Craniosynostotic Syndromes Research Articles

The Genetics and Learning Disorders of the Syndromes Involving Craniosynostosis

Prenatal genetic vehicles that lead to facial and cranial dysmorphias, specifically craniosynostosis, are seen in a spectrum of synostotic syndromes that include apert, crouzon, Kleeblattschadel deformity, saethre-chotzen, muenke, cranio-fronto-nasal syndrome, Robinow-Sorauf syndrome and beare-stevenson-cutis-gyrata syndrome. Specific genes involved in cranio-synostotic syndromes include: TWIST1, EFNB1, GLI2, DMD, YWHAE, IRAK2, FGFR1, FGFR2, FGFR3, CNTNAP2, ADAMTS18, SKI, MECP2, KIFBP, TCF12, H2AL1P, GAGE12D and possibly HDAC9. Regarding protein expression, conserved domains found in rpsblast for craniosynostosis using the NCBI homologene tool show IGc2 (smart00408) immunoglobulin C-2 Type, PKc_like (cl09925) Protein Kinases, catalytic domain, Ig (cl11960) Immunoglobulin domain. A discussion of all the syndromes involving craniosynostosis is beyond the scope of this paper. We will discuss the clinical features, genetics, cognitive development and associated psychiatric conditions of the more common syndromes involving craniosynostosis. We theorize that the clinical features and genetics of craniosynostosis involve a spectrum of syndromes on which there is variable severity and involvement of impaired cognition and developmental disorders.

The Genetics and Learning Disorders of the Syndromes Involving Craniosynostosis

Prenatal genetic vehicles that lead to facial and cranial dysmorphias, specifically craniosynostosis, are seen in a spectrum of synostotic syndromes that include apert, crouzon, Kleeblattschadel deformity, saethre-chotzen, muenke, cranio-fronto-nasal syndrome, Robinow-Sorauf syndrome and beare-stevenson-cutis-gyrata syndrome. Specific genes involved in cranio-synostotic syndromes include: TWIST1, EFNB1, GLI2, DMD, YWHAE, IRAK2, FGFR1, FGFR2, FGFR3, CNTNAP2, ADAMTS18, SKI, MECP2, KIFBP, TCF12, H2AL1P, GAGE12D and possibly HDAC9. Regarding protein expression, conserved domains found in rpsblast for craniosynostosis using the NCBI homologene tool show IGc2 (smart00408) immunoglobulin C-2 Type, PKc_like (cl09925) Protein Kinases, catalytic domain, Ig (cl11960) Immunoglobulin domain. A discussion of all the syndromes involving craniosynostosis is beyond the scope of this paper. We will discuss the clinical features, genetics, cognitive development and associated psychiatric conditions of the more common syndromes involving craniosynostosis. We theorize that the clinical features and genetics of craniosynostosis involve a spectrum of syndromes on which there is variable severity and involvement of impaired cognition and developmental disorders.

Fibroblast Growth Factor Receptor 2 (FGFR2) Mutation Related Syndromic Craniosynostosis.

Craniosynostosis results from the premature fusion of cranial sutures, with an incidence of 1 in 2,100-2,500 live births. The majority of cases are non-syndromic and involve single suture fusion, whereas syndromic cases often involve complex multiple suture fusion. The fibroblast growth factor receptor 2 (FGFR2) gene is perhaps the most extensively studied gene that is mutated in various craniosynostotic syndromes including Crouzon, Apert, Pfeiffer, Antley-Bixler, Beare-Stevenson cutis gyrata, Jackson-Weiss, Bent Bone Dysplasia, and Seathre-Chotzen-like syndromes. The majority of these mutations are missense mutations that result in constitutive activation of the receptor and downstream molecular pathways. Treatment involves a multidisciplinary approach with ultimate surgical fixation of the cranial deformity to prevent further sequelae. Understanding the molecular mechanisms has allowed for the investigation of different therapeutic agents that can potentially be used to prevent the disorders. Further research efforts are need to better understand screening and effective methods of early intervention and prevention. Herein, the authors provide a comprehensive update on FGFR2-related syndromic craniosynostosis.

