Identical mutations in three different fibroblast growth factor receptor genes in autosomal dominant craniosynostosis syndromes

Sustained ERK1/2 but not STAT1 or 3 activation is required for thanatophoric dysplasia phenotypes in PC12 cells

Mutations in fibroblast growth factor receptor 3 (FGFR3) cause the most common genetic form of short-limbed dwarfism, achondroplasia (ACH), as well as neonatal lethal forms, thanatophoric dysplasia (TD) I and II. The causative mutations induce graded levels of constitutive activation of the receptor that correspond to the severity of the disorder, resulting in premature entry into hypertrophic differentiation and reduced proliferation of chondrocytes in developing cartilage. Although FGFR3 promotes growth in most tissues, it is a negative regulator of endochondral bone growth. Several signaling pathways have been implicated in these skeletal disorders including the Ras/MEK/ERK pathway and the JAK/STAT, the latter in the most severe phenotypes, however their functional relevance remains incompletely understood. Using PC12 cell lines stably expressing inducible mutant receptors containing the TDII mutation, K650E, sustained activation of ERK1/2 and activation of STAT1 and STAT3, but not STAT5, is observed in the absence of ligand. This activation leads to neurite outgrowth, a phenotypic readout of constitutive receptor activity, and sustained ERK1/2 activity is required for this ligand-independent differentiation. To assess the functional relevance of STAT activation induced by the mutant receptor, STATs were specifically downregulated using RNA-interference. Silencing of STAT1 or 3 independently or in combination had no significant effect on ligand-independent neurite outgrowth, ERK1/2 activation or p21(WAF1/CIP1) protein levels. These results support a model in which sustained activation of ERK1/2 is a key regulator of the increased transition to hypertrophic differentiation of the growth plate, whereas activation of STATs 1 and 3 is not required.

FGF signaling in the developing endochondral skeleton

Mutations in fibroblast growth factor receptors (Fgfrs) are the etiology of many craniosynostosis and chondrodysplasia syndromes in humans. The phenotypes associated with these human syndromes and the phenotypes resulting from targeted mutagenesis in the mouse have defined essential roles for FGF signaling in both endochondral and intramembranous bone development. In this review, I will focus on the role of FGF signaling in chondrocytes and osteoblasts and how FGFs regulate the growth and development of endochondral bone.

Bad bones, absent smell, selfish testes: The pleiotropic consequences of human FGF receptor mutations

The discovery in 1994 that highly specific mutations of fibroblast growth factor (FGF) receptor 3 caused the most common form of human short-limbed dwarfism, achondroplasia, heralded a new era in FGF receptor (FGFR) biology. A decade later, the purpose of this review is to survey how the study of humans with FGFR mutations continues to provide insights into FGFR function in health and disease, and the clinical applications of these findings. Amongst the most interesting recent discoveries have been the description of novel phenotypes associated with FGFR1 and FGFR3 mutations; identification of fundamental differences in the cellular mechanisms of mutant FGFR2 and FGFR3 action; and the direct identification of FGFR2 and FGFR3 mutations in sperm. These clinical observations illustrate the pleiotropism of FGFR action and fuel ongoing efforts to understand the rich biology and pathophysiology of the FGF signalling system.

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.

Nasal capsular cartilage is required for rat transpalatal suture morphogenesis

In the cranial vault, suture morphogenesis occurs when the growing cranial bones approximate and overlap or abut one another. Patency of developing sutures is regulated by the underlying dura mater. Once cranial sutures form, bone growth proceeds from the sutures in response to growth signals from the rapidly expanding neurocranium. Facial sutures do not develop in contact with the dura mater. It was therefore hypothesized that facial suture morphogenesis and bone growth from facial sutures are regulated by tissues with an equivalent role to the dura mater. The present study was designed to test this hypothesis by characterizing the morphology and growth factor expression in developing transpalatal (TP) sutures and their surrounding tissues, and then assessing the role of the overlying nasal capsular (NC) cartilages in maintaining suture patency. TP sutures develop as overlapping sutures, similar to cranial coronal sutures, and expression of Tgf-betas in TP sutures was similar to their distribution in cranial coronal sutures. To establish whether NC cartilages play a role in regulating TP suture morphogenesis, fetal rat TP sutures were cultured with associated attached NC cartilages or with NC cartilages removed. Sutures cultured for upward of 5 days with intact NC cartilages remained patent and maintained their cellular and fibrous components. However, in the absence of NC cartilages, the cellular nature of the sutures was not maintained and they became progressively acellular, with bony bridging across the suture. This finding is similar to that for cranial vault sutures cultured in the absence of dura mater, indicating that NC cartilages play an equivalent role to dura mater in maintaining the patency of developing sutures. These studies indicate that tissue interactions likely regulate morphogenesis of all cranial and facial sutures.

Paternal origin of FGFR3 mutations in Muenke-type craniosynostosis

Muenke syndrome, also known as FGFR3-associated coronal synostosis, is defined molecularly by the presence of a heterozygous nucleotide transversion, c.749C>G, encoding the amino acid substitution Pro250Arg, in the fibroblast growth factor receptor type 3 gene (FGFR3). This frequently occurs as a new mutation, manifesting one of the highest documented rates for any transversion in the human genome. To understand the biology of this mutation, we have investigated its parental origin, and the ages of the parents, in 19 families with de novo c.749C>G mutations. All ten informative cases originated from the paternal allele (95% confidence interval 74-100% paternal); the average paternal age at birth overall was 34.7 years. An exclusive paternal origin of mutations, and increased paternal age, were previously described for a different mutation (c.1138G>A) of the FGFR3 gene causing achondroplasia, as well as for mutations of the related FGFR2 gene causing Apert, Crouzon and Pfeiffer syndromes. We conclude that similar biological processes are likely to shape the occurrence of this c.749C>G mutation as for other mutations of FGFR3 as well as FGFR2.

Muenke syndrome

BACKGROUND

Muenke syndrome is a genetically determined craniosynostosis that involves one or both coronal sutures. In some patients it is associated with skeletal abnormalities such as thimble-like middle phalanges, coned epiphysis, and/or neurological impairment, namely sensorineural hearing loss or mental retardation. In spite of a variable phenotype, Muenke syndrome has been related to a unique mutation on the FGFR3 gene, Pro 250 to Arg, which is characteristic of this disease. Because of the incomplete penetrance of this anomaly, the suspicion of Muenke syndrome must be raised in any child with uni- or bilateral coronal craniosynostosis, and the genetic analysis propounded even in the absence of extracranial features.

ILLUSTRATIVE CASES

We report the cases of two sisters who presented with Muenke syndrome and whose affected mother did not have any form of craniosynostosis.

