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J Bonaventure

Publications and source records attributed to J Bonaventure.

At least 19 recordsLinked to original sources
PubMed2001

Mutations in the basic domain and the loop-helix II junction of TWIST abolish DNA binding in Saethre-Chotzen syndrome.

Saethre-Chotzen syndrome is an autosomal dominant skull disorder resulting from premature fusion of coronal sutures (craniosynostosis). It is caused by mutations in the TWIST gene encoding a basic Helix-Loop-Helix transcription factor. Here we report on the identification of a novel mutation affecting a highly conserved residue of the basic domain. Unlike nonsense and missense mutations lying within helices, this mutation does not affect protein stability or heterodimerisation of TWIST with its partner E12. However, it does abolish TWIST binding capacity to a target E-box as efficiently as two missense mutations in the loop-helix II junction. By contrast, elongation of the loop through a 7 amino acid insertion appears not to hamper binding to the DNA target. We conclude that loss of TWIST protein function in Saethre-Chotzen patients can occur at three different levels, namely protein stability, dimerisation, and DNA binding and that the loop-helix II junction is essential for effective protein-DNA interaction.

Acrocephalosyndactylia↗
PubMed2001

Frequent FGFR3 mutations in papillary non-invasive bladder (pTa) tumors.

We recently identified activating mutations of fibroblast growth factor receptor 3 (FGFR3) in bladder carcinoma. In this study we assessed the incidence of FGFR3 mutations in a series of 132 bladder carcinomas: 20 carcinoma in situ (CIS), 50 pTa, 19 pT1, and 43 pT2-4. All 48 mutations identified were identical to the germinal activating mutations that cause thanatophoric dysplasia, a lethal form of dwarfism. The S249C mutation, found in 33 of the 48 mutated tumors, was the most common. The frequency of mutations was higher in pTa tumors (37 of 50, 74%) than in CIS (0 of 20, 0%; P < 0.0001), pT1 (4 of 19, 21%; P < 0.0001) and pT2-4 tumors (7 of 43, 16%; P < 0.0001). FGFR3 mutations were detected in 27 of 32 (84%) G1, 16 of 29 (55%) G2, and 5 of 71 (7%) G3 tumors. This association between FGFR3 mutations and low grade was highly significant (P < 0.0001). FGFR3 is the first gene found to be mutated at a high frequency in pTa tumors. The absence of FGFR3 mutations in CIS and the low frequency of FGFR3 mutations in pT1 and pT2-4 tumors are consistent with the model of bladder tumor progression in which the most common precursor of pT1 and pT2-4 tumors is CIS.

Carcinoma in Situ↗
PubMed2001

Genotype-phenotype correlation in hereditary multiple exostoses.

Hereditary multiple exostoses (HME) is a genetically heterogeneous autosomal dominant disorder characterised by the development of bony protuberances mainly located on the long bones. Three HME loci have been mapped to chromosomes 8q24 (EXT1), 11p11-13 (EXT2), and 19p (EXT3). The EXT1 and EXT2 genes encode glycosyltransferases involved in biosynthesis of heparan sulphate proteoglycans. Here we report on a clinical survey and mutation analysis of 42 HME French families and show that EXT1 and EXT2 accounted for more than 90% of HME cases in our series. Among them, 27/42 cases were accounted for by EXT1 (64%, four nonsense, 19 frameshift, three missense, and one splice site mutations) and 9/42 cases were accounted for by EXT2 (21%, four nonsense, two frameshift, two missense, and one splice site mutation). Overall, 31/36 mutations were expected to cause loss of protein function (86%). The most severe forms of the disease and malignant transformation of exostoses to chondrosarcomas were associated with EXT1 mutations. These findings provide the first genotype-phenotype correlation in HME and will, it is hoped, facilitate the clinical management of these patients.

Age of Onset↗
PubMed2000

Saethre-Chotzen mutations cause TWIST protein degradation or impaired nuclear location.

