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PubMed2001

A splicing switch and gain-of-function mutation in FgfR2-IIIc hemizygotes causes Apert/Pfeiffer-syndrome-like phenotypes.

Intercellular signaling by fibroblast growth factors plays vital roles during embryogenesis. Mice deficient for fibroblast growth factor receptors (FgfRs) show abnormalities in early gastrulation and implantation, disruptions in epithelial-mesenchymal interactions, as well as profound defects in membranous and endochondrial bone formation. Activating FGFR mutations are the underlying cause of several craniosynostoses and dwarfism syndromes in humans. Here we show that a heterozygotic abrogation of FgfR2-exon 9 (IIIc) in mice causes a splicing switch, resulting in a gain-of-function mutation. The consequences are neonatal growth retardation and death, coronal synostosis, ocular proptosis, precocious sternal fusion, and abnormalities in secondary branching in several organs that undergo branching morphogenesis. This phenotype has strong parallels to some Apert's and Pfeiffer's syndrome patients.

Acrocephalosyndactylia↗
PubMed2001

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.

Acrocephalosyndactylia↗
PubMed2000

Loss of fibroblast growth factor receptor 2 ligand-binding specificity in Apert syndrome.

Craniosynostosis syndromes are autosomal dominant human skeletal diseases that result from various mutations in fibroblast growth factor receptor genes (Fgfrs). Apert syndrome (AS) is one of the most severe craniosynostosis syndromes and is associated with severe syndactyly of the hands and feet and with central nervous system malformations. AS is caused by specific missense mutations in one of two adjacent amino acid residues (S252W or P253R) in the highly conserved region linking Ig-like domains II and III of FGFR2. Here we demonstrate that these mutations break one of the cardinal rules governing ligand specificity of FGFR2. We show that the S252W mutation allows the mesenchymal splice form of FGFR2 (FGFR2c) to bind and to be activated by the mesenchymally expressed ligands FGF7 or FGF10 and the epithelial splice form of FGFR2 (FGFR2b) to be activated by FGF2, FGF6, and FGF9. These data demonstrate loss of ligand specificity of FGFR2 with retained ligand dependence for receptor activation. These data suggest that the severe phenotypes of AS likely result from ectopic ligand-dependent activation of FGFR2.

3T3 Cells↗
PubMed1996

Ligand-independent activation of fibroblast growth factor receptors by point mutations in the extracellular, transmembrane, and kinase domains.

The fibroblast growth factor receptors (FGFRs) are a family of receptor protein tyrosine kinases that have been shown to mediate a variety of cellular processes including angiogenesis, wound healing, tumorigenesis, and embryonic development. Distinct FGFR mutations in individuals with autosomal dominant disorders of bone growth and development provide a unique opportunity to determine the function of FGFRs during embryonic development. To determine the consequences of these mutations on receptor function, we have made mutations in Xenopus FGFR1 (XFGFR1) and FGFR2 (XFGFR2) that correspond to several of the mutations identified in these dysmorphic syndromes. Analysis of mutant receptor proteins expressed in Xenopus oocytes indicates that all but one have elevated tyrosine kinase activity relative to their wild-type counterparts. Those mutations that give an unpaired cysteine residue in the extracellular domain result in intermolecular disulfide bond formation and covalent receptor dimerization. Microinjection of Xenopus embryos with RNA encoding mutant receptors with elevated tyrosine kinase activity results in ligand-independent induction of mesoderm in animal pole explants. Wild-type XFGFR1 and XFGFR2 do not induce mesoderm when injected at similar doses. Co-injection of RNA encoding a dominant negative FGF receptor, lacking the tyrosine kinase domain, together with RNA encoding various activated FGFRs inhibits mesoderm induction by a receptor activated by a transmembrane domain mutation or extracellular mutations that introduce an unpaired cysteine residue into the extracellular domain but does not inhibit mesoderm induction by receptors bearing a tyrosine kinase domain mutation. These results indicate that different point mutations may activate FGFRs by distinct mechanisms and that ligand-independent FGFR activation may be a feature in common to many skeletal disorders.

Acrocephalosyndactylia↗
PubMed2004

A soluble form of fibroblast growth factor receptor 2 (FGFR2) with S252W mutation acts as an efficient inhibitor for the enhanced osteoblastic differentiation caused by FGFR2 activation in Apert syndrome.

