TFAP2 paralogs regulate midfacial development in part through a conserved ALX genetic pathway.

Cranial neural crest development is governed by positional gene regulatory networks (GRNs). Fine-tuning of the GRN components underlies facial shape variation, yet how those networks in the midface are connected and activated remain poorly understood. Here, we show that concerted inactivation of Tfap2a and Tfap2b in the murine neural crest, even during the late migratory phase, results in a midfacial cleft and skeletal abnormalities. Bulk and single-cell RNA-seq profiling reveal that loss of both TFAP2 family members dysregulates numerous midface GRN components involved in midface morphogenesis, patterning and differentiation. Notably, Alx1, Alx3 and Alx4 (ALX) transcript levels are reduced, whereas ChIP-seq analyses suggest TFAP2 family members directly and positively regulate ALX gene expression. Tfap2a, Tfap2b and ALX co-expression in midfacial neural crest cells of both mouse and zebrafish implies conservation of this regulatory axis across vertebrates. Consistent with this notion, tfap2a zebrafish mutants present with abnormal alx3 expression patterns, Tfap2a binds ALX loci and tfap2a-alx3 genetic interactions are observed. Together, these data demonstrate TFAP2 paralogs regulate vertebrate midfacial development in part by activating expression of ALX transcription factor genes.

Lineage-specific requirements of Alx4 function in craniofacial and hair development.

BACKGROUND: Disruption of ALX4 causes autosomal dominant parietal foramina and autosomal recessive frontonasal dysplasia with alopecia, but the mechanisms involving ALX4 in craniofacial and other developmental processes are not well understood. Although mice carrying distinct mutations in Alx4 have been previously reported, the perinatal lethality of homozygous mutants together with dynamic patterns of Alx4 expression in multiple tissues have hindered systematic elucidation of the cellular and molecular mechanisms involving Alx4 in organogenesis and disease pathogenesis. RESULTS: We report generation of Alx4f/f conditional mice and show that tissue-specific Cre-mediated inactivation of Alx4 in cranial neural crest and limb bud mesenchyme, respectively, recapitulated craniofacial and limb developmental defects as found in Alx4-null mice but without affecting postnatal survival. While Alx4-null mice that survive postnatally exhibited dorsal alopecia, mice lacking Alx4 function in the neural crest lineage exhibited a highly restricted region of hair loss over the anterior skull whereas mice lacking Alx4 in the cranial mesoderm lineage exhibited normal hair development, suggesting that Alx4 plays partly redundant roles in multiple cell lineages during hair follicle development. CONCLUSION: The Alx4f/f mice provide a valuable resource for systematic investigation of cell type- and stage-specific function of ALX family transcription factors in development and disease.

Prenatal diagnosis of a severe form of frontonasal dysplasia with severe limb anomalies, hydrocephaly, a hypoplastic corpus callosum, and a ventricular septal defect using 3D ultrasound: a case report and literature review.

BACKGROUND: Frontonasal dysplasia (FND) is a rare congenital anomaly resulting from the underdevelopment of the frontonasal process, and it can be syndromic or nonsyndromic. The typical features of FND include a deformed nose and ocular hypertelorism, which are sometimes associated with cleft lip and/or palate. Only approximately 10 cases of prenatally diagnosed nonsyndromic FND have been reported in the past 30 years. CASE PRESENTATION: A 33-year-old woman (G2P1) was referred to our center at 20 gestational weeks for bilateral hydrocephaly. We detected typical features of FND, including severe hypertelorism, median nasal bifidity, a minor cleft lip, and multiple limb anomalies using three-dimensional (3D) ultrasound. A hypoplastic corpus callosum, unilateral microtia, and a ventricular septal defect were also detected. Genetic testing, including karyotype analysis, copy number variation (CNV) analysis, trio-whole exome sequencing (trio-WES), and trio-whole-gene sequencing (trio-WGS), was performed; however, we did not find any de novo gene variants in the fetus as compared to the parents. Postmortem examination confirmed the prenatal diagnosis of FND. CONCLUSION: The present case expands the wide phenotypic spectrum of prenatal FND patients. 3D ultrasound is a useful tool for detecting facial and limb deformities.

Dominant frontonasal dysplasia with ectodermal defects results from increased activity of ALX4.

Frontonasal dysplasia (FND) refers to a group of rare developmental disorders characterized by abnormal morphology of the craniofacial region. We studied a family manifesting with clinical features typical for FND2 including neurobehavioral abnormalities, hypotrichosis, hypodontia, and facial dysmorphism. Whole-exome sequencing analysis identified a novel heterozygous frameshift insertion in ALX4 (c.985_986insGTGC, p.Pro329Argfs*115), encoding aristaless homeobox 4. This and a previously reported dominant FND2-causing variant are predicted to result in the formation of a similar abnormally elongated protein tail domain. Using a reporter assay, we showed that the elongated ALX4 displays increased activity. ALX4 negatively regulates the Wnt/ß-catenin pathway and accordingly, patient keratinocytes showed altered expression of genes associated with the WNT/ß-catenin pathway, which in turn may underlie ectodermal manifestations in FND2. In conclusion, dominant FND2 with ectodermal dysplasia results from frameshift variants in ALX4 exerting a gain-of-function effect.

Oculoauriculofrontonasal syndrome: Refining the phenotype through a new case series and literature review.

