Syndromes of the first and second pharyngeal arches: A review

A Technique of Autologous Costal Cartilage Graft Combined With Auricular Cartilage Folding to Correct Question Mark Ear in a Single Procedure

Background: Question mark ear is a rare congenital deformity, mainly characterized the interruption of the natural continuity between the lower border of the helix and the earlobe. In severe cases, the earlobe may be absent. In addition, there may be protrusion and outward expansion of the upper part of the auricle, with partial or complete disappearance of the antihelix. This article aims to introduce a technique that combines autologous costal cartilage carving with auricular cartilage folding to achieve a stable and aesthetic auricle. Method: This study included 26 patients with sporadic question mark ear deformity who were treated at our clinical center from January 2020 to December 2022. Based on the different appearances of the lower part of the auricle, they were divided into 2 categories:11 cases showed a natural continuity interruption between the helix and the earlobe, while 15 cases showed the absence of the earlobe. All patients underwent corrective surgery using costal cartilage transplantation combined with the upper part of the auricular cartilage folding, performed by senior surgeons. Results: Question mark ear was effectively improved and with no significant rebound. The average follow-up period was 8.4 months (ranging from 6 to 12 months). A satisfaction survey showed that 23 patients (88%) were satisfied, 3 patients (12%) were partially satisfied, and no patients were dissatisfied. Most patients experienced temporary swelling after surgery, which resolved within 3 months to half a year. Conclusion: Autologous costal cartilage transplantation combined with folding of the auricular cartilage is an ideal surgical method to correct question mark ear.

Personal essay of a rookie's journey with Bill Pak and his legacy: tales and perspectives on PI-PLC, NorpA and cyclophilin, NinaA - William L. Pak, PhD., 1932-2023: in memoriam

The neurogenetics and vision community recently mourned William L. Pak, PhD, whose pioneering work spearheaded the genetic, electrophysiological, and molecular bases of biological processes underpinning vision. This essay provides a historical background to the daunting challenges and personal experiences that carved the path to seminal findings. It also reflects on the intellectual framework, mentoring philosophy, and inspirational legacy of Bill Pak's research. An emphasis and perspectives are placed on the discoveries and implications to date of the phosphatidylinositol-specific phospholipase C (PI-PLC), NorpA, and the cyclophilin, NinaA of the fruit fly, Drosophila melanogaster, and their respective mammalian homologues, PI-PLCβ4, and cyclophilin-related protein, Ran-binding protein 2 (Ranbp2) in critical biological processes and diseases of photoreceptors and other neurons.

Practical Classification and Management of Accessory Auricle

BACKGROUND

Accessory auricle is a common congenital abnormal auricular appendage with various forms of presentation. The authors proposed a practical classification system based on the involved anatomical subunits (tragus, the anterior notch and the intertragal notch) and described the corresponding surgical procedures.

METHODS

The authors reviewed and analyzed 80 patients (96 ears) who underwent accessory auricle excisions form January 2018 to December 2021. Accessory auricles were classified into three categories: simple (no deformed subunits), complex (several deformed subunits) and compound (coexistence of simple and complex type). The complex type was subclassified into notch and tragal subtypes. The tragal subtype was subclassified into subtype A, B and C, according to the location, contour and size of the involved tragus. Surgical methods were described, and postoperative outcomes were assessed.

RESULTS

Simple type was the most common type (54%) and compound type was less common (15%). In addition, there were 28 (29%) tragal subtype accessory auricles and 2 (2%) notch subtype. Among the tragal subtype, A was the most commonly observed (25%), followed by B (2%) and C (2%). Patients were followed for an average of 11.3 months. One patient experienced delayed wound healing and 6 patients showed hypertrophic scars. The average aesthetic score, evaluated by a 4-point Likert scale (1 = poor, 2 = fair, 3 = good, 4 = excellent), was 3.67 ± 0.06 points. The OSAS and PSAS scores were 9.29 ± 0.44 and 10.84 ± 0.40, respectively.

CONCLUSIONS

The innovative classification system of accessory auricles can reflect whether there was a combined deformity and the deformed subunits, and guide decisions on surgical approaches.

LEVEL OF EVIDENCE IV

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Auriculocondylar syndrome 2 caused by a novel PLCB4 variant in a male Chinese neonate: A case report and review of the literature

BACKGROUND

Auriculocondylar syndrome (ARCND) is a rare congenital craniofacial developmental malformation syndrome of the first and second pharyngeal arches with external ear malformation at the junction between the lobe and helix, micromaxillary malformation, and mandibular condylar hypoplasia. Four subtypes of ARCND have been described so far, that is, ARCND1 (OMIM # 602483), ARCND2 (ARCND2A, OMIM # 614669; ARCND2B, OMIM # 620458), ARCND3 (OMIM # 615706), and ARCND4 (OMIM # 620457).

METHODS

This study reports a case of ARCND2 resulting from a novel pathogenic variant in the PLCB4 gene, and summarizes PLCB4 gene mutation sites and phenotypes of ARCND2.

RESULTS

The proband, a 5-day-old male neonate, was referred to our hospital for respiratory distress. Micrognathia, microstomia, distinctive question mark ears, as well as mandibular condyle hypoplasia were identified. Trio-based whole-exome sequencing identified a novel missense variant of NM_001377142.1:c.1928C>T (NP_001364071.1:p.Ser643Phe) in the PLCB4 gene, which was predicted to impair the local structural stability with a result that the protein function might be affected. From a review of the literature, only 36 patients with PLCB4 gene mutations were retrieved.

CONCLUSION

As with other studies examining familial cases of ARCND2, incomplete penetrance and variable expressivity were observed within different families' heterozygous mutations in PLCB4 gene. Although, motor and intellectual development are in the normal range in the vast majority of patients with ARCND2, long-term follow-up and assessment are still required.

Two Chinese Patients of Auriculocondylar Syndrome 2: A Novel PLCB4 Splicing Variant and 5-Year Follow-up

OBJECTIVE

Auriculocondylar syndrome (ARCND) is a set of rare craniofacial malformations characterized by variable micrognathia, ear malformations, and mandibular condyle hypoplasia, and other accompanying features with phenotypic complexity. ARCND2 caused by pathogenic variants in the PLCB4 gene is a very rare disease with less than 50 patients reported and only 36 different variants of the PLCB4 gene recorded in HGMD. This study aims to enrich the patient resources, clinical data and mutational spectrum of ARCND2.

DESIGN

Case series study.

SETTING

Guangzhou Women and Children's Medical Center and Guangdong Women and Children Hospital.

PATIENTS

Two Chinese patients with ARCND2.

MAIN OUTCOME MEASURES

Clinical, radiological and molecular findings.

RESULTS

Both the two patients presented with craniofacial and ear malformations, and feeding difficulties. Whole exome sequencing identified two different variants of the PLCB4 gene in these two patients with a heterozygous allele and a de novo mode of inheritance respectively. Patient 1 carried a known pathogenic c.1861C > T(p.Arg621Cys) missense variant, whereas Patient 2 had a novel c.225 + 1G > A splicing variant. Sanger sequencing confirmed the presence of PLCB4 variants in the proband and absence in the unaffected parents. These two PLCB4 variants were suggested as disease-causing candidates for these two patients. During a 5-year follow-up, Patient 2 gradually manifested crowded teeth, underweight, motor delay and intellectual disability.

CONCLUSIONS

In this study, we report two Chinese patients with ARCND2, describe their clinical and mutational features, and share a 5-year follow-up of one patient. Our study adds two additional patients to ARCND2, reveals a novel PLCB4 variant, and expands the phenotypic and genotypic spectrum.