Postmortem Computed Tomography in a Case of Apert Syndrome

There have been very few small studies or case reports in the literature considering noninvasive postmortem imaging as supplement to autopsy, especially in fetuses with skeletal dysplasias. Apert syndrome accounts for 4.5% of all patients with craniosynostotic syndromes. It is classically characterized by the triad of coronal craniosynostosis, midfacial hypoplasia, and symmetric bony syndactyly of the hands and feet. Illustrate the accuracy of a postmortem computed tomography compared with a conventional autopsy as well as review common imaging findings in a case of prenatally diagnosed Apert syndrome. A 31-year-old woman was seen for a routine prenatal ultrasound. A craniofacial syndrome was suspected by prenatal ultrasound, and the anomalies raised the suspicion of Apert syndrome. After genetic counseling, it was chosen to terminate the pregnancy. A postmortem computed tomographic scan was performed, followed by a conventional autopsy that confirmed the findings. Computed tomography provides many advantages in postmortem assessment. Postmortem imaging cannot replace conventional autopsy but is superior in axial and appendicular skeleton assessment. These studies provide supplemental information that may guide the autopsy. In situations where the parents wish not to pursue an autopsy, postmortem imaging can provide useful clinical information.

Audiologic Findings in Pfeiffer Syndrome

Hearing loss has been described in patients with certain craniosynostotic syndromes but is poorly defined in Pfeiffer syndrome (PS). Our objective was to characterize the otologic and audiologic findings in PS. The records of PS patients evaluated at our craniofacial center over a 30-year period were culled. Only patients with a confirmed diagnosis and formal audiologic examination were included. Diagnostic criteria were characteristic mutations in fibroblast growth factor receptor 1 or 2 (FGFR1, FGFR2) or, in the absence of genetic testing, typical clinical findings of PS as determined by a clinical geneticist or the most senior author. Twenty patients met the inclusion criteria, and all had hearing loss. Twenty patients had traditional audiologic testing: 14 (70%) had pure conductive loss (minor to severe), and 3 (15%) had a mixed conductive/sensorineural loss (minor to severe). Two additional patients had hearing loss by Behavioral Observational Audiometry (sound fields method). One patient with early conductive hearing loss was subsequently determined to have a pure sensorineural deficit. Nine patients (45%) had permanent hearing loss significant enough to require audiologic amplification. All patients with PS demonstrated hearing loss, although the severity and the anatomic basis (ie., neural vs conductive) were variable. Conductive hearing loss, possibly caused by structural abnormalities, was most common. Sensorineural hearing loss was less common and may be related to the effect of FGFR mutations on cranial nerve and/or inner-ear development.

The missense mutation W290R in Fgfr2 causes developmental defects from aberrant IIIb and IIIc signaling

Missense mutations in the Fibroblast Growth Factor Receptor 2 (FGFR2) have been identified in human craniosynostotic syndromes such as Crouzon (CS) and Pfeiffer (PS). FGFR2 has two major isoforms, IIIb and IIIc, generated through alternative splicing with their own temporal, spatial, and ligand-binding specificities. In this study, we report the identification and characterization of a missense mutation in codon 290 of murine Fgfr2 (W290R). The defects in W290R mutants are suggestive of disruption of signalling in both IIIb and IIIc isoforms of the Fgfr2 gene. Heterozygous mutants presented with features resembling those found in patients with CS. Fgfr2(W290R) homozygotes displayed constitutive FGFR2 activation with increased, but correct tissue-specific, expression of the IIIb and IIIc isoforms in many of the defective organs. Our Fgfr2(W290R) mouse model thus represents an excellent mouse model of CS to probe the many questions around the pathogenesis of craniosynostotic birth defects consequent to defects in FGF signaling.