Apert syndrome is an autosomal dominant disease characterized by craniosynostosis and bony syndactyly associated with point mutations (S252W and P253R) in the fibroblast growth factor receptor (FGFR) 2 that cause FGFR2 activation. Here we investigated the role of the S252W mutation of FGFR2 on osteoblastic differentiation. Osteoblastic cells derived from digital bone in two Apert patients with the S252W mutation showed more prominent alkaline phosphatase activity, osteocalcin and osteopontin mRNA expression, and mineralized nodule formation compared with the control osteoblastic cells derived from two independent non-syndromic polydactyly patients. Stable clones of the human MG63 osteosarcoma cells (MG63-Ap and MG63-IIIc) overexpressing a splice variant form of FGFR2 with or without the S252W mutation (FGFR2IIIcS252W and FGFR2IIIc) showed a higher RUNX2 mRNA expression than parental MG63 cells. Furthermore MG63-Ap exhibited a higher osteopontin mRNA expression than did MG63-IIIc. The enhanced osteoblastic marker gene expression and mineralized nodule formation of the MG63-Ap was inhibited by the conditioned medium from the COS-1 cells overexpressing the soluble FGFR2IIIcS252W. Furthermore the FGF2-induced osteogenic response in the mouse calvarial organ culture system was blocked by the soluble FGFR2IIIcS252W. These results show that the S252W mutation in the FGFR2 gene enhances the osteoblast phenotype in human osteoblasts and that a soluble FGFR2 with the S252W mutation controls osteoblast differentiation induced by the S252W mutation through a dominant negative effect on FGFR2 signaling in Apert syndrome.

Acrocephalosyndactylia↗
PubMed2005

The Wnt-inducible transcription factor Twist1 inhibits chondrogenesis.

Wnt signaling is essential for many developmental processes, including skeletogenesis. To investigate the effects of Wnt signaling during skeletogenesis we studied the effects of Wnt on cultured chondrocytic cells and differentiating limb-bud mesenchyme. We showed that Wnt3a strongly repressed chondrogenesis and chondrocyte gene expression. Canonical Wnt signaling was responsible for the repression of differentiation, as evidenced by results showing that inhibition of glycogen synthase kinase 3 or expression of beta-catenin caused similar repression of differentiation. Significantly, we showed that the transcription repressor Twist1 is induced by canonical Wnt signaling. Expression of Twist1 strongly inhibited chondrocyte gene expression and short hairpin RNA knockdown of Twist1 transcript levels caused increased expression of the chondrocyte-specific genes aggrecan and type II collagen. Interestingly, Twist1 interfered with BMP2-induced expression of aggrecan and type II collagen expression and knockdown of Twist1 augmented BMP2-induced aggrecan and type II collagen expression. These data support the conclusions that Twist1 contributes to the repression of chondrogenesis and chondrocyte gene expression resulting from canonical Wnt signaling and that Twist1 interferes with BMP-dependent signaling.

Acrocephalosyndactylia↗
PubMed2005

Inhibition or activation of Apert syndrome FGFR2 (S252W) signaling by specific glycosaminoglycans.

Most Apert syndrome patients harbor a single amino acid mutation (S252W) in fibroblast growth factor (FGF) receptor 2 (FGFR2), which leads to abnormal FGF/FGFR2 signaling. Here we show that specific combinations of FGFs and glycosaminoglycans activate both alternative splice forms of the mutant but not of the wild-type FGF receptors. More importantly, 2-O- and N-sulfated heparan sulfate, prepared by a combined chemical and enzymatic synthesis, antagonized the over-activated FGFR2b (S252W) to basal levels at nanomolar concentrations. These studies demonstrated that specific glycosaminoglycans could be useful in treating ligand-dependent FGFR signaling-related diseases, such as Apert syndrome and cancer.

Acrocephalosyndactylia↗
PubMed1998

Is craniofacial morphology in Apert and Crouzon syndromes the same?

This article reviews previous research on the craniofacial development in Apert and Crouzon syndromes and adds new roentgencephalometric information. It is concluded that craniofacial development in the two syndromes is not the same. Marked differences were found in the calvaria, cranial base, orbit, maxilla, zygoma, incisal occlusion, and soft tissue profile. In general, abnormal craniofacial morphology was more severe in Apert syndrome than in Crouzon syndrome.

Acrocephalosyndactylia↗
PubMed1969

Apert's syndrome.

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Acrocephalosyndactylia↗
PubMed2002

Correction of a deformed thumb by distraction of the phalanx.