Sf3b4 mutation in Xenopus tropicalis causes RNA splicing defects followed by massive gene dysregulation that disrupt cranial neural crest development

Nager syndrome is a rare craniofacial and limb disorder characterized by midface retrusion, micrognathia, absent thumbs, and radial hypoplasia. This disorder results from haploinsufficiency of SF3B4 (splicing factor 3b, subunit 4) a component of the pre-mRNA spliceosomal machinery. The spliceosome is a complex of RNA and proteins that function together to remove introns and join exons from transcribed pre-mRNA. While the spliceosome is present and functions in all cells of the body, most spliceosomopathies - including Nager syndrome - are cell/tissue-specific in their pathology. In Nager syndrome patients, it is the neural crest (NC)-derived craniofacial skeletal structures that are primarily affected. To understand the pathomechanism underlying this condition, we generated a Xenopus tropicalis sf3b4 mutant line using the CRISPR/Cas9 gene editing technology. Here we describe the sf3b4 mutant phenotype at neurula, tail bud, and tadpole stages, and performed temporal RNA-sequencing analysis to characterize the splicing events and transcriptional changes underlying this phenotype. Our data show that while loss of one copy of sf3b4 is largely inconsequential in Xenopus tropicalis, homozygous deletion of sf3b4 causes major splicing defects and massive gene dysregulation, which disrupt cranial NC cell migration and survival, thereby pointing at an essential role of Sf3b4 in craniofacial development.

Syndromic Craniofacial Disorders

This article reviews the most common craniofacial syndromes encountered in clinical practice. Key physical features of each condition are highlighted to aid in accurate recognition and diagnosis. Optimal individualized treatment approaches are discussed.

A homozygous missense variant in the PLCB4 gene causes severe phenotype of auriculocondylar syndrome type 2

Auriculocondylar syndrome (ARCND) is a rare craniofacial birth defect characterized by malformations in the mandible and external ear (Question Mark Ear). Genetically, three distinct subtypes of ARCND (ARCND1, ARCND2, and ARCND3) have been identified. ARCND2 is linked to pathogenic variants in the PLCB4 gene (phospholipase C β4). PLCB4 is a key effector of the EDN1-EDNRA pathway involved in craniofacial development via the induction, migration, and maintenance of neural crest cells. ARCND2 is typically inherited in an autosomal dominant pattern, with recessive inheritance pattern being rare. In this study, we report the first homozygous missense variant (NM_000933.4: c.2050G>A: p.(Gly684Arg)) in the PLCB4 gene causing ARCND in a 3-year-old patient with a severe clinical phenotype of the syndrome. The patient presented with typical craniofacial ARCND features, in addition to intestinal transit defect, macropenis, and hearing loss. These findings further delineate the phenotypic spectrum of ARCND associated with autosomal recessive PLCB4 loss of function variants. Notably, our results provide further evidence that these variants can result in a more severe and diverse manifestations of the syndrome. Clinicians should consider the rare features of this condition for better management of patients.

Auriculocondylar syndrome: Pathogenesis, clinical manifestations and surgical therapies

Auriculocondylar syndrome (ARCND) is a genetic and rare craniofacial condition caused by abnormal development of the first and second pharyngeal arches during the embryonic stage and is characterized by peculiar auricular malformations (question mark ears), mandibular condyle hypoplasia, micrognathia and other less-frequent features. GNAI3, PLCB4 and EDN1 have been identified as pathogenic genes in this syndrome so far, all of which are implicated in the EDN1-EDNRA signal pathway. Therefore, ARCND is genetically classified as ARCND1, ARCND2 and ARCND3 based on the mutations in GNAI3, PLCB4 and EDN1, respectively. ARCND is inherited in an autosomal dominant or recessive mode with significant intra- and interfamilial phenotypic variation and incomplete penetrance, rendering its diagnosis difficult and therapies individualized. To raise clinicians' awareness of the rare syndrome, we focused on the currently known pathogenesis, pathogenic genes, clinical manifestations and surgical therapies in this review.

Chromatin remodeler CHD7 targets active enhancer region to regulate cell type-specific gene expression in human neural crest cells

A mutation in the chromatin remodeler chromodomain helicase DNA-binding 7 (CHD7) gene causes the multiple congenital anomaly CHARGE syndrome. The craniofacial anomalies observed in CHARGE syndrome are caused by dysfunctions of neural crest cells (NCCs), which originate from the neural tube. However, the mechanism by which CHD7 regulates the function of human NCCs (hNCCs) remains unclear. We aimed to characterize the cis-regulatory elements governed by CHD7 in hNCCs by analyzing genome-wide ChIP-Seq data and identifying hNCC-specific CHD7-binding profiles. We compared CHD7-binding regions among cell types, including human induced pluripotent stem cells and human neuroepithelial cells, to determine the comprehensive properties of CHD7-binding in hNCCs. Importantly, analysis of the hNCC-specific CHD7-bound region revealed transcription factor AP-2α as a potential co-factor facilitating the cell type-specific transcriptional program in hNCCs. CHD7 was strongly associated with active enhancer regions, permitting the expression of hNCC-specific genes to sustain the function of hNCCs. Our findings reveal the regulatory mechanisms of CHD7 in hNCCs, thus providing additional information regarding the transcriptional programs in hNCCs.

Fgf8 dosage regulates jaw shape and symmetry through pharyngeal-cardiac tissue relationships

BACKGROUND

Asymmetries in craniofacial anomalies are commonly observed. In the facial skeleton, the left side is more commonly and/or severely affected than the right. Such asymmetries complicate treatment options. Mechanisms underlying variation in disease severity between individuals as well as within individuals (asymmetries) are still relatively unknown.

RESULTS

Developmental reductions in fibroblast growth factor 8 (Fgf8) have a dosage dependent effect on jaw size, shape, and symmetry. Further, Fgf8 mutants have directionally asymmetric jaws with the left side being more affected than the right. Defects in lower jaw development begin with disruption to Meckel's cartilage, which is discontinuous. All skeletal elements associated with the proximal condensation are dysmorphic, exemplified by a malformed and misoriented malleus. At later stages, Fgf8 mutants exhibit syngnathia, which falls into two broad categories: bony fusion of the maxillary and mandibular alveolar ridges and zygomatico-mandibular fusion. All of these morphological defects exhibit both inter- and intra-specimen variation.

CONCLUSIONS

We hypothesize that these asymmetries are linked to heart development resulting in higher levels of Fgf8 on the right side of the face, which may buffer the right side to developmental perturbations. This mouse model may facilitate future investigations of mechanisms underlying human syngnathia and facial asymmetry.

The Core Splicing Factors EFTUD2, SNRPB and TXNL4A Are Essential for Neural Crest and Craniofacial Development

Mandibulofacial dysostosis (MFD) is a human congenital disorder characterized by hypoplastic neural-crest-derived craniofacial bones often associated with outer and middle ear defects. There is growing evidence that mutations in components of the spliceosome are a major cause for MFD. Genetic variants affecting the function of several core splicing factors, namely SF3B4, SF3B2, EFTUD2, SNRPB and TXNL4A, are responsible for MFD in five related but distinct syndromes known as Nager and Rodriguez syndromes (NRS), craniofacial microsomia (CFM), mandibulofacial dysostosis with microcephaly (MFDM), cerebro-costo-mandibular syndrome (CCMS) and Burn–McKeown syndrome (BMKS), respectively. Animal models of NRS and MFDM indicate that MFD results from an early depletion of neural crest progenitors through a mechanism that involves apoptosis. Here we characterize the knockdown phenotype of Eftud2, Snrpb and Txnl4a in Xenopus embryos at different stages of neural crest and craniofacial development. Our results point to defects in cranial neural crest cell formation as the likely culprit for MFD associated with EFTUD2, SNRPB and TXNL4A haploinsufficiency, and suggest a commonality in the etiology of these craniofacial spliceosomopathies.

