Craniofacial morphology in Muenke syndrome

Quantitative Craniofacial Analysis and Generation of Human Induced Pluripotent Stem Cells for Muenke Syndrome: A Case Report

In this case report, we focus on Muenke syndrome (MS), a disease caused by the p.Pro250Arg variant in fibroblast growth factor receptor 3 (FGFR3) and characterized by uni- or bilateral coronal suture synostosis, macrocephaly without craniosynostosis, dysmorphic craniofacial features, and dental malocclusion. The clinical findings of MS are further complicated by variable expression of phenotypic traits and incomplete penetrance. As such, unraveling the mechanisms behind MS will require a comprehensive and systematic way of phenotyping patients to precisely identify the impact of the mutation variant on craniofacial development. To establish this framework, we quantitatively delineated the craniofacial phenotype of an individual with MS and compared this to his unaffected parents using three-dimensional cephalometric analysis of cone beam computed tomography scans and geometric morphometric analysis, in addition to an extensive clinical evaluation. Secondly, given the utility of human induced pluripotent stem cells (hiPSCs) as a patient-specific investigative tool, we also generated the first hiPSCs derived from a family trio, the proband and his unaffected parents as controls, with detailed characterization of all cell lines. This report provides a starting point for evaluating the mechanistic underpinning of the craniofacial development in MS with the goal of linking specific clinical manifestations to molecular insights gained from hiPSC-based disease modeling.

Use of Onlay Hydroxyapatite Cement for Secondary Cranioplasty

BACKGROUND

Children who undergo bi-fronto-orbital advancement (BFOA) frequently develop a contour deformity on the temporal and supra-orbital region, with an incidence reported as high as 55% and 75%, respectively. Up to 20% of patients may require correction. Hydroxyapatite cement (HAC) is a good alternative to autogenous tissue. The available literature on its use focusses on the reconstruction of bone defects, but little has been published on its efficacy and safety as an onlay graft over intact cranium.

OBJECTIVES

To describe our institution's experience with HAC in the pediatric population.

METHODS

Retrospective chart review from 1998 to 2018 on all patients from the Craniofacial Unit at the Sydney Children's Hospital who had either coronal or metopic craniosynostosis and underwent BFOA and later in life required cranioplasty with HAC for contour repair.

FINDINGS

We have performed 166 BFOA and nineteen secondary cranioplasties for contour repair using onlay HAC. The mean age at the time of operation was 14 years. Bi-coronal craniosynostosis was most frequently associated with secondary cranioplasty and 37% had an associated syndrome. The mean volume of HAC used was 37 mL. There was only 1 patient who had a complication (5.3%) and required partial removal of allograft. The mean length of admission was 2 days. Mean follow up time of 22.4 months.

CONCLUSIONS

HAC represents a safe option when used correctly, with low rates of complication and satisfactory cosmetic outcomes.

Facial Asymmetry in Nonsyndromic and Muenke Syndrome-Associated Unicoronal Synostosis: A 3-Dimensional Study Based on Facial Surfaces Extracted From CT Scans

OBJECTIVE

To quantify soft tissue facial asymmetry (FA) in children with nonsyndromic and Muenke syndrome-associated unicoronal synostosis (NS-UCS and MS-UCS), hypothesizing that MS-UCS presents with significantly larger FA than NS-UCS.

DESIGN

Retrospective cohort study.

PATIENTS AND METHODS

Twenty-one children (mean age: 0.6 years; range: 0.1-1.4 years) were included in the study (NS-UCS = 14; MS-UCS = 7). From presurgical computed tomography scans, facial surfaces were constructed for analysis. A landmark guided atlas was deformed to match each patient's surface, obtaining spatially detailed left-right point correspondence. Facial asymmetry was calculated in each surface point across the face, as the length (mm) of an asymmetry vector, with its Cartesian components providing 3 directions. Mean FA was calculated for the full face, and the forehead, eye, nose, cheek, mouth, and chin regions.

RESULTS

For the full face, a significant difference of 2.4 mm (P = .001) was calculated between the 2 groups, predominately in the transverse direction (1.5 mm; P < .001). The forehead and chin regions presented with the largest significant difference, 3.5 mm (P = .002) and 3.2 mm (P < .001), respectively; followed by the eye (2.4 mm; P = .004), cheek (2.2 mm; P = .004), nose (1.7 mm; P = .001), and mouth (1.4 mm; P = .009) regions. The transverse direction presented with the largest significant difference in the forehead, chin, mouth, and nose regions, the sagittal direction in the cheek region, and the vertical direction in the eye region.

CONCLUSIONS

Muenke syndrome-associated unicoronal synostosis presented with significantly larger FA in all regions compared to NS-UCS. The largest significant differences were found in the forehead and chin regions, predominantly in the transverse direction.