Familial Crouzon syndrome

Crouzon syndrome is an autosomal dominant condition of the craniosynostotic syndromes without syndactyly and with various dentofacial anomalies. Craniosynostosis, maxillary hypoplasia, shallow orbits, ocular proptosis and hypertelorism are the characteristic features of Crouzon syndrome. This report describes the variable clinical features in affected individuals over two generations of a family with dentofacial deformities and review of literature.

Medical treatment of craniosynostosis: recombinant Noggin inhibits coronal suture closure in the rat craniosynostosis model

INTRODUCTION - The mechanisms underlying craniosynostosis remains unknown. However, mutations in FGFR2 are associated with craniosynostotic syndromes. We previously compared gene expression patterns of patent and synostosing coronal sutures in the nude rat and demonstrated down regulation of Noggin in synostosing sutures. Noggin expression is also suppressed by FGF2 and constitutive FGFR2 signaling [Warren et al. (2003) Nature, vol. 422, pp. 625-9; McMahon et al. (1998) Genes Dev, vol. 12, pp. 1438-52]. Thus, we therefore hypothesized that the addition of rhNoggin to prematurely fusing sutures should prevent synostosis. MATERIALS AND METHODS - Cohorts of nude rats were subjected to: 1) surgical elevation of the coronal suture (shams); 2) surgical elevation and placement of normal or FGFR2 mutant human osteoblasts onto the underlying dura (xenotransplants); or 3) xenotransplantation with co-application of heparin acrylic beads soaked with recombinant human (rh) Noggin. Eleven days post-surgery the sutures were harvested, stained, and histologically examined. RESULTS - Animals that received control osteoblasts, sham surgery, or no surgery demonstrated normal skull growth and coronal suture histology, whereas animals transplanted only with FGFR2 mutant osteoblasts showed evidence of bridging synostosis on the calvarial dural surface. Sutures treated with FGFR2 mutant osteoblasts and rhNoggin remained patent. CONCLUSION - The chimeric nude rate model is a viable model of craniosynostosis. FGFR2 mutations in osteoblasts induce bridging osteosynthesis demonstrating one of the mechanisms for premature suture fusion. Topical application of rhNoggin protein prevents craniosynostosis in the weanling nude rat xenotransplantation model of syndromic craniosynostosis.

The zebrafish dob/fgf20a mutant models human craniosynostotic syndromes with midfacial hypoplasia

The zebrafish dob/fgf20a mutant models human craniosynostotic syndromes with midfacial hypoplasia

Prevalence and causes of visual impairment in craniosynostotic syndromes

To assess the prevalence and causes of visual impairment in patients with craniosynostotic syndromes of Apert, Crouzon, Pfeiffer, Saethre-Chotzen and craniofrontonasal dysplasia. The medical records of patients who attended the Craniofacial Clinic at two large paediatric hospitals in Sydney, Australia between 1983 and 2004 were retrospectively reviewed. Presenting visual acuity (VA) was assessed using tests appropriate to age and cognition: 'fix and follow' in infants (<18 months old), Teller card acuity in preverbal children (18 months to less than 3 years old), Kay picture test or Sheridan-Gardiner test in children aged between 3 and less than 6 years and Snellen chart in those aged 6 years or older. Visual impairment was defined as the inability to fix and follow or presenting VA < 6/12 in the better eye. Amblyopia was defined as a two-line difference in VA between both eyes in the absence of an organic eye disease. Sixty-three patients with craniosynostotic syndromes were identified, of whom 55 had VA assessed at the first visit. Of these 55, 19 (35.5%) had bilateral visual impairment and 5 (9.1%) had unilateral visual impairment. Causes of visual impairment include amblyopia (16.7%), ametropia (25%), optic atrophy (16.7%) and exposure keratopathy (4.2%). Risk factors for amblyopia include strabismus (43.3%), astigmatism (> or =1.5 dioptres) (39.5%), hypermetropia (18.4%) and anisometropia (> or =1.5 dioptre difference between both eyes) (15.8%). Six of the 63 patients (9.5%) had papilloedema; those who were followed up showed gradual resolution of papilloedema following timely decompressive surgery. A high prevalence of visual impairment in patients with craniosynostotic syndromes was found, almost half of them due to potentially correctable causes, including amblyopia and ametropia. Optic atrophy remains an important cause of visual impairment. Further studies are needed to assess the timing and efficacy of intervention for modifiable causes of visual loss in craniosynostotic syndromes.

