Mutations in MYT1, encoding the myelin transcription factor 1, are a rare cause of OAVS

Goldenhar Syndrome Complicated by Hemifacial Microsomia and Unilateral Cleft Palate Absence

Goldenhar syndrome, also known as oculo-auriculo-vertebral spectrum (OAVS) or hemifacial microsomia (HFM), is characterized by developmental anomalies in structures such as the eyes, ears, upper jaw, lower jaw, upper palate, and spine. The facial abnormalities, stemming predominantly from branchial arch malformation, are sometimes categorized as the first and second branchial arch syndromes. Its incidence is estimated to be ∼1 in 3500. Here, the authors present a case of Goldenhar syndrome in a male infant at the age of 10 months, showcasing a particularly unique manifestation of cleft palate, for which we employed myomucosal flap reconstruction of the soft palate.

Overlapping Spectrum of Craniofacial Microsomia Phenotype in Cat-Eye Syndrome

This study reports three patients with Cat-eye Syndrome (CES), two of which present a previous clinical diagnosis of Craniofacial microsomia (CFM). Chromosomal microarray analysis (CMA) revealed a tetrasomy of 1,7 Mb at the 22q11.2q11.21 region, which is the typical region triplicated in the CES, in all patients. The most frequent craniofacial features found in individuals with CFM and CES are preauricular tags and/or pits and mandibular hypoplasia. We reinforce that the candidate genes for CFM features, particularly ear malformation, preauricular tags/pits, and facial asymmetry, can be in the proximal region of the 22q11.2 region.

Whole genome sequencing of a family with autosomal dominant features within the oculoauriculovertebral spectrum

Background

Oculoauriculovertebral Spectrum (OAVS) encompasses abnormalities on derivatives from the first and second pharyngeal arches including macrostomia, hemifacial microsomia, micrognathia, preauricular tags, ocular and vertebral anomalies. We present genetic findings on a three-generation family affected with macrostomia, preauricular tags and uni- or bilateral ptosis following an autosomal dominant pattern.

Methods

We generated whole genome sequencing data for the proband, affected parent and unaffected paternal grandparent followed by Sanger sequencing on 23 family members for the top 10 candidate genes: KCND2, PDGFRA, CASP9, NCOA3, WNT10A, SIX1, MTF1, KDR/VEGFR2, LRRK1, and TRIM2 We performed parent and sibling-based transmission disequilibrium tests and burden analysis via a penalized linear mixed model, for segregation and mutation burden respectively. Next, via bioinformatic tools we predicted protein function, mutation pathogenicity and pathway enrichment to investigate the biological relevance of mutations identified.

Results

Rare missense mutations in SIX1, KDR/VEGFR2, and PDGFRA showed the best segregation with the OAV phenotypes in this family. When considering any of the 3 OAVS phenotypes as an outcome, SIX1 had the strongest associations in parent-TDTs and sib-TDTs (p=0.025, p=0.052) (unadjusted p-values). Burden analysis identified SIX1 (RC=0.87) and PDGFRA (RC=0.98) strongly associated with OAVS severity. Using phenotype-specific outcomes, sib-TDTs identified SIX1 with uni- or bilateral ptosis (p=0.049) and ear tags (p=0.01), and PDGFRA and KDR/VEGFR2 with ear tags (both p<0.01).

Conclusion

SIX1, PDGFRA, and KDR/VEGFR2 are strongly associated to OAVS phenotypes. SIX1 has been previously associated with OAVS ear malformations and is co-expressed with EYA1 during ear development. Efforts to strengthen the genotype-phenotype co-relation underlying the OAVS are key to discover etiology, family counseling and prevention.

FBLN2 is associated with Goldenhar syndrome and is essential for cranial neural crest cell development

Goldenhar syndrome, a rare craniofacial malformation, is characterized by developmental anomalies in the first and second pharyngeal arches. Its etiology is considered to be heterogenous, including both genetic and environmental factors that remain largely unknown. To further elucidate the genetic cause in a five-generation Goldenhar syndrome pedigree and exploit the whole-exome sequencing (WES) data of this pedigree, we generated collapsed haplotype pattern markers based on WES and employed rare variant nonparametric linkage analysis. FBLN2 was identified as a candidate gene via analysis of WES data across the significant linkage region. A fbln2 knockout zebrafish line was established by CRISPR/Cas9 to examine the gene's role in craniofacial cartilage development. fbln2 was expressed specifically in the mandible during the zebrafish early development, while fbln2 knockout zebrafish exhibited craniofacial malformations with abnormal chondrocyte morphologies. Functional studies revealed that fbln2 knockout caused abnormal chondrogenic differentiation, apoptosis, and proliferation of cranial neural crest cells (CNCCs), and downregulated the bone morphogenic protein (BMP) signaling pathway in the zebrafish model. This study demonstrates the role of FBLN2 in CNCC development and BMP pathway regulation, and highlights FBLN2 as a candidate gene for Goldenhar syndrome, which may have implications for the selection of potential screening targets and the development of treatments for conditions like microtia-atresia.

Genetics and Epigenetics in the Genesis and Development of Microtia

Microtia is a congenital malformation of the external and middle ear associated with varying degrees of severity that range from mild structural abnormalities to the absence of the external ear and auditory canal. Globally, it is the second most common congenital craniofacial malformation and is typically caused by inherited defects, external factors, or the interaction between genes and external factors. Epigenetics notably represents a bridge between genetics and the environment. This review has devoted attention to the current proceedings of the genetics and epigenetics of microtia and related syndromes.

Emerging Trends in Big Data Analysis in Computational Biology and Bioinformatics in Health Informatics: A Case Study on Epilepsy and Seizures

Advanced technology innovations allow cost-effective, high-throughput profiling of biological systems. It enabled genome sequencing in days using advanced technologies (e.g., next-generation sequencing, microarrays, and mass spectrometry). Since technology has been developed, massive biological data (e.g., genomics, proteomics) has been produced cheaply, allowing the "big data" era to create new opportunities to solve medical and biological complications in many disciplines-preventive medicine, biology, Personalized Medicine, gene sequencing, healthcare, and industry. Computational biology and bioinformatics are interdisciplinary fields that develop and apply computational methods (e.g., analytical methods, mathematical modeling, and simulation) to analyze large collections of biological data, such as genetic sequences, cell populations, or protein samples, to make new predictions or discover new biology. Biological data storage, mining, and analysis have challenges because data is much more heterogeneous. In this study, the big data resources of genomics, proteomics, and metabolomics have been explored to solve biological problems using big data analysis approaches. The goal is to build a network of relationship-based gene-disease associations to prioritize phenotypes common to epilepsy and seizure disease. Through network analysis, The 10 seed genes, 22 associated genes, 132 microRNAs, and 38 transcription factors have been identified that have a direct effect on all forms of epilepsy and seizures. The majority of seed genes, according to the results of a functional analysis of seed genes, are involved in the acetylcholine-gated channel complex (10%) and the heterotrimeric G-protein complex (10%) pathways related to cellular components, followed by a role in the regulation of action potential (20%) and positive regulation of vascular endothelial growth factor production (20%) in Epilepsy and Seizures pathways related to biological processes. This study might provide insight into the workings of the disease and shows the importance of continued research into epilepsy and other conditions that can trigger seizure activity.

