Tracheal cartilaginous sleeves in children with syndromic craniosynostosis

Pitfall of Monobloc Advancement in Beare-Stevenson Syndrome

Beare-Stevenson syndrome (BSS) is an extremely rare form of craniosynostosis. Half of patients with BSS died within the first year of life due to cardiorespiratory arrest or unexpected sudden death. In addition, there have only been fewer than 30 cases, which limits prognostication for clinicians. We currently have an 8-year-old patient who is being followed up. She underwent tracheostomy, cranioplasty, and shunting. After waiting for growth, for improvement of ocular herniation, monobloc advancement was performed at the age of 5 years. The temporal fossa was quite narrow due to severe midface hypoplasia. In addition, even though midface advancement, it was difficult to remove tracheostomy. This was because midfacial hypoplasia was so severe that it was hard to notice, but there was also micrognathia. We report our experience with this midface treatment.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

Autopsy Case of Pfeiffer Syndrome Type 2, a Phenotype of Fibroblast Growth Factor Receptor-Associated Craniosynostosis Syndromes, with Tracheal Cartilage Sleeve and Abnormal Hyperplasia of Bronchial Cartilages

BACKGROUND Pfeiffer syndrome (PS) is a fibroblast growth factor receptor (FGFR)-associated craniosynostosis syndrome, characterized by abnormally broad and medially deviated thumbs and great toes. Tracheal cartilage sleeve (TCS) is associated with several FGFR-associated craniosynostosis syndromes, including PS. TCS is an airway malformation in which the tracheal cartilage rings fuse with each other to form a sleeve of cartilage. CASE REPORT The patient was a 4-year-old girl with PS, TCS, and abnormal hyperplasia of non-fused intrapulmonary cartilages. The patient showed cranial dysplasia on prenatal ultrasonography. At birth, a cloverleaf skull in association with hydrocephalus and digital malformations was apparent. These findings were consistent with PS type 2. The diagnosis of PS type 2 was confirmed from a genetic test detecting a FGFR2 mutation (Y340C). During the clinical course, she underwent several surgeries, including ventriculoperitoneal shunts, sequential cranioplasty surgeries, and tracheotomy due to upper airway abnormalities. At 4 years old, she died of multiple organ failure following aspiration pneumonia. The autopsy revealed that the tracheal cartilages had fused with each other, resulting in a condition called TCS, in which the cartilage rings and tracheal ligaments were absent. The lungs were poorly aerated, and the dilated bronchi had thickened walls surrounded by many cartilage fragments, mainly at the hilum. These cartilages tended to overlap at both ends, did not fuse, and were greatly altered in size and shape. CONCLUSIONS We report the results of autopsy for PS with the first histopathological findings for the lungs and other visceral organs.

Complex Airway Management in Patients with Tracheal Cartilaginous Sleeves

OBJECTIVES/HYPOTHESIS

A tracheal cartilaginous sleeve (TCS) is a rare anomaly characterized by anterior fusion of tracheal cartilages. TCS is associated with syndromic craniosynostoses including Apert, Crouzon and Pfeiffer syndromes and FGFR2, FGFR3, and TWIST1 variants. This study presents a 30-year review of patients with syndromic craniosynostosis and TCS and describes diagnostic methods, genetic variants, surgical interventions, and long-term outcomes.

STUDY DESIGN

Retrospective, single-institution review.

METHODS

This review included patients with syndromic craniosynostosis and TCS treated at Seattle Children's Hospital from 1990 to 2020. Tracheostomy, genetic variants, and additional surgery were primary measures. Fisher's exact test compared need for tracheostomy in patients with proposed high-risk (FGFR2 p.W290 or FGFR2 p.C342) versus low-risk genetic variants.

RESULTS

Thirty patients with TCS were identified. Average age at diagnosis was 12 months (range 2-weeks to 7.9-years; standard deviation 19.8 months). Syndromes included Pfeiffer (37%), Apert (37%), and Crouzon (26%). Severe obstructive sleep apnea was present in 76% of patients. Tracheostomy was performed in 17 patients (57%); five were successfully decannulated. Additional interventions included adenotonsillectomy (57%), nasal (20%), laryngeal (17%), and craniofacial skeletal surgery (87%). All patients with Pfeiffer syndrome and FGFR2 p.W290C variants and 83% of patients with FGFR2 p.C342 variants required tracheostomy, differing from other variants (P = .02, odds ratio 33, 95% confidence interval 1.56-697.96). One patient (3%) died.

CONCLUSION

TCS contributes to multilevel airway obstruction in patients with syndromic craniosynostosis. Genetic testing in patients with FGFR2-related syndromic craniosynostoses may identify those at risk of TCS and facilitate early intervention. A better understanding of this patient population may foster individualized airway management strategies and improve outcomes.