Model for the Pharmacologic Treatment of Crouzon Syndrome

Crouzon syndrome is caused by mutations in fibroblast growth factor receptor 2 (FGFR2) leading to constitutive activation of receptors in the absence of ligand binding. The syndrome is characterized by premature fusion of the cranial sutures that leads to abnormal cranium shape, restricted brain growth, and increased intracranial pressure. Surgical remodeling of the cranial vault is currently used to treat affected infants. The purpose of this study was to develop a pharmacological strategy using tyrosine kinase inhibition as a novel treatment for craniosynostotic syndromes caused by constitutive FGFR activation. Characterization of cranial suture fusion in Fgfr2 mutant mice, which carry the most common Crouzon mutation, was performed using micro-computed tomographic analysis from embryogenesis through maturation. Whole calvarial cultures from wild-type and Fgfr2 mice were established and cultured for 2 weeks in the presence of dimethyl sulfoxide control or PD173074, an FGFR tyrosine kinase inhibitor. Paraffin sections were prepared to show suture morphology and calcium deposition. In untreated Fgfr2 cultures, the coronal suture fused bilaterally with loss of overlap between the frontal bone and parietal bone. Calvaria treated with PD173074 (2 micromol/L) showed patency of the coronal suture and were without evidence of any synostosis. We report the successful use of PD173074 to prevent in vitro suture fusion in a model for Crouzon syndrome. Further studies are underway to develop an in vivo treatment protocol as a novel therapeutic modality for FGFR associated craniosynostotic syndromes.

MODEL FOR THE PHARMACOLOGIC TREATMENT OF CROUZON SYNDROME

OBJECTIVE Crouzon syndrome is caused by mutations in FGFR2 leading to constitutive activation of receptors in the absence of ligand binding. The syndrome is characterized by premature fusion of the cranial sutures that leads to abnormal skull shape, restricted brain growth, and increased intracranial pressure. Surgical remodeling of the cranial vault is currently used to treat affected infants. The purpose of this study was to develop a pharmacologic strategy using tyrosine kinase inhibition as a novel treatment for craniosynostotic syndromes caused by constitutive FGFR activation. METHODS Characterization of cranial suture fusion in Fgfr2C342Y/+ mutant mice, which carry the most common Crouzon mutation, was performed using MicroCT analysis from embryogenesis through maturation. Whole calvarial cultures from wild-type and Fgfr2C342Y/+ mice were then established and calvaria cultured for 2 weeks in the presence of DMSO control or PD173074, an FGFR tyrosine kinase inhibitor. Paraffin sections were prepared to show suture morphology and calcium deposition. RESULTS In untreated Fgfr2C342Y/+ cultures, the coronal suture fused bilaterally with loss of overlap between the frontal bone and parietal bone. Calvaria treated with PD173074 (2 (M) showed patency of the coronal suture and were without evidence of any synostosis. CONCLUSION: We report the successful use of PD173074 to prevent in-vitro suture fusion in a model for Crouzon syndrome. Further studies are underway to develop an in-vivo treatment protocol as a novel therapeutic modality for FGFR associated craniosynostotic syndromes.

