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Apert syndrome results from localized mutations of FGFR2 and is allelic with Crouzon syndrome.

Apert syndrome is a distinctive human malformation comprising craniosynostosis and severe syndactyly of the hands and feet. We have identified specific missense substitutions involving adjacent amino acids (Ser252Trp and Pro253Arg) in the linker between the second and third extracellular immunoglobulin (Ig) domains of fibroblast growth factor receptor 2 (FGFR2) in all 40 unrelated cases of Apert syndrome studied. Crouzon syndrome, characterized by craniosynostosis but normal limbs, was previously shown to result from allelic mutations of the third Ig domain of FGFR2. The contrasting effects of these mutations provide a genetic resource for dissecting the complex effects of signal transduction through FGFRs in cranial and limb morphogenesis.

Acrocephalosyndactylia↗

Identical mutations in the FGFR2 gene cause both Pfeiffer and Crouzon syndrome phenotypes.

Mutations in the fibroblast growth factor receptor 2 (FGFR2) gene have been identified in Crouzon syndrome, an autosomal dominant condition causing premature fusion of the cranial sutures (craniosynostosis). A mutation in FGFR1 has been established in several families with Pfeiffer syndrome, where craniosynostosis is associated with specific digital abnormalities. We now report point mutations in FGFR2 in seven sporadic Pfeiffer syndrome patients. Six of the seven Pfeiffer syndrome patients share two missense mutations, which have also been reported in Crouzon syndrome. The Crouzon and Pfeiffer phenotypes usually breed true within families and the finding of identical mutations in unrelated individuals giving different phenotypes is a highly unexpected observation.

Acrocephalosyndactylia↗

Exclusive paternal origin of new mutations in Apert syndrome.

Apert syndrome results from one or other of two specific nucleotide substitutions, both C-->G transversions, in the fibroblast growth factor receptor 2 (FGFR2) gene. The frequency of new mutations, estimated as 1 per 65,000 live births, implies germline transversion rates at these two positions are currently the highest known in the human genome. Using a novel application of the amplification refractory mutation system (ARMS), we have determined the parental origin of the new mutation in 57 Apert families: in every case, the mutation arose from the father. This identifies the biological basis of the paternal age effect for new mutations previously suggested for this disorder.

Acrocephalosyndactylia↗

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

Pfeiffer syndrome (PS; McKusick MIM 101,600) is an autosomal dominant craniosynostosis syndrome with characteristic craniofacial anomalies and broad thumbs and big toes. We have previously demonstrated genetic heterogeneity in PS and mapped a gene to chromosome 8 (ref. 3) and a second to chromosome 10 (ref. 4). The gene on chromosome 8 is the fibroblast growth factor receptor 1 (FGFR1) with a common mutation (C755G) predicting a Pro252Arg substitution. The gene on chromosome 10 is FGFR2 with several different mutations causing sporadic and familial PS (Table 1). We report a recurrent single point mutation in the FGFR3 gene, located on chromosome 4p, in ten unrelated families with craniosynostosis syndromes. This mutation (C749G) predicts a Pro250Arg amino acid substitution in the extracellular domain of the FGFR3 protein. Interestingly, this common mutation occurs precisely at the analogous position within the FGFR3 protein as the mutations in FGFR1 (Pro252Arg) and FGFR2 (Pro253Arg) previously reported in Pfeiffer and Apert syndromes, respectively.

Acrocephalosyndactylia↗

Altered Twist1 and Hand2 dimerization is associated with Saethre-Chotzen syndrome and limb abnormalities.

Autosomal dominant mutations in the gene encoding the basic helix-loop-helix transcription factor Twist1 are associated with limb and craniofacial defects in humans with Saethre-Chotzen syndrome. The molecular mechanism underlying these phenotypes is poorly understood. We show that ectopic expression of the related basic helix-loop-helix factor Hand2 phenocopies Twist1 loss of function in the limb and that the two factors have a gene dosage-dependent antagonistic interaction. Dimerization partner choice by Twist1 and Hand2 can be modulated by protein kinase A- and protein phosphatase 2A-regulated phosphorylation of conserved helix I residues. Notably, multiple Twist1 mutations associated with Saethre-Chotzen syndrome alter protein kinase A-mediated phosphorylation of Twist1, suggesting that misregulation of Twist1 dimerization through either stoichiometric or post-translational mechanisms underlies phenotypes of individuals with Saethre-Chotzen syndrome.