H-TWIST belongs to the family of basic helix-loop-helix (bHLH) transcription factors known to exert their activity through dimer formation. We have demonstrated recently that mutations in H-TWIST account for Saethre-Chotzen syndrome (SCS), an autosomal dominant craniosynostosis syndrome characterized by premature fusion of coronal sutures and limb abnormalities of variable severity. Although insertions, deletions, nonsense and missense mutations have been identified, no genotype-phenotype correlation could be found, suggesting that the gene alterations lead to a loss of protein function irrespective of the mutation. To assess this hypothesis, we studied stability, dimerization capacities and subcellular distribution of three types of TWIST mutant. Here, we show that: (i) nonsense mutations resulted in truncated protein instability; (ii) missense mutations involving the helical domains led to a complete loss of H-TWIST heterodimerization with the E12 bHLH protein in the two-hybrid system and dramatically altered the ability of the TWIST protein to localize in the nucleus of COS-transfected cells; and (iii) in-frame insertion or missense mutations within the loop significantly altered dimer formation but not the nuclear location of the protein. We conclude that at least two distinct mechanisms account for loss of TWIST protein function in SCS patients, namely protein degradation and subcellular mislocalization.

Animals↗
PubMed2000

Autosomal recessive disorder otospondylomegaepiphyseal dysplasia is associated with loss-of-function mutations in the COL11A2 gene.

Otospondylomegaepiphyseal dysplasia (OSMED) is an autosomal recessive skeletal dysplasia accompanied by severe hearing loss. The phenotype overlaps that of the autosomal dominant disorders-Stickler and Marshall syndromes-but can be distinguished by disproportionately short limbs, severe hearing loss, and lack of ocular involvement. In one family with OSMED, a homozygous Gly-->Arg substitution has been described in COL11A2, which codes for the alpha2 chain of type XI collagen. We report seven further families with OSMED. All affected individuals had a remarkably similar phenotype: profound sensorineural hearing loss, skeletal dysplasia with limb shortening and large epiphyses, cleft palate, an extremely flat face, hypoplasia of the mandible, a short nose with anteverted nares, and a flat nasal bridge. We screened affected individuals for mutations in COL11A2 and found different mutations in each family. Individuals from four families, including three with consanguineous parents, were homozygous for mutations. Individuals from three other families, in whom parents were nonconsanguineous, were compound heterozygous. Of the 10 identified mutations, 9 are predicted to cause premature termination of translation, and 1 is predicted to cause an in-frame deletion. We conclude that the OSMED phenotype is highly homogenous and results from homozygosity or compound heterozygosity for COL11A2 mutations, most of which are predicted to cause complete absence of alpha2(XI) chains.

Adult↗
PubMed2000

Overlap between Baller-Gerold and Rothmund-Thomson syndrome.

We report a male patient with craniosysnostosis, bilateral radial and ulnar hypoplasia, absent thumbs, poikiloderma, and short stature. His parents are first cousins. Although this patient was originally diagnosed as having Baller-Gerold syndrome it is more likely that he has Rothmund-Thomson syndrome or a similar disorder. This report confirms the overlap between these two syndromes, and that Baller-Gerold syndrome is essentially a diagnosis of exclusion.

Abnormalities, Multiple↗
PubMed2000

EXT 1 gene mutation induces chondrocyte cytoskeletal abnormalities and defective collagen expression in the exostoses.