Hemifacial microsomia is linked to a rare homozygous variant V162I in FRK and validated in zebrafish

OBJECTIVES

Hemifacial microsomia (HFM) is a common birth defect involving the first and second branchial arch derivatives. Although several chromosomal abnormalities and causal gene variants have been identified, genetic etiologies in a majority of cases with HFM remain unknown. This study aimed to identify genetic mutations in affected individuals with HFM.

METHODS

Whole-exome sequencing and bioinformatics analysis were performed for 16 affected individuals and their family members. Sanger sequencing was applied for confirmation of selected mutations. Zebrafish embryos were used for in situ hybridization of candidate gene, microinjection with antisense morpholino, and cartilage staining.

RESULTS

A homozygous missense mutation (c.484G > A; p.V162I) in the FRK gene was identified in an 18-year-old girl with HFM and dental abnormalities. Heterozygous mutation of this mutation was identified in her parents, who are first cousins in a consanguineous family. FRK is highly expressed in the Meckel's cartilage during embryonic development in mouse and zebrafish. Knockdown of frk in zebrafish showed a lower length and width ratio of Meckel's cartilage, abnormal mandibular jaw joint, and disorganized ceratobranchial cartilage and bone.

CONCLUSIONS

We identified a recessive variant in the FRK gene as a novel candidate gene for a patient with HFM and mandibular hypoplasia and revealed its effects on craniofacial and embryonic development in zebrafish.

Focuses, Trends, and Developments in Craniofacial Microsomia From 1992 to 2022: A Bibliometric Analysis

There is a current lack of scientific bibliometric analyses in craniofacial microsomia (CFM) and relevant fields. Craniofacial microsomia is a congenital disease resulting from a series of structural malformations involving the first and second branchial arches. Craniofacial microsomia and related fields have attracted the attention of clinicians and interested researchers worldwide. This study summarizes the research status and focuses to help researchers fully grasp the current research situation of CFM and relevant fields in the past three decades and drive future research into new publications. Literature data were retrieved from the Web of Science Core Collection database. Results Analysis and Citation Report of Web of Science, and CiteSpace software were used to evaluate and visualize the results, including publication characteristics, disciplines, journals, literature, countries/regions, institutions, authors, research focuses, etc. A total of 949 original articles and reviews were included after manual screening, and the overall trend of the number of annual publications and citations was increasing. According to the analysis, the description of the clinical characteristics of CFM, the classification of CFM, and mandibular distraction osteogenesis have always been the focus of research in this field. Besides, with the continuous progress of new technologies such as gene sequencing and the expansion of researchers' understanding of diseases, research on genetics and etiology related to CFM has been a developing trend.

Craniofacial Microsomia, Associated Congenital Anomalies, and Risk Factors in 63 Cases from the Alberta Congenital Anomalies Surveillance System

OBJECTIVE

To report associated congenital anomalies with unexplained craniofacial microsomia (CFM) and the phenotypic overlap with other recurrent constellations of embryonic malformations (RCEM), and to assess prenatal and perinatal risk factors.

STUDY DESIGN

This is a retrospective cross-sectional study. Cases with CFM, delivered between January 1, 1997, and December 31, 2019, were abstracted from the population-based Alberta Congenital Anomalies Surveillance System. Livebirths, stillbirths, and early fetal losses were reviewed to include all types of pregnancy outcomes along the spectrum of this condition. Prenatal and perinatal risk factors were compared with the Alberta birth population to assess differences between the 2 groups.

RESULTS

There were 63 cases with CFM, yielding a frequency of 1 per 16 949. There was a high rate of cases (65%) with anomalies outside the craniofacial and vertebral regions. Congenital heart defects were the most common (33.3%). A single umbilical artery was found in 12.7% of cases. The twin/triplet rate of 12.7% was significantly higher than the Alberta rate of 3.3% (P < .0001). There was an overlap with a second RCEM condition in 9.5% of cases.

CONCLUSIONS

Although CFM is primarily a craniofacial condition, the majority of cases have congenital anomalies affecting other systems requiring additional assessments, including an echocardiogram, renal ultrasound examination, and a complete vertebral radiograph. The high rate of an associated single umbilical artery raises the possibility of a related etiological mechanism. Our findings support the proposed concept of RCEM conditions.

Diagnosis, treatment, and research status of rare diseases related to birth defects

Rare diseases are diseases that occur at low prevalence, and most of them are chronic and serious diseases that are often life-threatening. Currently, there is no unified definition for rare diseases. The diagnosis, treatment, and research of rare diseases have become the focus of medicine and biopharmacology, as well as the breakthrough point of clinical and basic research. Birth defects are the hard-hit area of rare diseases and the frontiers of its research. Since most of these defects have a genetic basis, early screening and diagnosis have important scientific value and social significance for the prevention and control of such diseases. At present, there is no effective treatment for most rare diseases, but progress in prenatal diagnosis and screening can prevent the occurrence of diseases and help prevent and treat rare diseases. This article discusses the progress in genetic-related birth defects and rare diseases.

FOXI3 pathogenic variants cause one form of craniofacial microsomia

Craniofacial microsomia (CFM; also known as Goldenhar syndrome), is a craniofacial developmental disorder of variable expressivity and severity with a recognizable set of abnormalities. These birth defects are associated with structures derived from the first and second pharyngeal arches, can occur unilaterally and include ear dysplasia, microtia, preauricular tags and pits, facial asymmetry and other malformations. The inheritance pattern is controversial, and the molecular etiology of this syndrome is largely unknown. A total of 670 patients belonging to unrelated pedigrees with European and Chinese ancestry with CFM, are investigated. We identify 18 likely pathogenic variants in 21 probands (3.1%) in FOXI3. Biochemical experiments on transcriptional activity and subcellular localization of the likely pathogenic FOXI3 variants, and knock-in mouse studies strongly support the involvement of FOXI3 in CFM. Our findings indicate autosomal dominant inheritance with reduced penetrance, and/or autosomal recessive inheritance. The phenotypic expression of the FOXI3 variants is variable. The penetrance of the likely pathogenic variants in the seemingly dominant form is reduced, since a considerable number of such variants in affected individuals were inherited from non-affected parents. Here we provide suggestive evidence that common variation in the FOXI3 allele in trans with the pathogenic variant could modify the phenotypic severity and accounts for the incomplete penetrance.