LEVEL OF EVIDENCE

4 Laryngoscope, 2021.

Septal chondrocyte hypertrophy contributes to midface deformity in a mouse model of Apert syndrome

Midface hypoplasia is a major manifestation of Apert syndrome. However, the tissue component responsible for midface hypoplasia has not been elucidated. We studied mice with a chondrocyte-specific Fgfr2^S252W mutation (Col2a1-cre; Fgfr2^S252W/+) to investigate the effect of cartilaginous components in midface hypoplasia of Apert syndrome. In Col2a1-cre; Fgfr2^S252W/+ mice, skull shape was normal at birth, but hypoplastic phenotypes became evident with age. General dimensional changes of mutant mice were comparable with those of mice with mutations in EIIa-cre; Fgfr2^S252W/+, a classic model of Apert syndrome in mice. Col2a1-cre; Fgfr2^S252W/+ mice showed some unique facial phenotypes, such as elevated nasion, abnormal fusion of the suture between the premaxilla and the vomer, and decreased perpendicular plate of the ethmoid bone volume, which are related to the development of the nasal septal cartilage. Morphological and histological examination revealed that the presence of increased septal chondrocyte hypertrophy and abnormal thickening of nasal septum is causally related to midface deformities in nasal septum-associated structures. Our results suggest that careful examination and surgical correction of the nasal septal cartilage may improve the prognosis in the surgical treatment of midface hypoplasia and respiratory problems in patients with Apert syndrome.

Tracheal cartilaginous sleeve diagnosed on ultrasound in a child with Pfeiffer syndrome

The tracheal cartilaginous sleeve (TCS) is a rare, difficult to diagnose airway malformation in which segmented tracheal rings are replaced by a solid sheath of cartilage. TCS is a significant cause of morbidity and mortality in patients with syndromic craniosynostosis, and early diagnosis is essential. We report a case in which ultrasound (US) was used to diagnose TCS in a patient with Pfeiffer syndrome. This is the first case demonstrating the use of US as the initial tool to diagnose TCS. The case supports ongoing research investigating the use of US as a screening and diagnostic imaging modality for TCS.

Genotype-Phenotype Correlation of Tracheal Cartilaginous Sleeves and Fgfr2 Mutations in Mice

OBJECTIVES

To characterize tracheal cartilage morphology in mouse models of fibroblast growth factor receptor (Fgfr2)-related craniosynostosis syndromes. To establish relationships between specific Fgfr2 mutations and tracheal cartilaginous sleeve (TCS) phenotypes in these mouse models.

METHODS

Postnatal day 0 knock-in mouse lines with disease-specific genetic variations in the Fgfr2 gene (Fgfr2^C342Y/C342Y , Fgfr2^C342Y/+ , Fgfr2^+/Y394C , Fgfr2^+/S252W , and Fgfr2^+/P253R ) as well as line-specific controls were utilized. Tracheal cartilage morphology as measured by gross analyses, microcomputed tomography (μCT), and histopathology were compared using Chi-squared and single-factor analysis of variance statistical tests.

RESULTS

A greater proportion of rings per trachea were abnormal in Fgfr2^C342Y/+ tracheas (63%) than Fgfr2^+/S252W (17%), Fgfr2^+/P253R (17%), Fgfr2^+/Y394C (12%), and controls (10%) (P < .001 for each vs. Fgfr2^C342Y/+ ). TCS segments were found only in Fgfr2^C342Y/C342Y (100%) and Fgfr2^C342Y/+ (72%) tracheas. Cricoid and first-tracheal ring fusion was noted in all Fgfr2^C342Y/C342Y and 94% of Fgfr2^C342Y/+ samples. The Fgfr2^C342Y/C342Y and Fgfr2^C342Y/+ groups were found to have greater areas and volumes of cartilage than other lines on gross analysis and μCT. Histologic analyses confirmed TCS among the Fgfr2^C342Y/C342Y and Fgfr2^C342Y/+ groups, without appreciable differences in cartilage morphology, cell size, or density; no histologic differences were observed among other Fgfr2 lines compared to controls.

CONCLUSION

This study found TCS phenotypes only in the Fgfr2^C342Y mouse lines. These lines also had increased tracheal cartilage compared to other mutant lines and controls. These data support further study of the Fgfr2 mouse lines and the investigation of other Fgfr2 variants to better understand their role in tracheal development and TCS formation.

LEVEL OF EVIDENCE

NA Laryngoscope, 131:E1349-E1356, 2021.

Pfeiffer Syndrome type 2; A case report of cranio-orbitofaciostenosis with bilateral choanal atresia at Muhimbili National Hospital, Tanzania

Pfeiffer syndrome is a rare genetic disorder with heterogenous phenotype and prognosis. Due to its diverse clinical presentation, it can easily be misdiagnosed. Where genetic testing still remains a challenge, antenatal sonogram can aid in early diagnosis. The cranioorbito-faciostenosis demands aggressive management to permit survival instead of uniform early demise.

