No evidence of genetic heterogeneity in Crouzon craniofacial dysostosis

Crouzon syndrome in a fraternal twin: A case report and review of the literature

BACKGROUND

Crouzon syndrome (CS; OMIM 123500) is an autosomal dominant inherited craniofacial disorder caused by mutations in the fibroblast growth factor receptor 2 (FGFR2) gene. CS is characterized by craniofacial dysostosis, exophthalmos, and facial anomalies with hypoplastic maxilla and relative mandibular prognathism.

CASE SUMMARY

Our report involves a 6-year-old fraternal twin boy with many caries in the oral cavity who presented with characteristic features of CS based on clinical and radiographic examinations along with Sanger sequencing. The fraternal girl did not show any abnormalities indicating CS. Carious teeth and poor oral hygiene were managed promptly through administering appropriate behavior guidance, orthodontic treatment was planned, and preventive procedures were described.

CONCLUSION

CS could occur in a fraternal twin caused by a de novo mutation of the FGFR2 gene. Oral hygiene instruction, preventive programs on oral hygiene, orthodontic treatment, and maxillary osteotomy were required for treatment.

Classification of Subtypes of Crouzon Syndrome Based on the Type of Vault Suture Synostosis

BACKGROUND

Patients with Crouzon syndrome develop various types of anatomic deformities due to different forms of craniosynostosis, yet they have similar craniofacial characteristics. However, exact homology is not evident. Different pathology then may be best treated by different forms of surgical technique. Therefore, precise classification of Crouzon syndrome, based on individual patterns of cranial suture involvement is needed.

METHODS

Ninety-five computed tomography (CT) scans (Crouzon, n = 33; control, n = 62) were included in this study. All the CT scans are divided into 4 types based on premature closure of sutures: class I = coronal and lambdoidal synostosis; class II = sagittal synostosis; class III = pansynostosis; and class IV = "Others." The CT scan anatomy was measured by Materialise software.

RESULTS

The class III, pansynostosis, is the most prevalent (63.6%). The classes I, III, and IV of Crouzon have significantly shortened entire anteroposterior cranial base length, with the shortest base length in class III. The external cranial measurements in class I show primarily a decreased posterior facial skeleton, while the class III presented with holistic facial skeleton reduction. Class II has the least severe craniofacial malformations, while class III had the most severe.

CONCLUSION

The morphology of patients with Crouzon syndrome is not identical in both cranial base and facial characteristics, especially when they associated with different subtypes of cranial suture synostosis. The classification of Crouzon syndrome proposed in this study, summarizes the differences among each subgroup of craniosynostosis suture involvement, which, theoretically, may ultimately influence both the timing and type of surgical intervention.

FGFR2 mutation in a Chinese family with unusual Crouzon syndrome

AIM

To describe the clinical characteristics with genetic lesions in a Chinese family with Crouzon syndrome.

METHODS

All five patients from this family were included and received comprehensive ophthalmic and systemic examinations. Direct sequencing of the FGFR2 gene was employed for mutation identification. Crystal structure analysis was applied to analyze the structural changes associated with the substitution.

RESULTS

All patients presented typical Crouzon features, including short stature, craniosynostosis, mandibular prognathism, shallow orbits with proptosis, and exotropia. Intrafamilial phenotypic diversities were observed. Atrophic optic nerves were exclusively detected in the proband and her son. Cranial magnetic resonance imaging (MRI) implied a cystic lesion in her sellar and third ventricular regions. A missense mutation, FGFR2 p.Cys342Trp, was found as disease causative. This substitution would generate conformational changes in the extracellular Ig-III domain of the FGFR-2 protein, thus altering its physical and biological properties.

CONCLUSION

We describe the clinical presentations and genotypic lesions in a Chinese family with Crouzon syndrome. The intrafamilial phenotypic varieties in this family suggest that other genetic modifiers may also play a role in the pathogenesis of Crouzon syndrome.

Understanding craniosynostosis as a growth disorder

Craniosynostosis is a condition of complex etiology that always involves the premature fusion of one or multiple cranial sutures and includes various anomalies of the soft and hard tissues of the head. Steady progress in the field has resulted in identifying gene mutations that recurrently cause craniosynostosis. There are now scores of mutations on many genes causally related to craniosynostosis syndromes, though the genetic basis for the majority of nonsyndromic cases is unknown. Identification of these genetic mutations has allowed significant progress in understanding the intrinsic properties of cranial sutures, including mechanisms responsible for normal suture patency and for pathogenesis of premature suture closure. An understanding of morphogenesis of cranial vault sutures is critical to understanding the pathophysiology of craniosynostosis conditions, but the field is now poised to recognize the repeated changes in additional skeletal and soft tissues of the head that typically accompany premature suture closure. We review the research that has brought an understanding of premature suture closure within our reach. We then enumerate the less well-studied, but equally challenging, nonsutural phenotypes of craniosynostosis conditions that are well characterized in available mouse models. We consider craniosynostosis as a complex growth disorder of multiple tissues of the developing head, whose growth is also targeted by identified mutations in ways that are poorly understood. Knowledge gained from studies of humans and mouse models for these conditions underscores the diverse, associated developmental anomalies of the head that contribute to the complex phenotypes of craniosynostosis conditions presenting novel challenges for future research. WIREs Dev Biol 2016, 5:429-459. doi: 10.1002/wdev.227 For further resources related to this article, please visit the WIREs website.

