different pathogenic variants. On the other hand, it would be important to include other genes, such as TCF12 (OMIM 600,480), MSX2 (OMIM 123,101), RAB23 (OMIM 606,144), and EFNB1 (OMIM 300,035), to determine their participation in craniosynostosis in the Mexican population.

Post-Translational Regulations of Transcriptional Activity of RUNX2

Runt-related transcription factor 2 (RUNX2) is a key transcription factor for bone formation and osteoblast differentiation. Various signaling pathways and mechanisms that regulate the expression and transcriptional activity of RUNX2 have been thoroughly investigated since the involvement of RUNX2 was first reported in bone formation. As the regulation of Runx2 expression by extracellular signals has recently been reviewed, this review focuses on the regulation of post-translational RUNX2 activity. Transcriptional activity of RUNX2 is regulated at the post-translational level by various enzymes including kinases, acetyl transferases, deacetylases, ubiquitin E3 ligases, and prolyl isomerases. We describe a sequential and linear causality between post-translational modifications of RUNX2 by these enzymes. RUNX2 is one of the most important osteogenic transcription factors; however, it is not a suitable drug target. Here, we suggest enzymes that directly regulate the stability and/or transcriptional activity of RUNX2 at a post-translational level as effective drug targets for treating bone diseases.

Muenke syndrome: long-term outcome of a syndrome-specific treatment protocol

OBJECTIVE

The authors evaluated the long-term outcome of their treatment protocol for Muenke syndrome, which includes a single craniofacial procedure.

METHODS

This was a prospective observational cohort study of Muenke syndrome patients who underwent surgery for craniosynostosis within the first year of life. Symptoms and determinants of intracranial hypertension were evaluated by longitudinal monitoring of the presence of papilledema (fundoscopy), obstructive sleep apnea (OSA; with polysomnography), cerebellar tonsillar herniation (MRI studies), ventricular size (MRI and CT studies), and skull growth (occipital frontal head circumference [OFC]). Other evaluated factors included hearing, speech, and ophthalmological outcomes.

RESULTS

The study included 38 patients; 36 patients underwent fronto-supraorbital advancement. The median age at last follow-up was 13.2 years (range 1.3-24.4 years). Three patients had papilledema, which was related to ophthalmological disorders in 2 patients. Three patients had mild OSA. Three patients had a Chiari I malformation, and tonsillar descent < 5 mm was present in 6 patients. Tonsillar position was unrelated to papilledema, ventricular size, or restricted skull growth. Ten patients had ventriculomegaly, and the OFC growth curve deflected in 3 patients. Twenty-two patients had hearing loss. Refraction anomalies were diagnosed in 14/15 patients measured at ≥ 8 years of age.

CONCLUSIONS

Patients with Muenke syndrome treated with a single fronto-supraorbital advancement in their first year of life rarely develop signs of intracranial hypertension, in accordance with the very low prevalence of its causative factors (OSA, hydrocephalus, and restricted skull growth). This illustrates that there is no need for a routine second craniofacial procedure. Patient follow-up should focus on visual assessment and speech and hearing outcomes.

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.

Genetic Causes of Craniosynostosis: An Update

In 1993, Jabs et al. were the first to describe a genetic origin of craniosynostosis. Since this discovery, the genetic causes of the most common syndromes have been described. In 2015, a total of 57 human genes were reported for which there had been evidence that mutations were causally related to craniosynostosis. Facilitated by rapid technological developments, many others have been identified since then. Reviewing the literature, we characterize the most common craniosynostosis syndromes followed by a description of the novel causes that were identified between January 2015 and December 2017.