Three-dimensional imaging of soft and hard facial tissues in patients with craniofacial syndromes: a systematic review of methodological quality

OBJECTIVES

To systematically review the methodological quality of three-dimensional imaging studies of patients with craniofacial syndromes and to propose recommendations for future research.

METHODS

PubMed, Embase and Cochrane databases as well as Grey literature were electronically searched. Inclusion criteria were patients with genetic syndromes with craniofacial manifestations and three-dimensional imaging of facial soft and/or hard tissues. Exclusion criteria consisted of non-syndromic conditions or conditions owing to environmental causes, injury or trauma, facial soft and hard tissues not included in the image analysis, case reports, reviews, opinion articles. No restrictions were made for patients' ethnicity nor age, publication language or publication date. Study quality was evaluated using the Methodological Index for Non-Randomized Studies (MINORS).

RESULTS

The search yielded 2228 citations of which 116 were assessed in detail and 60 were eventually included in this review. Studies showed a large heterogeneity in study design, sample size and patient age. An increase was observed in the amount of studies with time, and the imaging method most often used was CT. The most studied craniofacial syndromes were Treacher Collins, Crouzon and Apert syndrome. The articles could be divided into three main groups: diagnostic studies (34/60, 57%), evaluation of surgical outcomes (21/60, 35%) and evaluation of imaging techniques (5/60, 8%). For comparative studies, the median MINORS score was 13 (12-15, 25-75th percentile), and for non-comparative studies, the median MINORS score was 8 (7-9, 25-75th percentile).

CONCLUSIONS

The median MINORS scores were only 50 and 54% of the maximum scores and there was a lack of prospective, controlled trials with sufficiently large study groups. To improve the quality of future studies in this domain and given the low incidence of craniofacial syndromes, more prospective multicentre controlled trials should be set up.

Assessing the midface in Muenke syndrome: A cephalometric analysis and review of the literature

BACKGROUND

Max Muenke included midface hypoplasia as part of the clinical syndrome caused by the Pro250Arg FGFR3 mutation that now bears his name. Murine models have demonstrated midface hypoplasia in homozygous recessive mice only, with heterozygotes having normal midfaces; as the majority of humans with the syndrome are heterozygotes, we investigated the incidence of midface hypoplasia in our institution's clinical cohort.

METHODS

We retrospectively reviewed all patients with a genetic and clinical diagnosis of Muenke syndrome from 1990 to 2014. Review of clinical records and photographs included skeletal Angle Class, dental occlusion, and incidence of orthognathic intervention. Cephalometric evaluation of our patients was compared to the Eastman Standard Values.

RESULTS

18 patients met inclusion criteria - 7 females and 11 males, with average follow-up of 11.2 years (1.0-23.1). Cephalometric analysis revealed an average sella-nasion-A point angle (SNA) of 82.5 (67.8-88.8) and an average sella-nasion-B point angle (SNB) of 77.9 (59.6-84.1). The SNA of our cohort was found to be significantly different from the Eastman Standards (p = 0.017); subgroup analysis revealed that this was due to the mixed dentition group which had a higher than average SNA. 12 patients were noted to be in Class I occlusion, 4 in Class II malocclusion, and 2 in Class III malocclusion. Only one patient (6%) underwent orthognathic surgery for Class III malocclusion.

CONCLUSIONS

While a part of the original description of Muenke syndrome, clinically significant midface hypoplasia is not a common feature. This data is important, as it allows more accurate counseling of patients and families.

LEVEL OF EVIDENCE

III.

Photometric evaluation of cranial and facial symmetry in hemicoronal single suture synostosis treated with surgical fronto-orbital remodeling

OBJECTIVE

Evaluation of frontal vault symmetry and progressive facial symmetrization in a cohort of patients with hemicoronal single suture synostosis treated with a standardized cranioplasty and rigid fixation.

PATIENTS AND METHODS

Fifty-four patients with hemicoronal synostosis operated between 1999 and 2014 were reviewed retrospectively. Pre, immediately postoperative and yearly photographs from the top of the skull and frontal views of the face were taken with the same head position and projection. A photogrammetric method was applied to quantify the pre and postoperative contour changes. The anterior skull hemispheres were traced, divided into two equal parts and the areas were compared. Angular measurements obtained by the intersection of the interpupillary line and the glabella perpendicular vertical line were calculated. The average photographic follow-up was 6.8 years. Range 1-14 years.

RESULTS

The average advancement on the affected side was 18 mm (range: 16-23 mm). The pre-surgical cranial area on the affected side was increased on average 14.6 + 2.4% (range: 10-18%). The angular measurements documented the frontal symmetry obtained and the progressive improvement of facial symmetry.

