The Craniofacial and Upper Limb Management of Nager Syndrome

Fgf8 contributes to the pathogenesis of Nager syndrome

Nager syndrome (NS, OMIM 154400) is a rare disease characterized by craniofacial and limb malformations due to variants in the gene encoding splicing factor 3B subunit 4 (SF3B4). Although various noncanonical functions of SF3B4 unrelated to splicing have been previously described, limited studies elucidate molecular mechanisms underlying NS pathogenesis. Here we showed that sf3b4-deficient fish displayed craniofacial and segmentation defects associated with suppression of fgf8 levels, which perturbed FGF signaling and neural crest cell (NCC) expression. Our finding also pointed out that oxidative stress-induced apoptosis was prominently detected in sf3b4-deficient fish and may further exaggerate the bone remodeling process. Notably, injection of exogenous FGF8 significantly rescued the demonstrated defects in sf3b4-deficient fish, which further supported the participation of Fgf8 in NS pathogenesis. Overall, our study provides valuable insights into the molecular mechanism underlying developmental abnormalities observed in NS and suggests future therapeutic strategies to protect against the pathogenesis of NS and possibilities for preventing severe outcomes.

Optimal Diagnostic and Treatment Practices for Facial Dysostosis Syndromes: A Clinical Consensus Statement Among European Experts

Facial dysostosis syndromes (FDS) are rare congenital conditions impacting facial development, often leading to diverse craniofacial abnormalities. This study addresses the scarcity of evidence on these syndromes about optimal diagnostic and treatment practices. To overcome this scarcity, European experts from ERN CRANIO collaborated to develop a clinical consensus statement through the Delphi consensus method. A systematic search of Embase, MEDLINE/PubMed, Cochrane, and Web of Science databases was conducted until February 2023. The quality of evidence was evaluated using various tools depending on the study design. Statements were subsequently formed based on literature and expert opinion, followed by a Delphi process with expert health care providers and patient representatives. In total, 92 experts from various specialties and three patient representatives were involved in the Delphi process. Over 3 voting rounds, consensus was achieved on 92 (46.9%), 58 (59.2%), and 19 (70.4%) statements, respectively. These statements cover the topics of general care; craniofacial reconstruction; the eyes and lacrimal system; upper airway management; genetics; hearing; speech; growth, feeding, and swallowing; dental treatment and orthodontics; extracranial anomalies; and psychology and cognition. The current clinical consensus statement provides valuable insights into optimal diagnostic and treatment practices and identifies key research opportunities for FDS. This consensus statement represents a significant advancement in FDS care, underlining the commitment of health care professionals to improve the understanding and management of these rare syndromes in Europe.

Mechanical stress can regulate temporomandibular joint cavitation via signalling pathways

The temporomandibular joint (TMJ), composed of temporal fossa, mandibular condyle and a fibrocartilage disc with upper and lower cavities, is the biggest synovial joint and biomechanical hinge of the craniomaxillofacial musculoskeletal system. The initial events that give rise to TMJ cavities across diverse species are not fully understood. Most studies focus on the pivotal role of molecules such as Indian hedgehog (Ihh) and hyaluronic acid (HA) in TMJ cavitation. Although biologists have observed that mechanical stress plays an irreplaceable role in the development of biological tissues and organs, few studies have been concerned with how mechanical stress regulates TMJ cavitation. Based on the evidence from human or other animal embryos today, it is implicated that mechanical stress plays an essential role in TMJ cavitation. In this review, we discuss the relationship between mechanical stress and TMJ cavitation from evo-devo perspectives and review the clinical features and potential pathogenesis of TMJ dysplasia.

SF3B4 Frameshift Variants Represented a More Severe Clinical Manifestation in Nager Syndrome

Nager syndrome (NS) is a rare disease marked with craniofacial and preaxial limb anomalies. In this report, we summarized the current evidence to determine a possible genotype-phenotype association among NS individuals. Twenty-four articles comprising of 84 NS (including 9 patients with a severe form of NS [Rodriguez syndrome]) patients were examined, of which 76% were caused by variants in SF3B4 (OMIM *605593, Splicing Factor 3B, Subunit 4). Within the SF3B4 gene, variants located in exon 3 commonly occurred (20%) from a total identified variant, while hotspot location was identified in exon 1 (12%), and primarily occurred as frameshift variants (64%). Thirty-five distinct pathogenic variants within SF3B4 gene were identified with two common sites, c.1A > G and c.1060dupC in exons 1 and 5, respectively. Although no significant genotype-phenotype association was found, it is notable that patients with frameshift SF3B4 variants and predicted to lead to nonsense-mediated RNA decay (NMD) of the transcripts tended to have a more severe clinical manifestation. Additionally, patients harboring variants in exons 2 and 3 displayed a higher proportion of cardiac malformations. Taken together, this article summarizes the pathogenic variants observed in SF3B4 and provides a possible genotype-phenotype relationship in this disease.