Exploration of Novel Genetic Evidence and Clinical Significance Into Hemifacial Microsomia Pathogenesis

The authors browsed through past genetic findings in hemifacial microsomia along with our previously identified mutations in ITGB4 and PDE4DIP from whole genome sequencing of hemifacial microsomia patients. Wondering whether these genes influence mandibular bone modeling by regulation on osteogenesis, the authors approached mechanisms of hemifacial microsomia through this investigation into gene knockdown effects in vitro. MC3T3E1 cells were divided into 5 groups: the negative control group without osteogenesis induction or siRNA, the positive control group with only osteogenesis induction, and 3 gene silenced groups with both osteogenesis induction and siRNA. Validation of transfection was through fluorescence microscopy and quantitative real-time Polymerase chain reaction on knockdown efficiency. Changes in expression levels of the 3 genes during osteogenesis and impact of Itgb4 and Pde4dip knockdown on osteogenesis were examined by quantitative real-time Polymerase chain reaction, alkaline phosphatase, and alizarin red staining. Elevation of osteogenic genes Alpl, Col1a1, Bglap, Spp1, and Runx2 verified successful osteogenesis. Both genes were upregulated under osteogenic induction, while they had different trends over time. Intracellular fluorophores under microscope validated successful transfection and si-m-Itgb4_003, si-m-Pde4dip_002 had satisfactory knockdown effects. During osteogenesis, Pde4dip knockdown enhanced Spp1 expression (1.95±0.13 folds, P =0.045). The authors speculated that these genes may have different involvements in osteogenesis. Stimulated expression of Spp1 by Pde4dip knockdown may suggest that Pde4dip inhibits osteogenesis.

Mutations in the TBX15-ADAMTS2 pathway associate with a novel soft palate dysplasia

We reported de novo variants in specific exons of the TBX15 and ADAMTS2 genes in a hitherto undescribed class of patients with unique craniofacial developmental defects. The nine unrelated patients represent unilateral soft palate hypoplasia, lost part of the sphenoid bone in the pterygoid process, but the uvula developed completely. Interestingly, these clinical features are contrary to the palate's anterior-posterior (A-P) developmental direction. Based on developmental characteristics, we suggested that these cases correspond to a novel craniofacial birth defect different from cleft palate, and we named it soft palate dysplasia (SPD). However, little is known about the molecular mechanism of the ADAMTS2 and TBX15 genes in the regulation of soft palate development. Phylogenetic analysis showed that the sequences around these de novo mutation sites are conserved between species. Through cellular co-transfections and chromatin immunoprecipitation assays, we demonstrate that TBX15 binds to the promoter regions of the ADAMTS2 gene and activates the promoter activity. Furthermore, we show that TBX15 and ADAMTS2 are colocalization in the posterior palatal mesenchymal cells during soft palate development in E13.5 mice embryos. Based on these data, we propose that the disruption of the TBX15-ADAMTS2 signaling pathway during embryogenesis leads to a novel SPD.

Gene-environment interactions in the pathogenesis of common craniofacial anomalies

Craniofacial anomalies often exhibit phenotype variability and non-mendelian inheritance due to their multifactorial origin, involving both genetic and environmental factors. A combination of epidemiologic studies, genome-wide association, and analysis of animal models have provided insight into the effects of gene-environment interactions on craniofacial and brain development and the pathogenesis of congenital disorders. In this chapter, we briefly summarize the etiology and pathogenesis of common craniofacial anomalies, focusing on orofacial clefts, hemifacial microsomia, and microcephaly. We then discuss how environmental risk factors interact with genes to modulate the incidence and phenotype severity of craniofacial anomalies. Identifying environmental risk factors and dissecting their interaction with different genes and modifiers is central to improved strategies for preventing craniofacial anomalies.

OTX2 duplications: a recurrent cause of oculo-auriculo-vertebral spectrum

Background

Oculo-auriculo-vertebral spectrum (OAVS) is the second most common cause of head and neck malformations in children after orofacial clefts. OAVS is clinically heterogeneous and characterised by a broad range of clinical features including ear anomalies with or without hearing loss, hemifacial microsomia, orofacial clefts, ocular defects and vertebral abnormalities. Various genetic causes were associated with OAVS and copy number variations represent a recurrent cause of OAVS, but the responsible gene often remains elusive.

Methods

We described an international cohort of 17 patients, including 10 probands and 7 affected relatives, presenting with OAVS and carrying a 14q22.3 microduplication detected using chromosomal microarray analysis. For each patient, clinical data were collected using a detailed questionnaire addressed to the referring clinicians. We subsequently studied the effects ofOTX2overexpression in a zebrafish model.

Results

We defined a 272 kb minimal common region that only overlaps with theOTX2gene. Head and face defects with a predominance of ear malformations were present in 100% of patients. The variability in expressivity was significant, ranging from simple chondromas to severe microtia, even between intrafamilial cases. Heterologous overexpression ofOTX2in zebrafish embryos showed significant effects on early development with alterations in craniofacial development.

Conclusions

Our results indicate that properOTX2dosage seems to be critical for the normal development of the first and second branchial arches. Overall, we demonstrated thatOTX2genomic duplications are a recurrent cause of OAVS marked by auricular malformations of variable severity.

The Enigmatic Etiology of Oculo-Auriculo-Vertebral Spectrum (OAVS): An Exploratory Gene Variant Interaction Approach in Candidate Genes

The clinical diagnosis of oculo-auriculo-vertebral spectrum (OAVS) is established when microtia is present in association with hemifacial hypoplasia (HH) and/or ocular, vertebral, and/or renal malformations. Genetic and non-genetic factors have been associated with microtia/OAVS. Although the etiology remains unknown in most patients, some cases may have an autosomal dominant, autosomal recessive, or multifactorial inheritance. Among the possible genetic factors, gene−gene interactions may play important roles in the etiology of complex diseases, but the literature lacks related reports in OAVS patients. Therefore, we performed a gene−variant interaction analysis within five microtia/OAVS candidate genes (HOXA2, TCOF1, SALL1, EYA1 and TBX1) in 49 unrelated OAVS Mexican patients (25 familial and 24 sporadic cases). A statistically significant intergenic interaction (p-value < 0.001) was identified between variants p.(Pro1099Arg) TCOF1 (rs1136103) and p.(Leu858=) SALL1 (rs1965024). This intergenic interaction may suggest that the products of these genes could participate in pathways related to craniofacial alterations, such as the retinoic acid (RA) pathway. The absence of clearly pathogenic variants in any of the analyzed genes does not support a monogenic etiology for microtia/OAVS involving these genes in our patients. Our findings could suggest that in addition to high-throughput genomic approaches, future gene−gene interaction analyses could contribute to improving our understanding of the etiology of microtia/OAVS.