Radiographic and genetic diagnosis of sporadic hypochondroplasia early in the neonatal period

Hypochondroplasia is an autosomal dominant skeletal dysplasia expressing postnatal onset of short stature with mild rhizomelic shortening of the limbs. This manifestation leads to restricted prenatal diagnosis of the disorder. We report here on a sporadic case of a hypochondroplastic baby, whose prenatal sonographic measurements were serially recorded from 19 weeks of gestation. Mild shortening of the limbs became manifest after 26 weeks of gestation. Biparietal diameter was within the normal range throughout gestation. Both parents were of average stature. A tentative diagnosis of a nonlethal short-limb skeletal dysplasia was made. At birth, the clinical manifestations of the neonate were not characteristic, but the radiographic features raised the possibility of hypochondroplasia. Molecular analyses revealed a C to G mutation at nucleotide 1659 of the fibroblast growth factor receptor 3 (FGFR3) gene, a common mutation in hypochondroplasia.

Genetic disorders of the skeleton: a developmental approach

Although disorders of the skeleton are individually rare, they are of clinical relevance because of their overall frequency. Many attempts have been made in the past to identify disease groups in order to facilitate diagnosis and to draw conclusions about possible underlying pathomechanisms. Traditionally, skeletal disorders have been subdivided into dysostoses, defined as malformations of individual bones or groups of bones, and osteochondrodysplasias, defined as developmental disorders of chondro-osseous tissue. In light of the recent advances in molecular genetics, however, many phenotypically similar skeletal diseases comprising the classical categories turned out not to be based on defects in common genes or physiological pathways. In this article, we present a classification based on a combination of molecular pathology and embryology, taking into account the importance of development for the understanding of bone diseases.

Screening of patients with craniosynostosis: molecular strategy

Craniosynostosis is the premature fusion of calvarial bones leading to an abnormal head shape. The craniosynostosis syndromes are clinically heterogeneous with overlapping features, which make an accurate diagnosis difficult at times. Although the clarification of a genetic lesion does not have a direct impact on patient management in many cases, there is a significant benefit in providing accurate prenatal diagnosis. Genetic counsellors are also able to offer better risk estimates of recurrences to non-manifesting carriers and their extended family members and for affected patients of reproductive age. Advances in gene discovery have shown that craniosynostosis syndromes delineated on clinical bases, with the possible exception of Apert syndrome, are genetically heterogeneous, and mutations have been found in fibroblast growth factor receptors (FGFR) 1, 2, 3 and TWIST. We surveyed 99 craniosynostosis patients at the molecular level and found mutations in 50 of them. Six novel point mutations were identified: three in FGFR2 and three in TWIST. Two Saethre-Chotzen patients with TWIST microdeletions at 7p21 were also found. The other mutations identified have been previously reported. In studying these 99 patients, we developed a diagnostic strategy for craniosynostosis testing, where sequential analysis of recurrent mutations was followed by selective sequencing. This algorithm makes testing of craniosynostosis disorders more efficient and cost-effective.

Erk pathway and activator protein 1 play crucial roles in FGF2-stimulated premature cranial suture closure

Cranial sutures are an important growth center of the cranial bones, and the suture space must be maintained to permit the cranial adjustments needed to accommodate brain growth. Craniosynostosis, characterized by premature suture closure, mainly results from mutations that generate constitutively active fibroblast growth factor (FGF) receptors. FGF signaling, thus, is responsible for the pathogenesis of craniosynostosis. Even though FGF activates many different signaling pathways, the one involved in premature suture closure has not been defined. We observed that placing FGF2-soaked bead on the osteogenic fronts of cultured mouse calvaria accelerates cranial suture closure and strongly induces the expression of osteopontin, an early marker of differentiated osteoblasts. FGF2 treatment also induced fos and jun mRNAs and later increased the nuclear levels of activator protein 1 (AP1). FGF2 stimulates the expression of osteopontin by inducing expression of AP1, which then binds to its response element in the osteopontin promoter. Blocking of the Erk pathway by PD98059 suppressed the AP1 and osteopontin expression stimulated by FGF2. Coincidently, blocking of the Erk pathway also significantly retarded FGF2-accelerated cranial suture closure. Thus, the Erk pathway mediates FGF/FGF receptor-stimulated cranial suture closure, probably by stimulating synthesis of AP1 that then stimulates the differentiation of osteoblasts.

[Typical features of craniofacial growth of the FGFR3-associated coronal synostosis syndrome (so-called Muenke craniosynostosis)]

BACKGROUND

The FGFR3-associated coronal synostosis syndrome (Muenke craniosynostosis) is caused by a point mutation (C749G) on the FGFR3 gene resulting in a Pro250Arg substitution.

METHODS

To characterize this malformation, the neuro- and viscerocranium were analyzed by axial CT scans of the skull and cephalometric radiographs of up to 13 affected children before and in part after fronto-orbital advancement.

RESULTS

Preoperative analysis of the intracranial volume of four patients showed a mean decrease of 3.6%, indicating a compensatory growth pattern of the skull in cases of coronal synostosis. The typical brachycephaly could be verified by the significant shortening of the skull length of 13.2% on average and by the significant reduction of the anterior cranial base length of maximal 5.9% on average. The anterior part of the skull was characterized by a significant mean increase of the intercoronal distance of 8.6%, which indicates a compensatory transversal growth in this malformation. The widened bilateral interorbital and anterior interorbital distances were increased by 7.3 or 9.0%, respectively, confirming a hypertelorism typical for this syndrome. The "frontal bossing" frequently found in brachycephaly was characterized by the preoperatively increased sagittal extension of the forehead (about 112.9% above the norm) and by the increased height of the frontal prominence (about 47.8% above the norm). Following surgery, both variables defining the morphology of the forehead were reduced and appeared to be constant throughout the follow-up. Hypoplasia of the midface described by Muenke et al. (1997) was confirmed in the present study only by the significant reduction of the sagittal length of the maxillary base, which was decreased by 6.8%.

CONCLUSION

In accordance with the current literature, the skull configuration described for Muenke craniosynostosis shows similarities with the Saethre-Chotzen syndrome.