A Qualitative Study to Explore the Views and Attitudes towards Prenatal Testing in Adults Who Have Muenke Syndrome and their Partners

Muenke syndrome constitutes the most common syndromic form of craniosynostosis, occurring in 1 in 30,000 live births. The phenotype is variable, ranging from no clinical findings to complex presentation. Facilitating reproductive decision making for couples at genetic risk of having a child with Muenke syndrome is an important aspect of genetic counselling. Prenatal genetic testing for Muenke syndrome is accurate; however the value of testing is uncertain with a variable phenotype. The purpose of this study was to explore attitudes towards prenatal testing in couples where one partner had tested positive for the Muenke mutation. We used a qualitative approach based on thematic analysis and collected data using individual semi-structured interviews with eight parents. Five key themes were: The Muenke journey; Impact and knowledge of diagnosis; Knowledge and attitude to prenatal testing; Stigma and sharing of information; and Information retention. Knowledge of Muenke syndrome and prenatal testing was poor. Genetic information was provided when treatment of their affected child was their paramount concern. Couples reported not sharing genetic information with family due to fear of stigmatisation. Couples cannot make reproductive decisions if lacking appropriate understanding of the choices: timely genetic counselling regarding prenatal testing is needed when relevant to them.

Expansion of the variable expression of Muenke syndrome: Hydrocephalus without craniosynostosis

Muenke syndrome (MS) is an autosomal dominant coronal craniosynostosis syndrome with variable extracranial anomalies. We studied 56 unrelated patients with non-syndromic uni- or bicoronal craniosynostosi to identify the frequency and clinical characteristics of MS in a cohort of Mexican childrens. The FGFR3 pathogenic variation p.Pro250Arg responsible for MS was characterized in all probands by PCR-restriction assay; available first-degree relatives (15 parents, 5 siblings) of the confirmed p.Pro250Arg carriers were also tested. All heterozygotes for p.Pro250Arg underwent clinical and audiologic assessment, as well as X-ray evaluations of hands and feet. Eight of 56 probands (14%) were found to carry the p.Pro250Arg variant and half of them were familial cases. Four p.Pro250Arg heterozygous familial members had been considered unaffected before the molecular testing. In one MS family, hydrocephalus without craniosynostosis, was documented as the only clinical manifestation in a previously undetected heterozygous male sibling. Hydrocephalus without craniosynostosis in a patient with the p.Pro250Arg variant suggests that some patients with MS might present only this manifestation; to our knowledge, hydrocephalus has not been described as isolated feature in MS, so we propose to consider this feature as an expansion of the MS phenotype rather than an unrelated finding. Our data also reinforce the notion that molecular testing of FGFR3 must be included in the diagnostic approach of coronal craniosynostosis. This will allow accurate genetic counseling and optimal management of MS, which might otherwise go undiagnosed because of mild manifestations and wide variability of expression. © 2016 Wiley Periodicals, Inc.

Genetic Syndromes Associated with Craniosynostosis

Craniosynostosis is defined as the premature fusion of one or more of the cranial sutures. It leads not only to secondary distortion of skull shape but to various complications including neurologic, ophthalmic and respiratory dysfunction. Craniosynostosis is very heterogeneous in terms of its causes, presentation, and management. Both environmental factors and genetic factors are associated with development of craniosynostosis. Nonsyndromic craniosynostosis accounts for more than 70% of all cases. Syndromic craniosynostosis with a certain genetic cause is more likely to involve multiple sutures or bilateral coronal sutures. FGFR2, FGFR3, FGFR1, TWIST1 and EFNB1 genes are major causative genes of genetic syndromes associated with craniosynostosis. Although most of syndromic craniosynostosis show autosomal dominant inheritance, approximately half of patients are de novo cases. Apert syndrome, Pfeiffer syndrome, Crouzon syndrome, and Antley-Bixler syndrome are related to mutations in FGFR family (especially in FGFR2), and mutations in FGFRs can be overlapped between different syndromes. Saethre-Chotzen syndrome, Muenke syndrome, and craniofrontonasal syndrome are representative disorders showing isolated coronal suture involvement. Compared to the other types of craniosynostosis, single gene mutations can be more frequently detected, in one-third of coronal synostosis patients. Molecular diagnosis can be helpful to provide adequate genetic counseling and guidance for patients with syndromic craniosynostosis.