Oculo-auriculo-vertebral spectrum: new genes and literature review on a complex disease

Oculo-auriculo-vertebral spectrum (OAVS) or Goldenhar syndrome is due to an abnormal development of first and second branchial arches derivatives during embryogenesis and is characterised by hemifacial microsomia associated with auricular, ocular and vertebral malformations. The clinical and genetic heterogeneity of this spectrum with incomplete penetrance and variable expressivity, render its molecular diagnosis difficult. Only a few recurrent CNVs and genes have been identified as causatives in this complex disorder so far. Prenatal environmental causal factors have also been hypothesised. However, most of the patients remain without aetiology. In this review, we aim at updating clinical diagnostic criteria and describing genetic and non-genetic aetiologies, animal models as well as novel diagnostic tools and surgical management, in order to help and improve clinical care and genetic counselling of these patients and their families.

The crucial role of model systems in understanding the complexity of cell signaling in human neurocristopathies

Animal models are useful to study the molecular, cellular, and morphogenetic mechanisms underlying normal and pathological development. Cell-based study models have emerged as an alternative approach to study many aspects of human embryonic development and disease. The neural crest (NC) is a transient, multipotent, and migratory embryonic cell population that generates a diverse group of cell types that arises during vertebrate development. The abnormal formation or development of the NC results in neurocristopathies (NCPs), which are characterized by a broad spectrum of functional and morphological alterations. The impaired molecular mechanisms that give rise to these multiphenotypic diseases are not entirely clear yet. This fact, added to the high incidence of these disorders in the newborn population, has led to the development of systematic approaches for their understanding. In this article, we have systematically reviewed the ways in which experimentation with different animal and cell model systems has improved our knowledge of NCPs, and how these advances might contribute to the development of better diagnostic and therapeutic tools for the treatment of these pathologies. This article is categorized under: Congenital Diseases > Genetics/Genomics/Epigenetics Congenital Diseases > Stem Cells and Development Congenital Diseases > Molecular and Cellular Physiology Neurological Diseases > Genetics/Genomics/Epigenetics.

Mir24-2-5p suppresses the osteogenic differentiation with Gnai3 inhibition presenting a direct target via inactivating JNK-p38 MAPK signaling axis

Background: Congenital anomalies are increasingly becoming a global pediatric health concern, which requires immediate attention to its early diagnosis, preventive strategies, and efficient treatments. Guanine nucleotide binding protein, alpha inhibiting activity polypeptide 3 (Gnai3) gene mutation has been demonstrated to cause congenital small jaw deformity, but the functions of Gnai3 in the disease-specific microRNA (miRNA) upregulations and their downstream signaling pathways during osteogenesis have not yet been reported. Our previous studies found that the expression of Mir24-2-5p was significantly downregulated in the serum of young people with overgrowing mandibular, and bioinformatics analysis suggested possible binding sites of Mir24-2-5p in the Gnai3 3'UTR region. Therefore, this study was designed to investigate the mechanism of Mir24-2-5p-mediated regulation of Gnai3 gene expression and explore the possibility of potential treatment strategies for bone defects.

Methods: Synthetic miRNA mimics and inhibitors were transduced into osteoblast precursor cells to regulate Mir24-2-5p expression. Dual-luciferase reporter assay was utilized to identify the direct binding of Gnai3 and its regulator Mir24-2-5p. Gnai3 levels in osteoblast precursor cells were downregulated by shRNA (shGnai3). Agomir, Morpholino Oligo (MO), and mRNA were microinjected into zebrafish embryos to control mir24-2-5p and gnai3 expression. Relevant expression levels were determined by the qRT-PCR and Western blotting. CCK-8 assay, flow cytometry, and transwell migration assays were performed to assess cell proliferation, apoptosis, and migration. ALP, ARS and Von Kossa staining were performed to observe osteogenic differentiation. Alcian blue staining and calcein immersions were performed to evaluate the embryonic development and calcification of zebrafish.

Results: The expression of Mir24-2-5p was reduced throughout the mineralization process of osteoblast precursor cells. miRNA inhibitors and mimics were transfected into osteoblast precursor cells. Cell proliferation, migration, osteogenic differentiation, and mineralization processes were measured, which showed a reverse correlation with the expression of Mir24-2-5p. Dual-luciferase reporter gene detection assay confirmed the direct interaction between Mir24-2-5p and Gnai3 mRNA. Moreover, in osteoblast precursor cells treated with Mir24-2-5p inhibitor, the expression of Gnai3 gene was increased, suggesting that Mir24-2-5p negatively targeted Gnai3. Silencing of Gnai3 inhibited osteoblast precursor cells proliferation, migration, osteogenic differentiation, and mineralization. Promoting effects of osteoblast precursor cells proliferation, migration, osteogenic differentiation, and mineralization by low expression of Mir24-2-5p was partially rescued upon silencing of Gnai3. In vivo, mir24-2-5p Agomir microinjection into zebrafish embryo resulted in shorter body length, smaller and retruded mandible, decreased cartilage development, and vertebral calcification, which was partially rescued by microinjecting gnai3 mRNA. Notably, quite similar phenotypic outcomes were observed in gnai3 MO embryos, which were also partially rescued by mir24-2-5p MO. Besides, the expression of phospho-JNK (p-JNK) and p-p38 were increased upon Mir24-2-5p inhibitor treatment and decreased upon shGnai3-mediated Gnai3 downregulation in osteoblast precursor cells. Osteogenic differentiation and mineralization abilities of shGnai3-treated osteoblast precursor cells were promoted by p-JNK and p-p38 pathway activators, suggesting that Gnai3 might regulate the differentiation and mineralization processes in osteoblast precursor cells through the MAPK signaling pathway.

Conclusions: In this study, we investigated the regulatory mechanism of Mir24-2-5p on Gnai3 expression regulation in osteoblast precursor cells and provided a new idea of improving the prevention and treatment strategies for congenital mandibular defects and mandibular protrusion.

Prenatal diagnosis of auriculocondylar syndrome with a novel missense variant of GNAI3: a case report

BACKGROUND

Auriculocondylar syndrome (ACS) is a rare disorder characterized by micrognathia, mandibular condyle hypoplasia, and auricular abnormalities. Only 6 pathogenic variants of GNAI3 have been identified associated with ACS so far. Here, we report a case of prenatal genetic diagnosis of ACS carrying a novel GNAI3 variant.

CASE PRESENTATION

A woman with 30 weeks of gestation was referred to genetic counseling for polyhydramnios and fetal craniofacial anomaly. Severe micrognathia and mandibular hypoplasia were identified on ultrasonography. The mandibular length was 2.4 cm, which was markedly smaller than the 95th percentile. The ears were low-set with no cleft or notching between the lobe and helix. The face was round with prominent cheeks. Whole-exome sequencing identified a novel de novo missense variant of c.140G > A in the GNAI3 gene. This mutation caused an amino acid substitution of p.Ser47Asn in the highly conserved G1 motif, which was predicted to impair the guanine nucleotide-binding function. All ACS cases with GNAI3 mutations were literature reviewed, revealing female-dominated severe cases and right-side-prone deformities.

CONCLUSION

Severe micrognathia and mandibular hypoplasia accompanied by polyhydramnios are prenatal indicators of ACS. We expanded the mutation spectrum of GNAI3 and summarized clinical features to promote awareness of ACS.