BMP signals regulate Dlx5 during early avian skull development

The vertebrate skull vault forms almost entirely by the direct mineralisation of mesenchyme, without the formation of a cartilaginous template, a mechanism called membranous ossification. Dlx5 gene mutation leads to cranial dismorphogenesis which differs from the previously studied craniosynostosis syndromes [Development 126 (1999), 3795; Development 126 (1999), 3831]. In avians, little is known about the genetic regulation of cranial vault development. In this study, we analyze Dlx5 expression and regulation during skull formation in the chick embryo. We compare Dlx5 expression pattern with that of several genes involved in mouse cranial suture regulation. This provides an initial description of the expression in the developing skull of the genes encoding the secreted molecules BMP 2, BMP 4, BMP 7, the transmembrane FGF receptors FGFR 1, FGFR 2, FGFR 4, the transcription factors Msx1, Msx2, and Twist, as well as Goosecoid and the early membranous bone differentiation marker osteopontin. We show that Dlx5 is activated in proliferating osteoblast precursors, before osteoblast differentiation. High levels of Dlx5 transcripts are observed at the osteogenic fronts (OFs) and at the edges of the suture mesenchyme, but not in the suture itself. Dlx5 expression is initiated in areas where Bmp4 and Bmp7 genes become coexpressed. In a calvarial explant culture system, Dlx5 transcription is upregulated by BMPs and inhibited by the BMP-antagonist Noggin. In addition, FGF4 activates Bmp4 but not Bmp7 gene transcription and is not sufficient to induce ectopic Dlx5 expression in the immature calvarial mesenchyme. From these data, we propose a model for the regulatory network implicated in early steps of chick calvarial development.

Broad thumbs and halluces with deafness: a patient with Keipert syndrome

Clinical, radiological, and audiological features are described in a boy whose condition closely parallels the profile of patients previously described with Keipert syndrome. This case represents the fourth report of this rare disorder.

Fibroblast growth factors lead to increased Msx2 expression and fusion in calvarial sutures

Craniosynostosis, the premature fusion of the skull bones at the sutures, represents a disruption to the coordinated growth and development of the expanding brain and calvarial vault and is the second most common birth defect that affects the craniofacial complex. Mutations in the human homeobox-containing gene, Msx2, have been shown to cause Boston type craniosynostosis, and we have shown that overexpression of Msx2 leads to craniosynostosis in mice. Activating mutations in fibroblast growth factor (FGF) receptors are thought to cause craniosynostosis in Crouzon, Apert, Jackson-Weiss, Beare-Stevenson, and Muenke syndromes. To mimic activated signaling by mutated FGF receptors, we used heparin acrylic beads to deliver FGF ligands to mouse calvaria and demonstrated increased Msx2, Runx2, Bsp, and Osteocalcin gene expression, decreased cell proliferation, and suture obliteration and fusion. FGF2 elicited the greatest increase in Msx2 expression, and FGF1 was most likely to cause suture obliteration and fusion. Of the three sutures studied, the coronal suture exhibited the greatest increase in Msx2 expression and was the most likely to undergo obliteration and fusion. These results are intriguing because the coronal suture is the most commonly affected suture in syndromic craniosynostosis. These results suggest that Msx2 is a downstream target of FGF receptor signaling and that increased FGF signaling leads to osteogenic differentiation by sutural mesenchyme in mouse calvaria. These results are consistent with the hypotheses that increased Msx2 expression and activated signaling by mutated FGF receptors lead to craniosynostosis.

Craniosynostosis in Alagille syndrome

Alagille syndrome is a multisystem developmental disorder with primary involvement of the liver, heart, skeleton, eyes and facial structures, and demonstrates highly variable expressivity with respect to all of the involved systems. Alagille syndrome is caused by mutations in the Jagged1 gene. Jagged1 is a ligand in the Notch signaling pathway that has been shown to regulate early cell fate determination. Mutations in Jagged1 have been identified in approximately 80% of patients with Alagille syndrome. We have recently identified two patients with mutation proven Alagille syndrome who also had unilateral coronal craniosynostosis. Both individuals were screened for mutations in fibroblast growth factor receptor 1, 2, 3 and TWIST genes, all associated with various types of craniosynostosis and no mutations were identified. The finding of a conserved form of craniosynostosis in two unrelated patients with Alagille syndrome and mutations in Jagged1 may indicate that Jagged1 plays a role in cranial suture formation.

Mesomelic and rhizomelic short stature: The phenotype of combined Leri-Weill dyschondrosteosis and achondroplasia or hypochondroplasia

We studied two children with combined genetic skeletal disorders. Both had Leri-Weill dyschondrosteosis (LWD); one also had achondroplasia and the other had hypochondroplasia. Both had severe short stature and evidence of rhizomelia and mesomelia as well as other phenotypic features of their individual genetic disorders. Achondroplasia was due to the G380R FGF3R mutation and hypochondroplasia to a N540K mutation in the same gene. The patient with hypochondroplasia had a heterozygous SHOX deletion; no SHOX mutation was identified in the child with achondroplasia. The phenotypes of combined LWD and achondroplasia or hypochondroplasia appeared to be less than additive, suggesting that SHOX and FGFR3 act on overlapping pathways of bone growth and development.

Craniosynostosis associated with ocular and distal limb defects is very likely caused by mutations in a gene different from FGFR, TWIST, and MSX2

Craniosynostosis caused by genetic factors includes a heterogeneous group of over 100 syndromes, most with autosomal dominant inheritance. Mutations in five genes (FGFR1-, -2, -3, TWIST, and MSX2) causing craniosynostosis as the main clinical feature were described. In most of these conditions, there are also limb malformations. We report a two-generation kindred segregating microcornea, optic nerve alterations and cataract since childhood, craniosynostosis, and distal limb alterations, with a great clinical intrafamilial variability. The ophthalmological problems here described seem to be unique to this genealogy while similar feet alterations were apparently only described in two other affected siblings with acro-cranial-facial dysostosis syndrome (ADS). However, ADS has an autosomal recessive inheritance instead of the dominant pattern of the present genealogy. The candidate exons of the five genes previously mentioned were tested through sequencing analysis presenting normal results in all cases. Therefore, clinical and laboratory analyses in our patients suggest that their phenotype represents a new syndrome very likely caused by mutation in a gene different from those studied.