Insights into the development of molecular therapies for craniosynostosis

For the past 2 decades, clinical and basic science researchers have gained significant insights into the molecular and genetic pathways associated with common forms of craniosynostosis. This has led to invaluable information for families and physicians in their attempts to understand the heterogeneity of craniosynostosis. Genetic mutations have been identified in the fibroblast growth factor receptors (FGFRs) as well as in other targets, including TWIST1, BMP, and RUNX2. Greater understanding of these and other pathways has led to the development of innovative approaches for applying medical therapies to the treatment of craniosynostosis, in particular by maintaining suture patency. In this article, the authors discuss the molecular pathophysiological mechanisms underlying various forms of craniosynostosis. They also highlight recent developments in the field of molecular craniosynostosis research with the hope of identifying targets for medical therapies that might augment the results of surgical intervention.

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.

The Fibroblast Growth Factor signaling pathway

The signaling component of the mammalian Fibroblast Growth Factor (FGF) family is comprised of eighteen secreted proteins that interact with four signaling tyrosine kinase FGF receptors (FGFRs). Interaction of FGF ligands with their signaling receptors is regulated by protein or proteoglycan cofactors and by extracellular binding proteins. Activated FGFRs phosphorylate specific tyrosine residues that mediate interaction with cytosolic adaptor proteins and the RAS-MAPK, PI3K-AKT, PLCγ, and STAT intracellular signaling pathways. Four structurally related intracellular non-signaling FGFs interact with and regulate the family of voltage gated sodium channels. Members of the FGF family function in the earliest stages of embryonic development and during organogenesis to maintain progenitor cells and mediate their growth, differentiation, survival, and patterning. FGFs also have roles in adult tissues where they mediate metabolic functions, tissue repair, and regeneration, often by reactivating developmental signaling pathways. Consistent with the presence of FGFs in almost all tissues and organs, aberrant activity of the pathway is associated with developmental defects that disrupt organogenesis, impair the response to injury, and result in metabolic disorders, and cancer. For further resources related to this article, please visit the WIREs website.

Phenotypic variability in two families of Muenke syndrome with FGFR3 mutation

Muenke syndrome is a nonsyndromic coronal craniosynostosis, characterised by clinical and radiological variability, with occurrence of both familial and sporadic cases. Pro250Arg (P250R) is a pathogenic mutation, causing this highly clinically heterogeneous syndrome reported worldwide irrespective of race and ethnicity. The authors describe three Indian cases in two different families showing phenotypic spectrum of the disease, which was later confirmed by genetic testing.

Closing the Gap: Genetic and Genomic Continuum from Syndromic to Nonsyndromic Craniosynostoses

Craniosynostosis, a condition that includes the premature fusion of one or multiple cranial sutures, is a relatively common birth defect in humans and the second most common craniofacial anomaly after orofacial clefts. There is a significant clinical variation among different sutural synostoses as well as significant variation within any given single-suture synostosis. Craniosynostosis can be isolated (i.e., nonsyndromic) or occurs as part of a genetic syndrome (e.g., Crouzon, Pfeiffer, Apert, Muenke, and Saethre-Chotzen syndromes). Approximately 85 % of all cases of craniosynostosis are nonsyndromic. Several recent genomic discoveries are elucidating the genetic basis for nonsyndromic cases and implicate the newly identified genes in signaling pathways previously found in syndromic craniosynostosis. Published epidemiologic and phenotypic studies clearly demonstrate that nonsyndromic craniosynostosis is a complex and heterogeneous condition supporting a strong genetic component accompanied by environmental factors that contribute to the pathogenetic network of this birth defect. Large population, rather than single-clinic or hospital-based studies is required with phenotypically homogeneous subsets of patients to further understand the complex genetic, maternal, environmental, and stochastic factors contributing to nonsyndromic craniosynostosis. Learning about these variables is a key in formulating the basis of multidisciplinary and lifelong care for patients with these conditions.