Monogenic Syndromes with Congenital Heart Diseases in Newborns (Diagnostic Clues for Neonatologists): A Critical Analysis with Systematic Literature Review

Congenital heart disease (CHD), the most common major congenital anomaly, is associated with a genetic syndrome (chromosomal anomalies, genomic disorders, or monogenic disease) in 30% of patients. The aim of this systematic review was to evaluate if, in the neonatal setting, clinical clues that orient the diagnostic path can be identified. For this purpose, we revised the most frequent dysmorphic features described in newborns with CHD, comparing those associated with monogenic syndromes (MSG) with the ones reported in newborns with genomic disorders. For this systematic review according to PRISMA statement, we used PubMed, Medline, Google Scholar, Scopus database, and search terms related to CHD and syndrome. We found a wide range of dysmorphisms (ocular region, ears, mouth, and/or palate and phalangeal anomalies) detected in more than half of MSGs were found to be associated with CHDs, but those anomalies are also described in genomic rearrangements syndromes with equal prevalence. These findings confirmed that etiological diagnosis in newborns is challenging, and only the prompt and expert recognition of features suggestive of genetic conditions can improve the selection of appropriate, cost-effective diagnostic tests. However, in general practice, it is crucial to recognize clues that can suggest the presence of a genetic syndrome, and neonatologists often have the unique opportunity to be the first to identify abnormalities in the neonate.

The Mandibular and Hyoid Arches-From Molecular Patterning to Shaping Bone and Cartilage

The mandibular and hyoid arches collectively make up the facial skeleton, also known as the viscerocranium. Although all three germ layers come together to assemble the pharyngeal arches, the majority of tissue within viscerocranial skeletal components differentiates from the neural crest. Since nearly one third of all birth defects in humans affect the craniofacial region, it is important to understand how signalling pathways and transcription factors govern the embryogenesis and skeletogenesis of the viscerocranium. This review focuses on mouse and zebrafish models of craniofacial development. We highlight gene regulatory networks directing the patterning and osteochondrogenesis of the mandibular and hyoid arches that are actually conserved among all gnathostomes. The first part of this review describes the anatomy and development of mandibular and hyoid arches in both species. The second part analyses cell signalling and transcription factors that ensure the specificity of individual structures along the anatomical axes. The third part discusses the genes and molecules that control the formation of bone and cartilage within mandibular and hyoid arches and how dysregulation of molecular signalling influences the development of skeletal components of the viscerocranium. In conclusion, we notice that mandibular malformations in humans and mice often co-occur with hyoid malformations and pinpoint the similar molecular machinery controlling the development of mandibular and hyoid arches.

An adverse outcome pathway on the disruption of retinoic acid metabolism leading to developmental craniofacial defects

Adverse outcome pathway (AOP) is a conceptual framework that links a molecular initiating event (MIE) via intermediate key events (KEs) with adverse effects (adverse outcomes, AO) relevant for risk assessment, through defined KE relationships (KERs). The aim of the present work is to describe a linear AOP, supported by experimental data, for skeletal craniofacial defects as the AO. This AO was selected in view of its relative high incidence in humans and the suspected relation to chemical exposure. We focused on inhibition of CYP26, a retinoic acid (RA) metabolizing enzyme, as MIE, based on robust previously published data. Conazoles were selected as representative stressors. Intermediate KEs are RA disbalance, aberrant HOX gene expression, disrupted specification, migration, and differentiation of neural crest cells, and branchial arch dysmorphology. We described the biological basis of the postulated events and conducted weight of evidence (WoE) assessments. The biological plausibility and the overall empirical evidence were assessed as high and moderate, respectively, the latter taking into consideration the moderate evidence for concordance of dose-response and temporal relationships. Finally, the essentiality assessment of the KEs, considered as high, supported the robustness of the presented AOP. This AOP, which appears of relevance to humans, thus contributes to mechanistic underpinning of selected test methods, thereby supporting their application in integrated new approach test methodologies and strategies and application in a regulatory context.

Molecular mechanisms of hearing loss in Nager syndrome

Nager syndrome is a rare human developmental disorder characterized by hypoplastic neural crest-derived craniofacial bones and limb defects. Mutations in SF3B4 gene, which encodes a component of the spliceosome, are a major cause for Nager. A review of the literature indicates that 45% of confirmed cases are also affected by conductive, sensorineural or mixed hearing loss. Conductive hearing loss is due to defective middle ear ossicles, which are neural crest derived, while sensorineural hearing loss typically results from defective inner ear or vestibulocochlear nerve, which are both derived from the otic placode. Animal model of Nager syndrome indicates that upon Sf3b4 knockdown cranial neural crest progenitors are depleted, which may account for the conductive hearing loss in these patients. To determine whether Sf3b4 plays a role in otic placode formation we analyzed the impact of Sf3b4 knockdown on otic development. Sf3b4-depleted Xenopus embryos exhibited reduced expression of several pan-placodal genes six1, dmrta1 and foxi4.1. We confirmed the dependence of placode genes expression on Sf3b4 function in animal cap explants expressing noggin, a BMP antagonist critical to induce placode fate in the ectoderm. Later in development, Sf3b4 morphant embryos had reduced expression of pax8, tbx2, otx2, bmp4 and wnt3a at the otic vesicle stage, and altered otic vesicle development. We propose that in addition to the neural crest, Sf3b4 is required for otic development, which may account for sensorineural hearing loss in Nager syndrome.

A novel missense variant of the GNAI3 gene and recognisable morphological characteristics of the mandibula in ARCND1

Auriculocondylar syndrome (ARCND) is an autosomal monogenic disorder characterised by external ear abnormalities and micrognathia due to hypoplasia of the mandibular rami, condyle and coronoid process. Genetically, three subtypes of ARCND (ARCND1, ARCND2 and ARCND3) have been reported. To date, five pathogenic variants of GNAI3 have been reported in ARCND1 patients. Here, we report a novel variant of GNAI3 (NM_006496:c.807C>A:p.(Asn269Lys)) in a Japanese girl with micrognathia using trio-based whole exome sequencing analysis. The GNAI3 gene encodes a heterotrimeric guanine nucleotide-binding protein. The novel variant locates the guanine nucleotide-binding site, and the substitution was predicted to interfere with guanine nucleotide-binding by in silico structural analysis. Three-dimensional computer tomography scan, or cephalogram, displayed severely hypoplastic mandibular rami and fusion to the medial and lateral pterygoid plates, which have been recognised in other ARCND1 patients, but have not been described in ARCND2 and ARCND3, suggesting that these may be distinguishable features in ARCND1.

Tracking the movement of individual avian neural crest cells in vitro

The origin, migratory pathways and adult derivatives of neural crest cells (NCCs) are well known. However, less is known about how these cells migrate. In this study, in a laboratory based in a low-resource setting, a hanging drop culture assay was utilised to study the movement of individual avian trunk neural crest cells. Mode of migration by means of lamellipodia and filopodia was studied in live cell cultures with a laser scanning confocal microscope and Airyscan module. Both distance migrated and speed of migration were calculated. NCCs migrated in a chain soon after emerging from the explanted neural tube, but were more dispersed and had random movements when they reached the periphery of the culture. While the distances travelled by these NCCs were less and the cells were slower on gelatine than on other extracellular matrices reported in the literature, the assay afforded detailed observation of actin filament distribution and cytoplasmic protrusions. The study has provided unique evidence of individual NCC movements in vitro, in a simple hanging drop assay optimized for the study of NCCs. The assay could be used for further analysis of the behaviour of NCCs on different extracellular matrices or with targeted action.