Acrocephalosyndactylia↗

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↗

A further mutation of the FGFR2 tyrosine kinase domain in mild Crouzon syndrome.

We report a family heterozygous for a newly identified mutation in the tyrosine kinase I domain of the FGFR2 gene (1576A > G, encoding the missense substitution Lys526Glu), associated with variable expressivity of Crouzon syndrome, including clinical nonpenetrance. Our observations expand both the clinical and molecular spectrum of this unusual subset of FGFR2 mutations.

Acrocephalosyndactylia↗

Saethre-Chotzen syndrome caused by TWIST 1 gene mutations: functional differentiation from Muenke coronal synostosis syndrome.

The Saethre-Chotzen syndrome (SCS) is an autosomal dominant craniosynostosis syndrome with uni- or bilateral coronal synostosis and mild limb deformities. It is caused by loss-of-function mutations of the TWIST 1 gene. In an attempt to delineate functional features separating SCS from Muenke's syndrome, we screened patients presenting with coronal suture synostosis for mutations in the TWIST 1 gene, and for the Pro250Arg mutation in FGFR3. Within a total of 124 independent pedigrees, 39 (71 patients) were identified to carry 25 different mutations of TWIST 1 including 14 novel mutations, to which six whole gene deletions were added. The 71 patients were compared with 42 subjects from 24 pedigrees carrying the Pro250Arg mutation in FGFR3 and 65 subjects from 61 pedigrees without a detectable mutation. Classical SCS associated with a TWIST 1 mutation could be separated phenotypically from the Muenke phenotype on the basis of the following features: low-set frontal hairline, gross ptosis of eyelids, subnormal ear length, dilated parietal foramina, interdigital webbing, and hallux valgus or broad great toe with bifid distal phalanx. Functional differences were even more important: intracranial hypertension as a consequence of early progressive multisutural fusion was a significant problem in SCS only, while mental delay and sensorineural hearing loss were associated with the Muenke's syndrome. Contrary to previous reports, SCS patients with complete loss of one TWIST allele showed normal mental development.

Acrocephalosyndactylia↗

Mutation screening in patients with syndromic craniosynostoses indicates that a limited number of recurrent FGFR2 mutations accounts for severe forms of Pfeiffer syndrome.

Crouzon Syndrome (CS), Pfeiffer syndrome (PS) and the phenotypically related Jackson-Weiss (JW) variant are three craniosynostotic conditions caused by heterozygous mutations in Fibroblast Growth Factor Receptor (FGFR) genes. Screening a large cohort of 84 patients with clinical features of CS, PS or JW by direct sequencing of genomic DNA, enabled FGFR1, 2 or 3 mutation detection in 79 cases. Mutations preferentially occurred in exons 8 and 10 of FGFR2 encoding the third Ig loop of the receptor. Among the 74 FGFR2 mutations that we identified, four were novel including three missense substitutions causing CS and a 2 bp deletion creating a premature stop codon and producing JW phenotype. Five FGFR2 mutations were found in one of the two tyrosine kinase subdomains and one in the Ig I loop. Interestingly, two FGFR2 mutations creating cysteine residues (W290C and Y340C) caused severe forms of PS while conversion of the same residues into another amino-acid (W290G/R, Y340H) resulted in Crouzon phenotype exclusively. Our data provide conclusive evidence that the mutational spectrum of FGFR2 mutations in CS and PS is wider than originally thought. Genotype-phenotype analyses based on our cohort and previous studies further indicate that in spite of some overlap, PS and CS are preferentially accounted for by two distinct sets of FGFR2 mutations. A limited number of recurrent amino-acid changes (W290C, Y340C, C342R and S351C) is commonly associated with the most severe Pfeiffer phenotypes of poor prognosis.

Acrocephalosyndactylia↗

Case report: orthodontic and dentofacial orthopedic considerations in Apert's syndrome.

Apert's syndrome is a developmental malformation characterized by: craniosynostosis, a cone-shaped calvarium, midface hypoplasia, pharyngeal attenuation, ocular manifestations, and syndactyly of the hands and feet. The prodromal characteristic for the typical craniofacial appearance is early craniosynostosis of the coronal suture, the cranial base, and an agenesis of the sagittal suture. These craniofacial characteristics predispose the patient to maxillary transverse and sagittal hypoplasia with concomitant dental crowding, a maxillary pseudocleft palate, and a skeletal and dental anterior open bite. This is a case report of an Apert's syndrome patient with a discussion of the orthodontic and dentofacial orthopedic considerations that influenced the treatment plan.

