Analysis of the mutational spectrum of the FGFR2 gene in Pfeiffer syndrome

Perinatal imaging findings of a fetus with Pfeiffer syndrome and a heterozygous c.1019A>G, p.Tyr340Cys (Y340C) mutation in FGFR2 presenting a cloverleaf skull, craniosynostosis and short limbs on prenatal ultrasound mimicking thanatophoric dysplasia type II

OBJECTIVE

We present perinatal imaging findings of a fetus with Pfeiffer syndrome and a heterozygous c.1019A>G, p.Tyr340Cys (Y340C) mutation in FGFR2 presenting a cloverleaf skull, craniosynostosis and short limbs on prenatal ultrasound mimicking thanatophoric dysplasia type II (TD2).

CASE REPORT

A 37-year-old, gravida 2, para 1, woman underwent amniocentesis at 17 weeks of gestation because of advanced maternal age. Amniocentesis revealed a karyotype of 46,XY. However, craniofacial anomaly was found on prenatal ultrasound at 21 weeks of gestation, which showed a cloverleaf skull with severe craniosynostosis and relatively short straight long bones. Fetal magnetic resonance imaging (MRI) analysis at 22 weeks of gestation showed a cloverleaf skull, proptosis and relatively shallowing of the sylvian fissures. Prenatal ultrasound at 24 weeks of gestation showed a fetus with a cloverleaf skull with a biparietal diameter (BPD) of 6.16 cm (equivalent to 24 weeks), an abdominal circumference (AC) of 18.89 cm (equivalent to 24 weeks) and a femur length (FL) of 3.65 cm (equivalent to 21 weeks). A tentative diagnosis of TD2 was made. The pregnancy was subsequently terminated, and a 928-g malformed fetus was delivered with severe craniosynostosis, proptosis, midface retrusion, a cloverleaf skull, broad thumbs and broad big toes. The broad thumbs were medially deviated. Whole body X-ray showed a cloverleaf skull and straight long bones. However, molecular analysis of FGFR3 on the fetus revealed no mutation in the target regions. Subsequent whole exome sequencing (WES) on the DNA extracted from umbilical cord revealed a heterozygous c.1019A>G, p.Tyr340Cys (Y340C) mutation in the FGFR2 gene.

CONCLUSION

Fetuses with a Y340C mutation in FGFR2 may present a cloverleaf skull on prenatal ultrasound, and WES is useful for a rapid differential diagnosis of Pfeiffer syndrome from TD2 under such a circumstance.

Benchmarking splice variant prediction algorithms using massively parallel splicing assays

BACKGROUND

Variants that disrupt mRNA splicing account for a sizable fraction of the pathogenic burden in many genetic disorders, but identifying splice-disruptive variants (SDVs) beyond the essential splice site dinucleotides remains difficult. Computational predictors are often discordant, compounding the challenge of variant interpretation. Because they are primarily validated using clinical variant sets heavily biased to known canonical splice site mutations, it remains unclear how well their performance generalizes.

RESULTS

We benchmark eight widely used splicing effect prediction algorithms, leveraging massively parallel splicing assays (MPSAs) as a source of experimentally determined ground-truth. MPSAs simultaneously assay many variants to nominate candidate SDVs. We compare experimentally measured splicing outcomes with bioinformatic predictions for 3,616 variants in five genes. Algorithms' concordance with MPSA measurements, and with each other, is lower for exonic than intronic variants, underscoring the difficulty of identifying missense or synonymous SDVs. Deep learning-based predictors trained on gene model annotations achieve the best overall performance at distinguishing disruptive and neutral variants, and controlling for overall call rate genome-wide, SpliceAI and Pangolin have superior sensitivity. Finally, our results highlight two practical considerations when scoring variants genome-wide: finding an optimal score cutoff, and the substantial variability introduced by differences in gene model annotation, and we suggest strategies for optimal splice effect prediction in the face of these issues.

CONCLUSION

SpliceAI and Pangolin show the best overall performance among predictors tested, however, improvements in splice effect prediction are still needed especially within exons.

Oncogenic activation revealed by FGFR2 genetic alterations in intrahepatic cholangiocarcinomas

BACKGROUND

Except for gene fusions, FGFR2 genetic alterations in intrahepatic cholangiocarcinomas (ICCs) have received limited attention, leaving patients harboring activating FGFR2 gene mutations with inadequate access to targeted therapies.

EXPERIMENTAL DESIGN

We sought to survey FGFR2 genetic alterations in ICC and pan-cancers using fluorescence in situ hybridization and next-generation sequencing. We conducted an analysis of the clinical and pathological features of ICCs with different FGFR2 alterations, compared FGFR2 lesion spectrum through public databases and multicenter data, and performed cellular experiments to investigate the oncogenic potential of different FGFR2 mutants.

RESULTS

FGFR2 gene fusions were identified in 30 out of 474 ICC samples, while five FGFR2 genetic alterations aside from fusion were present in 290 ICCs. The tumors containing FGFR2 translocations exhibited unique features, which we designated as the "FGFR2 fusion subtypes of ICC". Molecular analysis revealed that FGFR2 fusions were not mutually exclusive with other oncogenic driver genes/mutations, whereas FGFR2 in-frame deletions and site mutations often co-occurred with TP53 mutations. Multicenter and pan-cancer studies demonstrated that FGFR2 in-frame deletions were more prevalent in ICCs (0.62%) than in other cancers, and were not limited to the extracellular domain. We selected representative FGFR2 genetic alterations, including in-frame deletions, point mutations, and frameshift mutations, to analyze their oncogenic activity and responsiveness to targeted drugs. Cellular experiments revealed that different FGFR2 genetic alterations promoted ICC tumor growth, invasion, and metastasis but responded differently to FGFR-selective small molecule kinase inhibitors (SMKIs).

CONCLUSIONS

FGFR2 oncogenic alterations have different clinicopathological features and respond differently to SMKIs.

FGF signaling in cranial suture development and related diseases

Suture mesenchymal stem cells (SMSCs) are a heterogeneous stem cell population with the ability to self-renew and differentiate into multiple cell lineages. The cranial suture provides a niche for SMSCs to maintain suture patency, allowing for cranial bone repair and regeneration. In addition, the cranial suture functions as an intramembranous bone growth site during craniofacial bone development. Defects in suture development have been implicated in various congenital diseases, such as sutural agenesis and craniosynostosis. However, it remains largely unknown how intricate signaling pathways orchestrate suture and SMSC function in craniofacial bone development, homeostasis, repair and diseases. Studies in patients with syndromic craniosynostosis identified fibroblast growth factor (FGF) signaling as an important signaling pathway that regulates cranial vault development. A series of in vitro and in vivo studies have since revealed the critical roles of FGF signaling in SMSCs, cranial suture and cranial skeleton development, and the pathogenesis of related diseases. Here, we summarize the characteristics of cranial sutures and SMSCs, and the important functions of the FGF signaling pathway in SMSC and cranial suture development as well as diseases caused by suture dysfunction. We also discuss emerging current and future studies of signaling regulation in SMSCs.