Imaging of the Fetal Zygomatic Bone: A Key Role in Prenatal Diagnosis of First Branchial Arch Syndrome

OBJECTIVES

First arch syndromes are congenital defects caused by failure of neural crest cells to migrate into the first branchial arch. First arch syndrome is classified into 2 main clinical manifestations: Treacher Collins syndrome, characterized by bilateral underdevelopment of the zygomatic bones; and Pierre Robin sequence. The aim of this study was to describe the feasibility of visualization of the fetal zygomatic bone and assess its application in cases referred for features suggestive of first arch syndrome.

METHODS

A prospective cohort study was conducted. The feasibility of visualization of the zygomatic bone was performed in 50 sequential fetuses with a normal anatomic scan between 12 and 24 weeks' gestation using 3-dimensional sonography. Following this, cases referred for targeted scans for suspected first branchial arch syndrome were assessed for the presence or absence of the zygomatic bones.

RESULTS

Visualization of the fetal zygomatic bone was feasible in all low-risk cases. Cases referred for targeted scans included 11 isolated cases of micrognathia or retrognathia, 3 cases of microtia, and 3 cases of auricular or facial vestiges. Within this group, the zygomatic bones were visualized in all but 2 cases. No associated extrafacial malformations were detected; therefore, this phenotype was consistent with Treacher Collins syndrome.

CONCLUSIONS

Prenatal imaging of the zygomatic bones offers a clinically based sonographic approach to cases referred for features suggestive of first arch syndrome and enables differentiation between the 2 main clinical manifestations: Treacher Collins syndrome and Pierre Robin sequence.

Further phenotypic delineation of the auriculocondylar syndrome type 2 with literature review

Auriculocondylar syndrome (ACS) is an ultra-rare disorder that arises from developmental defects of the first and second pharyngeal arches. Three subtypes of ACS have been described so far, i.e., ACS1 (MIM: 602483), ACS2 (MIM: 600810), and ACS3 (MIM: 131240). The majority of patients, however, are affected by ACS2, which results from the mutations in the PLCB4 gene. Herein, we have described an 8-year-old male patient presenting with ACS2 and summarized the molecular and phenotypic spectrum of the syndrome. We have also compared the clinical features of our case to three other previously described cases (one sporadic and two familial) harboring the same heterozygous missense variant c.1862G>A, p.Arg621His in the PLCB4 gene. The mutation was detected using whole-exome sequencing (WES). Due to low coverage of WES and suspicion of somatic mosaicism, the variant was additionally reassessed by deep targeted next-generation sequencing panel of genes related to the craniofacial disorders, and next confirmed by Sanger sequencing. ACS2 presents high intra- and interfamilial phenotypic heterogeneity that impedes reaching an exact clinical and molecular diagnosis. Thus, describing additional cases, carrying even the known mutation, but resulting in variable phenotypes, is essential for better understanding of such orphan Mendelian diseases.

A familial PLCB4 mutation causing auriculocondylar syndrome 2 with variable severity

Auriculocondylar syndrome (ARCND, MIM #614669, #602483, and #615706); also known as ''question-mark ear syndrome'' or ''dysgnathia complex'', is a rare craniofacial malformation of first and second branchial arches with a prevalence of <1/1,000,000. It is characterized by a distinctive auricular malformation (question mark ear (QME)) and highly variable mandibular anomalies. Variants found in PLCB4, GNAI3, and in EDN1 genes are responsible for >90% of tested ARCND patients. Whole exome sequencing in a multigenerational Egyptian kindred with high intrafamilial variability revealed a known heterozygous missense variant in PLCB4 (NM_000933.3:c.1862G>A:p.(Arg621His)). This report increases the number of molecularly characterized ARCND patients to 29 and emphasizes the highly variable clinical presentation within families.

Latin American contributions to the neural crest field

The neural crest (NC) is one of the most fascinating structures during embryonic development. Unique to vertebrate embryos, these cells give rise to important components of the craniofacial skeleton, such as the jaws and skull, as well as melanocytes and ganglia of the peripheral nervous system. Worldwide, several groups have been studying NC development and specifically in the Latin America (LA) they have been growing in numbers since the 1990s. It is important for the world to recognize the contributions of LA researchers on the knowledge of NC development, as it can stimulate networking and improvement in the field. We developed a database of LA publications on NC development using ORCID and PUBMED as search engines. We thoroughly describe all of the contributions from LA, collected in five major topics on NC development mechanisms: i) induction and specification; ii) migration; iii) differentiation; iv) adult NC; and, v) neurocristopathies. Further analysis was done to correlate each LA country with topics and animal models, and to access collaboration between LA countries. We observed that some LA countries have made important contributions to the comprehension of NC development. Interestingly, some LA countries have a topic and an animal model as their strength; in addition, collaboration between LA countries is almost inexistent. This review will help LA NC research to be acknowledged, and to facilitate networking between students and researchers worldwide.

Neurocristopathies: New insights 150 years after the neural crest discovery

The neural crest (NC) is a transient, multipotent and migratory cell population that generates an astonishingly diverse array of cell types during vertebrate development. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others. Neurocristopathies (NCP) are a class of pathologies occurring in vertebrates, especially in humans that result from the abnormal specification, migration, differentiation or death of neural crest cells during embryonic development. Various pigment, skin, thyroid and hearing disorders, craniofacial and heart abnormalities, malfunctions of the digestive tract and tumors can also be considered as neurocristopathies. In this review we revisit the current classification and propose a new way to classify NCP based on the embryonic origin of the affected tissues, on recent findings regarding the molecular mechanisms that drive NC formation, and on the increased complexity of current molecular embryology techniques.

Low-set ears and associated anomalies in human foetuses

OBJECTIVES

To determine the prevalence of low-set ears (LSE) in a group of human foetuses, to analyse the associated anomalies, and to review the development mechanisms possibly involved.

METHODS

A total of 1759 human foetuses from spontaneous abortion were evaluated. Foetuses were obtained from the Foetuses and Embryos Collection of the Embryology Department of the Faculty of Medicine of the Autonomous University of Nuevo León. The Ethics Committee gave its approval for this study (EH-230-16). The position of the auricles was determined according to the standards recommended by the Elements of Morphology. Two study groups were created: foetuses with LSE and foetuses with normal ears. In both groups, a detailed examination of the external morphology was performed, followed by thoraco-abdominal micro dissection. Statistical analysis was performed.

RESULTS

Two hundred two of the foetuses presented LSE (1148 per 10,000). In this group, 68.8% did not present associated anomalies, while 31.2% had an associated anomaly. The most frequently affected organ was the heart (53.6%), followed by the digestive tract (23.9%), urinary system (16.9%), head and neck (4.2%), and limbs (1.4%). In the group of foetuses with normal ears, only 7.4% of the specimens had associated anomalies, which was a significant difference compared with the LSE group.

CONCLUSIONS

Based on the obtained results, we consider that LSE can be used as a sensitive indicator of major anomalies. It is recommended to include a systematic assessment of the position of the auricles in the initial clinical evaluation of any newborn.

