Q289P Mutation in FGFR2 Gene Causes Saethre-Chotzen Syndrome: Some Considerations About Familial Heterogeneity

Genetic Heterogeneity, Craniofacial Surgical Burden, and Surgical Techniques in Patients With Saethre-Chotzen Syndrome

OBJECTIVE

While genotype correlates with phenotype in patients with many forms of syndromic craniosynostosis, the relationship between molecular diagnosis and craniofacial surgical history in patients with Saethre-Chotzen syndrome (SCS) is more variable. This manuscript characterizes that relationship and evaluates operative trends in these patients over the past 3 decades.

METHODS

Demographic information, molecular diagnosis, and craniofacial surgical history in patients born with SCS between 1989 and 2023 were compared with appropriate statistics, including t tests and analysis of variance.

RESULTS

Thirty-five patients with SCS were included, and there was no difference in total craniofacial procedures among those with TWIST1 substitutions (2.1 ± 1.6), duplications (3.0 ± 4.2), insertions (3.5 ± 0.7), or deletions (2.4 ± 1.9; P = 0.97). Cranial expansion rates were also similar across all genetic diagnoses (P>0.05), and surgical incidence was similar across patients with unicoronal, bicoronal, and multisuture involvement (P > 0.05). Those with an initial fronto-orbital advancement had a lower incidence of secondary cranial vault procedures compared with those with an initial posterior vault distraction osteogenesis (29% versus 71%, P < 0.05), though this did not control for phenotypic severity. On average, total cranial vault surgical burden (1.35 ± 0.67 versus 1.75 ± 0.46) and cranial expansion surgical burden (1.40 ± 0.68 versus 1.88 ± 0.64) between the fronto-orbital advancement-first and posterior vault distraction osteogenesis-first cohorts were similar (P = 0.11, P = 0.17, respectively).

CONCLUSION

While SCS is molecularly and phenotypically heterogeneous, genetic diagnosis does not appear associated with rates of craniofacial surgery. Additional prospective study of correlations between genotype, severity of craniofacial manifestations, and treatment algorithms is warranted; but, in the end, it may be that this highly variable form of syndromic craniosynostosis warrants tailored, expectant management.

The outcome of targeted NGS screening in patients with syndromic forms of sagittal and pansynostosis - IL11RA is an emerging core-gene for pansynostosis

Here, we have studied the prevalence and spectrum of genetic alterations in syndromic forms of sagittal and pansynostosis. Eighteen patients with sagittal synostosis (isolated or combined with other synostoses, except coronal) or pansynostosis were phenotypically assessed by retrospective analysis of medical records, three-dimensional computed tomography skull reconstructions, and registered photos. Patient DNAs were analyzed using a targeted next-generation sequencing (NGS) panel including 63 craniosynostosis (CS) related genes. Pathogenic and likely pathogenic variants were found in 72% of the cases, mainly affecting FGFR2, TWIST1, IL11RA, and SKI. Two patients that were negative at NGS screening - one with a supernumerary marker chromosome with duplication of 15q25.2q26.3 and one with a pathogenic PHEX variant - were identified using microarray and single gene analysis, respectively. The overall diagnostic rate in the cohort was thus 83%. We identified two novel likely pathogenic variants in FGFR2 (NM_022970.3: c.811_812delGGinsCC, p.Gly271Pro) and TWIST1 (NM_000474.3: c.476T  >  A, p.Leu159His), and a novel variant of unclear phenotypic significance in RUNX2 (NM_001024630.3: c.340G > A, p.Val114Ile) which could suggest a modulatory effect. Notably, we also identified three new patients with pansynostosis and a Crouzon-like phenotype with IL11RA mutation. Targeted NGS using a broad panel of CS-related genes is a simple and powerful tool for detecting pathogenic mutations in patients with syndromic forms of CS and multiple suture involvement, in particular pansynostosis. Our results provide additional evidence of an association between pansynostosis and IL11RA, an emerging core gene for autosomal recessive CS.

Fibroblast Growth Factor Receptor 2 (FGFR2) Mutation Related Syndromic Craniosynostosis

Craniosynostosis results from the premature fusion of cranial sutures, with an incidence of 1 in 2,100-2,500 live births. The majority of cases are non-syndromic and involve single suture fusion, whereas syndromic cases often involve complex multiple suture fusion. The fibroblast growth factor receptor 2 (FGFR2) gene is perhaps the most extensively studied gene that is mutated in various craniosynostotic syndromes including Crouzon, Apert, Pfeiffer, Antley-Bixler, Beare-Stevenson cutis gyrata, Jackson-Weiss, Bent Bone Dysplasia, and Seathre-Chotzen-like syndromes. The majority of these mutations are missense mutations that result in constitutive activation of the receptor and downstream molecular pathways. Treatment involves a multidisciplinary approach with ultimate surgical fixation of the cranial deformity to prevent further sequelae. Understanding the molecular mechanisms has allowed for the investigation of different therapeutic agents that can potentially be used to prevent the disorders. Further research efforts are need to better understand screening and effective methods of early intervention and prevention. Herein, the authors provide a comprehensive update on FGFR2-related syndromic craniosynostosis.