Benchmarking splice variant prediction algorithms using massively parallel splicing assays

Background

Variants that disrupt mRNA splicing account for a sizable fraction of the pathogenic burden in many genetic disorders, but identifying splice-disruptive variants (SDVs) beyond the essential splice site dinucleotides remains difficult. Computational predictors are often discordant, compounding the challenge of variant interpretation. Because they are primarily validated using clinical variant sets heavily biased to known canonical splice site mutations, it remains unclear how well their performance generalizes.

Results

We benchmarked eight widely used splicing effect prediction algorithms, leveraging massively parallel splicing assays (MPSAs) as a source of experimentally determined ground-truth. MPSAs simultaneously assay many variants to nominate candidate SDVs. We compared experimentally measured splicing outcomes with bioinformatic predictions for 3,616 variants in five genes. Algorithms' concordance with MPSA measurements, and with each other, was lower for exonic than intronic variants, underscoring the difficulty of identifying missense or synonymous SDVs. Deep learning-based predictors trained on gene model annotations achieved the best overall performance at distinguishing disruptive and neutral variants. Controlling for overall call rate genome-wide, SpliceAI and Pangolin also showed superior overall sensitivity for identifying SDVs. Finally, our results highlight two practical considerations when scoring variants genome-wide: finding an optimal score cutoff, and the substantial variability introduced by differences in gene model annotation, and we suggest strategies for optimal splice effect prediction in the face of these issues.

Conclusion

SpliceAI and Pangolin showed the best overall performance among predictors tested, however, improvements in splice effect prediction are still needed especially within exons.

Clinical and Genetic Studies of the First Monozygotic Twins with Pfeiffer Syndrome

Objective: To report the clinical and radiographic findings and molecular etiology of the first monozygotic twins affected with Pfeiffer syndrome. Methods: Clinical and radiographic examination and whole exome sequencing were performed on two monozygotic twins with Pfeiffer syndrome. Results: An acceptor splice site mutation in FGFR2 (c.940-2A>G) was detected in both twins. The father and both twins shared the same haplotype, indicating that the mutant allele was from their father’s chromosome who suffered severe upper airway obstruction and subsequent obstructive sleep apnea. Hypertrophy of nasal turbinates appears to be a newly recognized finding of Pfeiffer syndrome. Increased intracranial pressure in both twins were corrected early by fronto-orbital advancement with skull expansion and open osteotomy, in order to prevent the more severe consequences of increased intracranial pressure, including hydrocephalus, the bulging of the anterior fontanelle, and the diastasis of suture. Conclusions: Both twins carried a FGFR2 mutation and were discordant for lambdoid synostosis. Midface hypoplasia, narrow nasal cavities, and hypertrophic nasal turbinates resulted in severe upper airway obstruction and subsequent obstructive sleep apnea in both twins. Hypertrophy of the nasal turbinates appears to be a newly recognized finding of Pfeiffer syndrome. Fronto-orbital advancement with skull expansion and open osteotomy was performed to treat increased intracranial pressure in both twins. This is the first report of monozygotic twins with Pfeiffer syndrome.

De Novo Heterozygous Mutation in FGFR2 Causing Type II Pfeiffer Syndrome

Pfeiffer syndrome (PS) is an autosomal dominant disorder with three subtypes stemming from heterozygous mutations in the fibroblast growth factors FGFR1 and FGFR2. The subtypes overlap with heterogeneous clinical manifestations and variable prognosis dependent on neurological and respiratory compromise that impact short- and long-term outcomes and survival. We present a male, term infant with type II PS that was diagnostically suspected antenatally based on three-dimensional ultrasonographic findings that were confirmed postnatally by craniofacial tomography and magnetic resonance imaging. A new generation sequencing panel identified a unique de novo FGFR2, c.335 A > G p. Tyr112Cys variant, the first of its kind, and features that closely aligned with subtype II PS. Initial molecular results categorized the mutation as nonpathogenic, but it was later reclassified as pathogenic. Antenatal, multidisciplinary parental counseling about the tentative diagnosis and prognosis facilitated postnatal decisions that culminated in an informed choice for palliative care and early demise.

Differential diagnosis of syndromic craniosynostosis: a case series

Purpose

Syndromic craniosynostosis is a rare genetic disease caused by premature fusion of one or multiple cranial sutures combined with malformations of other organs. The aim of this publication is to investigate sonographic signs of different syndromic craniosynostoses and associated malformations to facilitate a precise and early diagnosis.

Methods

We identified in the period of 2000–2019 thirteen cases with a prenatal suspected diagnosis of syndromic craniosynostosis at our department. We analyzed the ultrasound findings, MRI scans, genetic results as well as the mode of delivery, and postnatal procedures.

Results

Eight children were diagnosed with Apert Syndrome, two with Saethre Chotzen syndrome, one with Crouzon syndrome, and one with Greig cephalopolysyndactyly syndrome. One child had a mutation p.(Pro253Leu) in the FGFR2 gene. We identified characteristic changes of the head shape as well as typical associated malformations.

Conclusion

Second trimester diagnosis of syndromic craniosynostosis is feasible based on the identified sonographic signs. In case of a suspected diagnosis a genetic, neonatal as well as surgical counseling is recommended. We also recommend to offer a fetal MRI. The delivery should be planned in a perinatal center.

FGFR2 Extracellular Domain In-Frame Deletions are Therapeutically Targetable Genomic Alterations that Function as Oncogenic Drivers in Cholangiocarcinoma

We conducted next generation DNA sequencing on 335 biliary tract cancers and characterized the genomic landscape by anatomic site within the biliary tree. In addition to frequent FGFR2 fusions among patients with intrahepatic cholangiocarcinoma (IHCC), we identified FGFR2 extracellular domain in-frame deletions (EIDs) in 5 of 178 (2.8%) patients with IHCC, including two patients with FGFR2 p.H167_N173del. Expression of this FGFR2 EID in NIH3T3 cells resulted in constitutive FGFR2 activation, oncogenic transformation, and sensitivity to FGFR inhibitors. Three patients with FGFR2 EIDs were treated with Debio 1347, an oral FGFR-1/2/3 inhibitor, and all showed partial responses. One patient developed an acquired L618F FGFR2 kinase domain mutation at disease progression and experienced a further partial response for 17 months to an irreversible FGFR2 inhibitor, futibatinib. Together, these findings reveal FGFR2 EIDs as an alternative mechanism of FGFR2 activation in IHCC that predict sensitivity to FGFR inhibitors in the clinic.

Limb reduction in squamate reptiles correlates with the reduction of the chondrocranium: A case study on serpentiform anguids

BACKGROUND

In vertebrates, the skull evolves from a complex network of dermal bones and cartilage-the latter forming the pharyngeal apparatus and the chondrocranium. Squamates are particularly important in this regard as they maintain at least part of the chondrocranium throughout their whole ontogeny until adulthood. Anguid lizards represent a unique group of squamates, which contains limbed and limbless forms and show conspicuous variation of the adult skull.