Otologische Manifestationen des Apert-Syndroms

The Apert syndrome (Acrocephalosyndactyly) is one of the craniosynostotic syndromes, which is often associated with congenial malformation in the temporal bone. We present a case of a 13 year old girl with Apert syndrome. By planning a tympanoplasty we arranged a CT-scan of the temporal bones. It demonstrated next to some other malformations a high jugular bulb on both sides, on the right side just with a membraneous bound to the external ear canal. In a recherche we did not find a higher incidence of high jugular bulb in Apert-syndrome and other craniosynostotic syndromes. However as we expect different malformations of the temporal bone in Apert syndrome we recommend an otorhinolaryngeal examination in each of these patients and a ct scan of the temporal bone before any operation of the middle ear.

Aberrant bony vasculature associated with activating fibroblast growth factor receptor mutations accompanying Crouzon syndrome.

Fibroblast growth factor receptor mutations are associated with and, in fact, cause most syndromes presenting with craniosynostosis. This knowledge has resulted in a shift in the paradigm of suture fusion causation; it was thought previously that abnormal tensional forces arising in the cranial base caused fusion of the vault sutures, but it is now understood that aberrant intercellular signaling in the developing skull leads to abnormal suture morphogenesis. Although the mutations associated with these syndromes are known and the phenotypic consequences are well documented, the pathway from mutation to phenotype has yet to be elucidated. Surgical reconstruction is the primary treatment of craniofacial abnormalities associated with craniosynostotic syndromes such as Crouzon syndrome. In many cases, calvarial vault reshaping is dependent on the quality of the autologous bone available; however, the bone of patients with craniosynostosis syndrome is often more brittle, thinner, and less robust than cranial bone from nonaffected donors. The relation between syndromic craniosynostoses and this bone has not been previously described. In this study, the osteon and blood vessel diameters of calvarial bone from patients with Crouzon syndrome and age- and sex-matched normal calvarial bone are measured. Statistical analysis demonstrates a quantitative and significant difference in the blood vessel diameter but not in the osteon diameter. This finding could be a result of abnormal blood vessel development caused by the fibroblast growth factor receptor mutation occurring before and coincident with bone formation and leading to weakened and fragile bone tissue.

Blocking Endogenous FGF-2 Activity Prevents Cranial Osteogenesis

Normal growth and morphogenesis of the cranial vault reflect a balance between cell proliferation in the sutures and osteogenesis at the margins of the cranial bones. In the clinical condition craniosynostosis, the sutures fuse prematurely as a result of precocious osteogenic differentiation and craniofacial malformation results. Mutations in several fibroblast growth factor receptor (FGFR) genes have now been identified as being responsible for the major craniosynostotic syndromes. We have used a grafting technique to manipulate the levels of endogenous FGF-2 ligand in embryonic chick cranial vaults and thereby perturb morphogenesis. Implantation of beads loaded with FGF-2 did not affect normal cranial development at physiological concentrations, although they elicited a morphogenetic response in the limb. Implantation of beads loaded with a neutralising antibody to FGF-2 generated a concentration-dependent response. When a single bead was implanted, the grafts grew to a massive size as a result of increased cell division in the tissue. With greater inactivation of FGF-2 protein (two to three beads implanted), all further bone differentiation and cell proliferation was blocked. These data further support the emerging idea that the intensity of FGF-mediated signalling determines the developmental fate of the skeletogenic cells in the cranial vault. High and low levels correlate with differentiation and proliferation, respectively. A balance between the two ensures normal cranial vault morphogenesis. This is consistent with the observation that several FGFR mutations causing craniosynostosis result in constitutive activation of the receptor.

Immunolocalization of fibroblast growth factor receptors 1 and 2 in mouse palate development.