Targeted molecular investigation in patients within the clinical spectrum of Auriculocondylar syndrome

Auriculocondylar syndrome, mainly characterized by micrognathia, small mandibular condyle, and question mark ears, is a rare disease segregating in an autosomal dominant pattern in the majority of the families reported in the literature. So far, pathogenic variants in PLCB4, GNAI3, and EDN1 have been associated with this syndrome. It is caused by a developmental abnormality of the first and second pharyngeal arches and it is associated with great inter- and intra-familial clinical variability, with some patients not presenting the typical phenotype of the syndrome. Moreover, only a few patients of each molecular subtype of Auriculocondylar syndrome have been reported and sequenced. Therefore, the spectrum of clinical and genetic variability is still not defined. In order to address these questions, we searched for alterations in PLCB4, GNAI3, and EDN1 in patients with typical Auriculocondylar syndrome (n = 3), Pierre Robin sequence-plus (n = 3), micrognathia with additional craniofacial malformations (n = 4), or non-specific auricular dysplasia (n = 1), which could represent subtypes of Auriculocondylar syndrome. We found novel pathogenic variants in PLCB4 only in two of three index patients with typical Auriculocondylar syndrome. We also performed a detailed comparative analysis of the patients presented in this study with those previously published, which showed that the pattern of auricular abnormality and full cheeks were associated with molecularly characterized individuals with Auriculocondylar syndrome. Finally, our data contribute to a better definition of a set of parameters for clinical classification that may be used as a guidance for geneticists ordering molecular testing for Auriculocondylar syndrome. © 2017 Wiley Periodicals, Inc.

EIF4A3 deficient human iPSCs and mouse models demonstrate neural crest defects that underlie Richieri-Costa-Pereira syndrome

Biallelic loss-of-function mutations in the RNA-binding protein EIF4A3 cause Richieri-Costa-Pereira syndrome (RCPS), an autosomal recessive condition mainly characterized by craniofacial and limb malformations. However, the pathogenic cellular mechanisms responsible for this syndrome are entirely unknown. Here, we used two complementary approaches, patient-derived induced pluripotent stem cells (iPSCs) and conditional Eif4a3 mouse models, to demonstrate that defective neural crest cell (NCC) development explains RCPS craniofacial abnormalities. RCPS iNCCs have decreased migratory capacity, a distinct phenotype relative to other craniofacial disorders. Eif4a3 haploinsufficient embryos presented altered mandibular process fusion and micrognathia, thus recapitulating the most penetrant phenotypes of the syndrome. These defects were evident in either ubiquitous or NCC-specific Eif4a3 haploinsufficient animals, demonstrating an autonomous requirement of Eif4a3 in NCCs. Notably, RCPS NCC-derived mesenchymal stem-like cells (nMSCs) showed premature bone differentiation, a phenotype paralleled by premature clavicle ossification in Eif4a3 haploinsufficient embryos. Likewise, nMSCs presented compromised in vitro chondrogenesis, and Meckel's cartilage was underdeveloped in vivo. These findings indicate novel and essential requirements of EIF4A3 for NCC migration and osteochondrogenic differentiation during craniofacial development. Altogether, complementary use of iPSCs and mouse models pinpoint unique cellular mechanisms by which EIF4A3 mutation causes RCPS, and provide a paradigm to study craniofacial disorders.

Viable Ednra Y129F mice feature human mandibulofacial dysostosis with alopecia (MFDA) syndrome due to the homologue mutation

Animal models resembling human mutations are valuable tools to research the features of complex human craniofacial syndromes. This is the first report on a viable dominant mouse model carrying a non-synonymous sequence variation within the endothelin receptor type A gene (Ednra c.386A>T, p.Tyr129Phe) derived by an ENU mutagenesis program. The identical amino acid substitution was reported recently as disease causing in three individuals with the mandibulofacial dysostosis with alopecia (MFDA, OMIM 616367) syndrome. We performed standardized phenotyping of wild-type, heterozygous, and homozygous Ednra^Y129F mice within the German Mouse Clinic. Mutant mice mimic the craniofacial phenotypes of jaw dysplasia, micrognathia, dysplastic temporomandibular joints, auricular dysmorphism, and missing of the squamosal zygomatic process as described for MFDA-affected individuals. As observed in MFDA-affected individuals, mutant Ednra^Y129F mice exhibit hearing impairment in line with strong abnormalities of the ossicles and further, reduction of some lung volumetric parameters. In general, heterozygous and homozygous mice demonstrated inter-individual diversity of expression of the craniofacial phenotypes as observed in MFDA patients but without showing any cleft palates, eyelid defects, or alopecia. Mutant Ednra^Y129F mice represent a valuable viable model for complex human syndromes of the first and second pharyngeal arches and for further studies and analysis of impaired endothelin 1 (EDN1)–endothelin receptor type A (EDNRA) signaling. Above all, Ednra^Y129F mice model the recently published human MFDA syndrome and may be helpful for further disease understanding and development of therapeutic interventions.

Genetic Advances in the Understanding of Microtia

Microtia is a genetic condition affecting the external ears and presents clinically along a wide spectrum: minimally affected ears are small with minor shape abnormalities; extremely affected ears lack all identifiable structures, with the most extreme being absence of the entire external ear. Multiple genetic causes have been linked to microtia in both animal models and humans, which are improving our understanding of the condition and may lead to the identification of a unified cause for the condition. Microtia is also a prominent feature of several genetic syndromes, the study of which has provided further insight into the possible causes and genetic mechanisms of the condition. This article reviews our current understanding of microtia including epidemiological characteristics, classification systems, environmental and genetic causative factors leading to microtia. Despite our increased understanding of the genetics of microtia, we do not have a means of preventing the condition and still rely on complex staged, surgical correction.

Respiratory and gastrointestinal dysfunctions associated with auriculo-condylar syndrome and a homozygous PLCB4 loss-of-function mutation

Auriculo-Condylar Syndrome (ACS) is a craniofacial malformation syndrome characterized by external ear anomalies, hypoplasia of the mandibular condyle, temporomandibular joint abnormalities, micrognathia, and microstomia. Glossoptosis, masticatory abnormalities, orthodontic problems, and malocclusion occur in a majority of affected subjects. The clinical diagnosis is usually suggested by the pathognomonic ear appearance ("question mark ear"), consisting of a variable degree of clefting between the helix and earlobe. The genetic mechanisms underlying ACS have recently been identified. Both autosomal dominant and recessive inheritance of mutations in phospholipase C, beta 4 (PLCB4) and endothelin 1 (EDN1) have been reported along with autosomal dominant mutations in guanine nucleotide-binding protein (G protein) α inhibiting activity polypeptide 3 (GNAI3). We report 6 years of follow-up of a child with a clinical phenotype consistent with ACS due to a homozygous frameshift mutation in PLCB4. The baby presented feeding difficulties associated with failure to thrive and a complex sleep-related respiratory disorder, characterized by central and obstructive apnoeas. Our observations of this case further delineate the phenotype of ACS associated with autosomal recessive PLCB4 loss-of-function mutations, underscoring gastrointestinal dysfunction and severe sleep-related breathing abnormalities as additional features when compared to patients with heterozygous mutations with a presumed dominant negative effect. © 2016 Wiley Periodicals, Inc.

Sf3b4-depleted Xenopus embryos: A model to study the pathogenesis of craniofacial defects in Nager syndrome

Mandibulofacial dysostosis (MFD) is a human developmental disorder characterized by defects of the facial bones. It is the second most frequent craniofacial malformation after cleft lip and palate. Nager syndrome combines many features of MFD with a variety of limb defects. Mutations in SF3B4 (splicing factor 3b, subunit 4) gene, which encodes a component of the pre-mRNA spliceosomal complex, were recently identified as a cause of Nager syndrome, accounting for 60% of affected individuals. Nothing is known about the cellular pathogenesis underlying Nager type MFD. Here we describe the first animal model for Nager syndrome, generated by knocking down Sf3b4 function in Xenopus laevis embryos, using morpholino antisense oligonucleotides. Our results indicate that Sf3b4-depleted embryos show reduced expression of the neural crest genes sox10, snail2 and twist at the neural plate border, associated with a broadening of the neural plate. This phenotype can be rescued by injection of wild-type human SF3B4 mRNA but not by mRNAs carrying mutations that cause Nager syndrome. At the tailbud stage, morphant embryos had decreased sox10 and tfap2a expression in the pharyngeal arches, indicative of a reduced number of neural crest cells. Later in development, Sf3b4-depleted tadpoles exhibited hypoplasia of neural crest-derived craniofacial cartilages, phenocopying aspects of the craniofacial skeletal defects seen in Nager syndrome patients. With this animal model we are now poised to gain important insights into the etiology and pathogenesis of Nager type MFD, and to identify the molecular targets of Sf3b4.