Increased fibroblast growth factor-like autoantibodies in serum from a subset of patients with cancer-associated hypercalcemia

Basic fibroblast growth factor (bFGF) is a potent tumor angiogenesis factor which lacks an amino-terminal signal sequence and does not normally circulate in serum from normal subjects. Naturally-occurring autoantibodies which mimicked basic fibroblast growth factor were described in serum from patients with multiple endocrine neoplasia type 1 prolactinoma or sporadic growth-hormone-secreting adenoma associated with increased bFGF. Since bFGF was increased in serum from a variety of cancers, we used endothelial cell proliferation assay(s) to test for bioactivity in the IgG fraction of serum from 56 patients with cancer-associated hypercalcemia, and normal or control subjects. We now report increased IgG-like endothelial cell activity in serum from a hyper prolactinemic subset (4/19 breast cancer; 1/14 renal cancer; 0/23 lung cancer) of cancer-associated hypercalcemic subjects. Highest activity was found in serum from three breast cancer patients who suffered spinal cord compression/metastases. The activity had properties of antiidiotype bFGF antibodies including reaction with anti-human IgG antibodies, and complete neutralization by rabbit antibodies to intact bFGF. The activity in endothelial cells persisted after storage at 0-4 C for 5 yrs; and [prepared by SDS-PAGE and immunoblotting with anti-human IgG] had apparent mol wt corresponding to the heavy chains of IgG. Serum IgG-like activity from 5 of 5 breast cancer patients and 2 of 2 prostate cancer subjects tested [prepared by anti-bFGF antibody, protein-A immunoaffinity, and hydroxyapatite (HA) chromatography] yielded peak HA-adsorbed activity that eluted with 0.4 M sodium phosphate, and was neutralized 70% by antibodies to intact bFGF. Cancer sera mean peak specific activity (12.0 ng-eq bFGF/ug protein) (n = 7) significantly exceeded (P < 0.001) normal sera mean peak specific activity (0.46 ng-eq bFGF/ug protein) (n = 6) in the 0.4 M sodium phosphate eluate fraction from hydroxyapatite columns. These results imply that long-lasting, bioactive FGF-like autoantibodies may arise spontaneously (and contribute to pathophysiology) in subsets of cancer patients with osseous metastases.

Tgf-beta1, Tgf-beta2, Tgf-beta3 and Msx2 expression is elevated during frontonasal suture morphogenesis and during active postnatal facial growth

OBJECTIVES

It is hypothesized that regulation of facial suture morphogenesis is similar to that of cranial sutures, with expression of similar regulatory molecules, governing suture formation and patency. The present study was designed to characterize the morphology of the frontonasal (FN) suture of the rat at different developmental stages and to investigate the presence and temporal-spatial expression of transforming growth factor-beta 1 (Tgf-beta1), Tgf-beta2, Tgf-beta3 and Msx2 mRNA within these structures.

SETTING AND SAMPLE POPULATION

The Department of Biomedical Sciences at Texas A&M University System Health Science Center, Baylor College of Dentistry, Dallas, TX USA. Histological sections and RNA isolated from FN suture tissues of Sprague-Dawley rats, aged embryonic day 16 through postnatal day 20.

METHOD

Sections were examined after immunohistochemical staining. Gene expression was determined by densitometric analysis of RT-PCR products run on agarose gels.

RESULTS

FN sutures develop slightly later than cranial sutures and show increased complexity over time when compared to cranial sutures. FN sutures were closely associated with the nasal capsular cartilage, with intervening layers of perichondrium and periosteum. The pattern of expression of Tgf-betas within the FN suture tissues was similar to that seen in the cranial sutures. However, mRNA and protein of the Tgf-betas were differentially expressed over time compared to cranial sutures. In FN sutures, Tgf-beta mRNA levels were elevated both during the period of suture morphogenesis and during active bone growth from the suture in the early postnatal period. Msx2 mRNA expression was elevated in both the prenatal and postnatal periods, similar to Tgf-beta mRNA expression.

CONCLUSION

Tgf-beta and Msx2 are present in facial sutures similar to cranial sutures, but are differentially expressed over time, perhaps reflecting different bone growth rates from these sutures.

The IIIc alternative of Fgfr2 is a positive regulator of bone formation

Fibroblast growth factor receptor type 2 (FGFR2) plays major roles in development. Like FGFR1 and FGFR3, it exists as two splice variants, IIIb and IIIc. We have investigated in the mouse the function of FGFR2IIIc, the mesenchymal splice variant of FGFR2. Fgfr2IIIc is expressed in early mesenchymal condensates and in the periosteal collar around the cartilage models; later it is expressed in sites of both endochondral and intramembranous ossification. A translational stop codon inserted into exon 9 disrupted the synthesis of Fgfr2IIIc without influencing the localized transcription of Fgfr2IIIb, the epithelial Fgfr2 variant. The recessive phenotype of Fgfr2IIIc–/– mice was characterized initially by delayed onset of ossification, with continuing deficiency of ossification in the sphenoid region of the skull base. During subsequent stages of skeletogenesis, the balance between proliferation and differentiation was shifted towards differentiation, leading to premature loss of growth, synostosis in certain sutures of the skull base and in the coronal suture of the skull vault, with dwarfism in the long bones and axial skeleton. The retarded ossification was correlated with decrease in the localized transcription of the osteoblast markers secreted phosphoprotein 1 (Spp1) and Runx2/Cbfa1. A decrease in the domain of transcription of the chondrocyte markers Ihh and PTHrP (Pthlh) corresponded with a decrease in their transcripts in the proliferative and hypertrophic chondrocyte zones. These results suggest that Fgfr2IIIc is a positive regulator of ossification affecting mainly the osteoblast, but also the chondrocyte, lineages. This role contrasts with the negative role of Fgfr3, although recent reports implicate FGF18, a ligand for FGFR3IIIc and FGFR2IIIc, as a co-ordinator of osteogenesis via these two receptors.

Comparison of hedgehog and patched-1 protein expression in the cranial sutures of craniosynostotic and wild-type rabbits

Craniosynostosis is characterized by premature fusion of the cranial sutures. At the molecular level, mutations in homeobox genes, transcription factors, and growth factor receptors have been implicated in the pathogenesis of this disorder, but the specific etiologic pathways have not yet been elucidated. To further study the molecular biology behind craniosynostosis, perisutural tissues in a unique rabbit model with congenital delayed-onset coronal craniosynostosis were examined for the presence of the hedgehog family of growth factors and their receptor, patched-1. Expression of desert hedgehog, Indian hedgehog, sonic hedgehog, and patched-1 was evaluated in four areas: suture, endosteum, periosteum, and osteocytes, using immuno-histochemistry (n = 8). Protein levels in affected animals were compared with protein levels in wild-type control rabbits (n = 8). Overall, sonic hedgehog, Indian hedgehog, and patched-1 protein levels were greater in affected animals. Specifically, areas of increased staining were seen along the bony interface of the endosteum and periosteum and in the osteocytes of the synostotic rabbits. Interestingly, in the suture, increased levels of Indian hedgehog and sonic hedgehog, but not patched-1, were seen. There was minimal expression of desert hedgehog in both rabbit types. The increased overall presence of hedgehog and patched-1 proteins in synostotic rabbits may be a reactive change to the disorder or part of the pathogenic process. Although the specific cause cannot be determined from the data, it is clear that the molecular milieu of the cranial sutures in synostotic rabbits is markedly different from that of wild-type rabbits.