Hereditary multiple exostoses (HME), an autosomal skeletal disorder characterized by cartilage-capped excrescences, has been ascribed to mutations in EXT 1 and EXT 2, two tumor suppressor-related genes encoding glycosyltransferases involved in the heparan sulfate proteoglycan (HSPG) biosynthesis. Taking advantage of the availability of three different exostoses from a patient with HME harboring a premature termination codon in the EXT 1 gene, morphological, immunologic, and biochemical analyses of the samples were carried out. The cartilaginous exostosis, when compared with control cartilage, exhibited alterations in the distribution and morphology of chondrocytes with abundant bundles of actin filaments indicative of cytoskeletal defects. Chondrocytes in the exostosis were surrounded by an extracellular matrix containing abnormally high amounts of collagen type X. The unexpected presence of collagen type I unevenly distributed in the cartilage matrix further suggested that some of the hypertrophic chondrocytes detected in the cartilaginous caps of the exostoses underwent accelerated differentiation. The two mineralized exostoses presented lamellar bone arrangement undergoing intense remodeling as evidenced by the presence of numerous reversal lines. The increased electrophoretic mobility of chondroitin sulfate and dermatan sulfate proteoglycans (PGs) extracted from the two bony exostoses was ascribed to an absence of the decorin core protein. Altogether, these data indicate that EXT mutations might induce a defective endochondral ossification process in exostoses by altering actin distribution and chondrocyte differentiation and by promoting primary calcification through decorin removal.

Adolescent↗
PubMed2000

Fibroblast growth factor receptor 3 mutation in nonsyndromic coronal synostosis: clinical spectrum, prevalence, and surgical outcome.

OBJECT: A recurrent point mutation in the fibroblast growth factor receptor 3 gene that converts proline 250 into arginine has been reported recently in cases of apparently nonsyndromic coronal craniosynostosis. The goal of the present study was to examine the phenotype of patients in whom this mutation was present, to determine the prevalence of the condition, and to assess the functional and the morphological outcome of the surgically treated patients. METHODS: A DNA analysis was performed in 103 children suffering from apparently isolated coronal synostosis, 41 of whom had bilateral and 62 of whom had unilateral disease. There were 31 boys and 72 girls in the study group. Sixty cases were sporadic and 43 were familial; the 43 familial cases arose in 33 unrelated families. The mutation was found in seven (12%) of 60 sporadic cases and in 24 (73%) of the 33 families. The functional and morphological results were assessed in all surgically treated patients who had at least 1 year of follow up and who were at least 3 years of age at the time of assessment. A comparison was made between patients with the mutation and those without. CONCLUSIONS: The most typical presentation was seen in girls and consisted of a bicoronal synostosis resulting in a severe brachycephaly associated with mild hypertelorism and marked bulging of the temporal fossae, which resulted in a huge enlargement of the upper part of the face. The most frequently associated extracranial anomaly was brachydactyly, identified either clinically or radiologically. Based on the proportion of bilateral and unilateral coronal synostoses, the present data indicate that the mutation is associated with more severe cases and that girls with the mutation are more severely affected than boys. The functional and morphological results were worse in patients in whom the mutation was present as compared with those in whom it was not.

Arginine↗
PubMed1999

Mutations within or upstream of the basic helix-loop-helix domain of the TWIST gene are specific to Saethre-Chotzen syndrome.

Saethre-Chotzen syndrome (ACS III) is an autosomal dominant craniosynostosis syndrome recently ascribed to mutations in the TWIST gene, a basic helix-loop-helix (b-HLH) transcription factor regulating head mesenchyme cell development during cranial neural tube formation in mouse. Studying a series of 22 unrelated ACS III patients, we have found TWIST mutations in 16/22 cases. Interestingly, these mutations consistently involved the b-HLH domain of the protein. Indeed, mutant genotypes included frameshift deletions/insertions, nonsense and missense mutations, either truncating or disrupting the b-HLH motif of the protein. This observation gives additional support to the view that most ACS III cases result from loss-of-function mutations at the TWIST locus. The P250R recurrent FGFR 3 mutation was found in 2/22 cases presenting mild clinical manifestations of the disease but 4/22 cases failed to harbour TWIST or FGFR 3 mutations. Clinical re-examination of patients carrying TWIST mutations failed to reveal correlations between the mutant genotype and severity of the phenotype. Finally, since no TWIST mutations were detected in 40 cases of isolated coronal craniosynostosis, the present study suggests that TWIST mutations are specific to Saethre-Chotzen syndrome.