Developmental mechanisms underlying variation in craniofacial disease and evolution

Craniofacial disease phenotypes exhibit significant variation in penetrance and severity. Although many genetic contributions to phenotypic variation have been identified, genotype-phenotype correlations remain imprecise. Recent work in evolutionary developmental biology has exposed intriguing developmental mechanisms that potentially explain incongruities in genotype-phenotype relationships. This review focuses on two observations from work in comparative and experimental animal model systems that highlight how development structures variation. First, multiple genetic inputs converge on relatively few developmental processes. Investigation of when and how variation in developmental processes occurs may therefore help predict potential genetic interactions and phenotypic outcomes. Second, genetic mutation is typically associated with an increase in phenotypic variance. Several models outlining developmental mechanisms underlying mutational increases in phenotypic variance are discussed using Satb2-mediated variation in jaw size as an example. These data highlight development as a critical mediator of genotype-phenotype correlations. Future research in evolutionary developmental biology focusing on tissue-level processes may help elucidate the "black box" between genotype and phenotype, potentially leading to novel treatment, earlier diagnoses, and better clinical consultations for individuals affected by craniofacial anomalies.

Cheek fistula from the ectopic salivary gland: a variant of the oculo-auriculo-vertebral spectrum

OBJECTIVES/HYPOTHESIS

This study aimed to investigate the diagnosis and management of a distinct developmental deformity syndrome characterized by congenital cheek fistula, ectopic accessory parotid gland, and preauricular appendage.

STUDY DESIGN

Retrospective study.

METHODS

We analyzed the medical records, radiologic and histopathologic findings, and follow-up data for seven patients (four males) with a congenital cheek salivary fistula. Computed tomography, fistulography, and sialography had been performed for diagnosis. Surgical treatment effect was evaluated.

RESULTS

The mean age of the patients was 8.1 years (range, 2-16 years). The distinctive clinical feature was a congenital skin orifice lateral to the commissure with saliva discharge during eating. The cheek fistulae were accompanied by ipsilateral preauricular appendages in all seven patients. The skin orifice connected to an ectopic gland anterior to the masseter and inferior to Stensen's duct. Parotid sialography demonstrated an intact Stensen's duct in all cases. Hypoplasia of the ipsilateral mandible could be observed in five cases. Excision of the ectopic gland, skin orifice, and fistula was performed in five cases resulting in optimal treatment outcomes with no recurrent or adverse events.

CONCLUSIONS

A congenital saliva-discharging fistula with an ectopic accessory parotid gland, ipsilateral preauricular appendage, and mandibular hypoplasia constitutes a rare developmental syndrome. Surgical excision can effectively treat congenital cheek salivary fistula.

LEVEL OF EVIDENCE

4.

Morphologic Variations of Clinically Normal Mallei and Incudes

Objectives:

Various features and shapes of malleus and incus are reported. Partially or unaddressed are their bilateral symmetry, correlation with otitis media, and concordance of features and shapes. Such information may contribute to the understanding of malleus and incus ontogeny and the installation and function of implantable middle ear devices. We sought to address the following hypotheses: (1) a cranium’s malleus and incus have bilateral symmetry, with respect to their features and shapes; (2) features and shapes of malleus and incus are unrelated to the mastoid size indicator of childhood otitis media; and (3) an ear’s malleus and incus have concordant features and shapes (ie, the presence or absence of a feature or shape of a malleus or incus is associated with the presence or absence of another feature or shape in that ear’s malleus or incus).

Methods:

Postmortem material-analysis prevalence study of 41 adult crania without clinical otitis media. Mastoid sizes were assessed radiographically.

Results:

Most mallei had lateral processes and inflected manubrium tips. Most incudes had concave superior borders of their short processes, non-notched inferior borders of their short processes, and anteriorly curved anterior edges of their long processes. Only 1 feature, absence of the lateral process of the malleus, was suggested to have a relationship to small mastoid size. Concordance was not found for any shape or feature of the malleus or incus.

Conclusion:

Clinically normal mallei and incudes have feature and shape variations that are mostly bilaterally symmetric.

Foxi transcription factors promote pharyngeal arch development by regulating formation of FGF signaling centers

The bones of the vertebrate face develop from transient embryonic branchial arches that are populated by cranial neural crest cells. We have characterized a mouse mutant for the Forkhead family transcription factor Foxi3, which is expressed in branchial ectoderm and endoderm. Foxi3 mutant mice are not viable and display severe branchial arch-derived facial skeleton defects, including absence of all but the most distal tip of the mandible and complete absence of the inner, middle and external ear structures. Although cranial neural crest cells of Foxi3 mutants are able to migrate, populate the branchial arches, and display some elements of correct proximo-distal patterning, they succumb to apoptosis from embryonic day 9.75 onwards. We show this cell death correlates with a delay in expression of Fgf8 in branchial arch ectoderm and a failure of neural crest cells in the arches to express FGF-responsive genes. Zebrafish foxi1 is also expressed in branchial arch ectoderm and endoderm, and morpholino knock-down of foxi1 also causes apoptosis of neural crest in the branchial arches. We show that heat shock induction of fgf3 in zebrafish arch tissue can rescue cell death in foxi1 morphants. Our results suggest that Foxi3 may play a role in the establishment of signaling centers in the branchial arches that are required for neural crest survival, patterning and the subsequent development of branchial arch derivatives.

SAMS, a syndrome of short stature, auditory-canal atresia, mandibular hypoplasia, and skeletal abnormalities is a unique neurocristopathy caused by mutations in Goosecoid

Short stature, auditory canal atresia, mandibular hypoplasia, and skeletal abnormalities (SAMS) has been reported previously to be a rare, autosomal-recessive developmental disorder with other, unique rhizomelic skeletal anomalies. These include bilateral humeral hypoplasia, humeroscapular synostosis, pelvic abnormalities, and proximal defects of the femora. To identify the genetic basis of SAMS, we used molecular karyotyping and whole-exome sequencing (WES) to study small, unrelated families. Filtering of variants from the WES data included segregation analysis followed by comparison of in-house exomes. We identified a homozygous 306 kb microdeletion and homozygous predicted null mutations of GSC, encoding Goosecoid homeobox protein, a paired-like homeodomain transcription factor. This confirms that SAMS is a human malformation syndrome resulting from GSC mutations. Previously, Goosecoid has been shown to be a determinant at the Xenopus gastrula organizer region and a segment-polarity determinant in Drosophila. In the present report, we present data on Goosecoid protein localization in staged mouse embryos. These data and the SAMS clinical phenotype both suggest that Goosecoid is a downstream effector of the regulatory networks that define neural-crest cell-fate specification and subsequent mesoderm cell lineages in mammals, particularly during shoulder and hip formation. Our findings confirm that Goosecoid has an essential role in human craniofacial and joint development and suggest that Goosecoid is an essential regulator of mesodermal patterning in mammals and that it has specific functions in neural crest cell derivatives.