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.

Genotype and clinical care correlations in craniosynostosis: findings from a cohort of 630 Australian and New Zealand patients

Craniosynostosis is one of the most common craniofacial disorders encountered in clinical genetics practice, with an overall incidence of 1 in 2,500. Between 30% and 70% of syndromic craniosynostoses are caused by mutations in hotspots in the fibroblast growth factor receptor (FGFR) genes or in the TWIST1 gene with the difference in detection rates likely to be related to different study populations within craniofacial centers. Here we present results from molecular testing of an Australia and New Zealand cohort of 630 individuals with a diagnosis of craniosynostosis. Data were obtained by Sanger sequencing of FGFR1, FGFR2, and FGFR3 hotspot exons and the TWIST1 gene, as well as copy number detection of TWIST1. Of the 630 probands, there were 231 who had one of 80 distinct mutations (36%). Among the 80 mutations, 17 novel sequence variants were detected in three of the four genes screened. In addition to the proband cohort there were 96 individuals who underwent predictive or prenatal testing as part of family studies. Dysmorphic features consistent with the known FGFR1-3/TWIST1-associated syndromes were predictive for mutation detection. We also show a statistically significant association between splice site mutations in FGFR2 and a clinical diagnosis of Pfeiffer syndrome, more severe clinical phenotypes associated with FGFR2 exon 10 versus exon 8 mutations, and more frequent surgical procedures in the presence of a pathogenic mutation. Targeting gene hot spot areas for mutation analysis is a useful strategy to maximize the success of molecular diagnosis for individuals with craniosynostosis.

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.

Genetic basis of single-suture synostoses: genes, chromosomes and clinical implications

BACKGROUND

Non syndromic craniosynostoses are the most frequent craniofacial malformations worldwide. They represent a wide and heterogeneous group of entities, in which the dysmorphism may occur in a single (simple forms) or in multiple sutures (complex forms). Simple forms present a higher birth prevalence and are classified according to the involved suture and to the corresponding abnormal cranial shape: scaphocephaly (SC; sagittal suture), trigonocephaly (TC; metopic suture), anterior plagiocephaly (unilateral coronal suture), posterior plagiocephaly (unilateral lambdoid suture). They occur commonly as sporadic forms, although a familiar recurrence is sometimes observed, suggesting a mendelian inheritance. The genetic causes of simple craniosynostosis are still largely unknown, as mutations in common craniosynostosis-associated genes and structural chromosomal aberrations have been rarely found in these cases.

AIMS

This review is intended to dissect comprehensively the state-of-the art on the genetic etiology of single suture craniosynostoses, in the attempt to categorize all known disease-associated genes and chromosomal aberrations. Possible genotype/phenotype correlations are discussed as useful clues towards the definition of optimized clinical management flowcharts.

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.

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.

Molecular signaling in pathogenesis of craniosynostosis: the role of fibroblast growth factor and transforming growth factor–β

The interplay of signals between dura mater, suture mesenchyme, and brain is essential in determining the fate of cranial sutures and the pathogenesis of premature suture fusion leading to craniosynostosis. At the forefront of research into suture fusion is the role of fibroblast growth factor and transforming growth factor–β, which have been found to be critical in the cell-signaling cascade involved in aberrant suture fusion. In this review, the authors discuss recent and ongoing research into the role of fibroblast growth factor and transforming growth factor–β in the etiopathogenesis of craniosynostosis.

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.