RESULTS

Based on several emboadryonic stages of the limbless lizards Pseudopus apodus and Anguis fragilis, and by comparing with other squamates, we identified and interpreted major differences in chondrocranial anatomy. Among others, the most important differences are in the orbitotemporal region. P. apodus shows a strikingly similar development of this region to other squamates. Unexpectedly, however, A. fragilis differs considerably in the composition of the orbitotemporal region. In addition, A. fragilis retains a paedomorphic state of the nasal region.

CONCLUSIONS

Taxonomic comparisons indicate that even closely related species with reduced limbs show significant differences in chondrocranial anatomy. The Pearson correlation coefficient suggests strong correlation between chondrocranial reduction and limb reduction. We pose the hypothesis that limb reduction could be associated with the reduction in chondrocrania by means of genetic mechanisms.

Prenatal Diagnosis of Pfeiffer Syndrome Patient with FGFR2 C.940-1G>C Variant: A Case Report

Background

Pfeiffer syndrome (PS) is an autosomal dominant disorder caused by mutations in fibroblast growth factor receptor FGFR1 and FGFR2 genes, occurring in approximately 1:100,000 live births. PS has a wide range of clinical expression and severity, so early prenatal diagnosis is difficult and genetic counseling is desirable. We describe a PS newborn with her ultrasound and molecular studies.

Case Report

We describe a female term newborn with cloverleaf-shaped skull, facial hypoplasia, low ears, exophthalmos and wide, broad and deviated thumbs and hallux. The patient was diagnosed by ultrasound at 29 WGA and referred to a tertiary care hospital for her follow-up. Molecular test revealed a heterozygous pathogenic variant in intron 8 of the FGFR2 gene (FGFR2: c.940-1G>C). It was a de-novo mutation. At 17 days of life, craniosynostosis correction and a Lefort-III frontomaxillary advancement were performed.

Conclusion

Pfeiffer syndrome is a devastating genetic disorder. Prenatal diagnosis according PS morphological features in prenatal ultrasound allows timely genetic counseling, early referral to third-level centers, and close follow-up in the prenatal and postnatal stages.

GnRH Deficient Patients With Congenital Hypogonadotropic Hypogonadism: Novel Genetic Findings in ANOS1, RNF216, WDR11, FGFR1, CHD7, and POLR3A Genes in a Case Series and Review of the Literature

Background: Congenital hypogonadotropic hypogonadism (CHH) is a rare genetic disease caused by Gonadotropin-Releasing Hormone (GnRH) deficiency. So far a limited number of variants in several genes have been associated with the pathogenesis of the disease. In this original research and review manuscript the retrospective analysis of known variants in ANOS1 (KAL1), RNF216, WDR11, FGFR1, CHD7, and POLR3A genes is described, along with novel variants identified in patients with CHH by the present study. Methods: Seven GnRH deficient unrelated Cypriot patients underwent whole exome sequencing (WES) by Next Generation Sequencing (NGS). The identified novel variants were initially examined by in silico computational algorithms and structural analysis of their predicted pathogenicity at the protein level was confirmed. Results: In four non-related GnRH males, a novel X-linked pathogenic variant in ANOS1 gene, two novel autosomal dominant (AD) probably pathogenic variants in WDR11 and FGFR1 genes and one rare AD probably pathogenic variant in CHD7 gene were identified. A rare autosomal recessive (AR) variant in the SRA1 gene was identified in homozygosity in a female patient, whilst two other male patients were also, respectively, found to carry novel or previously reported rare pathogenic variants in more than one genes; FGFR1/POLR3A and SRA1/RNF216. Conclusion: This report embraces the description of novel and previously reported rare pathogenic variants in a series of genes known to be implicated in the biological development of CHH. Notably, patients with CHH can harbor pathogenic rare variants in more than one gene which raises the hypothesis of locus-locus interactions providing evidence for digenic inheritance. The identification of such aberrations by NGS can be very informative for the management and future planning of these patients.

Pfeiffer type 2 syndrome: review with updates on its genetics and molecular biology

INTRODUCTION

Pfeiffer syndrome is a rare autosomal dominant inherited disorder associated with craniosynostosis, midfacial hypoplasia, and broad thumbs and toes. The syndrome has been divided into three clinical subtypes based on clinical findings.

METHODS

This review will specifically examine the most severe type, Pfeiffer syndrome type 2, focusing on its genetics and molecular biology.

CONCLUSION

This subtype of the syndrome is caused by de novo sporadic mutations, the majority of which occur in the fibroblast growth factor receptor type 1 and 2 (FGFR1/2) genes. There is not one specific mutation, however. This disorder is genetically heterogeneous and may have varying phenotypic expressions that in various cases have overlapped with other similar craniosynostoses. A specific missense mutation of FGFR2 causing both Pfeiffer and Crouzon syndromes has been identified, with findings suggesting that gene expression may be affected by polymorphism within the same gene. Compared to other craniosynostosis-related disorders, Pfeiffer syndrome is the most extreme phenotype, as the underlying mutations cause wider effects on the secondary and tertiary protein structures and exhibit harsher clinical findings.

Pfeiffer type 2 syndrome: review with updates on its genetics and molecular biology

INTRODUCTION

Pfeiffer syndrome is a rare autosomal dominant inherited disorder associated with craniosynostosis, midfacial hypoplasia, and broad thumbs and toes. The syndrome has been divided into three clinical subtypes based on clinical findings.

METHODS

This review will specifically examine the most severe type, Pfeiffer syndrome type 2, focusing on its genetics and molecular biology.

CONCLUSION

This subtype of the syndrome is caused by de novo sporadic mutations, the majority of which occur in the fibroblast growth factor receptor type 1 and 2 (FGFR1/2) genes. There is not one specific mutation, however. This disorder is genetically heterogeneous and may have varying phenotypic expressions that in various cases have overlapped with other similar craniosynostoses. A specific missense mutation of FGFR2 causing both Pfeiffer and Crouzon syndromes has been identified, with findings suggesting that gene expression may be affected by polymorphism within the same gene. Compared to other craniosynostosis-related disorders, Pfeiffer syndrome is the most extreme phenotype, as the underlying mutations cause wider effects on the secondary and tertiary protein structures and exhibit harsher clinical findings.