We used distraction osteogenesis to correct six deformed thumbs in four patients ranging in age from 4 to 7 years. Two of the patients had Apert syndrome (syndromic craniosynostosis with symmetrical syndactyly) and two had polydactyly. We used a small fixator with a ball joint and successfully corrected the angular deformity after lengthening the proximal phalanx by distraction. This single inclusive procedure was extremely useful. We found the optimal distraction regimen for the digital phalanx was a one day waiting period and lengthening at 1 mm/day. The mean healing indexes were 37.2 days/cm (range 24.2 to 41.5) in those with Apert syndrome and 64.3 days/cm in those with polydactyly (62.5 and 66.0). Our results suggest that osteogenesis at the distraction site may be quicker in patients with Apert syndrome than in those with polydactyly.

Acrocephalosyndactylia↗
PubMed1998

Spring mediated dynamic craniofacial reshaping. Case report.

A new technique of using implantable springs as an adjunct after corrective surgery for craniofacial malformations is presented. A 6-month-old boy with multiple premature craniosynostoses and extreme turricephaly underwent surgery of limited extensiveness but supplemented with a set of indwelling springs for gradual postoperative skull reshaping. At spring removal three months later the skull was normalised both clinically and on cephalogram. A 5-year-old boy with Apert syndrome, severe midface retrusion, exorbitism, and sleep apnoea underwent a monobloc full face disjunction without repositioning, but was fitted with two springs for postoperative facial advancement. Three months postoperatively cephalometric analysis revealed 14 mm advancement at incisor level and at least 16 mm in the frontal region. There was no more exorbitism or clinically noticeable midface retrusion. Sleep studies revealed that the sleep apnoea was significantly improved, meaning complete cure except when sleeping flat on the back. It was concluded from these first clinical applications of spring assisted craniofacial distraction that springs hold significant promise for the future in many respects.

Acrocephalosyndactylia↗
PubMed2003

Effective treatment of relapsing idiopathic nodular panniculitis (Pfeifer-Weber-Christian disease) with mycophenolate mofetil.

Relapsing idiopathic nodular panniculitis is the term used to describe a group of diseases that presents as subcutaneous inflammatory nodules, fever and systemic symptoms and histopathologically displays inflammation within the fat lobules. There is no specific test for diagnosis and extensive investigations are required to exclude systemic causes of panniculitis. No uniform effective therapy is available and various drugs used include mainly corticosteroids alone or in combination with other immunosuppressive agents. Presented in this paper is an intractable case of idiopathic nodular panniculitis whose corticotherapy failed and could not be continued because of serious adverse effects. The rapid and good therapeutic response of the patient to mycophenolate mofetil monotherapy is discussed.

Acrocephalosyndactylia↗
PubMed2003

Acne in Apert's syndrome: treatment with isotretinoin.

Apert's syndrome is an uncommon disease characterized by synostosis of extremities, vertebrae and skull. A clear association between Apert's syndrome and acne vulgaris with resistance to usual acne treatments has been described. A case of Apert's syndrome treated with oral isotretinoin with good results is reported and the pathogenic mechanisms of acne in this syndrome are discussed.

Acne Vulgaris↗
PubMedDate not supplied

Speech and language skills and cognitive functioning in children with Apert syndrome: a pilot study.

There are few studies that report findings on the speech and language characteristics of Apert syndrome and little is known about the cognitive profile of the syndrome. The current study addresses this gap and explores speech, language, resonance/voice, attention oro-motor and cognitive skills in a group of 10 children (4;1-5;11) with Apert syndrome. The speech and language battery included: the CELF-Pre-school, the PLS-3, the Vocal Profile Analysis, GOS.SP.ASS, PACS; and the Brodsky Drooling Scale. Subscales of the BAS II-Early Years Version were used to assess cognition. Data were also collected on other factors that could influence developmental outcome such as audiological history and management; occlusion/dentition; respiratory problems and management; neuroanatomical abnormalities; the number and nature of cranial surgeries; and the occurrence of raised intracranial pressure. All children for whom a Performance IQ was obtained (n = 8) had abilities within the average range and IQ scores were considerably higher than those reported in previous studies. Eight children had moderate or severe language difficulties and expressive language difficulties were the most frequent. These language difficulties were not associated with a general cognitive deficit. All the children had problems with attention, speech and oro-motor skills. Nine had abnormal voice. In addition, a range of other associated factors that could affect functioning were identified. The discrepancies between the current study and previous investigations are outlined. Parameters for assessment are considered. The implications of these findings for valid assessments of children with Apert syndrome are discussed. Multidisciplinary assessment of children with Apert syndrome across a broad range of dimensions is recommended to obtain a profile of each child's strengths and weaknesses to ensure that appropriate educational placements and early interventions are implemented. Considering patterns of development over time at key ages is also argued to be of central importance.

Acrocephalosyndactylia↗