Alloplastic Temporomandibular Joint Reconstruction in Congenital Craniofacial Deformities

ABSTRACT

Temporomandibular joint (TMJ) reconstruction with alloplastic prosthesis is a commonly performed procedure, which can be used as a treatment for improving pathologic conditions affecting the TMJ. Depending of the severity of the condition, the patient's ability to eat can be impaired, which in turn can affect their quality of life. Several syndromes can affect the patient's facial features, and some of those also affect TMJ's. Use of alloplastic prosthesis in TMJ's affecting syndromes, by means of correcting TMJ conditions and mandibular deformities, is still rather uncommon. Purpose of our study is to review the use TMJ total prosthesis as a treatment modality for correcting TMJ conditions and the reconstruction of mandibular deformities in congenital syndromes affecting the facial features. This study consists of a retrospective cohort of patients treated with TMJ reconstruction with alloplastic prosthesis at the Helsinki University Hospital during the past decade. All subjects with congenital syndrome who underwent TMJ reconstruction were included the study. The cohort consisted of seven patients and ten joints treated. Temporomandibular joints affecting syndromes were Goldenhar syndrome, hemifacial macrosomia, Nager syndrome, and Treacher-Collins syndrome. The majority of the patients have had several previous operative treatments on the facial skeleton during their childhood, which in turn probably affected and compromised the TMJ surgery outcome. Mouth opening was sufficiently achieved as average maximal opening was 34 mm (range 24-42 mm) postoperatively. Temporomandibular joint reconstruction with alloplastic prosthesis can offer new tools and approaches for treatment of facial deformities in syndromes with craniofacial abnormalities. Impaired jaw functions and asymmetry can be addressed with the use of alloplastic prostheses, achieving sufficient mouth opening and restoring the symmetry of the lower facial skeleton.

Nager syndrome in patient lacking acrofacial dysostosis: Expanding the phenotypic spectrum of SF3B4-related disease

Nager syndrome epitomizes the acrofacial dysostoses, which are characterized by craniofacial and limb defects. The craniofacial defects include midfacial retrusion, downslanting palpebral fissures, prominent nasal bridge, and micrognathia. Limb malformations typically include hypoplasia or aplasia of radial elements including the thumb. Nager syndrome is caused by haploinsufficiency of SF3B4, encoding a spliceosomal protein called SAP49. Here, we report a patient with a loss of function variant in SF3B4 without acrofacial dysostosis or limb defects, whose reason for referral was developmental and growth delay. This patient is evidence of a broader phenotypic spectrum associated with SF3B4 variants than previously appreciated.

Microtia and Related Facial Anomalies

Infants may be born with external ear deformities or malformations that can present a diagnostic clue to an affiliated syndrome while also presenting the possibility of surgical intervention. Microtia is a malformation of the ear that is associated with other craniofacial or systemic anomalies in 50% of cases. Surgical correction of microtia and associated facial anomalies is complex and must be integrated thoughtfully into the overall care plan for children with complex medical needs. Familiarity with types of ear and facial anomalies and their association with more global concerns can allow perinatal practitioners to better serve their patients.

Modified Lefort Distraction Osteogenesis for the Treatment of Nager Syndrome-Associated Midface Hypoplasia: Technique and Review

The surgical management of midface hypoplasia in the setting of Nager syndrome remains a significant challenge for craniofacial surgeons. This study describes a novel technique using distraction osteogenesis and modified osteotomies for the treatment of midface bony defects in an 11-year-old child with Nager syndrome.

Presurgical 3-dimensional planning was performed to design the osteotomies and placement of distractors. The surgical approach required upper buccal sulcus and extended transconjunctival incisions only. Osteotomies were performed from the pyriform aperture through the orbit to include the lateral orbital wall, with bilateral osteotomy of the zygomas through the anterior arch via the transconjunctival incision. Distraction of the en bloc midface segment was successfully performed using external distractors. Bone grafting was not required. There were no complications.

External distraction was well tolerated and there were no intraoperative or postoperative complications. The distractors were removed uneventfully after consolidation. The midface was successfully advanced without the need for bone grafting or bicoronal incision. The occlusal plane was leveled and the aesthetic appearance of the child was improved.

Symmetrical midface hypoplasia in the context of Nager syndrome can be successfully corrected with en bloc distraction osteogenesis of the maxilla and bilateral zygomas through modified osteotomies that exclude the upper nasal pyramid. The approach is simplified and the need for bicoronal incision and bone grafting is mitigated in this technique, which the authors have named Lefort 2.5.