Atypical Skin Manifestations in FGFR2-Related Craniosynostosis Syndromes Broaden the Phenotypic Spectrum

Crouzon syndrome (CS) and Beare-Stevenson syndrome (BSS) are craniosynostosis syndromes caused by mutations in the fibroblast growth factor 2 (FGFR2) gene. CS is more common (1 in 60,000 live births) than BSS, where fewer than 20 individuals have been reported. The cardinal features of BSS are craniosynostosis, cutis gyrata, acanthosis nigricans, skin furrows, skin tags, anogenital anomalies, and a prominent umbilical stump. Previously described individuals with BSS have typically had mutations in exon 11 of FGFR2. Here, we present 2 patients with CS who have significant skin manifestations and some phenotypic overlap with BSS. De novo mutations in exon 8 of FGFR2 were identified in both; one is a mutation (c.799T>C; p.Ser267Pro) previously identified in individuals with CS and the other a novel in-frame deletion (c.820_824delinsTT; p.Val274_Glu275delinsLeu). No mutations in exon 11 of FGFR2, where previously reported BSS mutations have been located, were identified. This case expands the phenotypic spectrum of CS and highlights the overlap between conditions caused by mutations in FGFR2.

Genetic Analysis of Syndromic and Nonsyndromic Patients With Craniosynostosis Identifies Novel Mutations in the TWIST1 and EFNB1 Genes

INTRODUCTION

Craniosynostosis, the premature fusion of cranial sutures, is usually divided into 2 major categories: syndromic and nonsyndromic. Mutations in the FGFR1, FGFR2, FGFR3, TWIST1, and EFNB1 genes cause the common craniosynostosis syndromes Muenke, Crouzon and Crouzon with acanthosis nigricans, Apert, Pfeiffer, Saethre-Chotzen, and Craniofrontonasal. Overlapping features among craniosynostosis syndromes, phenotypic heterogeneity even within the same syndrome, especially in the case of Muenke syndrome, and inadequate clinical evaluation can lead to misdiagnosis, which molecular testing can help clarify.

OBJECTIVE

The aim of this study is to investigate the underlying genetic cause in 46 patients with syndromic or nonsyndromic craniosynostosis by direct sequencing and/or microdeletion/microduplication analysis of the FGFR1-3, TWIST1, and EFNB1 genes.

RESULTS

Genetic analysis identified 3 novel mutations, c.413T>C - p.(Leu138Pro) [p.(L138P)] in TWIST1, the previously reported c.373G>A - p.(Glu125Lys) [p.(E125K)], and c.717dupA - p.(Leu240IlefsTer79) [p.(L240fs)] mutation in EFNB1 gene as well as 6 previously known mutations and a heterozygous TWIST1 gene deletion. The 2 novel mutations within EFNB1 gene arose de novo, but the novel mutation p.(L138P) within TWIST1 gene was inherited from the patient's father, who was found to be mosaic for the mutation. To our knowledge, this is the first case of mosaicism described for TWIST1 gene.

CONCLUSIONS

The contribution of molecular genetic analysis to the diagnosis of patients with syndromic craniosynostosis was useful because some were originally misdiagnosed. Conversely, thorough clinical evaluation can guide molecular testing and result in a correct diagnosis.

Genetic Overview of Syndactyly and Polydactyly

Syndactyly and polydactyly-respectively characterized by fused and supernumerary digits-are among the most common congenital limb malformations, with syndactyly presenting at an estimated incidence of 1 in 2,000-3,000 live births and polydactyly at a frequency of 1 in approximately 700-1,000 live births. Despite their relatively regular manifestation in the clinic, the etiologies of syndactyly and polydactyly remain poorly understood because of their phenotypic and genetic diversity. Further, even though concrete knowledge of genotypic links has been established for some variants of syndactyly and polydactyly, there appears to be no single comprehensive published summary of all syndromic and nonsyndromic syndactyly and polydactyly presentations, and there is decidedly no resource that maps all syndromic and nonsyndromic syndactylies and polydactylies to their genetic bases. This gap in the literature problematizes comprehensive carrier screening and prenatal diagnosis and complicates novel diagnostic attempts. This review thus attempts to collect all that is known about the genetic bases of syndromic and nonsyndromic syndactylies and polydactylies, as well as to highlight the dactyly manifestations for which no genetic bases are as yet known. Then, having established a summation of existing and missing knowledge, this work briefly outlines the diagnostic techniques that a genetics-reinforced understanding of syndactyly and polydactyly could inform.

Mutation analysis of FGFR1-3 in 11 Japanese patients with syndromic craniosynostoses

Syndromic craniosynostoses usually occur as single gene disorders. In this study, we analyzed FGFR1-3 genes in four patients with Crouzon syndrome (CS), four patients with Pfeiffer syndrome type 2 (PS-2), one patient with Jackson-Weiss syndrome (JWS), and two patients (sisters) with Muenke syndrome (MS). FGFR2 and FGFR3 mutations were identified in 10 of the 11 patients. Notably, we found a novel FGFR2 p.Asn549Thr mutation in a patient with CS, and a novel FGFR2 p.Ser347Cys mutation in a patient with JWS (thus, this patient was turned out to have an FGFR2-related PS-variant). We also identified an FGFR2 p.Ser252Leu mutation in a phenotypically normal father of a daughter with CS, and an FGFR3 p.Pro250Arg mutation in a mildly macrocephalic father of sisters with MS. These findings, together with previous data, imply that the same FGFR2 mutations can be associated with a wide range of phenotypes including clinically different forms of syndromic craniosynostosis and apparently normal phenotype, depending on other (epi)genetic and environmental factors. Thus, genetic studies are recommended not only for obviously affected individuals but also for family members with apparently normal phenotype or non-specific subtle abnormal phenotype, to allow for pertinent genetic counseling. © 2016 Wiley Periodicals, Inc.

FGFR-associated craniosynostosis syndromes and gastrointestinal defects

Craniosynostosis is a relatively common birth defect characterized by the premature fusion of one or more cranial sutures. Examples of craniosynostosis syndromes include Crouzon (CS), Pfeiffer (PS), and Apert (AS) syndrome, with clinical characteristics such as midface hypoplasia, hypertelorism, and in some cases, limb defects. Mutations in Fibroblast Growth Factor Receptor-2 comprise the majority of known mutations in syndromic forms of craniosynostosis. A number of clinical reports of FGFR-associated craniosynostosis patients and mouse mutants have been linked to gastrointestinal tract (GIT) disorders, leading to the hypothesis of a direct link between FGFR-associated craniosynostosis syndromes and GIT malformations. We conducted an investigation to determine GIT symptoms in a sample of FGFR-associated craniosynostosis syndrome patients and a mouse model of CS containing a mutation (W290R) in Fgfr2. We found that, compared to the general population, the incidence of intestinal/bowel malrotation (IM) was present at a higher level in our sample population of patients with FGFR-associated craniosynostosis syndromes. We also showed that the mouse model of CS had an increased incidence of cecal displacement, suggestive of IM. These findings suggest a direct relationship between FGFR-related craniosynostosis syndromes and GIT malformations. Our study may shed further light on the potential widespread impact FGFR mutations on different developmental systems. Based on reports of GIT malformations in children with craniosynostosis syndromes and substantiation with our animal model, GIT malformations should be considered in any child with an FGFR2-associated craniosynostosis syndrome. © 2016 Wiley Periodicals, Inc.