Acrocephalosyndactylia↗
PubMed1999

COL9A3: A third locus for multiple epiphyseal dysplasia.

Multiple epiphyseal dysplasia (MED), an autosomal dominant osteochondrodysplasia, is a clinically and genetically heterogeneous disorder characterized by mild short stature and early-onset osteoarthritis. The phenotypic spectrum includes the mild Ribbing type, the more severe Fairbank type, and some unclassified forms. Linkage studies have identified two loci for MED. One of these, EDM1, is on chromosome 19, in a region that contains the cartilage oligomeric matrix protein (COMP) gene. Mutations have been identified in this gene in patients with the Ribbing type, the Fairbank type, and unclassified forms of MED. The second locus, EDM2, maps to chromosome 1, in a region spanning COL9A2. Recently, a splice-site mutation was found in COL9A2, causing skipping of exon 3 in one family with MED. Because of the exclusion of the EDM1 and EDM2 loci in some families, the existence of a third locus has been postulated. We report here one family with MED, evaluated clinically and radiologically and tested for linkage with candidate genes, including COMP, COL9A1, COL9A2, and COL9A3. No linkage was found with COMP, COL9A1, or COL9A2, but an inheritance pattern consistent with linkage was observed with COL9A3. Mutation analysis of COL9A3 identified an A-->T transversion in the acceptor splice site of intron 2 in affected family members. The mutation led to skipping of exon 3 and an in-frame deletion of 12 amino acid residues in the COL3 domain of the alpha3(IX) chain and thus appeared to be similar to that reported for COL9A2. This is the first disease-causing mutation identified in COL9A3. Our results also show that COL9A3, located on chromosome 20, is a third locus for MED.

Adolescent↗
PubMed1999

Clinical variability in patients with Apert's syndrome.

OBJECT: Apert's syndrome is characterized by faciocraniosynostosis and severe bony and cutaneous syndactyly of all four limbs. The molecular basis for this syndrome appears remarkably specific: two adjacent amino acid substitutions (either S252W or P253R) occurring in the linking region between the second and third immunoglobulin domains of the fibroblast growth factor receptor (FGFR)2 gene. The goal of this study was to examine the phenotype/genotype correlations in patients with Apert's syndrome. METHODS: In the present study, 36 patients with Apert's syndrome were screened for genetic mutations. Mutations were detected in all cases. In one of the patients there was a rare mutation consisting of a double-base pair substitution in the same codon (S252F). A phenotypical survey of our cases was performed and showed the clinical variability of this syndrome. In two patients there was no clinical or radiological evidence of craniosynostosis. In two other patients with atypical forms of syndactyly and cranial abnormalities, the detection of a specific mutation was helpful in making the diagnosis. CONCLUSIONS: The P253R mutation appears to be associated with the more severe forms, with regard to the forms of syndactyly and to mental outcome. The fact that mutations found in patients with Apert' s syndrome are usually confined to a specific region of the FGFR2 exon IIIa may be useful in making the diagnosis and allowing genetic counseling in difficult cases.

Acrocephalosyndactylia↗
PubMed1999

Sex related expressivity of the phenotype in coronal craniosynostosis caused by the recurrent P250R FGFR3 mutation.

A recurrent point mutation in the fibroblast growth factor receptor 3 (FGFR3) gene that converts proline 250 into arginine is commonly associated with coronal craniosynostosis and has allowed definition of a new syndrome on a molecular basis. Sixty-two patients with sporadic or familial forms of coronal craniosynostosis were investigated for the P250R FGFR3 mutation. It was identified in 20 probands originating from 27 unrelated families (74%), while only 6/35 sporadic cases (17%) harboured the mutation. In both familial and sporadic cases, females were significantly more severely affected than males. Hence, while 68% of females carrying the P250R mutation showed brachycephaly, only 35% of males had the same phenotype. In the most severe forms of the disease, the association of bicoronal craniosynostosis with hypertelorism and marked bulging of the temporal fossae were common hallmarks that might be helpful for clinical diagnosis. Taken together, these results indicate that the P250R FGFR3 mutation is mostly familial and is associated with a more severe phenotype in females than in males. The sex related severity of the condition points to the possible implication of modifier genes in this syndrome.