Recent evidence has implicated mutations of fibroblast growth factor receptors (FGF-R) in the pathogenesis of craniosynostotic syndromes. Cleft palate can be a component of such syndromes. The expression of FGF-R1 and FGF-R2 has been delineated in normally developing cranium, where they seem to regulate cellular differentiation and proliferation, respectively. The specific role of fibroblast growth factor signaling in mammalian palate development is unclear. The authors investigated the patterns of expression of FGF-R1 and FGF-R2 throughout mouse palatal development in the embryo. Time-dated CD-1 mouse heads (n = 135) were harvested at embryonic ages 12.5, 13.5, 14.5, 15.5, and 16.5 days (term gestation = 19.5 days), fixed in paraformaldehyde, embedded in paraffin, and sectioned. In addition, paired palatal shelves (n = 30) were isolated by means of microdissection from embryonic day--13.5 embryos, grown on Millipore filters in serum-free medium in vitro for 24, 48, 72, or 96 hours and processed for histological analysis. Immunohistochemical analysis for FGF-R1 and FGF-R2 was performed on the in vivo and in vitro specimens. FGF-R1 and FGF-R2 were found to be specifically expressed in the epithelium of the developing palatal shelves from the time of their outgrowth from the maxillary processes through completion of fusion in vivo and in vitro. Expression of both receptors was particularly strong during the phases of medial epithelial-medial epithelial contact between the individual shelves, through the formation of the medial epithelial seam, to the ultimate dissolution of the seam. Such a pattern of expression seems to implicate fibroblast growth factor signaling in the regulation of the critical phase of fusion of the bilateral shelves. The expression of both FGF-R1 and FGF-R2 in the lateral palatal mesenchyme, where such secondary structures as tooth primordia and bone begin to appear, also suggests a role for fibroblast growth factor signaling in the induction of ongoing differentiation and maturation of the palate after fusion. These data suggest that fibroblast growth factor signaling may play a role in the epithelial-mesenchymal interactions that dictate fusion and maturation of the developing palate. Furthermore, the data are consistent with the correlation of cleft palate formation with aberrant fibroblast growth factor signaling.

R-twist gene expression during rat palatogenesis.

Palatal clefting is often associated with premature fusion of cranial sutures in human craniosynostosis syndromes, many of which are characterised by mutations affecting the fibroblast growth factor receptor (FGFR) gene family. In palatal fusion, epithelio-mesenchymal transition (EMT) contributes to the dispersion of the midline epithelial seam. EMT has also been observed in neoplastic epithelial cells in relation to the acquisition of malignant characteristics where morphological changes are accompanied by rapid switching in the expression of fgfr2 from the epithelial type (kgfr) to the mesenchymal type (bek). The twist gene codes for a basic helix-loop-helix transcription factor putatively involved in regulation of transcription of fgfr2. Mutations in the TWIST gene have been described as being responsible for the Saethre-Chotzen syndrome, an autosomal dominant craniosynostosis associated with cleft palate as well as other disturbances of the facial skeleton. In this study we have analysed the distribution of twist transcripts during rat palatogenesis in vivo from 14.5 to 17.5 days post coitum by in situ hybridisation with digoxygenin-labelled ssDNA probes. twist transcripts were found to be concentrated in mesenchymal cells beneath the epithelium at the tip of the palatal shelves immediately prior to, and during fusion as well as in a localised epithelial area at the tip of the shelves prior to fusion, thereby implicating twist gene expression in the process of palatogenesis. This pattern of expression illuminates the disturbances of maxillary growth that occur in human craniosynostotic syndromes.

The pathogenesis of craniosynostosis in the fetus.

Craniosynostosis occurs in approximately 1:2000 live births. It may affect the coronal, sagittal, metopic and lambdoid sutures in isolation or in combination. Although non-syndromic synostoses are more common, over 150 genetic syndromes have been identified. Recent advances in genetic mapping have linked chromosomal mutations with craniosynostotic syndromes. Despite the identification of these genetic mutations, the fundamental biomolecular mechanisms mediating cranial suture biology remain unknown. Today, many laboratories are investigating murine cranial suture biology as a model for human cranial suture development and fusion. Normal murine cranial suture biology is very complex, but evidence suggests that the dura mater provides the biomolecular blueprints (e.g. the soluble growth factors), which guide the fate of the pleuripotent osteogenic fronts. While our knowledge of these dura-derived signals has increased dramatically in the last decade, we have barely begun to understand the fundamental mechanisms that mediate cranial suture fusion or patency. Interestingly, recent advances in both premature human and programmed murine suture fusion have revealed unexpected results, and have generated more questions than answers.