CONCLUSION

Cranioplasty with rigid fixation achieved a stable correction of anterior plagiocephaly leading to subsequent symmetrical facial growth. Photogrammetry allowed fora quantitative long-term validation.

Phenotype profile of a genetic mouse model for Muenke syndrome

PURPOSE

The Muenke syndrome mutation (FGFR3 (P250R)), which was discovered 15 years ago, represents the single most common craniosynostosis mutation. Muenke syndrome is characterized by coronal suture synostosis, midface hypoplasia, subtle limb anomalies, and hearing loss. However, the spectrum of clinical presentation continues to expand. To better understand the pathophysiology of the Muenke syndrome, we present collective findings from several recent studies that have characterized a genetically equivalent mouse model for Muenke syndrome (FgfR3 (P244R)) and compare them with human phenotypes.

CONCLUSIONS

FgfR3 (P244R) mutant mice show premature fusion of facial sutures, premaxillary and/or zygomatic sutures, but rarely the coronal suture. The mice also lack the typical limb phenotype. On the other hand, the mutant mice display maxillary retrusion in association with a shortening of the anterior cranial base and a premature closure of intersphenoidal and spheno-occipital synchondroses, resembling human midface hypoplasia. In addition, sensorineural hearing loss is detected in all FgfR3 (P244R) mutant mice as in the majority of Muenke syndrome patients. It is caused by a defect in the mechanism of cell fate determination in the organ of Corti. The mice also express phenotypes that have not been previously described in humans, such as reduced cortical bone thickness, hypoplastic trabecular bone, and defective temporomandibular joint structure. Therefore, the FgfR3 (P244R) mouse provides an excellent opportunity to study disease mechanisms of some classical phenotypes of Muenke syndrome and to test novel therapeutic strategies. The mouse model can also be further explored to discover previously unreported yet potentially significant phenotypes of Muenke syndrome.

Genetic basis of single-suture synostoses: genes, chromosomes and clinical implications

BACKGROUND

Non syndromic craniosynostoses are the most frequent craniofacial malformations worldwide. They represent a wide and heterogeneous group of entities, in which the dysmorphism may occur in a single (simple forms) or in multiple sutures (complex forms). Simple forms present a higher birth prevalence and are classified according to the involved suture and to the corresponding abnormal cranial shape: scaphocephaly (SC; sagittal suture), trigonocephaly (TC; metopic suture), anterior plagiocephaly (unilateral coronal suture), posterior plagiocephaly (unilateral lambdoid suture). They occur commonly as sporadic forms, although a familiar recurrence is sometimes observed, suggesting a mendelian inheritance. The genetic causes of simple craniosynostosis are still largely unknown, as mutations in common craniosynostosis-associated genes and structural chromosomal aberrations have been rarely found in these cases.

AIMS

This review is intended to dissect comprehensively the state-of-the art on the genetic etiology of single suture craniosynostoses, in the attempt to categorize all known disease-associated genes and chromosomal aberrations. Possible genotype/phenotype correlations are discussed as useful clues towards the definition of optimized clinical management flowcharts.

The Muenke syndrome mutation (FgfR3P244R) causes cranial base shortening associated with growth plate dysfunction and premature perichondrial ossification in murine basicranial synchondroses

Muenke syndrome caused by the FGFR3(P250R) mutation is an autosomal dominant disorder mostly identified with coronal suture synostosis, but it also presents with other craniofacial phenotypes that include mild to moderate midface hypoplasia. The Muenke syndrome mutation is thought to dysregulate intramembranous ossification at the cranial suture without disturbing endochondral bone formation in the skull. We show in this study that knock-in mice harboring the mutation responsible for the Muenke syndrome (FgfR3(P244R)) display postnatal shortening of the cranial base along with synchondrosis growth plate dysfunction characterized by loss of resting, proliferating and hypertrophic chondrocyte zones and decreased Ihh expression. Furthermore, premature conversion of resting chondrocytes along the perichondrium into prehypertrophic chondrocytes leads to perichondrial bony bridge formation, effectively terminating the postnatal growth of the cranial base. Thus, we conclude that the Muenke syndrome mutation disturbs endochondral and perichondrial ossification in the cranial base, explaining the midface hypoplasia in patients.

Craniofacial growth in patients with FGFR3Pro250Arg mutation after fronto-orbital advancement in infancy

BACKGROUND

The facial features of children with FGFR3Pro250Arg mutation (Muenke syndrome) differ from those with the other eponymous craniosynostotic disorders. We documented midfacial growth and position of the forehead after fronto-orbital advancement (FOA) in patients with the FGFR3 mutation.