Fibroblast growth factor receptor signaling in hereditary and neoplastic disease: biologic and clinical implications

Fibroblast growth factors (FGFs) and their receptors (FGFRs) are transmembrane growth factor receptors with wide tissue distribution. FGF/FGFR signaling is involved in neoplastic behavior and also development, differentiation, growth, and survival. FGFR germline mutations (activating) can cause skeletal disorders, primarily dwarfism (generally mutations in FGFR3), and craniofacial malformation syndromes (usually mutations in FGFR1 and FGFR2); intriguingly, some of these activating FGFR mutations are also seen in human cancers. FGF/FGFR aberrations reported in cancers are mainly thought to be gain-of-function changes, and several cancers have high frequencies of FGFR alterations, including breast, bladder, or squamous cell carcinomas (lung and head and neck). FGF ligand aberrations (predominantly gene amplifications) are also frequently seen in cancers, in contrast to hereditary syndromes. There are several pharmacologic agents that have been or are being developed for inhibition of FGFR/FGF signaling. These include both highly selective inhibitors as well as multi-kinase inhibitors. Of note, only four agents (ponatinib, pazopanib, regorafenib, and recently lenvatinib) are FDA-approved for use in cancer, although the approval was not based on their activity against FGFR. Perturbations in the FGFR/FGF signaling are present in both inherited and malignant diseases. The development of potent inhibitors targeting FGF/FGFR may provide new tools against disorders caused by FGF/FGFR alterations.

Fibroblast growth factor (FGF) signaling in development and skeletal diseases

Fibroblast growth factors (FGF) and their receptors serve many functions in both the developing and adult organism. Humans contain 18 FGF ligands and four FGF receptors (FGFR). FGF ligands are polypeptide growth factors that regulate several developmental processes including cellular proliferation, differentiation, and migration, morphogenesis, and patterning. FGF-FGFR signaling is also critical to the developing axial and craniofacial skeleton. In particular, the signaling cascade has been implicated in intramembranous ossification of cranial bones as well as cranial suture homeostasis. In the adult, FGFs and FGFRs are crucial for tissue repair. FGF signaling generally follows one of three transduction pathways: RAS/MAP kinase, PI3/AKT, or PLCγ. Each pathway likely regulates specific cellular behaviors. Inappropriate expression of FGF and improper activation of FGFRs are associated with various pathologic conditions, unregulated cell growth, and tumorigenesis. Additionally, aberrant signaling has been implicated in many skeletal abnormalities including achondroplasia and craniosynostosis. The biology and mechanisms of the FGF family have been the subject of significant research over the past 30 years. Recently, work has focused on the therapeutic targeting and potential of FGF ligands and their associated receptors. The majority of FGF-related therapy is aimed at age-related disorders. Increased understanding of FGF signaling and biology may reveal additional therapeutic roles, both in utero and postnatally. This review discusses the role of FGF signaling in general physiologic and pathologic embryogenesis and further explores it within the context of skeletal development.

Apparently synonymous substitutions in FGFR2 affect splicing and result in mild Crouzon syndrome

Background

Mutations of fibroblast growth factor receptor 2 (FGFR2) account for a higher proportion of genetic cases of craniosynostosis than any other gene, and are associated with a wide spectrum of severity of clinical problems. Many of these mutations are highly recurrent and their associated features well documented. Crouzon syndrome is typically caused by heterozygous missense mutations in the third immunoglobulin domain of FGFR2.

Case presentation

Here we describe two families, each segregating a different, previously unreported FGFR2 mutation of the same nucleotide, c.1083A>G and c.1083A>T, both of which encode an apparently synonymous change at the Pro361 codon. We provide experimental evidence that these mutations affect normal FGFR2 splicing and document the clinical consequences, which include a mild Crouzon syndrome phenotype and reduced penetrance of craniosynostosis.

Conclusions

These observations add to a growing list of FGFR2 mutations that affect splicing and provide important clinical information for genetic counselling of families affected by these specific mutations.

Upper extremity anomalies in Pfeiffer syndrome and mutational correlations

BACKGROUND

Pfeiffer syndrome is characterized by craniosynostosis and a variety of associated upper and lower extremity anomalies. The authors reviewed presentation and treatment of upper extremity anomalies in a series of genotyped patients with Pfeiffer syndrome.

METHODS

Medical records of patients with Pfeiffer syndrome seen at the authors' institution over a 16-year period were reviewed. Data on clinical presentation, genetic testing, and treatment were collected. The upper extremity anomalies were documented using plain radiographs and physical examinations by a multidisciplinary craniofacial team.

RESULTS

Of 15 patients identified as having FGFR1- or FGFR2-confirmed Pfeiffer syndrome, 12 (80 percent) presented with upper extremity anomalies, most commonly broad thumbs [n = 10 (83 percent)], radial clinodactyly (thumbs) [n = 7 (58 percent)], and symphalangism [n = 7 each (58 percent)]. All patients with upper extremity anomalies had lower extremity anomalies. Six of the 12 patients (50 percent) with upper extremity findings underwent surgical correction. FGFR1 or FGFR2 genotype did not correlate with upper extremity phenotype.

CONCLUSIONS

Although broad thumbs are common, patients with Pfeiffer syndrome often present with other upper extremity anomalies that may not require surgical intervention. Genetic and allelic heterogeneity may explain phenotypic variability in these upper extremity anomalies. Characterization of these limb differences should be made by pediatric hand surgeons as part of a craniofacial team. Treatment decisions should be individualized and dictated by the type and severity of clinical presentation.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Risk, IV.

Clinicogenetic study of Turkish patients with syndromic craniosynostosis and literature review

BACKGROUND

Fibroblast growth factor receptor 2 mutations have been associated with the craniosynostotic conditions of Apert, Crouzon, Pfeiffer, Saethre-Chotzen, Jackson-Weiss, Beare-Stevenson cutis gyrata, and Antley-Bixler syndromes in various ethnic groups.

METHODS

Thirty-three unrelated Turkish patients (12 with Apert syndrome, 14 with Crouzon syndrome, six with Pfeiffer syndrome, and one with Saethre-Chotzen syndrome) and 67 nonsyndromic craniosynostosis patients were screened for mutations in exons IIIa and IIIc of the FGFR2 gene by denaturing high-performance liquid chromatography and confirmed by direct sequencing.

RESULTS

We detected several pathogenic mutations in 11/33 (33%) patients with Apert syndrome (four with p.Pro253Arg; seven with p.Ser252Trp) and 8/33 (24%) patients with Crouzon syndrome (three with p.Trp290Arg, one with p.Cys342Tyr, p.Cys278Phe, p.Gln289Pro, and a novel p.Tyr340Asn mutation) and five (15%) with Pfeiffer syndrome (p.Cys342Arg, p.Pro253Arg, p.Trp290Arg, and p.Ser351Cys). No FGFR2 gene mutation was detected in any of the patients with Saethre-Chotzen syndrome and nonsyndromic craniosynostosis.