Ultrasound diagnosis of tracheal cartilaginous sleeve in a patient with Pfeiffer syndrome

There is an association between tracheal cartilaginous sleeve and syndromic craniosynostosis. We present a case of tracheal cartilaginous sleeve diagnosed by ultrasound (US) in a patient with Pfeiffer syndrome. The patient developed respiratory failure and was suspected at bronchoscopy to have tracheal cartilaginous sleeve. US performed before tracheostomy placement demonstrated continuous hypoechoic cartilage along the anterior surface of the trachea, confirming the diagnosis. Our report shows that US can make a definitive diagnosis of tracheal cartilaginous sleeve and raises the possibility of using US to screen for the condition in patients with syndromic craniosynostosis without the need for anesthesia or ionizing radiation.

Midface and upper airway dysgenesis in FGFR2-related craniosynostosis involves multiple tissue-specific and cell cycle effects

Midface dysgenesis is a feature of more than 200 genetic conditions in which upper airway anomalies frequently cause respiratory distress, but its etiology is poorly understood. Mouse models of Apert and Crouzon craniosynostosis syndromes exhibit midface dysgenesis similar to the human conditions. They carry activating mutations of Fgfr2, which is expressed in multiple craniofacial tissues during development. Magnetic resonance microscopy of three mouse models of Apert and Crouzon syndromes revealed decreased nasal passage volume in all models at birth. Histological analysis suggested overgrowth of the nasal cartilage in the two Apert syndrome mouse models. We used tissue-specific gene expression and transcriptome analysis to further dissect the structural, cellular and molecular alterations underlying midface and upper airway dysgenesis in Apert Fgfr2^+/S252W mutants. Cartilage thickened progressively during embryogenesis because of increased chondrocyte proliferation in the presence of Fgf2 Oral epithelium expression of mutant Fgfr2, which resulted in a distinctive nasal septal fusion defect, and premature facial suture fusion contributed to the overall dysmorphology. Midface dysgenesis in Fgfr2-related craniosynostosis is a complex phenotype arising from the combined effects of aberrant signaling in multiple craniofacial tissues.

Clinical genetics of craniosynostosis

PURPOSE OF REVIEW

When providing accurate clinical diagnosis and genetic counseling in craniosynostosis, the challenge is heightened by knowledge that etiology in any individual case may be entirely genetic, entirely environmental, or anything in between. This review will scope out how recent genetic discoveries from next-generation sequencing have impacted on the clinical genetic evaluation of craniosynostosis.

RECENT FINDINGS

Survey of a 13-year birth cohort of patients treated at a single craniofacial unit demonstrates that a genetic cause of craniosynostosis can be identified in one quarter of cases. The substantial contributions of mutations in two genes, TCF12 and ERF, is confirmed. Important recent discoveries are mutations of CDC45 and SMO in specific craniosynostosis syndromes, and of SMAD6 in nonsyndromic midline synostosis. The added value of exome or whole genome sequencing in the diagnosis of difficult cases is highlighted.

SUMMARY

Strategies to optimize clinical genetic diagnostic pathways by combining both targeted and next-generation sequencing are discussed. In addition to improved genetic counseling, recent discoveries spotlight the important roles of signaling through the bone morphogenetic protein and hedgehog pathways in cranial suture biogenesis, as well as a key requirement for adequate cell division in suture maintenance.

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.

Analysis of the Fgfr2C342Y mouse model shows condensation defects due to misregulation of Sox9 expression in prechondrocytic mesenchyme

Syndromic craniosynostosis caused by mutations in FGFR2 is characterised by developmental pathology in both endochondral and membranous skeletogenesis. Detailed phenotypic characterisation of features in the membranous calvarium, the endochondral cranial base and other structures in the axial and appendicular skeleton has not been performed at embryonic stages. We investigated bone development in the Crouzon mouse model (Fgfr2^C342Y) at pre- and post-ossification stages to improve understanding of the underlying pathogenesis. Phenotypic analysis was performed by whole-mount skeletal staining (Alcian Blue/Alizarin Red) and histological staining of sections of CD1 wild-type (WT), Fgfr2^C342Y/+ heterozygous (HET) and Fgfr2^C342Y/C342Y homozygous (HOM) mouse embryos from embryonic day (E)12.5-E17.5 stages. Gene expression (Sox9, Shh, Fgf10 and Runx2) was studied by in situ hybridisation and protein expression (COL2A1) by immunohistochemistry. Our analysis has identified severely decreased osteogenesis in parts of the craniofacial skeleton together with increased chondrogenesis in parts of the endochondral and cartilaginous skeleton in HOM embryos. The Sox9 expression domain in tracheal and basi-cranial chondrocytic precursors at E13.5 in HOM embryos is increased and expanded, correlating with the phenotypic observations which suggest FGFR2 signalling regulates Sox9 expression. Combined with abnormal staining of type II collagen in pre-chondrocytic mesenchyme, this is indicative of a mesenchymal condensation defect. An expanded spectrum of phenotypic features observed in the Fgfr2^C342Y/C342Y mouse embryo paves the way towards better understanding the clinical attributes of human Crouzon-Pfeiffer syndrome. FGFR2 mutation results in impaired skeletogenesis; however, our findings suggest that many phenotypic aberrations stem from a primary failure of pre-chondrogenic/osteogenic mesenchymal condensation and link FGFR2 to SOX9, a principal regulator of skeletogenesis.