Postoperative mental and morphological outcome for nonsyndromic brachycephaly

Bilateral coronal synostosis causes functional and morphological problems that require fronto-orbital advancement in infancy to correct the brachycephalic deformity and to prevent mental impairment caused by the intracranial hypertension. In this study, 99 children with isolated cases of brachycephaly were prospectively followed to study their preoperative and postoperative mental outcome, which was evaluated using developmental or intelligence quotients. Several factors were analyzed: age before treatment, age at the time of surgery, and the correlation between mental assessments before and after surgery. In a subgroup or patients tested for the FGFR3 P250R mutation (n = 48), mental and morphological assessments were analyzed. Before surgery, mental status was better in the patients tested before 1 year of age (p < 0.001). The preoperative mental assessment always correlated with the postoperative assessment (p < 0.0001). The postoperative mental outcome was better when surgery was performed before the patient reached 1 year of age (p < 0.02). Although both the morphological and functional outcomes were better in the subgroup of noncarriers of the mutation, the differences were not statistically significant. Prominent bulging of the temporal fossae was frequently responsible for poor morphological outcome in carriers of the mutation. This study confirms the need for early corrective surgery before 1 year of age in brachycephalic patients to prevent impairment of their mental development. Suboptimal morphological and mental outcomes can be expected in patients with nonsyndromic brachycephaly who carry the FGFR3 P250R mutation. Primary correction of the temporal bulging should be performed in conjunction with fronto-orbital advancement to improve the morphological outcome in patients with the mutation.

Genetic analysis of patients with the Saethre-Chotzen phenotype

Saethre-Chotzen syndrome is a common craniosynostosis syndrome characterized by craniofacial and limb anomalies. Intragenic mutations of the TWIST gene within 7p21 have been identified as a cause of this disorder. There is phenotypic overlap with other craniosynostosis syndromes, and intragenic mutations in FGFR2 (fibroblast growth factor receptor 2) and FGFR3 (fibroblast growth factor receptor 3) have been demonstrated in the other conditions. Furthermore, complete gene deletions of TWIST have also been found in a significant proportion of patients with Saethre-Chotzen syndrome. We investigated 11 patients clinically identified as having the Saethre-Chotzen phenotype and 4 patients with craniosynostosis but without a clear diagnosis. Of the patients with the Saethre-Chotzen phenotype, four were found to carry the FGFR3 P250R mutation, three were found to be heterozygous for three different novel mutations in the coding region of TWIST, and two were found to have a deletion of one copy of the entire TWIST gene. Developmental delay was a distinguishing feature of the patients with deletions, compared to patients with intragenic mutations of TWIST, in agreement with the results of Johnson et al. [1998: Am J Hum Genet 63:1282-1293]. No mutations were found for the four patients with craniosynostosis without a clear diagnosis. Therefore, 9 of our 11 patients (82%) with the Saethre-Chotzen phenotype had detectable genetic changes in FGFR3 or TWIST. We propose that initial screening for the FGFR3 P250R mutation, followed by sequencing of TWIST and then fluorescence in situ hybridization (FISH) for deletion detection of TWIST, is sufficient to detect mutations in > 80% of patients with the Saethre-Chotzen phenotype.

Transforming growth factor-beta 3(Tgf-beta3) in a collagen gel delays fusion of the rat posterior interfrontal suture in vivo

Postnatal expansion of the intramembranous bones of the craniofacial skeleton occurs as bone growth at sutures. Loss of the bone growth site occurs when the suture fails to form, or when the newly formed sutures become ossified, resulting in premature obliteration. Previous experiments demonstrated that removal of dura mater from fetal rat coronal sutures, or neutralizing transforming growth factor-beta 2 (Tgf-beta2) activity using antibodies resulted in premature obliteration of the suture in vitro. Conversely, addition of Tgf-beta3 to coronal sutures in vitro rescued them from osseous obliteration. To examine whether Tgf-beta3 rescues sutures from obliteration in vivo, a collagen gel was used as a vehicle to deliver Tgf-beta3 to the normally fusing rat posterior interfrontal (IF) suture. Surgery was done on postnatal day 9 (P9) rats, in which collagen gels containing 0, 3, or 30 ng Tgf-beta3 were placed above the IF suture, underneath the periosteum for 2 weeks. By P24, 75-100% of animals in control unoperated, sham-operated, and collagen gel-only groups had fused IF sutures. In contrast, 40% of sutures exposed to 3 ng Tgf-beta3 remained open, while sutures exposed to 30 ng Tgf-beta were similar to controls. By immunohistochemistry, sutures rescued from obliteration by Tgf-beta3 had the same Tgf-beta receptor type II (Tbetar-II) distribution as controls. However, Tgf-beta3-treated sutures had altered Tgf-beta2 and Tbetar-I distribution compared to controls.

Identification and characterization of soluble isoform of fibroblast growth factor receptor 3 in human SaOS-2 osteosarcoma cells

We have previously reported the alternatively spliced transcripts of fibroblast growth factor 3 (FGFR3 ATs and MTs) derived by aberrant splicing and usage of cryptic splicing sites. Here, we describe a soluble variant of FGFR3 (FGFR3 AT-III) arising from skipping exons 8, 9, and 10 in human SaOS-2 osteosarcoma cell. This splicing event leads to the generation of an mRNA encoding a FGFR3 in which the COOH-terminal portion of the Ig-like-III domain and transmembrane domain are deleted while the remainder of the mature molecule is fused in-frame to the COOH-terminal cytoplasmic kinases domains. Sf9 cells transfected with the corresponding cDNA express the soluble form of FGFR3 AT-III into the condition medium and its secreted form was able to bind both FGF-1 and FGF-2 leading to loss of ligand binding specificity. These results indicate that the FGFR3 AT-III mRNAs are transcribed due to exon skipping with altered ligand binding specificity. These results suggest that the presence of soluble transcripts of FGFRs gene is a common feature due to mRNA splicing and this splicing plays an important role in the regulation of FGFRs function.