Extending the PAX1 spectrum: a dominantly inherited variant causes oculo-auriculo-vertebral syndrome

Oculo-auriculo-vertebral syndrome (OAVS) is a clinically heterogeneous disorder, with both genetic and environmental contributors. Multiple genes have been associated with OAVS and common molecular pathways, such as retinoic acid and the PAX-SIX-EYA-DACH (PSED) network, are being implicated in the disease pathophysiology. Biallelic homozygous nonsense or hypomorphic missense mutations in PAX1 cause otofaciocervical syndrome type 2 (OTFCS2), a similar but more severe multi-system disorder that can be accompanied by severe combined immunodeficiency due to thymic aplasia. Here we have identified a multi-generational family with mild features of OAVS segregating a heterozygous frameshift in PAX1. The four base duplication is expected to result in nonsense-mediated decay, and therefore cause a null allele. While there was full penetrance of the variant, expressivity of facial and ear features were variable. Our findings indicate there can be monoallelic and biallelic disorders associated with PAX1, and further implicate the PSED network in OAVS.

[Genetic characteristics of microtia-associated syndromes in neonates]

Microtia is the second most common maxillofacial birth defect in neonates and has an prevalence rate of 3.06/10 000 in China, and 20%-60% of microtia cases is associated with a certain type of syndrome. This article elaborates on the clinical phenotypes and genetic characteristics of three microtia-associated syndromes (MASs) with high prevalence, high incidence rate of ear deformity, and definite genetic etiology, i.e., oculo-auriculo-vertebral spectrum, branchio-oto-renal spectrum disorder, and Treacher-Collins syndrome, and summarizes another three common MASs, so as to provide a reference for the genetic diagnosis of neonatal MAS.

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.

Genetics of craniofacial malformations

The field of craniofacial malformations is comprehensive and does not allow to discuss all craniofacial malformations which have been described as single entities. Many of the syndromes with craniofacial malformations are ultrarare. In this review we have chosen craniofacial malformation syndromes which are of relevance for the pediatrician, especially neonatologist: different types of craniosynostoses, oculo-auriculo-vertebral spectrum, Pierre Robin sequence and Treacher Collins syndrome. These syndromes will be described in detail. Diagnostic and therapeutic options will be discussed.

A child with cat-eye syndrome and oculo-auriculo-vertebral spectrum phenotype: A discussion around molecular cytogenetic findings

Cat eye syndrome (CES) is a rare chromosomal disorder that may be evident at birth. A small supernumerary chromosome is present, frequently has 2 centromeres, is bisatellited, and represents an inv dup(22)(q11) in those affected. It's known that the 22q11 region is associated with disorders involving higher and lower gene dosages. Conditions such as CES, 22q11 microduplication syndrome (Dup22q11) and oculoauriculovertebral spectrum phenotype (OAVS) may share genes belonging to this same region, which is known to have a predisposition to chromosomal rearrangements. The conditions, besides being related to chromosome 22, also share similar phenotypes. Here we have added a molecular evaluation update and results found of the first patient described with CES and OAVS phenotype, trying to explain the potential mechanism involved in the occurrence of this association.

Craniofacial microsomia: Reflections on diagnosis and severity assessment based on a series of cases

This study aims to discuss diagnostic criteria and severity assessment for craniofacial microsomia (CFM). A series of 61 patients with diverse CFM phenotypes had their clinical data collected by experienced dysmorphologists using a single protocol. Genetic abnormalities were searched through karyotype and chromosomal microarray analysis. Sex ratio, prenatal risk factors, and recurrence rate corroborated the literature. Despite the wide variability of clinical findings, ear disruption was universal. Eight patients were assigned as syndromic, four of whom had demonstrable genetic alterations. The majority of patients (67.2%) fulfilled four known diagnostic criteria, while 9.8% fulfilled one of them. Data strengthened disruptions of the ear and deafness as a semiotically valuable sign in CFM. Facial impairment should consider asymmetry as a mild expression of microsomia. Spinal and cardiac anomalies, microcephaly, and developmental delay were prevalent among extra craniofacial features and should be screened before planning treatment and follow up. The severity index was able to recognize the less and the most affected patients. However, it was not useful to support therapeutic decisions and prognosis in the clinical scenario due to syndromic and non-syndromic phenotypes overlapping. These issues make contemporary the debate on diagnostic methods and disease severity assessment for CFM. They also impact care and etiopathogenetic studies.

GATA3 is essential for separating patterning domains during facial morphogenesis

Neural crest cells (NCCs) within the mandibular and maxillary prominences of the first pharyngeal arch are initially competent to respond to signals from either region. However, mechanisms that are only partially understood establish developmental tissue boundaries to ensure spatially correct patterning. In the 'hinge and caps' model of facial development, signals from both ventral prominences (the caps) pattern the adjacent tissues whereas the intervening region, referred to as the maxillomandibular junction (the hinge), maintains separation of the mandibular and maxillary domains. One cap signal is GATA3, a member of the GATA family of zinc-finger transcription factors with a distinct expression pattern in the ventral-most part of the mandibular and maxillary portions of the first arch. Here, we show that disruption of Gata3 in mouse embryos leads to craniofacial microsomia and syngnathia (bony fusion of the upper and lower jaws) that results from changes in BMP4 and FGF8 gene regulatory networks within NCCs near the maxillomandibular junction. GATA3 is thus a crucial component in establishing the network of factors that functionally separate the upper and lower jaws during development.

Investigation of Genetic Causes in a Developmental Disorder: Oculoauriculovertebral Spectrum

OBJECTIVE

Oculoauriculovertebral spectrum (OAVS) is a genetically and clinically heterogeneous disorder that occurs due to a developmental field defect of the first and second pharyngeal arches. Even though recent whole exome sequencing studies (WES) have led to identification of several genes associated with this spectrum in a subset of individuals, complete pathogenesis of OAVS remains unsolved. In this study, molecular genetic etiology of OAVS was systematically investigated.

DESIGN/SETTING/PATIENTS

A cohort of 23 Turkish patients with OAVS, referred to Hacettepe University Hospital, Department of Pediatric Genetics from 2008 to 2018, was included in this study. Minimal diagnostic criteria for OAVS were considered as unilateral microtia or hemifacial microsomia with preauricular skin tag. The cohort was clinically reevaluated for craniofacial and extracranial findings. Molecular etiology was investigated using candidate gene sequencing following copy number variant (CNV) analysis. WES was also performed for 2 of the selected patients.

RESULTS

Patients in the study cohort presented similar demographic and phenotypic characteristics to previously described patients in the literature except for a higher frequency of bilaterality, cardiac findings, and intellectual disability/developmental delay. CNV analysis revealed a possible genetic etiology for 3 patients (13%). Additional WES in 1 of the 2 patients uncovered a novel heterozygous nonsense variant in Elongation factor Tu GTP-binding domain-containing 2 (EFTUD2) causing mandibulofacial dysostosis with microcephaly (MFDM), which clinically overlaps with OAVS.

CONCLUSION

Detailed clinical evaluation for any patient with OAVS is recommended due to a high rate of accompanying systemic findings. We further expand the existing genetic heterogeneity of OAVS by identifying several CNVs and a phenotypically overlapping disorder, MFDM.