[Presentation of two cases of Crouzon syndrome: allelic cranio-stenotic conditions of FGFR genes]

INTRODUCTION

Craniosynostosis is an abnormal and premature fusion of any cranial suture. Twenty per cent of them involve any specific syndrome with Mendelian transmission; the other 80% are "non syndromic", although but 10-14% of them are genetically transmitted. Using the experience of two patients with Crouzon syndrome, a clinical and genetic review is performed.

PATIENTS AND METHODS

Patient 1: girl of 35 days of age with progressive macrocephaly, protrusion of fontanel, ocular proptosis, hypertelorism and divergent strabismus. Cranial RX with sagittal synostosis. Surgical operation was performed with 3 months and 8 months of age due to development of pansynostosis. Patient 2: boy of 3 years 8 months of age with headaches of migrainous type of one year onset. He had acanthosis nigricans. Cranial RX and cerebral CT with evident digital markings and fundus of eye with undefined papillary limits, but 18 month later oedematous papilla were evident and pansynostosis was detected, so surgery was performed.

RESULTS

We present a patient with classical Crouzon syndrome (patient 1) and another with acanthosis nigricans (patient 2), both diagnosed by the description of characteristic clinical features.

CONCLUSIONS

Ten craniosynostotic clinical forms are currently known as allelic variations of the FGFR genes, and as such have reviewed them. As in our two cases, in syndromic types is very important the accurate study of the phenotype to orientate the diagnosis, although the molecular study will confirm it in many patients and genetic counselling offered.

Exclusion of Class III malocclusion candidate loci in Brazilian families

The role played by genetic components in the etiology of the Class III phenotype, a class of dental malocclusion, is not yet understood. Regions that may be related to the development of Class III malocclusion have been suggested previously. The aim of this study was to search for genetic linkage with 6 microsatellite markers (D1S234, D4S3038, D6S1689, D7S503, D10S1483, and D19S566), near previously proposed candidate regions for Class III. We performed a two-point parametric linkage analysis for 42 affected individuals from 10 Brazilian families with a positive Class III malocclusion segregation. Analysis of our data indicated that there was no evidence for linkage of any of the 6 microsatellite markers to a Class III locus at = zero, with data supporting exclusion for 5 of the 6 markers evaluated. The present work reinforces that Class III is likely to demonstrate locus heterogeneity, and there is a dependency of the genetic background of the population in linkage studies.

Saethre-Chotzen syndrome: a case report

Saethre-Chotzen syndrome (acrocephalosyndactyly type III) is a craniosynostosis syndrome inherited in an autosomal dominant manner. Although similar to the other craniosynostosis syndromes in its clinical presentation, this syndrome is caused by a mutation in the TWIST1 gene. The TWIST1 gene product is a transcription factor containing a basic helix-loop-helix (bHLH) domain important in the development of the head and limbs. Clinical features of this syndrome include unilateral or bilateral coronal synostosis, ptosis, low-set ears, hearing loss, hypertelorism, maxillary hypoplasia, deviated nasal septum, broad great toes, clinodactyly, and syndactyly. We report a young girl with clinical features of Saethre-Chotzen syndrome who has a previously undescribed sequence variant in the TWIST1 gene, corresponding to p.R191M. The location of the altered amino acid in the Twist-box of TWIST1, the high conservation of this amino acid between different species, and the phenotype of the child all support a pathogenic role for this novel TWIST1 sequence alteration.

Q289P mutation in the FGFR2 gene: first report in a patient with type 1 Pfeiffer syndrome

When normal development and growth of the calvarial sutures is disrupted, craniosynostosis (premature calvarial suture fusion) may result. Classical craniosynostosis syndromes are autosomal dominant traits and include Apert, Pfeiffer, Crouzon, Jackson-Weiss, and Saethre-Chotzen syndromes. In these conditions, there is premature fusion of skull bones leading to an abnormal head shape, ocular hypertelorism with proptosis, and midface hypoplasia. It is known that mutations in the fibroblast growth factor receptors 1, 2, and 3 cause craniosynostosis. We report on a child with a clinically diagnosed Pfeiffer syndrome that shows the missense point mutation Q289P in exon 8 of the FGFR2 gene. This is a mutation not previously described in the Pfeiffer syndrome but reported in the Crouzon, Jackson-Weiss, and Saethre-Chotzen syndromes. In this paper, we propose the concept that these disorders may represent one genetic condition with phenotypic variability.