Analysis of Fronto-orbital Advancement for Apert, Crouzon, Pfeiffer, and Saethre-Chotzen Syndromes

The purposes of this study were (1) to document outcome after primary fronto-orbital advancement for the four major eponymous craniosynostotic syndromes (Apert, Crouzon, Pfeiffer, and Saethre-Chotzen) and (2) to identify factors that might influence need for primary and secondary fronto-orbital advancement or foreheadplasty. Also tested was the hypothesis that coincident sagittal synostosis could modulate brachycephaly and affect whether a primary or secondary frontal operation was necessary. Data were collected on age and indications for initial operation, type of primary and secondary frontal procedures, and concomitant sagittal synostosis. Patients initially managed by subcranial Le Fort III were included in the study group but excluded from analysis of fronto-orbital advancement. Patients treated by monobloc advancement or Le Fort III osteotomies with frontal grafting or Anderl modification were assessed as having had primary fronto-orbital advancement. Minimum time to follow-up was 5 years. A total of 126 patients met inclusion criteria. Lateral photographs were examined to assess preoperative and postoperative sagittal position of supraorbital rims-to-globes. Frontal re-advancement was indicated if the corneal apex was anterior to the supraorbital rim. Foreheadplasty was indicated for unacceptable frontal contour and normal supraorbital rim-to-globe relationship. Primary correction for frontal retrusion was not required in 4 percent of Apert (1 of 25), 16 percent of Crouzon (7 of 44), 6 percent of Pfeiffer (2 of 31), and 19 percent of Saethre-Chotzen (5 of 26) patients. Of those infants who had a primary fronto-orbital advancement, reoperation for either supraorbital retrusion or frontal deformity was necessary in all 16 Apert patients and in 5 of 19 Crouzon (26 percent), 10 of 26 Pfeiffer (38 percent), and 13 of 20 Saethre-Chotzen (65 percent) patients (p < 0.001). Age at initial fronto-orbital advancement did not influence reoperative rate. No correlation was found between concomitant sagittal synostosis and necessity for primary or secondary frontal correction (p = 0.22). In summary, phenotypic diagnosis was determinant for outcome as defined by need for secondary fronto-orbital advancement, foreheadplasty, or both. Apert patients had the highest incidence of reoperation for frontal retrusion or forehead contour. Crouzon and Saethre-Chotzen patients were most likely to express a minor phenotype and not require fronto-orbital correction. Coincident sagittal synostosis did not influence frontal projection, as reflected in need for either primary or secondary frontal advancement.

Role of the extracellular matrix and growth factors in skull morphogenesis and in the pathogenesis of craniosynostosis.

The complex and largely obscure regulatory processes that underlie ossification and fusion of the sutures during skull morphogenesis are dependent on the conditions of the extracellular microenvironment. The concept that growth factors are involved in the pathophysiology of craniosynostosis due to premature fusion of skull bone sutures, is supported by recent genetic data. Crouzon and Apert syndromes, for example, are characterized by point mutations in the extracellular or transmembrane domains of fibroblast growth factor-2 receptor. In primary cultures of periosteal fibroblasts and osteoblasts obtained from Apert and Crouzon patients, we observed that Crouzon and Apert cells behaved differently with respect to normal cells as regards the expression of cytokines and extracellular matrix (ECM) macromolecule accumulation. Further modulation of ECM components observed after the addition of cytokines provides support for an autocrine involvement of these cytokines in Crouzon and Apert phenotype. Changes in ECM composition could explain the altered osteogenic process and account for pathological variations in cranial development. We suggest that a correlation exists between in vitro phenotype, clinical features and genotype in the two craniosynostotic syndromes. New research into signal transduction pathways should establish further connections between the mutated genotype and the molecular biology of the cellular phenotype.