Craniosynostoses↗
PubMed1998

Fibroblast growth factor downregulates expression of a basic helix-loop-helix-type transcription factor, scleraxis, in a chondrocyte-like cell line, TC6.

Scleraxis is a basic helix-loop-helix-type transcription factor that is expressed in sclerotome. Fibroblast growth factor (FGF) is one of the cytokines produced by the cells in skeletal tissues and is a potent modulator of skeletogenesis. The aim of this study was to examine the effects of FGF on the expression of scleraxis in chondrocyte-like cells, TC6. In these cells, scleraxis mRNA was constitutively expressed as a 1 .2 kb message at a high level in contrast to its low levels of expression in fibroblast-like cells or osteoblast-like cells. Upon treatment with FGF, scleraxis mRNA level was decreased within 12 h. This effect was at its nadir at 24 h and the scleraxis mRNA level returned to its base line level by 48 h. The FGF effect was maximal at 1 ng/ml. FGF effects on scleraxis were blocked by actinomycin D but not by cycloheximide, suggesting the involvement of transcriptional events that do not require new protein synthesis. The FGF effects on scleraxis were blocked by genistein, suggesting the involvement of tyrosine kinase in the post-receptor signaling. TGFbeta treatment of TC6 cells enhanced scleraxis mRNA expression; however, combination of the saturation doses of FGF and TGFbeta resulted in suppression of scleraxis mRNA level. BMP2 also suppressed scleraxis mRNA expression in TC6 cells and no further suppression was observed in combination with FGF. These results indicate that scleraxis is expressed in chondrocyte-like TC6 cells and it is one of the targets of FGF action in these cells.

Basic Helix-Loop-Helix Proteins↗
PubMed1998

Absence of functional receptors for parathyroid hormone and parathyroid hormone-related peptide in Blomstrand chondrodysplasia.

We report the absence of functional parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptors (PTH/PTHrP receptor) in Blomstrand chondrodysplasia, a genetic disorder characterized by advanced endochondral bone maturation. Analysis of PTH/PTHrP receptor genomic DNA from a patient with Blomstrand chondrodysplasia demonstrated that the patient was heterozygous for a point mutation (G--> A substitution at nucleotide 1176) inherited from the mother. Analysis of PTH/PTHrP receptor cDNA demonstrated that: (a) this point mutation caused the deletion of the first 11 amino acids of exon M5 (encoding the fifth transmembrane domain of the receptor), resulting from the use of a novel splice site created by the base substitution; (b) the mutant receptor was well expressed in COS-7 cells, but did not bind PTH or PTHrP, and failed to induce detectable stimulation of either cAMP or inositol phosphate production in response to these ligands; and (c) the paternal allele was not expressed. Thus, only the abnormal and nonfunctional PTH/PTHrP receptors encoded by the maternal allele were expressed by chondrocytes from this patient. In view of the known role played by the PTH/PTHrP receptor in bone and cartilage development, these results strongly support the conclusion that the absence of functional PTH/ PTHrP receptors is responsible for the skeletal abnormalities seen in Blomstrand chondrodysplasia, abnormalities that are the mirror image of those observed in Jansen's chondrodysplasia. These findings emphasize the importance of signaling through this receptor in human fetal skeletal development.

Base Sequence↗
PubMed1998

Fibroblast growth factor receptor 3 mutations promote apoptosis but do not alter chondrocyte proliferation in thanatophoric dysplasia.