A Korean family with the Muenke syndrome

The Muenke syndrome (MS) is characterized by unicoronal or bicoronal craniosynostosis, midfacial hypoplasia, ocular hypertelorism, and a variety of minor abnormalities associated with a mutation in the fibroblast growth factor receptor 3 (FGFR3) gene. The birth prevalence is approximately one in 10,000 live births, accounting for 8-10% of patients with coronal synostosis. Although MS is a relatively common diagnosis in patients with craniosynostosis syndromes, with autosomal dominant inheritance, there has been no report of MS, in an affected Korean family with typical cephalo-facial morphology that has been confirmed by molecular studies. Here, we report a familial case of MS in a female patient with a Pro250Arg mutation in exon 7 (IgII-IGIII linker domain) of the FGFR3 gene. This patient had mild midfacial hypoplasia, hypertelorism, downslanting palpebral fissures, a beak shaped nose, plagio-brachycephaly, and mild neurodevelopmental delay. The same mutation was confirmed in the patient's mother, two of the mother's sisters and the maternal grandfather. The severity of the cephalo-facial anomalies was variable among these family members.

Increases in discontinuous rib cartilage and fused carpal bone in rat fetuses exposed to the teratogens, busulfan, acetazolamide, vitamin A, and ketoconazole

Skeletal changes induced by treatment of pregnant rats with four potent teratogens, busulfan, acetazolamide, vitamin A palmitate, and ketoconazole, were evaluated using Alizarin Red S and Alcian Blue double-staining to investigate the relationship between drug-induced skeletal malformations and cartilaginous changes in the fetuses. Pregnant rats (N = 8/group) were treated once or twice between gestation days (GDs) 10 to 13 with busulfan at doses of 3, 10, or 30 mg/kg; acetazolamide at 200, 400, or 800 mg/kg; vitamin A palmitate at 100,000, 300,000, or 1,000,000 IU/kg; or ketoconazole at doses of 10, 30, or 100 mg/kg. Uterine evaluations and fetal external and skeletal examinations were conducted on GD 20. Marked skeletal abnormalities in ribs and hand/forelimb bones such as absent/ short/bent ribs, fused rib cartilage, absent/fused forepaw phalanx, and misshapen carpal bones were induced at the mid- and high-doses of busulfan and acetazolamide and at the high-dose of vitamin A palmitate and ketoconazole. Increased incidences of discontinuous rib cartilage (DRC) and fused carpal bone (FCB) were observed from the low- or mid-dose in the busulfan and acetazolamide groups, and incidences of FCB were increased from the mid-dose in the vitamin A palmitate and ketoconazole groups. Therefore, DRC and FCB were detected at lower doses than those at which ribs and hand/forelimb malformations were observed in the four potent teratogens.

A young patient with polyarthralgia and hearing loss: a case report of Muenke syndrome

There are few reports of the typical radiographic findings in the hands and feet of patients with Muenke syndrome. We present a case report of a young girl with Muenke syndrome, whose diagnosis was made following the observation of coalitions and coned epiphyses on hand radiographs.

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.

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

BACKGROUND

Muenke-type craniosynostosis is defined as fibroblast growth factor receptor 3 (FGFR3)-associated coronal craniosynostosis with or without mental retardation. With complementary genetic information, more precise diagnosis and long-term functional outcome of cranial vault remodeling in affected patients can be studied, and additional distinct features of Muenke syndrome can now be investigated. This study was undertaken to assess craniofacial growth and long-term functional outcome in patients with Muenke-type craniosynostosis.

METHODS

A chart review of all FGFR3 patients at The Children's Hospital of Philadelphia who had undergone cranial vault remodeling for unicoronal or bicoronal synostosis (n = 16) was performed. Need for reoperation, midface surgery, and functional corrections were assessed. Audiology and orthodontic records were reviewed.

RESULTS

All patients underwent cranial remodeling during infancy. Repeated intracranial surgery was performed or is currently scheduled for aesthetic reasons only (n = 7). Sexual dimorphism with male preponderance in FGFR3 unicoronal synostosis was detected. Despite dental crowding amenable to palatal expansion in patients with bicoronal synostosis, significant midface hypoplasia was not observed. Sensorineural hearing loss with a distinctive pattern was present in all patients who had undergone audiology testing.