CONCLUSIONS

Our results indicate that the majority of Turkish patients with syndromic craniosynostosis have detectable genetic changes with an overall frequency of 72.7%. Because this is the first molecular genetic report from a Turkish cohort, the identified spectrum profile of FGFR2 mutations of the syndromic craniosynostotic patients would be very helpful for understanding the genotype-phenotype relationship and has a great value for diagnosis, prognosis, and genetic counseling.

Prenatal ultrasound and molecular diagnosis elucidate the prognosis of Pfeiffer syndrome1)

Background: Pfeiffer syndrome (PS) is one of several related craniosynostosis and occurs in 1 out of every 100,000 births. The diagnosis has historically been based on the clinical neonatal findings of bilateral coronal craniosynostosis, midface hypoplasia, with broad thumbs and great toes.

Case: A craniosynostosis suggestive of PS was identified on prenatal ultrasound at 34+3 weeks gestation by findings of polyhydramnios, a cloverleaf skull, ventriculomegaly, hypertelorism, marked orbital proptosis, short limbs, broad digits, and an abnormality of the spine. Prenatal molecular testing of the FGFR genes revealed an exon 10, p.Y340C mutation in the FGFR2 gene.

Conclusion: PS can now be diagnosed prenatally. In our case, the specific mutation was associated with an especially severe phenotype. The ultrasonographic findings in conjunction with the molecular diagnosis allowed us to better inform the patient and medical staff about the diagnosis and prognosis.

Syndromic craniosynostosis

Although most cases of craniosynostosis are nonsyndromic, craniosynostosis is known to occur in conjunction with other anomalies in well-defined patterns that make up clinically recognized syndromes. Patients with syndromic craniosynostoses are much more complicated to care for, requiring a multidisciplinary approach to address all of their needs effectively. This review describes the most common craniosynostosis syndromes, their characteristic features and syndrome-specific functional issues, and new modalities utilized in their management. General principles including skull development, the risk of developing increased intracranial pressure in craniosynostosis syndromes, and techniques to measure intracranial pressure are discussed. Evolving techniques of the established operative management of craniosynostosis are discussed together with more recent techniques including spring cranioplasty and posterior cranial vault distraction osteogenesis.

Craniosynostosis: molecular pathways and future pharmacologic therapy

Craniosynostosis describes the premature fusion of one or more cranial sutures and can lead to dramatic manifestations in terms of appearance and functional impairment. Contemporary approaches for this condition are primarily surgical and are associated with considerable morbidity and mortality. The additional post-operative problems of suture refusion and bony relapse may also necessitate repeated surgeries with their own attendant risks. Therefore, a need exists to not only optimize current strategies but also to develop novel biological therapies which could obviate the need for surgery and potentially treat or even prevent premature suture fusion. Clinical studies of patients with syndromic craniosynostosis have provided some useful insights into the important signaling pathways and molecular events guiding suture fate. Furthermore, the highly conserved nature of craniofacial development between humans and other species have permitted more focused and step-wise elucidation of the molecular underpinnings of craniosynostosis. This review will describe the clinical manifestations of craniosynostosis, reflect on our understanding of syndromic and non-syndromic craniosynostoses and outline the different approaches that have been adopted in our laboratory and elsewhere to better understand the pathogenesis of premature suture fusion. Finally, we will assess to what extent our improved understanding of the pathogenesis of craniosynostosis, achieved through laboratory-based and clinical studies, have made the possibility of a non-surgical pharmacological approach both realistic and tangible.

Central nervous system malformations and deformations in FGFR2-related craniosynostosis

Central nervous system anomalies in Pfeiffer syndrome (PS) due to mutations in the FGFR2 gene are poorly understood, even though PS is often associated with serious cognitive impairment. The aim of this study is to describe the neuropathological phenotype in PS. We present four severe fetal cases of sporadic PS with FGFR2 mutations who underwent termination followed by fetopathological and neuropathological examination. We studied the expression pattern of Fgfr2 in the mouse brain using radioactive fluorescence in situ hybridization. PS is associated with brain deformations due to the abnormal skull shape, but FGFR2 mutations also induce specific brain developmental anomalies: megalencephaly, midline disorders, amygdala, and hippocampus malformations, and ventricular wall alterations. The expression pattern of Fgfr2 in mice matches the distribution of malformations in humans. The brain anomalies in PS result from the combination of mechanical deformations and intrinsic developmental disorders due to FGFR2 hyperactivity. Several similarities are noted between these anomalies and the brain lesions observed in other syndromes due to mutations in FGF-receptor genes. The specific involvement of the hippocampus and the amygdala should encourage the precise cognitive screening of patients with mild forms of PS.

Paternal age effect mutations and selfish spermatogonial selection: causes and consequences for human disease

Advanced paternal age has been associated with an increased risk for spontaneous congenital disorders and common complex diseases (such as some cancers, schizophrenia, and autism), but the mechanisms that mediate this effect have been poorly understood. A small group of disorders, including Apert syndrome (caused by FGFR2 mutations), achondroplasia, and thanatophoric dysplasia (FGFR3), and Costello syndrome (HRAS), which we collectively term "paternal age effect" (PAE) disorders, provides a good model to study the biological and molecular basis of this phenomenon. Recent evidence from direct quantification of PAE mutations in sperm and testes suggests that the common factor in the paternal age effect lies in the dysregulation of spermatogonial cell behavior, an effect mediated molecularly through the growth factor receptor-RAS signal transduction pathway. The data show that PAE mutations, although arising rarely, are positively selected and expand clonally in normal testes through a process akin to oncogenesis. This clonal expansion, which is likely to take place in the testes of all men, leads to the relative enrichment of mutant sperm over time-explaining the observed paternal age effect associated with these disorders-and in rare cases to the formation of testicular tumors. As regulation of RAS and other mediators of cellular proliferation and survival is important in many different biological contexts, for example during tumorigenesis, organ homeostasis and neurogenesis, the consequences of selfish mutations that hijack this process within the testis are likely to extend far beyond congenital skeletal disorders to include complex diseases, such as neurocognitive disorders and cancer predisposition.

Craniosynostosis genetics: The mystery unfolds

Craniosynsostosis syndromes exhibit considerable phenotypic and genetic heterogeneity. Sagittal synostosis is common form of isolated craniosynostosis. The sutures involved, the shape of the skull and associated malformations give a clue to the specific diagnosis. Crouzon syndrome is one of the most common of the craniosynostosis syndromes. Apert syndrome accounts for 4.5% of all craniosynostoses and is one of the most serious of these syndromes. Most syndromic craniosynostosis require multidisciplinary management. The following review provides a brief appraisal of the various genes involved in craniosynostosis syndromes, and an approach to diagnosis and genetic counseling.