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.

Novel phenotype of craniosynostosis and ocular anterior chamber dysgenesis with a fibroblast growth factor receptor 2 mutation

Fibroblast growth factor receptor 2 (FGFR2) mutations are associated with syndromic and non-syndromic craniosynostoses. More recently it has been recognized that FGFR2 may have a role in the development of the anterior chamber of the eye following the finding of a specific FGFR2 mutation (p.Ser351Cys, c.1231 C --> G) with anterior chamber dysgenesis. Affected patients had a severe craniofacial phenotype and clinical course. A child with a different FGFR2 mutation (p.Ala344Ala, c1032 G --> A heterozygote), premature fusion of the sagittal suture, and an Axenfeld-Rieger anomaly but otherwise normal clinical course is reported. The case provides further evidence that FGFR2 has a role in anterior chamber embryogenesis.

Crouzon Syndrome: Phenotypic Signs and Symptoms of the Postnatally Expressed Subtype

In a retrospective study, the characteristics of a group of patients (n = 9) with a postnatally expressed Crouzon syndrome were described. Although they do not always display the physical signs of craniosynostosis, such patients are highly at risk of developing symptoms secondary to multiple suture synostosis. By reviewing the hospital files, radiographs, and three-dimensional computed tomography scans of these patients, it was possible to describe the pattern of suture obliteration chronologically. Furthermore, certain phenotypic signs and symptoms such as skull shape and development of digital impressions, a bulge at the bregma, and intracranial hypertension were inventoried as well as patients' genotypes. Interestingly, ossification started at the lambdoid sutures in at least four patients and most likely in three additional ones. The coronal sutures were the last to ossify in at least three of the patients. Various skull shapes were encountered. Furthermore, all nine patients developed digital impressions, starting occipitally in eight of them. Seven patients developed a bulge at the bregma, and four of them exhibited intracranial hypertension. The genotype varied in our patients. To recognize patients with postnatal Crouzon syndrome as soon as possible, special attention must be paid to 1) occipital development of digital impressions and/or ossification of sutures, 2) development of a prominent bregma, 3) development of intracranial hypertension, and/or 4) progressive characteristic "crouzonoid" features. Such patients can be considered as representing a subtype of Crouzon syndrome. To prevent or treat intracranial hypertension and/or loss of vision, surgical intervention should be performed at the onset of progressive craniosynostosis between 1 and 2 years of age.

Clinical spectrum of fibroblast growth factor receptor mutations

During the last few years, it has been demonstrated that some syndromic craniosynostosis and short-limb dwarfism syndromes, a heterogeneous group comprising of 11 distinct clinical entities, are caused by mutations in one of three fibroblast growth factor receptor genes (FGFR1, FGFR2, and FGFR3). The present review list all mutations described to date in these three genes and the phenotypes associated with them. In addition, the tentative phenotype-genotype correlation is discussed, including the most suggested causative mechanisms for these conditions.

Differential effects of FGFR2 mutations on syndactyly and cleft palate in Apert syndrome

Apert syndrome is a distinctive human malformation characterized by craniosynostosis and severe syndactyly of the hands and feet. It is caused by specific missense substitutions involving adjacent amino acids (Ser252Trp or Pro253Arg) in the linker between the second and third extracellular immunoglobulin domains of fibroblast growth factor receptor 2 (FGFR2). We have developed a simple PCR assay for these mutations in genomic DNA, based on the creation of novel (SfiI) and (BstUI) restriction sites. Analysis of DNA from 70 unrelated patients with Apert syndrome showed that 45 had the Ser252Trp mutation and 25 had the Pro253Arg mutation. Phenotypic differences between these two groups of patients were investigated. Significant differences were found for severity of syndactyly and presence of cleft palate. The syndactyly was more severe with the Pro253Arg mutation, for both the hands and the feet. In contrast, cleft palate was significantly more common in the Ser252Trp patients. No convincing differences were found in the prevalence of other malformations associated with Apert syndrome. We conclude that, although the phenotype attributable to the two mutations is very similar, there are subtle differences. The opposite trends for severity of syndactyly and cleft palate in relation to the two mutations may relate to the varying patterns of temporal and tissue-specific expression of different fibroblast growth factors, the ligands for FGFR2.