Mutations in endothelin 1 cause recessive auriculocondylar syndrome and dominant isolated question-mark ears

Auriculocondylar syndrome (ACS) is a rare craniofacial disorder with mandibular hypoplasia and question-mark ears (QMEs) as major features. QMEs, consisting of a specific defect at the lobe-helix junction, can also occur as an isolated anomaly. Studies in animal models have indicated the essential role of endothelin 1 (EDN1) signaling through the endothelin receptor type A (EDNRA) in patterning the mandibular portion of the first pharyngeal arch. Mutations in the genes coding for phospholipase C, beta 4 (PLCB4) and guanine nucleotide binding protein (G protein), alpha inhibiting activity polypeptide 3 (GNAI3), predicted to function as signal transducers downstream of EDNRA, have recently been reported in ACS. By whole-exome sequencing (WES), we identified a homozygous substitution in a furin cleavage site of the EDN1 proprotein in ACS-affected siblings born to consanguineous parents. WES of two cases with vertical transmission of isolated QMEs revealed a stop mutation in EDN1 in one family and a missense substitution of a highly conserved residue in the mature EDN1 peptide in the other. Targeted sequencing of EDN1 in an ACS individual with related parents identified a fourth, homozygous mutation falling close to the site of cleavage by endothelin-converting enzyme. The different modes of inheritance suggest that the degree of residual EDN1 activity differs depending on the mutation. These findings provide further support for the hypothesis that ACS and QMEs are uniquely caused by disruption of the EDN1-EDNRA signaling pathway.

Mouse Hoxa2 mutations provide a model for microtia and auricle duplication

External ear abnormalities are frequent in newborns ranging from microtia to partial auricle duplication. Little is known about the molecular mechanisms orchestrating external ear morphogenesis. In humans, HOXA2 partial loss of function induces a bilateral microtia associated with an abnormal shape of the auricle. In mice, Hoxa2 inactivation at early gestational stages results in external auditory canal (EAC) duplication and absence of the auricle, whereas its late inactivation results in a hypomorphic auricle, mimicking the human HOXA2 mutant condition. By genetic fate mapping we found that the mouse auricle (or pinna) derives from the Hoxa2-expressing neural crest-derived mesenchyme of the second pharyngeal arch, and not from a composite of first and second arch mesenchyme as previously proposed based on morphological observation of human embryos. Moreover, the mouse EAC is entirely lined by Hoxa2-negative first arch mesenchyme and does not develop at the first pharyngeal cleft, as previously assumed. Conditional ectopic Hoxa2 expression in first arch neural crest is sufficient to induce a complete duplication of the pinna and a loss of the EAC, suggesting transformation of the first arch neural crest-derived mesenchyme lining the EAC into an ectopic pinna. Hoxa2 partly controls the morphogenesis of the pinna through the BMP signalling pathway and expression of Eya1, which in humans is involved in branchio-oto-renal syndrome. Thus, Hoxa2 loss- and gain-of-function approaches in mice provide a suitable model to investigate the molecular aetiology of microtia and auricle duplication.

Extracellular metalloproteinases in neural crest development and craniofacial morphogenesis

The neural crest (NC) is a population of migratory stem/progenitor cells that is found in early vertebrate embryos. NC cells are induced during gastrulation, and later migrate to multiple destinations and contribute to many types of cells and tissues, such as craniofacial structures, cardiac tissues, pigment cells and the peripheral nervous system. Recently, accumulating evidence suggests that many extracellular metalloproteinases, including matrix metalloproteinases (MMPs), a disintegrin and metalloproteinases (ADAMs), and ADAMs with thrombospondin motifs (ADAMTSs), play important roles in various stages of NC development. Interference with metalloproteinase functions often causes defects in craniofacial structures, as well as in other cells and tissues that are contributed by NC cells, in humans and other vertebrates. In this review, we summarize the current state of the field concerning the roles of these three families of metalloproteinases in NC development and related tissue morphogenesis, with a special emphasis on craniofacial morphogenesis.

The neural crest

The neural crest (NC) is a highly migratory multipotent cell population that forms at the interface between the neuroepithelium and the prospective epidermis of a developing embryo. Following extensive migration throughout the embryo, NC cells eventually settle to differentiate into multiple cell types, ranging from neurons and glial cells of the peripheral nervous system to pigment cells, fibroblasts to smooth muscle cells, and odontoblasts to adipocytes. NC cells migrate in large numbers and their migration is regulated by multiple mechanisms, including chemotaxis, contact-inhibition of locomotion and cell sorting. Here, we provide an overview of NC formation, differentiation and migration, highlighting the molecular mechanisms governing NC migration.

Loss of function of the E3 ubiquitin-protein ligase UBE3B causes Kaufman oculocerebrofacial syndrome

Background

Kaufman oculocerebrofacial syndrome (KOS) is a developmental disorder characterised by reduced growth, microcephaly, ocular anomalies (microcornea, strabismus, myopia, and pale optic disk), distinctive facial features (narrow palpebral fissures, telecanthus, sparse and laterally broad eyebrows, preauricular tags, and micrognathia), mental retardation, and generalised hypotonia. KOS is a rare, possibly underestimated condition, with fewer than 10 cases reported to date. Here we investigate the molecular cause underlying KOS.

Methods

An exome sequencing approach was used on a single affected individual of an Italian consanguineous family coupled with mutation scanning using Sanger sequencing on a second unrelated subject with clinical features fitting the disorder.

Results

Exome sequencing was able to identify homozygosity for a novel truncating mutation (c.556C>T, p.Arg186stop) in UBE3B, which encodes a widely expressed HECT (homologous to the E6-AP carboxyl terminus) domain E3 ubiquitin-protein ligase. Homozygosity for a different nonsense lesion affecting the gene (c.1166G>A, p.Trp389stop) was documented in the second affected subject, supporting the recessive mode of inheritance of the disorder. Mutation scanning of the entire UBE3B coding sequence on a selected cohort of subjects with features overlapping, in part, those recurring in KOS did not reveal disease-causing mutations, suggesting phenotypic homogeneity of UBE3B lesions.

Discussion

Our data provide evidence that KOS is caused by UBE3B loss of function, and further demonstrate the impact of misregulation of protein ubiquitination on development and growth. The available clinical records, including those referring to four UBE3B mutation-positive subjects recently described as belonging to a previously unreported entity, which fits KOS, document the clinical homogeneity of this disorder.

Human genetic variation within neural crest enhancers: molecular and phenotypic implications

Developmental gene expression programmes are coordinated by the specialized distal cis-regulatory elements called enhancers, which integrate lineage- and signalling-dependent inputs to guide morphogenesis. In previous work, we characterized the genome-wide repertoire of active enhancers in human neural crest cells (hNCC), an embryonic cell population with critical roles in craniofacial development. We showed that in hNCC, co-occupancy of a master regulator TFAP2A with nuclear receptors NR2F1 and NR2F2 correlates with the presence of permissive enhancer chromatin states. Here, we take advantage of pre-existing human genetic variation to further explore potential cooperation between TFAP2A and NR2F1/F2. We demonstrate that isolated single nucleotide polymorphisms affecting NR2F1/F2-binding sites within hNCC enhancers can alter TFAP2A occupancy and overall chromatin features at the same enhancer allele. We propose that a similar strategy can be used to elucidate other cooperative relationships between transcription factors involved in developmental transitions. Using the neural crest and its major contribution to human craniofacial phenotypes as a paradigm, we discuss how genetic variation might modulate the molecular properties and activity of enhancers, and ultimately impact human phenotypic diversity.