CONCLUSIONS

Patients with FGFR3-associated craniosynostosis demonstrate a sexual dimorphism, with a male preponderance for unicoronal synostosis. A secondary major intracranial procedure is required for recurrent supraorbital retrusion in at least 43 percent of patients. A secondary or tertiary extracranial forehead contouring procedure should be anticipated in nearly all patients. No patient required any midface correctional procedure. These patients demonstrate characteristic bilateral, symmetric, low- to mid-frequency sensorineural hearing loss.

Muenke syndrome (FGFR3-related craniosynostosis): expansion of the phenotype and review of the literature

Muenke syndrome is an autosomal dominant disorder characterized by coronal suture craniosynostosis, hearing loss, developmental delay, carpal and tarsal fusions, and the presence of the Pro250Arg mutation in the FGFR3 gene. Reduced penetrance and variable expressivity contribute to the wide spectrum of clinical findings in Muenke syndrome. To better define the clinical features of this syndrome, we initiated a study of the natural history of Muenke syndrome. To date, we have conducted a standardized evaluation of nine patients with a confirmed Pro250Arg mutation in FGFR3. We reviewed audiograms from an additional 13 patients with Muenke syndrome. A majority of the patients (95%) demonstrated a mild-to-moderate, low frequency sensorineural hearing loss. This pattern of hearing loss was not previously recognized as characteristic of Muenke syndrome. We also report on feeding and swallowing difficulties in children with Muenke syndrome. Combining 312 reported cases of Muenke syndrome with data from the nine NIH patients, we found that females with the Pro250Arg mutation were significantly more likely to be reported with craniosynostosis than males (P < 0.01). Based on our findings, we propose that the clinical management should include audiometric and developmental assessment in addition to standard clinical care and appropriate genetic counseling.

Advances in the molecular pathogenesis of craniofacial conditions

The impact that the understanding of fibroblast growth factor receptor (FGFR) biology and its relevance to the pathogenesis of the craniosynostoses has made cannot be underestimated. As the genetic and molecular pathology of other conditions become increasingly understood, there is much hope that robust and relevant animal models of these conditions may be generated. From these models-and in conjunction with laboratory studies in vitro-comes a real hope of improved therapeutic strategies. The future lies in increased cooperation between clinicians working in high-volume centers and basic scientists. This article decribes the results of a decade of research in which the molecular pathology of the craniosynostoses was unravelled. The understanding of the importance of FGFR mutations to the genetic etiology of craniosynostosis opened up novel studies in developmental biology in various tissues. Such studies describe the functional effects of FGFR mutations. Investigations of FGFR expression in human craniofacial development have related functional molecular studies to human craniosynostosis syndromes, which provides a link between the gene mutation and the affected child.

Morphometric analysis of untreated adult skulls in syndromic and nonsyndromic craniosynostosis

The aim of this study was to perform a morphometric analysis of untreated adult skulls displaying syndromic and nonsyndromic craniosynostosis. We analyzed, in detail, 42 adult craniosynostoses (18 scaphocephaly, 11 anterior plagiocephaly, 2 trigonocephaly, 9 oxycephaly, and 2 brachycephaly) from archeological (three skulls) and pathoanatomical samples (39 skulls). The univariate and bivariate measurements from the pathological skulls were compared with 40 anatomical skulls with normal cranial vault morphology. Bony signs of chronic elevated intracranial pressure (ICP) are (1) diffuse beaten copper pattern, (2) dorsum sellae erosion, (3) suture diastasis, and (4) abnormalities of venous drainage that particularly affect the sigmoid-jugular sinus complex. The mean cranial length was significantly greater in scaphocephaly than in anatomical skulls (20.3 vs 18.0 cm), and the sagittal suture was also longer (14.3 vs 11.8 cm). There were three types of suture course in the bregma region in scaphocephaly: anterior spur (28%), normal configuration (61%), and posterior spur (11%). The plagiocephaly measurements showed nonsignificant differences, and there was no correlation between the length of the anterior and middle skull base (ipsilateral anterior-posterior shortening of the skull) and incomplete or complete suture synostosis. Bony signs of chronic elevated ICP were found in 82% of cases of oxycephaly and brachycephaly. In three such cases of oxycephaly, we found a marked (1.8-2.1 cm) elevation of bregma region. One skull (Saethre-Chotzen syndrome) yielded human DNA sufficient for polymerase chain reaction (PCR)-based amplification procedures. Mutation analyses in the FGFR3 gene revealed nucleotide alterations located in the mutational hot spot at amino acid residue 250 (g.C749). The mean cranial length in adult scaphocephaly was 12% greater than anatomical skulls. A unilateral complete or incomplete coronal synostosis can be found with or without plagiocephalic deformation. Elevation of the bregma region is a bony sign of chronic elevated ICP. These data on adult craniosynostosis could be of interest for physicians dealing with craniosynostotic children.