Haploinsufficiency of SF3B2 causes craniofacial microsomia

Craniofacial microsomia (CFM) is the second most common congenital facial anomaly, yet its genetic etiology remains unknown. We perform whole-exome or genome sequencing of 146 kindreds with sporadic (n = 138) or familial (n = 8) CFM, identifying a highly significant burden of loss of function variants in SF3B2 (P = 3.8 × 10^-10), a component of the U2 small nuclear ribonucleoprotein complex, in probands. We describe twenty individuals from seven kindreds harboring de novo or transmitted haploinsufficient variants in SF3B2. Probands display mandibular hypoplasia, microtia, facial and preauricular tags, epibulbar dermoids, lateral oral clefts in addition to skeletal and cardiac abnormalities. Targeted morpholino knockdown of SF3B2 in Xenopus results in disruption of cranial neural crest precursor formation and subsequent craniofacial cartilage defects, supporting a link between spliceosome mutations and impaired neural crest development in congenital craniofacial disease. The results establish haploinsufficient variants in SF3B2 as the most prevalent genetic cause of CFM, explaining ~3% of sporadic and ~25% of familial cases.

Description of a family with X-linked oculo-auriculo-vertebral spectrum associated with polyalanine tract expansion in ZIC3

Oculo-auriculo-vertebral spectrum (OAVS) [MIM:164210], or Goldenhar syndrome, is a developmental disorder associating defects of structures derived from the first and second branchial arches. The genetic origin of OAVS is supported by the description of rare deleterious variants in a few causative genes, and several chromosomal copy number variations. We describe here a large family with eight male members affected by a mild form of the spectrum, mostly auricular defects, harboring a hemizygous ZIC3 variant detected by familial exome sequencing: c.159_161dup p.(Ala55dup), resulting in an expansion of the normal 10 consecutive alanine residues to 11 alanines. Segregation analysis shows its presence in all the affected individuals, with a recessive X-linked transmission. Whole-genome sequencing performed in another affected male allowed to exclude linkage disequilibrium between this ZIC3 variant and another potential pathogenic variant in this family. Furthermore, by screening of a cohort of 274 OAVS patients, we found 1 male patient carrying an expansion of 10 to 12 alanines, a variant previously reported in patient presenting with VACTERL. Loss-of-function variants of ZIC3 are causing heterotaxy or cardiac malformations. These alanine expansion variants could have a different impact on the protein and thereby resulting in a different phenotype within the OAVS/VACTERL.

A Living Cell Repository of the Cranio-/Orofacial Region to Advance Research and Promote Personalized Medicine

The prevalence of congenital anomalies in newborns is estimated to be as high as 6%, many of which involving the cranio-/orofacial region. Such malformations, including several syndromes, are usually identified prenatally, at birth, or rarely later in life. The lack of clinically relevant human cell models of these often very rare conditions, the societal pressure to avoid the use of animal models and the fact that the biological mechanisms between rodents and human are not necessarily identical, makes studying cranio-/orofacial anomalies challenging. To overcome these limitations, we are developing a living cell repository of healthy and diseased cells derived from the cranio-/orofacial region. Ultimately, we aim to make patient-derived cells, which retain the molecular and genetic characteristics of the original anomaly or disease in vitro, available for the scientific community. We report our efforts in establishing a human living cell bank derived from the cranio-/orofacial region of otherwise discarded tissue samples, detail our strategy, processes and quality checks. Such specific cell models have a great potential for discovery and translational research and might lead to a better understanding and management of craniofacial anomalies for the benefit of all affected individuals.

Copy number variation analysis implicates novel pathways in patients with oculo-auriculo-vertebral-spectrum and congenital heart defects

Oculo-auriculo-vertebral spectrum (OAVS) is a developmental disorder of craniofacial morphogenesis. Its etiology is unclear, but assumed to be complex and heterogeneous, with contribution of both genetic and environmental factors. We assessed the occurrence of copy number variants (CNVs) in a cohort of 19 unrelated OAVS individuals with congenital heart defect. Chromosomal microarray analysis identified pathogenic CNVs in 2/19 (10.5%) individuals, and CNVs classified as variants of uncertain significance in 7/19 (36.9%) individuals. Remarkably, two subjects had small intragenic CNVs involving DACH1 and DACH2, two paralogs coding for key components of the PAX-SIX-EYA-DACH network, a transcriptional regulatory pathway controlling developmental processes relevant to OAVS and causally associated with syndromes characterized by craniofacial involvement. Moreover, a third patient showed a large duplication encompassing DMBX1/OTX3, encoding a transcriptional repressor of OTX2, another transcription factor functionally connected to the DACH-EYA-PAX network. Among the other relevant CNVs, a deletion encompassing HSD17B6, a gene connected with the retinoic acid signaling pathway, whose dysregulation has been implicated in craniofacial malformations, was also identified. Our findings suggest that CNVs affecting gene dosage likely contribute to the genetic heterogeneity of OAVS, and implicate the PAX-SIX-EYA-DACH network as novel pathway involved in the etiology of this developmental trait.

Whole-Exome Sequencing Reveals Rare Germline Mutations in Patients With Hemifacial Microsomia

Hemifacial microsomia (HFM) is a rare congenital disease characterized by a spectrum of craniomaxillofacial malformations, including unilateral hypoplasia of the mandible and surrounding structures. Genetic predisposition for HFM is evident but the causative genes have not been fully understood. Thus, in the present study, we used whole-exome sequencing to screen 52 patients with HFM for rare germline mutations. We revealed 3,341 rare germline mutations in this patient cohort, including those in 13 genes previously shown to be associated with HFM. Among these HFM-related genes, NID2 was most frequently mutated (in 3/52 patients). PED4DIP, which has not been previously associated with HFM, exhibited rare variants most frequently (in 7/52 patients). Pathway enrichment analysis of genes that were mutated in >2 patients predicted the "laminin interactions" pathway to be most significantly disrupted, predominantly by mutations in ITGB4, NID2, or LAMA5. In summary, this study is the first to identify rare germline mutations in HFM. The likely disruptions in the signaling pathways due to the mutations reported here may be considered potential causes of HFM.

Novel MYT1 variants expose the complexity of oculo-auriculo-vertebral spectrum genetic mechanisms

Oculo-auriculo-vertebral spectrum (OAVS) is a developmental disorder characterized by anomalies mainly involving the structures derived from the first and second pharyngeal arches. The spectrum presents with heterogeneous clinical features and complex etiology with genetic factors not yet completely understood. To date, MYT1 is the most important gene unambiguously associated with the spectrum and with functional data confirmation. In this work, we aimed to identify new single nucleotide variants (SNVs) affecting MYT1 in a cohort of 73 Brazilian patients diagnosed with OAVS. In addition, we investigated copy number variations (CNVs) encompassing this gene or its cis-regulatory elements and compared the frequency of these events in patients versus a cohort of 455 Brazilian control individuals. A new SNV, predicted as likely deleterious, was identified in five unrelated patients with OAVS. All five patients presented hearing impairment and orbital asymmetry suggesting an association with the variant. CNVs near MYT1, located in its neighboring topologically associating domain (TAD), were found to be enriched in patients when compared to controls, indicating a possible involvement of this region with OAVS pathogenicity. Our findings highlight the genetic complexity of the spectrum that seems to involve more than one variant type and inheritance patterns.