Effect of intravenous bisphosphonates on release of basic fibroblast growth factor in serum of patients with cancer-associated hypercalcemia

Basic fibroblast growth factor (bFGF) is a potent tumor angiogenesis factor and normal constituent of bone extracellular matrix which does not normally circulate in serum of nonpregnant adult humans. We examined the effects of acute administration of intravenous bisphosphonates on release of bFGF in human serum. Twenty seven men and women (mean age, 64 yr) with cancer-associated hypercalcemia, the majority of whom had osseous metastases, were treated once with an intravenous bisphosphonate. Nearly all twelve patients with elevated baseline serum bFGF ranging from 5-27 pg/mL showed significant decreases in serum bFGF (2-7 days) after iv bisphosphonate treatment. The mathematical product of the patients' initial serum bFGF and intial serum calcium concentration, the 'Ca x bFGF product', was significantly negatively (r = -0.91, P < 0.001) correlated with the acute change in serum bFGF level. No consistent relationship was observed between serum bFGF and serum parathyroid hormone related peptide (PTHrP) levels in the hypercalcemic cancer patients. In a subset of patients with non-hematological malignancies and low baseline serum bFGF, acute changes in serum bFGF were significantly negatively (r = -0.66, P < 0.01) correlated with acute change in serum calcium concentration. These results indicate that release of bFGF in serum of patients with cancer-associated hypercalcemia likely depends predominantly on increased bone resorption. Acute change in low serum levels of bFGF in patients with cancer-associated hypercalcemia treated with intravenous bisphosphonates may be physiologically inversely regulated by acute change in the serum calcium concentration.

Genomic screening of fibroblast growth-factor receptor 2 reveals a wide spectrum of mutations in patients with syndromic craniosynostosis

It has been known for several years that heterozygous mutations of three members of the fibroblast growth-factor-receptor family of signal-transduction molecules-namely, FGFR1, FGFR2, and FGFR3-contribute significantly to disorders of bone patterning and growth. FGFR3 mutations, which predominantly cause short-limbed bone dysplasia, occur in all three major regions (i.e., extracellular, transmembrane, and intracellular) of the protein. By contrast, most mutations described in FGFR2 localize to just two exons (IIIa and IIIc), encoding the IgIII domain in the extracellular region, resulting in syndromic craniosynostosis including Apert, Crouzon, or Pfeiffer syndromes. Interpretation of this apparent clustering of mutations in FGFR2 has been hampered by the absence of any complete FGFR2-mutation screen. We have now undertaken such a screen in 259 patients with craniosynostosis in whom mutations in other genes (e.g., FGFR1, FGFR3, and TWIST) had been excluded; part of this screen was a cohort-based study, enabling unbiased estimates of the mutation distribution to be obtained. Although the majority (61/62 in the cohort sample) of FGFR2 mutations localized to the IIIa and IIIc exons, we identified mutations in seven additional exons-including six distinct mutations of the tyrosine kinase region and a single mutation of the IgII domain. The majority of patients with atypical mutations had diagnoses of Pfeiffer syndrome or Crouzon syndrome. Overall, FGFR2 mutations were present in 9.8% of patients with craniosynostosis who were included in a prospectively ascertained sample, but no mutations were found in association with isolated fusion of the metopic or sagittal sutures. We conclude that the spectrum of FGFR2 mutations causing craniosynostosis is wider than previously recognized but that, nevertheless, the IgIIIa/IIIc region represents a genuine mutation hotspot.

Transforming growth factor-beta3 (Tgf-beta3) down-regulates Tgf-beta3 receptor type I (Tbetar-I) during rescue of cranial sutures from osseous obliteration

Appropriate biochemical regulation of intramembranous bone growth from sutures is necessary to achieve correct craniofacial morphology. Failure to form sutures (agenesis) or to maintain sutures in their unossified state (craniosynostosis) can result in severe facial dysmorphology. Several factors such as Twist, Msx2, fibroblast growth factors (Fgfs), bone morphogenetic proteins (Bmps) and transforming growth factors-beta (Tgf-betas) regulate suture patency, likely by interacting with one another. Tgf-beta2 and Tgf-beta3 use the same cell surface receptors, yet have opposite effects on suture patency, cellular proliferation and apoptosis within the suture. One possible mechanism by which Tgf-beta3 rescues sutures from obliteration is by regulating the ability of suture cells to respond to Tgf-beta2. As Tgf-beta3 does not regulate protein levels of Tgf-beta2 in sutures, Tgf-beta3 could regulate tissue responsiveness to Tgf-beta2 by regulating Tgf-beta2 access to receptors. Tgf-beta3 is a more potent competitor than Tgf-beta2 for cell surface receptors, so it is proposed that Tgf-beta3 binds to and down-regulates Tgf-beta receptor type I (Tbetar-I) expression by suture cells. This down-regulation would limit the ability of cells to respond to all Tgf-betas, including Tgf-beta2. To test this hypothesis, an in vitro culture model was used in which fetal rat sutures either remain patent or are induced to fuse when cultured in the presence or absence of dura mater, respectively. Tgf-beta3 was added to cultured calvaria and changes in the number of receptor positive cells within the suture were established. Data were compared with that seen in control sutures and in normal sutures in vivo. It was found that the numbers of cells expressing Tbetar-I within the suture matrix increased over time in sutures remaining patent. Osteoblastic cells lining the bone fronts on either side of sutures were Tbetar-I positive during early morphogenesis, but these numbers declined as sutures fused, both in vivo and in vitro. Addition of Tgf-beta3 to calvaria in culture decreased the number of Tbetar-I expressing cells in both fusing and non-fusing sutures, with dramatic decreases in the numbers of osteoblasts expressing Tbetar-I.

Tissue origins and interactions in the mammalian skull vault

During mammalian evolution, expansion of the cerebral hemispheres was accompanied by expansion of the frontal and parietal bones of the skull vault and deployment of the coronal (fronto-parietal) and sagittal (parietal-parietal) sutures as major growth centres. Using a transgenic mouse with a permanent neural crest cell lineage marker, Wnt1-Cre/R26R, we show that both sutures are formed at a neural crest-mesoderm interface: the frontal bones are neural crest-derived and the parietal bones mesodermal, with a tongue of neural crest between the two parietal bones. By detailed analysis of neural crest migration pathways using X-gal staining, and mesodermal tracing by DiI labelling, we show that the neural crest-mesodermal tissue juxtaposition that later forms the coronal suture is established at E9.5 as the caudal boundary of the frontonasal mesenchyme. As the cerebral hemispheres expand, they extend caudally, passing beneath the neural crest-mesodermal interface within the dermis, carrying with them a layer of neural crest cells that forms their meningeal covering. Exposure of embryos to retinoic acid at E10.0 reduces this meningeal neural crest and inhibits parietal ossification, suggesting that intramembranous ossification of this mesodermal bone requires interaction with neural crest-derived meninges, whereas ossification of the neural crest-derived frontal bone is autonomous. These observations provide new perspectives on skull evolution and on human genetic abnormalities of skull growth and ossification.