Acrocephalosyndactylia↗

Oral findings in Carpenter syndrome.

Acrocephalopolysyndactyly Type II (Carpenter Syndrome) is determined by autosomal recessive inheritance. Only some 40 cases have been described. Variable clinical signs have been described including prolonged retention of primary teeth and hypodontia. This paper describes the oral and dental findings in a family containing two affected brothers. The family pedigree is informative, as the mother has had children by three partners. The two affected individuals are full brothers. The first affected brother has delayed dental development, severe hypodontia and small tooth crown size. Mesio-distal and bucco-lingual dimensions were measured on the study models and compared with population data. The younger brother also has delayed dental development but only mild hypodontia. Their half sister has severe hypodontia but no signs of Carpenter Syndrome. This family study demonstrates two affected individuals with typical clinical features and a pedigree compatible with autosomal recessive inheritance. Small tooth crown size has been shown by standardized measurement and evidence advanced that hypodontia is not part of the syndrome but a coincidental finding which segregates independently. We have also shown that the marked delay in emergence of teeth is associated more with problems of tooth eruption, possibly related to the bony abnormalities, than to a generalized delay in dental development.

Acrocephalosyndactylia↗

Social adjustment of children with a severe craniofacial anomaly (Apert syndrome).

OBJECTIVE: Children with a severe craniofacial anomaly are at risk for emotional and behavioural problems. Do children with Apert syndrome present with a special psychological profile? METHOD: Parent reports (Child Behaviour Checklist) were obtained from 25 children with Apert syndrome. RESULTS: Fourteen children were characterized by clinically significant social problems, 10 by attentional problems, nine by social withdrawal. Total CBCL-scores were in the clinical range for eight children. CONCLUSION: Information on psychosocial state should be included in regular check-ups of children with a severe craniofacial anomaly in order to identify children who are in need of psychological interventions.

Acrocephalosyndactylia↗

Isotretinoin therapy for antibiotic-refractory acne in Apert's syndrome.

Apert's syndrome is a congenital disorder characterized by the premature fusion of the cranial sutures and early epiphyseal closure. Severe pustular acne is a common feature. We report a case that failed to respond to conventional antibiotic treatment but resolved following isotretinoin therapy. The patient's permanent tracheostomy proved a management challenge during isotretinoin treatment. The role of androgen-sensitivity is discussed in relation to the skin and bones.

Acne Vulgaris↗

Apert's syndrome: differential in vitro production of matrix macromolecules and its regulation by interleukins.

During embryonic development, variations in the composition of the extracellular matrix (ECM) macromolecules influence bone tissue differentiation. We present novel findings on the in vitro phenotypic expression of periosteal fibroblasts obtained from patients affected by Apert's syndrome, a rare craniofacial malformation, and the effects that interleukins (ILs) induce on the phenotype. Apert fibroblasts synthesized greater quantities of glycosaminoglycans (GAGs) and intracellular type I collagen, and also produced more type III collagen and fibronectin. The amount of hyaluronic acid (HA) secreted by Apert fibroblasts was much higher than that secreted by normal fibroblasts, but, as the absolute values of heparan sulphate (HS), chondroitin sulphate (CS) and dermatan sulphate (DS) also rose in Apert media, the HA-sulphated GAG ratio was similar in the media obtained from both populations. Both ILs triggered elevations of HA in normal cells, although relative percentage secretion remained unaltered, but significantly reduced HA secretion by Apert cells. IL-1 significantly increased CS in normal and Apert media, whereas IL-6 enhanced HS and DS in media of both populations. HA-sulphated GAG ratio decreased in Apert media after IL treatment. Both ILs boosted fibronectin production by Apert fibroblasts, whereas IL-1 increased type III but not type I collagen. Taken together, these data demonstrate that the synthesis and secretion of ECM macromolecules are markedly altered in Apert fibroblasts. The fact that treatment with ILs further modifies the Apert phenotype suggests that ILs may be implicated in the pathophysiology of the malformations during skull morphogenesis.

Acrocephalosyndactylia↗

Difficult tracheal intubation following midface distraction surgery.

A case of difficult intubation in a patient with Apert syndrome, who had recently undergone bilateral internal midface distraction, is described. The 14-year-old boy had no antecedent history of such difficulty, despite numerous previous anaesthetics. We suggest that trismus due to temporalis muscle fibrosis, and the altered relationships of the maxilla and mandible following midface advancement, were causal.

Acrocephalosyndactylia↗