Whole-exome sequencing analysis in 10 families of sporadic microtia with thoracic deformities

Background

Microtia is a congenital malformation of the external ear and may occur as an isolated deformity or as part of a syndrome. Our previous study found a high correlation between microtia and thoracic deformities, thus, we propose that external ear and thorax development may be regulated by certain genes in common.

Methods

We performed exome sequencing on 10 families of sporadic microtia with thoracic abnormalities. We identified mutated genes under different models of inheritance, and checked them through Mouse Genome Informatics and association analysis.

Results

We identified 45 rare mutations, including 9 de novo mutations, 20 heterozygous mutations, 3 homozygous mutations, and 13 hemizygous mutations, of which 2 are likely to be causative. They are de novo missense variant in PHF5A and compound heterozygous mutations in CYP26B1, of which CYP26B1 mutation is highly likely pathogenic.

Conclusion

The results indicate that certain genes may affect both external ear and thorax development, and demonstrate the benefits of whole‐exome sequencing in identifying candidate genes of microtia. This study provides a new way for genetic exploration in microtia.

ITPR1 Mutation Contributes to Hemifacial Microsomia Spectrum

Hemifacial microsomia (HM) is a craniofacial congenital defect involving the first and second branchial arch, mainly characterized by ocular, ear, maxilla-zygoma complex, mandible, and facial nerve malformation. HM follows autosomal dominant inheritance. Whole-exome sequencing of a family revealed a missense mutation in a highly conserved domain of ITPR1. ITPR1 is a calcium ion channel. By studying ITPR1's expression pattern, we found that ITPR1 participated in craniofacial development, especially the organs that corresponded to the phenotype of HM. In zebrafish, itpr1b, which is homologous to human ITPR1, is closely related to craniofacial bone formation. The knocking down of itpr1b in zebrafish could lead to a remarkable decrease in craniofacial skeleton formation. qRT-PCR suggested that knockdown of itpr1b could increase the expression of plcb4 while decreasing the mRNA level of Dlx5/6. Our findings highlighted ITPR1's role in craniofacial formation for the first time and suggested that ITPR1 mutation contributes to human HM.

Genome-Wide DNA Methylation Analysis of a Cohort of 41 Patients Affected by Oculo-Auriculo-Vertebral Spectrum (OAVS)

Oculo-auriculo-vertebral-spectrum (OAVS; OMIM 164210) is a rare disorder originating from abnormal development of the first and second branchial arch. The clinical phenotype is extremely heterogeneous with ear anomalies, hemifacial microsomia, ocular defects, and vertebral malformations being the main features. MYT1, AMIGO2, and ZYG11B gene variants were reported in a few OAVS patients, but the etiology remains largely unknown. A multifactorial origin has been proposed, including the involvement of environmental and epigenetic mechanisms. To identify the epigenetic mechanisms contributing to OAVS, we evaluated the DNA-methylation profiles of 41 OAVS unrelated affected individuals by using a genome-wide microarray-based methylation approach. The analysis was first carried out comparing OAVS patients with controls at the group level. It revealed a moderate epigenetic variation in a large number of genes implicated in basic chromatin dynamics such as DNA packaging and protein-DNA organization. The alternative analysis in individual profiles based on the searching for Stochastic Epigenetic Variants (SEV) identified an increased number of SEVs in OAVS patients compared to controls. Although no recurrent deregulated enriched regions were found, isolated patients harboring suggestive epigenetic deregulations were identified. The recognition of a different DNA methylation pattern in the OAVS cohort and the identification of isolated patients with suggestive epigenetic variations provide consistent evidence for the contribution of epigenetic mechanisms to the etiology of this complex and heterogeneous disorder.

A recurrent missense variant in EYA3 gene is associated with oculo-auriculo-vertebral spectrum

Goldenhar syndrome or oculo-auriculo-vertebral spectrum (OAVS) is a complex developmental disorder characterized by asymmetric ear anomalies, hemifacial microsomia, ocular and vertebral defects. We aimed at identifying and characterizing a new gene associated with OAVS. Two affected brothers with OAVS were analyzed by exome sequencing that revealed a missense variant (p.(Asn358Ser)) in the EYA3 gene. EYA3 screening was then performed in 122 OAVS patients that identified the same variant in one individual from an unrelated family. Segregation assessment in both families showed incomplete penetrance and variable expressivity. We investigated this variant in cellular models to determine its pathogenicity and demonstrated an increased half-life of the mutated protein without impact on its ability to dephosphorylate H2AFX following DNA repair pathway induction. Proteomics performed on this cellular model revealed four significantly predicted upstream regulators which are PPARGC1B, YAP1, NFE2L2 and MYC. Moreover, eya3 knocked-down zebrafish embryos developed specific craniofacial abnormalities corroborating previous animal models and supporting its involvement in the OAVS. Additionally, EYA3 gene expression was deregulated in vitro by retinoic acid exposure. EYA3 is the second recurrent gene identified to be associated with OAVS. Moreover, based on protein interactions and related diseases, we suggest the DNA repair as a key molecular pathway involved in craniofacial development.

Functional and genetic analyses of ZYG11B provide evidences for its involvement in OAVS

BACKGROUND

The Oculo-Auriculo-Vertebral Spectrum (OAVS) or Goldenhar Syndrome is an embryonic developmental disorder characterized by hemifacial microsomia associated with auricular, ocular and vertebral malformations. The clinical heterogeneity of this spectrum and its incomplete penetrance limited the molecular diagnosis. In this study, we describe a novel causative gene, ZYG11B.

METHODS

A sporadic case of OAVS was analyzed by whole exome sequencing in trio strategy. The identified candidate gene, ZYG11B, was screened in 143 patients by next generation sequencing. Overexpression and immunofluorescence of wild-type and mutated ZYG11B forms were performed in Hela cells. Moreover, morpholinos were used for transient knockdown of its homologue in zebrafish embryo.

RESULTS

A nonsense de novo heterozygous variant in ZYG11B, (NM_024646, c.1609G>T, p.Glu537*) was identified in a single OAVS patient. This variant leads in vitro to a truncated protein whose subcellular localization is altered. Transient knockdown of the zebrafish homologue gene confirmed its role in craniofacial cartilages architecture and in notochord development. Moreover, ZYG11B expression regulates a cartilage master regulator, SOX6, and is regulated by Retinoic Acid, a known developmental toxic molecule leading to clinical features of OAVS.

CONCLUSION

Based on genetic, cellular and animal model data, we proposed ZYG11B as a novel rare causative gene for OAVS.