Craniosynostosis, ectopia lentis, and congenital heart defects: further delineation of an autosomal dominant syndrome with incomplete penetrance

The association of craniosynostosis with ectopia lentis is extremely rare. This was recently reported in monozygotic twin sisters, supporting a genetic etiology for this syndromic association. We report on female first cousins once removed who were born with unilateral coronal synostosis. One cousin also had peripheral pulmonic branch stenosis at birth and was later found to have ectopia lentis and severe myopia. The other cousin had an atrial septal defect, mitral valve prolapse, and only mild myopia. Their intelligence is normal. The inheritance is likely autosomal dominant with variable expression and incomplete penetrance and further defines this syndrome to include congenital heart defects. These findings will have important implications for genetic counseling.

Clinical characteristics of patients with unicoronal synostosis and mutations of fibroblast growth factor receptor 3: a preliminary report

Clinical teaching dictates that isolated unicoronal synostosis is sporadic in occurrence and is possibly related to intrauterine constraint. Despite this, isolated reports document a familial occurrence. It has previously been recognized that there may be a familial pattern of inheritance. Recently, mutations in fibroblast growth factor receptors (FGFRs) have been implicated in several syndromic craniosynostoses. At the authors' institution, mutations in FGFR3, located at chromosome 4p16, have been found to cause coronal synostosis. Two cases of unicoronal synostosis were found to have the same Pro250Arg missense mutation in FGFR3. This finding suggested that all patients with a diagnosis of unicoronal synostosis be screened for the FGFR3 mutation. Between January and December of 1996, patients with a diagnosis of plagiocephaly at the Children's Hospital of Philadelphia were evaluated for the FGFR3 mutation. Thirty-seven patients with unicoronal synostosis had mutational studies. Two additional patients were known to have the FGFR3 mutation at the onset of the study. Of the 37 patients screened, four were found to have the FGFR3 mutation, for a total of six patients with both unicoronal synostosis and the FGFR3 mutation. All patients with unicoronal synostosis were evaluated for facial dysmorphology and operative outcome. The six patients with the FGFR3 mutation had more severe cranial dysmorphology and were more likely to need surgical revision than those without the FGFR3 mutation. The occurrence of the FGFR3 mutation among patients with unicoronal synostosis provides evidence for a genetic basis of certain forms of plagiocephaly. The clinical, radiologic, and molecular findings will be an important addition to the surgical management and counseling of patients with unicoronal synostosis.

Syndrome of coronal craniosynostosis, Klippel-Feil anomaly, and sprengel shoulder with and without Pro250Arg mutation in the FGFR3 gene

A unique Pro250Arg point mutation in fibroblast growth factor receptor 3 (FGFR3) was initially reported by Bellus et al. [1996: Nat Genet 14:174-176] and the phenotype subsequently by Muenke et al. [1997: Am J Hum Genet 60:555-564], Reardon et al. [1997: J Med Genet 34:632-636], and Graham et al. [1998: Am J Med Genet 77:322-329]. These authors emphasized the pleiotropic nature of this form of coronal craniosynostosis, including brachydactyly with carpal and/or tarsal coalitions, with other anomalies at lower frequency. We report on a family with autosomal dominant coronal synostosis, segmentation and fusion anomalies of the vertebra and ribs, and Sprengel shoulder due to the Pro250Arg mutation. We also report a single case with an identical phenotype without the mutation.

Standard variant venous dysplasia of the cerebellum in a patient suffering from Muenke's syndrome and tinnitus

BACKGROUND

Muenke's syndrome is a rarely seen craniosynostosis syndrome. Bilateral or unilateral coronal craniosynostosis, brachydactyly, tarsal and carpal coalitions are the typical clinical findings. Sensorineural hearing loss is reported in more than 30% of the affected patients. In patients with Muenke's syndrome intracranial vascular dysplasia has not been reported yet.

PATIENT AND METHODS

A 13-year-old boy suffering from Muenke's syndrome reported a pulsating left-sided light tinnitus. Clinically a bluish formation was found at the lower part of the left-sided ear drum. In order to clarify the cause of the tinnitus and the bluish formation, extensive diagnostics (e.g. audiometry, magnet resonance tomography, magnet resonance phlebography, angiography) were carried out.

RESULTS

Audiometry found a left sensorineural hearing loss with a conductive component. Radiological investigations found a standard variant venous dysplasia of the left petrous bone to be the reason for the tinnitus.

CONCLUSION

Awareness of intracranial vascular dysplasia should be noted in individuals with Muenke's syndrome especially in cases of clinically suggestive symptoms like pulsating tinnitus.

Sequence analyses and comparative modeling of fly and worm fibroblast growth factor receptors indicate that the determinants for FGF and heparin binding are retained in evolution

The presence of a large number of fibroblast growth factors (FGFs) and multiple splice forms of their receptors (FGFRs) in higher vertebrates makes the three-dimensional (3D) analysis of FGF interactions with their receptors a formidable task. The situation differs in Caenorhabditis elegans (worm) and Drosophila melanogaster (fruit fly), where only one or two FGF and FGFR sequences have been identified. Structural studies of the FGF-FGFR complexes in such primitive organisms should reveal the basic features of the ligand-receptor interactions as they first emerged through evolution. We have analysed the sequences of worm and fly FGFs and FGFRs and used the recently determined crystal structure of the human FGF1-FGFR2-heparin ternary complex [Pellegrini, L., Burke, D.F., von Delft, F., Mulloy, B. and Blundell, T.L. (2000) Nature 407, 1029-34] to construct 3D models of the homologous complexes. In spite of a low sequence similarity with their human counterparts, key structural features required for ligand-receptor and protein-heparin binding in humans are conserved in the fly and worm FGF-FGFR-heparin complexes. Analyses of the models show that tertiary interactions that are not conserved in sequence are maintained through novel interactions or complementary mutations in the fly and worm sequences. The overall charge distributions observed in the human FGF-FGFR-heparin complex are retained in the fly and worm models. The arginine residue at position 253 in the linker region between the Ig-like domains D2 and D3 in the wild type fly and worm sequences is particularly striking, as the Pro253Arg mutation in humans is responsible for Apert syndrome. This change may enhance the affinity of receptors for their FGF molecules as observed in Apert mutants.