Clinical dividends from the molecular genetic diagnosis of craniosynostosis

A dozen years have passed since the first genetic lesion was identified in a family with craniosynostosis, the premature fusion of the cranial sutures. Subsequently, mutations in the FGFR2, FGFR3, TWIST1, and EFNB1 genes have been shown to account for approximately 25% of craniosynostosis, whilst several additional genes make minor contributions. Using specific examples, we show how these discoveries have enabled refinement of information on diagnosis, recurrence risk, prognosis for mental development, and surgical planning. However, phenotypic variability can present a significant challenge to the clinical interpretation of molecular genetic tests. In particular, the difficulty of analyzing the complex interaction of genetic background and prenatal environment in determining clinical features, limits the value of identifying low penetrance mutations.

Pansynostosis: a review

INTRODUCTION

Although rare, pansynostoses are seen and treated by the craniofacial surgeon. To date, a single source that reviews these more severe forms of craniosynostosis is lacking in the literature.

MATERIALS AND METHODS

The present paper outlines and reviews the associations of both syndromic and nonsyndromic cases, potential mechanisms, and the anatomy involved with such forms of premature fusion of the cranial sutures.

RESULTS

Pansynostosis is seen in a myriad of syndromes but can also be identified in nonsyndromic cases. Raised intracranial pressure is a concern in these patients.

CONCLUSIONS

Early recognition and treatment of patients with pansynostosis of the cranial sutures is important.

Genetic analysis of non-syndromic craniosynostosis

Craniosynostosis is a common malformation occurring in 3-5 per 10,000 live births. Most often craniosynostosis occurs as an isolated (i.e. non-syndromic) anomaly. Non-syndromic craniosynostosis (NSC) is a clinically and genetically heterogeneous condition that has the characteristics of a multifactorial trait. It is believed that each sutural synostosis (e.g. sagittal, coronal) represents a different disease. Significant progress has been made in understanding the clinical and molecular aspects of monogenic syndromic craniosynostosis. However, the phenotypic characterization of NSC is incomplete and its causes remain unknown. This review summarizes the available knowledge on NSC and presents a systematic approach aimed at the identification of genetic and non-genetic factors contributing to the risk of this common craniofacial defect.

Syndromic craniosynostosis: from history to hydrogen bonds

The syndromic craniosynostoses, usually involving multiple sutures, are hereditary forms of craniosynostosis associated with extracranial phenotypes such as limb, cardiac, CNS and tracheal malformations. The genetic etiology of syndromic craniosynostosis in humans is only partially understood. Syndromic synostosis has been found to be associated with mutations of the fibroblast growth factor receptor family (FGFR1, -R2, -R3), TWIST1, MSX2, and EFNB1. Apert, Pfeiffer, Crouzon, and Jackson-Weiss syndromes are due to gain-of-function mutations of FGFR2 in either the Ig II-III linker region (Apert) or Ig III domain. Loss of function mutations of TWIST1 and gain-of-function mutations of MSX2 lead to Saethre-Chotzen and Boston-type syndromes, respectively. The mutations in Pfeiffer (FGFR1), Muenke (FGFR3), and Apert syndrome (FGFR2) are caused by the same amino acid substitution in a highly conserved region of the Ig II-III linker region of these proteins, which suggests that these receptor tyrosine kinases have an overlapping function in suture biology. In this review we will discuss the historical descriptions, current phenotypes and molecular causes of the more common forms of syndromic craniosynostosis.