METHODS

We retrospectively reviewed all patients who had an FGFR3Pro250Arg mutation and craniosynostosis. Only patients who had FOA in infancy or early childhood were included. The clinical records were evaluated for type of sutural fusion; midfacial hypoplasia and other clinical data, including age at operation; type of procedures and fixation (wire vs resorbable plate); frequency of frontal readvancement, forehead augmentation, midfacial advancement; and complications. Preoperative and postoperative sagittal orbital-globe relationship was measured by direct anthropometry. Outcome of FOA was graded according to the Whittaker classification as category I, no revision; category II, minor revisions, that is, foreheadplasty; category III, alternative bony work; category IV; redo of initial procedure (ie, secondary FOA). Midfacial position was determined by clinical examination and lateral cephalometry.

RESULTS

A total of 21 study patients with Muenke syndrome (8 males and 13 females) were analyzed. The types of craniosynostosis were bilateral coronal (n=15), of which 3 also had concurrent sagittal fusion, and unilateral coronal (n=5). Two patients had early endoscopic suturectomy, but later required FOA. Mean age at FOA was 22.9 months (range, 3-128 months). Secondary FOA was necessary in 40% of patients (n=8), and secondary foreheadplasty in 25% (n=5) of patients. No frontal revisions were needed in the remaining 35% of patients (n=7). Mean age at initial FOA was significantly younger in the group requiring repeat FOA or foreheadplasty compared with patients who did not require revision (P<0.05). Location of synostosis, type of fixation, and bone grafting did not significantly affect the need for revision. Only 30% (n=6) of patients developed midfacial retrusion.

CONCLUSIONS

The frequency of frontal revision in patients with Muenke syndrome who had FOA in infancy and early childhood is lower than previously reported. Age at forehead advancement inversely correlated with the incidence of relapse and need for secondary frontal procedures. Midfacial retrusion is relatively uncommon in FGFR3Pro250Arg patients.

Coronal synostosis syndrome (Muenke syndrome): the value of genetic testing versus clinical diagnosis

BACKGROUND

Muenke syndrome is a fibroblast growth factor receptor 3 (FGFR-3)-associated coronal craniosynostosis syndrome, which was first described in 1997.

CASE

We report an infant girl who was born to a 29-year-old primapara at 38 weeks' gestation. When evaluated at 3 days old, physical examination revealed a high forehead with frontal bossing, upturned nose, arched palate, shallow midface structures, and heavily ridged coronal sutures bilaterally. Clinically, the infant seemed to be neurologically normal. Skull radiographs and computed tomography confirmed the presence of bilateral coronal synostosis, with patency of all other sutures. Family history was remarkable, in that the infant's father, paternal grandmother, and a paternal cousin demonstrated subtle craniofacial features, which had not been previously identified. Mutation analysis of FGFR-3 revealed a missense mutation in exon 6, c.749 C>G, with a resultant amino acid change from proline to arginine at codon 250 (P250R), in keeping with Muenke syndrome (Am J Hum Genet 1997;60:555-564). The mutation was subsequently identified in her father, suggesting variable expression in this family, as he had only mild midfacial flattening. At 9 months of age, our patient underwent anterior cranial expansion, correction of orbital hypertelorism, intracranial orbital osteotomies, and advancement of the frontal bandeau. She tolerated the procedure well and has done well postoperatively.

CONCLUSIONS

We report the case of an infant with Muenke syndrome, with evidence of variable expressivity within the paternal family. The pertinent literature, in which only 2 prior Canadian cases were identified, is reviewed.

A Korean family with the Muenke syndrome

The Muenke syndrome (MS) is characterized by unicoronal or bicoronal craniosynostosis, midfacial hypoplasia, ocular hypertelorism, and a variety of minor abnormalities associated with a mutation in the fibroblast growth factor receptor 3 (FGFR3) gene. The birth prevalence is approximately one in 10,000 live births, accounting for 8-10% of patients with coronal synostosis. Although MS is a relatively common diagnosis in patients with craniosynostosis syndromes, with autosomal dominant inheritance, there has been no report of MS, in an affected Korean family with typical cephalo-facial morphology that has been confirmed by molecular studies. Here, we report a familial case of MS in a female patient with a Pro250Arg mutation in exon 7 (IgII-IGIII linker domain) of the FGFR3 gene. This patient had mild midfacial hypoplasia, hypertelorism, downslanting palpebral fissures, a beak shaped nose, plagio-brachycephaly, and mild neurodevelopmental delay. The same mutation was confirmed in the patient's mother, two of the mother's sisters and the maternal grandfather. The severity of the cephalo-facial anomalies was variable among these family members.