Premature calvarial synostosis and epidermal hyperplasia (Beare-Stevenson syndrome-like anomalies) resulting from a P250R missense mutation in the gene encoding fibroblast growth factor receptor 3

We report on a patient with a severe premature calvarial synostosis and epidermal hyperplasia. The phenotype was consistent with that of a mild presentation of Beare-Stevenson syndrome but molecular analysis of the IgIII-transmembrane linker region and the transmembrane domain of the gene encoding the FGFR2 receptor, revealed wild-type sequence only. Subsequently, molecular analysis of the FGFR3 receptor gene identified a heterozygous P250R missense mutation in both the proposita and her mildly affected father. This communication extends the clinical spectrum of the FGFR3 P250R mutation to encompass epidermal hyperplasia and documents the phenomenon of activated FGFR receptors stimulating common downstream developmental pathways, resulting in overlapping clinical outcomes.

Structural basis for fibroblast growth factor receptor 2 activation in Apert syndrome

Apert syndrome (AS) is characterized by craniosynostosis (premature fusion of cranial sutures) and severe syndactyly of the hands and feet. Two activating mutations, Ser-252 --> Trp and Pro-253 --> Arg, in fibroblast growth factor receptor 2 (FGFR2) account for nearly all known cases of AS. To elucidate the mechanism by which these substitutions cause AS, we determined the crystal structures of these two FGFR2 mutants in complex with fibroblast growth factor 2 (FGF2). These structures demonstrate that both mutations introduce additional interactions between FGFR2 and FGF2, thereby augmenting FGFR2-FGF2 affinity. Moreover, based on these structures and sequence alignment of the FGF family, we propose that the Pro-253 --> Arg mutation will indiscriminately increase the affinity of FGFR2 toward any FGF. In contrast, the Ser-252 --> Trp mutation will selectively enhance the affinity of FGFR2 toward a limited subset of FGFs. These predictions are consistent with previous biochemical data describing the effects of AS mutations on FGF binding. Alterations in FGFR2 ligand affinity and specificity may allow inappropriate autocrine or paracrine activation of FGFR2. Furthermore, the distinct gain-of-function interactions observed in each crystal structure provide a model to explain the phenotypic variability among AS patients.

Genetics of craniofacial development and malformation

The head is anatomically the most sophisticated part of the body and its evolution was fundamental to the origin of vertebrates; understanding its development is a formidable problem in biology. A synthesis of embryology, evolution and mouse genetics is shaping our understanding of head development and in this review we discuss its application to studies of human craniofacial malformations. Many of these disorders have their origins in specific embryological processes, including abnormalities of brain patterning, of the migration and fusion of tissues in the face, and of bone differentiation in the skull vault.

New Zealand Maori family with the pro250arg fibroblast growth factor receptor 3 mutation associated with craniosynostosis

Background: A large New Zealand Maori family has non-syndromic coronal craniosynostosis, which is inherited as an autosomal dominant mutation with variable expression. The aim of the study is to determine whether the family has the pro250 arg mutation in the gene for fibroblast growth factor receptor 3 (FGFR3), a mutation found in patients with various types of craniosynostosis. Patients: Fourteen members of a New Zealand Maori family were evaluated, of whom five have coronal synostosis. A family pedigree tracing six generations was recorded. Methods: Blood samples were drawn for genomic DNA analysis from 14 family members. Polymerase chain reaction, restriction-enzyme digestion and DNA sequencing was performed to identify the pro250arg mutation in FGFR3. Results: Seven family members were heterozygous for the pro250arg mutation in FGFR3. The mutation showed autosomal dominance with reduced penetrance and variable expressivity. Conclusion: Our data and those of other investigators suggest that we should begin integrating molecular diagnosis with phenotypic diagnosis of craniosynostoses. Copyright 2001 European Association for Cranio-Maxillofacial Surgery.

Prenatal diagnosis and genetic analysis of type I and type II thanatophoric dysplasia

Thanatophoric dysplasia (TD) is one of the most common neonatal lethal skeletal dysplasias. Prenatal sonographic and molecular genetic diagnoses of three cases of TD type I (TD1) and one case of TD type II (TD2) are presented here. Two fetuses of TD1 were characterized by polyhydramnios, macrocephaly, short limbs, a narrow thoracic cage and curved short femora, but without a cloverleaf skull at 27 and 31 weeks' gestation, respectively. The third fetus with TD1 was, however, not associated with macrocephaly, polyhydramnios, chest narrowing and severe femoral bowing on prenatal ultrasound at 18 weeks' gestation. The TD2 fetus was characterized by polyhydramnios, short limbs, a narrow thoracic cage, straight short femora, hydrocephalus and a cloverleaf skull at 24 weeks' gestation. Three-dimensional ultrasound was able to enhance the visualization of thickened, redundant skin folds and craniofacial and limb deformities associated with TD. Molecular analysis of the fibroblast growth factor receptor 3 (FGFR3) gene by restriction enzyme digestion analysis and direct sequencing using cultured amniotic fluid cells or cord blood cells revealed a missense mutation of 742C-->T (Arg248Cys) in all cases with TD1 and a missense mutation of 1948A-->G (Lys650Glu) in the case with TD2. The present report shows that adjunctive applications of molecular genetic analysis of the FGFR3 gene and three-dimensional ultrasound are useful for prenatal diagnosis of TD.

The load-displacement characteristics of neonatal rat cranial sutures

OBJECTIVE

Recently several centers have attempted to distract the craniofacial skeleton in infants with craniosynostosis. To effectively achieve this goal, we must first understand the normal sutural response to tensile forces. The objective of this study was to determine the load-displacement characteristics of neonatal rat sutures.

METHODS

Thirty cranial sutures were harvested from 1-week-old Wistar rats (10 each coronal, posterior frontal, and sagittal). The width of the harvested bone-suture-bone construct was standardized to 4 mm. The specimens, kept moist, were mounted fresh and distracted at 10 microm/sec until rupture using a Vitrodyne V1000 universal tester. Standard load-displacement curves were constructed. The stiffness, defined as tensile force/change in suture length, and the ultimate stress, defined as tensile force at suture rupture/cross sectional area, were calculated.

RESULTS

These sutures demonstrated classical viscoelastic behavior. During the elastic phase, they elongated approximately 1 microm for every 1 g of force (10(4) N/m). The ultimate tensile stress was approximately 4 MN/m2. The estimated mean elastic modulus was 10 megapascals. The posterior frontal sutures were significantly less stiff than the other two sutures (Kruskal-Wallis nonparametric analysis of variance, p = .0023). The difference in the ultimate stress was also significant (p = .0201).

CONCLUSIONS

This study provides data regarding the basic mechanical behavior of neonatal cranial sutures in a mammalian system.

Using three-dimensional ultrasound to detect craniosynostosis in a fetus with Pfeiffer syndrome

A case of fetal Pfeiffer's syndrome is presented, showing the contribution of three dimensional (3D) sonography in the diagnosis of craniosynostosis--a major feature of this syndrome.