Recurrent constellations of embryonic malformations re-conceptualized as an overlapping group of disorders with shared pathogenesis

Several recurrent malformation associations affecting the development of the embryo have been described in which a genetic etiology has not been found, including LBWC, MURCS, OAVS, OEIS, POC, VACTERL, referred to here as "recurrent constellations of embryonic malformations" (RCEM). All are characterized by an excess of reported monozygotic discordant twins and lack of familial recurrence. We performed a comprehensive review of published twin data across all six phenotypes to allow a more robust assessment of the association with twinning and potential embryologic timing of a disruptive event. We recorded the type of twinning, any overlapping features of another RCEM, maternal characteristics, and the use of ART. Statistically significant associations included an excess of monozygotic twins and 80% discordance rate for the phenotype across all twins. There was an 18.5% rate of ART and no consistently reported maternal adverse events during pregnancy. We found 24 instances of co-occurrence of two RCEM, suggesting a shared pathogenesis across all RCEM phenotypes. We hypothesize the following timing for RCEM phenotypes from the earliest perturbation in development to the latest: LBWC, POC, OEIS, VACTERL, OAVS, then MURCS. The RCEM group of conditions should be considered a spectrum that could be studied as a group.

MYT1 role in the microtia-craniofacial microsomia spectrum

Background

Craniofacial microsomia (CFM), also known as the oculo‐auriculo‐vertebral spectrum, comprises a variable phenotype with the most common features including microtia and mandibular hypoplasia on one or both sides, in addition to lateral oral clefts, epibulbar dermoids, cardiac, vertebral, and renal abnormalities. The etiology of CFM is largely unknown. The MYT1 gene has been reported as a candidate based in mutations found in three unrelated individuals. Additional patients with mutations in this gene are required to establish its causality. We present two individuals with CFM that have rare variants in MYT1 contributing to better understand the genotype and phenotype associated with mutations in this gene.

Methods/Results

We conducted genetic analysis using whole‐exome and ‐genome sequencing in 128 trios with CFM. Two novel MYT1 mutations were identified in two participants. Sanger sequencing was used to confirm these mutations.

Conclusion

We identified two additional individuals with CFM who carry rare variants in MYT1, further supporting the presumptive role of this gene in the CFM spectrum.

Rare single-nucleotide variants in oculo-auriculo-vertebral spectrum (OAVS)

Background

Oculo‐auriculo‐vertebral spectrum (OAVS) is a craniofacial developmental disorder that affects structures derived from the first and second pharyngeal arches. The clinically heterogeneous phenotype involves mandibular, oral, and ear development anomalies. Etiology is complex and poorly understood. Genetic factors have been associated, evidenced by chromosomal abnormalities affecting different genomic regions and genes. However, known pathogenic single‐nucleotide variants (SNVs) have only been identified in MYT1 in a restricted number of patients. Therefore, investigations of SNVs on candidate genes may reveal other pathogenic mechanisms.

Methods

In a cohort of 73 patients, coding and untranslated regions (UTR) of 10 candidate genes (CRKL, YPEL1, MAPK1, NKX3‐2, HMX1, MYT1, OTX2, GSC, PUF60, HOXA2) were sequenced. Rare SNVs were selected and in silico predictions were performed to ascertain pathogenicity. Likely pathogenic variants were validated by Sanger sequencing and heritability was assessed when possible.

Results

Four likely pathogenic variants in heterozygous state were identified in different patients. Two SNVs were located in the 5’UTR of YPEL1; one in the 3’UTR of CRKL and one in the 3’UTR of OTX2.

Conclusion

Our work described variants in candidate genes for OAVS and supported the genetic heterogeneity of the spectrum.

Soft Tissue Damage in Patients With Hemifacial Microsomia

OBJECTIVE

The aim of this study was to evaluate the extent of the damage to soft tissues on the affected side in patients with hemifacial microsomia (HFM).

MATERIALS AND METHODS

Nine patients with HFM were included in this study and underwent computed tomography (CT) examination in the craniofacial area. The axial and coronal CT images were used for evaluating the damage to related soft tissues.

RESULTS

The results showed that the masseter muscle, temporal muscle, pterygoid muscles, and parotid gland were damaged on the affected side in all 9 patients with HFM. However, the extent of the damage to the pterygoid muscles was less than that to the masseter muscle, temporal muscle, and parotid gland.

CONCLUSIONS

These findings indirectly support the crucial role of hemorrhage in the development of HFM, and the extent of damage to soft tissues may depend on the distance and barrier effect of the mandible between the hemorrhage and the affected tissues.

The oculoauriculofrontonasal syndrome: Further clinical characterization and additional evidence suggesting a nontraditional mode of inheritance

The oculoauriculofrontonasal syndrome (OAFNS) is a rare disorder characterized by the association of frontonasal dysplasia (widely spaced eyes, facial cleft, and nose abnormalities) and oculo-auriculo-vertebral spectrum (OAVS)-associated features, such as preauricular ear tags, ear dysplasia, mandibular asymmetry, epibulbar dermoids, eyelid coloboma, and costovertebral anomalies. The etiology is unknown so far. This work aimed to identify molecular bases for the OAFNS. Among a cohort of 130 patients with frontonasal dysplasia, accurate phenotyping identified 18 individuals with OAFNS. We describe their clinical spectrum, including the report of new features (micro/anophtalmia, cataract, thyroid agenesis, polymicrogyria, olfactory bulb hypoplasia, and mandibular cleft), and emphasize the high frequency of nasal polyps in OAFNS (56%). We report the negative results of ALX1, ALX3, and ALX4 genes sequencing and next-generation sequencing strategy performed on blood-derived DNA from respectively, four and four individuals. Exome sequencing was performed in four individuals, genome sequencing in one patient with negative exome sequencing result. Based on the data from this series and the literature, diverse hypotheses can be raised regarding the etiology of OAFNS: mosaic mutation, epigenetic anomaly, oligogenism, or nongenetic cause. In conclusion, this series represents further clinical delineation work of the rare OAFNS, and paves the way toward the identification of the causing mechanism.

Genome sequencing identifies multiple deleterious variants in autism patients with more severe phenotypes

PURPOSE

To maximize the discovery of potentially pathogenic variants to better understand the diagnostic utility of genome sequencing (GS) and to assess how the presence of multiple risk events might affect the phenotypic severity in autism spectrum disorders (ASD).

METHODS

GS was applied to 180 simplex and multiplex ASD families (578 individuals, 213 patients) with exome sequencing and array comparative genomic hybridization further applied to a subset for validation and cross-platform comparisons.

RESULTS

We found that 40.8% of patients carried variants with evidence of disease risk, including a de novo frameshift variant in NR4A2 and two de novo missense variants in SYNCRIP, while 21.1% carried clinically relevant pathogenic or likely pathogenic variants. Patients with more than one risk variant (9.9%) were more severely affected with respect to cognitive ability compared with patients with a single or no-risk variant. We observed no instance among the 27 multiplex families where a pathogenic or likely pathogenic variant was transmitted to all affected members in the family.