Targeting mutant fibroblast growth factor receptors in cancer

Fibroblast growth factor receptors (FGFRs) play diverse roles in the control of cell proliferation, cell differentiation, angiogenesis and development. Activating the mutations of FGFRs in the germline has long been known to cause a variety of skeletal developmental disorders, but it is only recently that a similar spectrum of somatic FGFR mutations has been associated with human cancers. Many of these somatic mutations are gain-of-function and oncogenic and create dependencies in tumor cell lines harboring such mutations. A combination of knockdown studies and pharmaceutical inhibition in preclinical models has further substantiated genomically altered FGFR as a therapeutic target in cancer, and the oncology community is responding with clinical trials evaluating multikinase inhibitors with anti-FGFR activity and a new generation of specific pan-FGFR inhibitors.

Audiologic findings in Pfeiffer syndrome

Hearing loss has been described in patients with certain craniosynostotic syndromes but is poorly defined in Pfeiffer syndrome (PS). Our objective was to characterize the otologic and audiologic findings in PS. The records of PS patients evaluated at our craniofacial center over a 30-year period were culled. Only patients with a confirmed diagnosis and formal audiologic examination were included. Diagnostic criteria were characteristic mutations in fibroblast growth factor receptor 1 or 2 (FGFR1, FGFR2) or, in the absence of genetic testing, typical clinical findings of PS as determined by a clinical geneticist or the most senior author. Twenty patients met the inclusion criteria, and all had hearing loss. Twenty patients had traditional audiologic testing: 14 (70%) had pure conductive loss (minor to severe), and 3 (15%) had a mixed conductive/sensorineural loss (minor to severe). Two additional patients had hearing loss by Behavioral Observational Audiometry (sound fields method). One patient with early conductive hearing loss was subsequently determined to have a pure sensorineural deficit. Nine patients (45%) had permanent hearing loss significant enough to require audiologic amplification. All patients with PS demonstrated hearing loss, although the severity and the anatomic basis (ie., neural vs conductive) were variable. Conductive hearing loss, possibly caused by structural abnormalities, was most common. Sensorineural hearing loss was less common and may be related to the effect of FGFR mutations on cranial nerve and/or inner-ear development.

Advances in the molecular pathogenesis of craniofacial conditions

The impact that the understanding of fibroblast growth factor receptor (FGFR) biology and its relevance to the pathogenesis of the craniosynostoses has made cannot be underestimated. As the genetic and molecular pathology of other conditions become increasingly understood, there is much hope that robust and relevant animal models of these conditions may be generated. From these models-and in conjunction with laboratory studies in vitro-comes a real hope of improved therapeutic strategies. The future lies in increased cooperation between clinicians working in high-volume centers and basic scientists. This article decribes the results of a decade of research in which the molecular pathology of the craniosynostoses was unravelled. The understanding of the importance of FGFR mutations to the genetic etiology of craniosynostosis opened up novel studies in developmental biology in various tissues. Such studies describe the functional effects of FGFR mutations. Investigations of FGFR expression in human craniofacial development have related functional molecular studies to human craniosynostosis syndromes, which provides a link between the gene mutation and the affected child.

A model for the pharmacological treatment of crouzon syndrome

OBJECTIVE

Crouzon syndrome is caused by mutations in fibroblast growth factor receptor 2 (FGFR2) leading to constitutive activation of receptors in the absence of ligand binding. The syndrome is characterized by premature fusion of the cranial sutures that leads to abnormal cranium shape, restricted brain growth, and increased intracranial pressure. Surgical remodeling of the cranial vault is currently used to treat affected infants. The purpose of this study was to develop a pharmacological strategy using tyrosine kinase inhibition as a novel treatment for craniosynostotic syndromes caused by constitutive FGFR activation.

METHODS

Characterization of cranial suture fusion in Fgfr2 mutant mice, which carry the most common Crouzon mutation, was performed using micro-computed tomographic analysis from embryogenesis through maturation. Whole calvarial cultures from wild-type and Fgfr2 mice were established and cultured for 2 weeks in the presence of dimethyl sulfoxide control or PD173074, an FGFR tyrosine kinase inhibitor. Paraffin sections were prepared to show suture morphology and calcium deposition.

RESULTS

In untreated Fgfr2 cultures, the coronal suture fused bilaterally with loss of overlap between the frontal bone and parietal bone. Calvaria treated with PD173074 (2 micromol/L) showed patency of the coronal suture and were without evidence of any synostosis.

CONCLUSION

We report the successful use of PD173074 to prevent in vitro suture fusion in a model for Crouzon syndrome. Further studies are underway to develop an in vivo treatment protocol as a novel therapeutic modality for FGFR associated craniosynostotic syndromes.

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.

Short/branched-chain acyl-CoA dehydrogenase deficiency due to an IVS3+3A>G mutation that causes exon skipping

Short/branched-chain acyl-CoA dehydrogenase deficiency (SBCADD) is an autosomal recessive disorder of L: -isoleucine catabolism. Little is known about the clinical presentation associated with this enzyme defect, as it has been reported in only a limited number of patients. Because the presence of C5-carnitine in blood may indicate SBCADD, the disorder may be detected by MS/MS-based routine newborn screening. It is, therefore, important to gain more knowledge about the clinical presentation and the mutational spectrum of SBCADD. In the present study, we have studied two unrelated families with SBCADD, both with seizures and psychomotor delay as the main clinical features. One family illustrates the fact that affected individuals may also remain asymptomatic. In addition, the normal level of newborn blood spot C5-acylcarnitine in one patient underscores the fact that newborn screening by MS/MS currently lacks sensitivity in detecting SBCADD. Until now, seven mutations in the SBCAD gene have been reported, but only three have been tested experimentally. Here, we identify and characterize an IVS3+3A>G mutation (c.303+3A>G) in the SBCAD gene, and provide evidence that this mutation is disease-causing in both families. Using a minigene approach, we show that the IVS3+3A>G mutation causes exon 3 skipping, despite the fact that it does not appear to disrupt the consensus sequence of the 5' splice site. Based on these results and numerous literature examples, we suggest that this type of mutation (IVS+3A>G) induces missplicing only when in the context of non-consensus (weak) 5' splice sites. Statistical analysis of the sequences shows that the wild-type versions of 5' splice sites in which +3A>G mutations cause exon skipping and disease are weaker on average than a random set of 5' splice sites. This finding is relevant to the interpretation of the functional consequences of this type of mutation in other disease genes.

FGF signaling in the developing endochondral skeleton

Mutations in fibroblast growth factor receptors (Fgfrs) are the etiology of many craniosynostosis and chondrodysplasia syndromes in humans. The phenotypes associated with these human syndromes and the phenotypes resulting from targeted mutagenesis in the mouse have defined essential roles for FGF signaling in both endochondral and intramembranous bone development. In this review, I will focus on the role of FGF signaling in chondrocytes and osteoblasts and how FGFs regulate the growth and development of endochondral bone.