Craniofacial morphology in Muenke syndrome

The purpose of this study was to test whether the severity of the cranial phenotype in Muenke syndrome infants with unicoronal synostosis is greater than in infants with nonsyndromic unicoronal synostosis. A total of 23 infants were included in the study. All infants included in the study had a computed tomography (CT)-verified synostosis of the coronal suture. The patients were either placed into the "Muenke" group (n=11) or the "non-Muenke" control group (n=12) on the basis of a test for the P250R mutation in the FGFR3 gene. On the basis of CT scans, a three-dimensional surface model corresponding to bone was created for each individual. The sutures were inspected for synostosis, and the degree of synostosis was assessed. Increased digital markings were recorded for both groups. Craniofacial morphology was assessed quantitatively using bony landmarks and recording of the midsagittal surface of the calvaria, cranial base, and maxillary complex. Increased digital markings were more severe posteriorly in Muenke patients than in non-Muenke patients. The Muenke patients with unilateral coronal synostosis showed a somewhat more severe asymmetry in the anterior part of the skull than the non-Muenke patients. The study indicates differences with regard to severity of increased digital markings and craniofacial asymmetry between the infants with Muenke syndrome and the infants with nonsyndromic unilateral coronal synostosis.

Congenital nasal malformations

The nose is a prominent feature of the human face. Congenital malformations of the nose, whether functional or anatomic, affect the physiologic and psychologic wellness of children who have these anomalies. Congenital nasal abnormalities may be overt or subtle and can occasionally cause life-threatening emergencies at birth. A discussion of nasal embryology and development provides the basis for the discussion of some of the important congenital abnormalities seen in clinical practice. The final portion of the article is devoted to several of the more common syndromes in which nasal abnormalities are encountered.

Craniectomy and noggin application in an infant model

INTRODUCTION

Noggin is an antagonist of bone morphogenetic proteins (BMP)-2, -4 and -7. Little data are available regarding its clinical utility. Two hypotheses were put forward: firstly, that spontaneous regeneration of calvarial defects with noggin protein would result in diminished bone volume when compared with calvarial defects not so treated. Secondly, that centrifugal cranial expansion would remain undisturbed whether noggin was applied or not.

MATERIAL AND METHODS

A unilateral defect of the frontal and parietal bones (2x4cm) was generated by excising the right coronal suture in 2-month-old minipigs (n=10) and in group 1 (n=5) no further intervention was undertaken. In the second group (n=5), a collagen type I tissue fleece and noggin protein (1.05mg/ml) were applied. After 4 months the coronal suture regions of frontal sides were examined in each animal by computed tomography and non-decalcified histology.

RESULTS

Bony gaps of equivalent size remained in animals of both groups. The differences in bone volumes of the experimental sides of group 1 were not statistically significantly different (p=0.117) when compared with those of group 2. A significant difference in the bone volumes of the experimental versus control (unoperated) sides was found in both group 1 (p=0.043) and group 2 (p=0.043). Internal skull diameters increased by 16.4% in both groups but the physiological centrifugal cranial expansion remained undisturbed. Bone densities of the experimental and control sides of groups 1 and 2 were not statistically significantly different (both p>0.05).

CONCLUSIONS

The first hypothesis was contradicted: the quantity and quality of spontaneous bone regenerates was not altered by application of noggin protein. The second hypothesis was confirmed: no disruption of subsequent cranial development was seen. It may be that a single application of noggin protein in this study was insufficient. However, it may well be suggested that the continuous supplementation of noggin, for example by adenoviral noggin gene transfer may significantly reduce the quantity of spontaneous bone regeneration in a similar experiment.