CONCLUSION

The study demonstrates the diagnostic utility of GS, especially for multiple risk variants that contribute to the phenotypic severity, shows the genetic heterogeneity in multiplex families, and provides evidence for new genes for follow up.

Prenatal retinoic acid exposure reveals candidate genes for craniofacial disorders

Syndromes that display craniofacial anomalies comprise a major class of birth defects. Both genetic and environmental factors, including prenatal retinoic acid (RA) exposure, have been associated with these syndromes. While next generation sequencing has allowed the discovery of new genes implicated in these syndromes, some are still poorly characterized such as Oculo-Auriculo-Vertebral Spectrum (OAVS). Due to the lack of clear diagnosis for patients, developing new strategies to identify novel genes involved in these syndromes is warranted. Thus, our study aimed to explore the link between genetic and environmental factors. Owing to a similar phenotype of OAVS reported after gestational RA exposures in humans and animals, we explored RA targets in a craniofacial developmental context to reveal new candidate genes for these related disorders. Using a proteomics approach, we detected 553 dysregulated proteins in the head region of mouse embryos following their exposure to prenatal RA treatment. This novel proteomic approach implicates changes in proteins that are critical for cell survival/apoptosis and cellular metabolism which could ultimately lead to the observed phenotype. We also identified potential molecular links between three major environmental factors known to contribute to craniofacial defects including maternal diabetes, prenatal hypoxia and RA exposure. Understanding these links could help reveal common key pathogenic mechanisms leading to craniofacial disorders. Using both in vitro and in vivo approaches, this work identified two new RA targets, Gnai3 and Eftud2, proteins known to be involved in craniofacial disorders, highlighting the power of this proteomic approach to uncover new genes whose dysregulation leads to craniofacial defects.

Etiology and Pathogenesis of Hemifacial Microsomia

Hemifacial microsomia (HFM) is a common congenital malformation of the craniofacial region. There are 3 possible pathogenic models of HFM—vascular abnormality and hemorrhage in the craniofacial region, damage to Meckel’s cartilage, and the abnormal development of cranial neural crest cells—and the most plausible hypothesis is the vascular abnormality and hemorrhage model. These 3 models are interrelated, and none of them is completely concordant with all the variable manifestations of HFM. External environmental factors (e.g., thalidomide, triazene, retinoic acid, and vasoactive medications), maternal intrinsic factors (e.g., maternal diabetes), and genetic factors (e.g., the recently reported mutations in OTX2, PLCD3, and MYT1) may lead to HFM through ≥1 of these pathogenic processes. Whole genome sequencing to identify additional pathogenic variants, biological functional studies to understand the exact molecular mechanisms, and additional animal model and clinical studies with large stratified samples to elucidate the pathogenesis of HFM will be necessary. Small-molecule drugs, as well as CRISPR/CAS9-based genetic interventions, for the prevention and treatment of HFM may also be a future research hotspot.

Oculoauriculovertebral spectrum and maxillary sinus volumes : CT-based comparative evaluation

OBJECTIVES

To evaluate, by comparing maxillary sinus volumes, how asymmetries related to oculoauriculovertebral spectrum (OAVS) affect upper-jaw development.

METHODS

From pre-existing multislice spiral computed tomography (MSCT) datasets, we selected 20 cases of 11 female and 9 male patients aged 6.1-24 years who were clinically and radiographically symmetrical (group 1) plus 20 cases of 8 female and 12 male patients aged 5.7-23.9 years who had OAVS (group 2). After three-dimensional reconstruction of the datasets, the volumes of the left and right maxillary sinuses were calculated and compared based on patient groups and based on the sides affected or unaffected by OAVS. To this end, the OAVS patients were subdivided into a group in whom both external acoustic pores were radiographically present (group 2a) and a group in whom the pore on the affected side was congenitally missing (group 2b).

RESULTS

Intrarater reliability was very high (0.997). Significantly larger volumes of the maxillary sinuses, amounting to a mean of 13.4 ml, were observed in the control group than in the asymmetric OAVS groups where the volumes averaged 9.8 ml or 10.3 ml, respectively (p = 0.03). No statistically significant differences in sinus volumes were found between the two OAVS groups (p = 0.557) and between the sides affected or unaffected by the OAVS (p = 0.8311 in group 2a and 0.4961 in group 2b).

CONCLUSIONS

Overall, we found the volumes of both maxillary sinuses to be somewhat smaller in the asymmetric patients than in the symmetric control group. This might indicate that OAVS was associated with a mild generalized hypoplasia of the maxilla, but significantly different sinus volumes were not seen between the affected and unaffected sides.

Clinical and cytogenomic findings in OAV spectrum

The oculoauriculovertebral spectrum (OAVS) is characterized by anomalies involving the development of the first and second pharyngeal arches during the embryonic period. The phenotype is highly heterogeneous, involving ears, eyes, face, neck, and other systems and organs. There is no agreement in the literature for the minimum phenotypic inclusion criteria, but the primary phenotype involves hemifacial microsomia with facial asymmetry and microtia. Most cases are sporadic and the etiology of this syndrome is not well known. Environmental factors, family cases that demonstrate Mendelian inheritance, such as preauricular appendages, microtia, mandibular hypoplasia, and facial asymmetry; chromosomal abnormalities and some candidate genes suggest a multifactorial inheritance model. We evaluated clinical, cytogenomic and molecularly 72 patients with OAVS, and compared our findings with patients from the literature. We found 15 CNVs (copy number variations) considered pathogenic or possibly pathogenic in 13 out of 72 patients. Our results did not indicated a single candidate genomic region, but recurrent chromosomal imbalances were observed in chromosome 4 and 22, in regions containing genes relevant to the OAVS phenotype or related to known OMIM diseases suggesting different pathogenic mechanisms involved in this genetically and phenotypic heterogeneous spectrum.

A novel de novo mutation in MYT1, the unique OAVS gene identified so far

Oculo-auriculo-vertebral spectrum (OAVS) is a developmental disorder characterized by hemifacial microsomia associated with ear, eyes and vertebrae malformations showing highly variable expressivity. Recently, MYT1, encoding the myelin transcription factor 1, was reported as the first gene involved in OAVS, within the retinoic acid (RA) pathway. Fifty-seven OAVS patients originating from Brazil were screened for MYT1 variants. A novel de novo missense variant affecting function, c.323C>T (p.(Ser108Leu)), was identified in MYT1, in a patient presenting with a severe form of OAVS. Functional studies showed that MYT1 overexpression downregulated all RA receptors genes (RARA, RARB, RARG), involved in RA-mediated transcription, whereas no effect was observed on CYP26A1 expression, the major enzyme involved in RA degradation, Moreover, MYT1 variants impacted significantly the expression of these genes, further supporting their pathogenicity. In conclusion, a third variant affecting function in MYT1 was identified as a cause of OAVS. Furthermore, we confirmed MYT1 connection to RA signaling pathway.