Thanatophoric dysplasia (TD) is a lethal skeletal disorder caused by recurrent mutations in the fibroblast growth factor receptor 3 (FGFR 3) gene. The mitogenic response of fetal TD I chondrocytes in primary cultures upon stimulation by either FGF 2 or FGF 9 did not significantly differ from controls. Although the levels of FGFR 3 mRNAs in cultured TD chondrocytes were similar to controls, an abundant immunoreactive material was observed at the perinuclear level using an anti-FGFR 3 antibody in TD cells. Transduction signaling via the mitogen-activated protein kinase pathway was assessed by measuring extracellular signal-regulated kinase activity (ERK 1 and ERK 2). Early ERKs activation following FGF 9 supplementation was observed in TD chondrocytes (2 min) as compared with controls (5 min) but no signal was detected in the absence of ligand. By contrast ligand-independent activation of the STAT signaling pathway was demonstrated in cultured TD cells and confirmed by immunodetection of Stat 1 in the nuclei of hypertrophic TD chondrocytes. Moreover, the presence of an increased number of apoptotic chondrocytes in TD fetuses was associated with a higher expression of Bax and the simultaneous decrease of Bcl-2 levels. Taken together, these results indicate that FGFR 3 mutations in TD I fetuses do not hamper chondrocyte proliferation but rather alter their differentiation by triggering premature apoptosis through activation of the STAT signaling pathway.

Apoptosis↗
PubMed1998

Spatio-temporal expression of FGFR 1, 2 and 3 genes during human embryo-fetal ossification.

Mutations in FGFR 1-3 genes account for various human craniosynostosis syndromes, while dwarfism syndromes have been ascribed exclusively to FGFR 3 mutations. However, the exact role of FGFR 1-3 genes in human skeletal development is not understood. Here we describe the expression pattern of FGFR 1-3 genes during human embryonic and fetal endochondral and membranous ossification. In the limb bud, FGFR 1 and FGFR 2 are initially expressed in the mesenchyme and in epidermal cells, respectively, but FGFR 3 is undetectable. At later stages, FGFR 2 appears as the first marker of prechondrogenic condensations. In the growing long bones, FGFR 1 and FGFR 2 transcripts are restricted to the perichondrium and periosteum, while FGFR 3 is mainly expressed in mature chondrocytes of the cartilage growth plate. Marked FGFR 2 expression is also observed in the periarticular cartilage. Finally, membranous ossification of the skull vault is characterized by co-expression of the FGFR 1-3 genes in preosteoblasts and osteoblasts. In summary, the simultaneous expression of FGFR 1-3 genes in cranial sutures might explain their involvement in craniosynostosis syndromes, whereas the specific expression of FGFR 3 in chondrocytes does correlate with the involvement of FGFR 3 mutations in inherited defective growth of human long bones.

Bone and Bones↗
PubMed1998

Diverse mutations in the gene for cartilage oligomeric matrix protein in the pseudoachondroplasia-multiple epiphyseal dysplasia disease spectrum.

Pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED) are autosomal dominant osteochondrodysplasias that result in mild to severe short-limb dwarfism and early-onset osteoarthrosis. PSACH and some forms of MED result from mutations in the gene for cartilage oligomeric matrix protein (COMP; OMIM 600310 [http://www3.ncbi.nlm. nih.gov:80/htbin-post/Omim/dispmim?600310]). We report the identification of COMP mutations in an additional 14 families with PSACH or MED phenotypes. Mutations predicted to result in single-amino acid deletions or substitutions, all in the region of the COMP gene encoding the calmodulin-like repeat elements, were identified in patients with moderate to severe PSACH. We also identified within this domain a missense mutation that produced MED Fairbank. In two families, one with mild PSACH and the second with a form of MED, we identified different substitutions for a residue in the carboxyl-terminal globular region of COMP. Both the clinical presentations of these two families and the identification of COMP-gene mutations provide evidence of phenotypic overlap between PSACH and MED. These data also reveal a role for the carboxyl-terminal domain in the structure and/or function of COMP.

Achondroplasia↗