Genomic screening of fibroblast growth-factor receptor 2 reveals a wide spectrum of mutations in patients with syndromic craniosynostosis

It has been known for several years that heterozygous mutations of three members of the fibroblast growth-factor-receptor family of signal-transduction molecules-namely, FGFR1, FGFR2, and FGFR3-contribute significantly to disorders of bone patterning and growth. FGFR3 mutations, which predominantly cause short-limbed bone dysplasia, occur in all three major regions (i.e., extracellular, transmembrane, and intracellular) of the protein. By contrast, most mutations described in FGFR2 localize to just two exons (IIIa and IIIc), encoding the IgIII domain in the extracellular region, resulting in syndromic craniosynostosis including Apert, Crouzon, or Pfeiffer syndromes. Interpretation of this apparent clustering of mutations in FGFR2 has been hampered by the absence of any complete FGFR2-mutation screen. We have now undertaken such a screen in 259 patients with craniosynostosis in whom mutations in other genes (e.g., FGFR1, FGFR3, and TWIST) had been excluded; part of this screen was a cohort-based study, enabling unbiased estimates of the mutation distribution to be obtained. Although the majority (61/62 in the cohort sample) of FGFR2 mutations localized to the IIIa and IIIc exons, we identified mutations in seven additional exons-including six distinct mutations of the tyrosine kinase region and a single mutation of the IgII domain. The majority of patients with atypical mutations had diagnoses of Pfeiffer syndrome or Crouzon syndrome. Overall, FGFR2 mutations were present in 9.8% of patients with craniosynostosis who were included in a prospectively ascertained sample, but no mutations were found in association with isolated fusion of the metopic or sagittal sutures. We conclude that the spectrum of FGFR2 mutations causing craniosynostosis is wider than previously recognized but that, nevertheless, the IgIIIa/IIIc region represents a genuine mutation hotspot.

Severe and mild phenotypes in Pfeiffer syndrome with splice acceptor mutations in exon IIIc of FGFR2

Pfeiffer syndrome is clinically and genetically heterogeneous. Three clinical subtypes have been delineated based on the severity of acrocephalysyndactyly and associated manifestations. Severe cases are usually sporadic and caused by a number of different mutations in exons IIIa and IIIc of the fibroblast growth factor receptor 2 (FGFR2) gene. Mild cases are either sporadic or familial and are caused by mutations in FGFR2 or FGFR1, respectively. We report on two individuals with different novel de novo mutations in FGFR2. The first is a 17-year-old male who has a severe phenotype, within the spectrum of subtype 1 including severe ocular proptosis, elbow ankylosis, visceral anomalies, and normal intelligence. This patient was found to have a novel complex mutation at the 3' acceptor site of exon IIIc of FGFR2, denoted as C952-3 del10insACC. The other patient, a 2-year-old female, has a mild phenotype, typical of the classic subtype 1 including brachycephaly with coronal synostosis and hypertelorism. She was also found to have a mutation at the 3' acceptor site (the same splice site) of exon IIIc of FGFR2, a point mutation designated as 952-1G-->A. Speculation on the molecular mechanisms that cause severe and mild phenotypes is presented in relation to these two cases.

Negative autoregulation of fibroblast growth factor receptor 2 expression characterizing cranial development in cases of Apert (P253R mutation) and Pfeiffer (C278F mutation) syndromes and suggesting a basis for differences in their cranial phenotypes

OBJECT

Heterogeneous mutations in the fibroblast growth factor receptor 2 gene (FGFR2) cause a range of craniosynostosis syndromes. The specificity of the Apert syndrome-affected cranial phenotype reflects its narrow mutational range: 98% of cases of Apert syndrome result from an Ser252Trp or Pro253Arg mutation in the immunoglobulin-like (Ig)IIIa extracellular subdomain of FGFR2. In contrast, a broad range of mutations throughout the extracellular domain of FGFR2 causes the overlapping cranial phenotypes of Pfeiffer and Crouzon syndromes and related craniofacial dysostoses.

METHODS

In this paper the expression of FGFR1, the IgIIIa/c and IgIIIa/b isoforms of FGFR2, and FGFR3 is investigated in Apert syndrome (P253R mutation)- and Pfeiffer syndrome (C278F mutation)-affected fetal cranial tissue and is contrasted with healthy human control tissues. Both FGFR1 and FGFR3 are normally expressed in the differentiated osteoblasts of the periosteum and osteoid, in domains overlapped by that of FGFR2, which widely include preosseous cranial mesenchyme. Expression of FGFR2, however, is restricted to domains of advanced osseous differentiation in both Apert syndrome- and Pfeiffer syndrome-affected cranial skeletogenesis in the presence of fibroblast growth factor (FGF)2, but not in the presence of FGF4 or FGF7. Whereas expression of the FGFR2-IgIIIa/b (KGFR) isoform is restricted in normal human cranial osteogenesis, there is preliminary evidence that KGFR is ectopically expressed in Pfeiffer syndrome-affected cranial osteogenesis.

CONCLUSIONS

Contraction of the FGFR2-IgIIIa/c (BEK) expression domain in cases of Apert syndrome- and Pfeiffer syndrome-affected fetal cranial ossification suggests that the mutant activation of this receptor, by ligand-dependent or ligand-independent means, results in negative autoregulation. This phenomenon, resulting from different mechanisms in the two syndromes, offers a model by which to explain differences in their cranial phenotypes.

Clustering of FGFR2 gene mutations inpatients with Pfeiffer and Crouzon syndromes (FGFR2-associated craniosynostoses)

A cohort of 36 unrelated German patients with craniosynostosis syndromes of the Crouzon and Pfeiffer type were analyzed for FGFR mutations. Mutations in FGFR2 were identified in 25 Crouzon and 5 Pfeiffer syndrome patients, whereas no sequence alterations were found in the remaining patients, even after screening of the relevant parts of FGFR1, FGFR3, and TWIST. Mutations in FGFR2 clustered at two critical cysteine residues, 278 and 342, which were involved in 18 of 30 cases (60%). These two mutational hot spots, therefore, are prime targets for an efficient mutation-screening strategy. The spectrum of mutations overlapped the two syndromes and thus reflected the phenotypic similarities observed in both patient groups. In 21 families, the origin of the mutation could be traced by analyzing parents and relatives. Eleven mutations arose de novo, indicating a high mutation rate for FGFR2. In the 10 familial cases, the clinical presentation varied considerably within the pedigree, but both syndromes "bred true," i.e., a Pfeiffer syndrome phenotype was never observed in a Crouzon syndrome family and vice versa.

Syndromes involving craniosynostosis and midface hypoplasia

This article reviews a number of well-known syndromes involving craniofacial synostosis and associated midface deficiencies. Syndromes discussed include Apert's, Crouzon's, Saethre-Chotzen, and Carpenter's. Clinical characteristics and genetic defects are discussed. A general approach to surgical management is outlined.