The oculoauriculofrontonasal syndrome (OAFNS) is a rare condition, with unknown etiology, characterized by the association of frontonasal dysplasia (FND) and oculoauriculovertebral spectrum (OAVS). Main clinical findings include widely spaced eyes, epibulbar dermoid, broad nose, mandibular hypoplasia, and preauricular tags. Here, we describe a case series of 32 Brazilian individuals with OAFNS and review the literature ascertaining individuals presenting phenotypes compatible with the diagnosis of OAFNS, aiming to refine the phenotype. This series emphasizes the phenotypic variability of the OAFNS and highlights the occurrence of rare craniofacial clefts as a part of the phenotype. The ectopic nasal bone, a hallmark of OAFNS, was frequent in our series, reinforcing the clinical diagnosis. The absence of recurrence, consanguinity, chromosomal, and genetic abnormalities reinforces the hypothesis of a nontraditional inheritance model. The phenotypic refinement provided by this series contributes to an investigation regarding the etiology of OAFNS.

Two novel mutations within FREM1 gene in patients with bifid nose.

BACKGROUND: Bifid nose is a rare congenital deformity and the etiology is unknown. The purpose of this study was to report genetic variation in family of patients with bifid nose. METHODS: Twenty-three consecutive patients who were diagnosed with mild bifid nose were operated with z-plasty from 2009 to 2021. Three underage patients (a pair of twins and a girl) from two family lines, who came to our hospital for surgical treatment, were enrolled. Whole exome sequencing and Sanger sequencing were conducted. Z-shaped flaps were created and the cartilago alaris major were re-stitched. Photographs and CT scan before and after surgery were obtained. Clinical outcomes, complications and patients' satisfaction were evaluated and analyzed. The follow-up time ranges from 2 to 3 years (2.4 ± 1.2 years). RESULTS: Most patients were satisfied with the outcome (96.2%). The nasal deformities were corrected successfully with z-plasty technique in one-stage. FREM1 c.870_876del and c.2 T > C were detected with Whole exome sequencing, which have not been reported before. The results of Sanger sequencing were consistent with those of Whole exome sequencing. CONCLUSIONS: The newly detected mutations of FREM1 have a certain heritability, and are helpful to make an accurate diagnosis and provide a better understanding of bifid nose mechanism. Z-plasty technique can be an effective technical approach for correcting mild bifid nose deformity.

Toward clinical and molecular dissection of frontonasal dysplasia with facial skin polyps: From Pai syndrome to differential diagnosis through a series of 27 patients.

Unique or multiple congenital facial skin polyps are features of several rare syndromes, from the most well-known Pai syndrome (PS), to the less recognized oculoauriculofrontonasal syndrome (OAFNS), encephalocraniocutaneous lipomatosis (ECCL), or Sakoda complex (SC). We set up a research project aiming to identify the molecular bases of PS. We reviewed 27 individuals presenting with a syndromic frontonasal polyp and initially referred for PS. Based on strict clinical classification criteria, we could confirm only nine (33%) typical and two (7%) atypical PS individuals. The remaining ones were either OAFNS (11/27-41%) or presenting with an overlapping syndrome (5/27-19%). Because of the phenotypic overlap between these entities, OAFNS, ECCL, and SC can be either considered as differential diagnosis of PS or part of the same spectrum. Exome and/or genome sequencing from blood DNA in 12 patients and from affected tissue in one patient failed to identify any replication in candidate genes. Taken together, our data suggest that conventional approaches routinely utilized for the identification of molecular etiologies responsible for Mendelian disorders are inconclusive. Future studies on affected tissues and multiomics studies will thus be required in order to address either the contribution of mosaic or noncoding variation in these diseases.

Nasal Reconstruction of a Frontonasal Dysplasia via Septal L-Strut Reconstruction Using Costal Cartilage.

OBJECTIVE: Frontonasal dysplasia (FND) is a rare congenital condition. Its major features include hypertelorism, a large and bifid nasal tip, and a broad nasal root. We present our technique of septal L-strut reconstruction using costal cartilage. DESIGN: Retrospective review from June 2008 and August 2017. METHODS: Under general anesthesia, 6 patients with FND underwent septal reconstruction using costal cartilage via open rhinoplasty. We reconstructed the nasal and septal cartilaginous framework by placing columellar struts and cantilever-type grafts. RESULTS: The patients ranged in age from 6 to 13 years old. All were female. The follow-up period ranged from 8 months to 2 years; we encountered no postoperative complications (infection, nasal obstruction, or recurrence). All patients were satisfied with their nasal appearance. CONCLUSIONS: Although the results were not entirely satisfactory from an esthetic point of view, we found that FND can be treated via septal reconstruction with costal cartilage and that the clinical outcomes are reliable and satisfactory. Our approach is a useful option for FND patients.

ALX-Related Frontonasal Dysplasias: Clinical Characteristics and Surgical Management.

AIM: The term frontonasal dysplasia (FND) represents a spectrum of anomalies and its genetics have not been well defined. Recently, the critical role of the aristaless-like homeobox (ALX) gene family on the craniofacial development has been discovered. In the present study, we aimed to propose a systematic surgical treatment plan for the ALX-related FNDs according to the genotypic classification as well as demonstrating their clinical characteristics to help surgeons diagnose the underlying pathology accurately. DESIGN: Single-institution retrospective. SETTING: Tertiary health care. PATIENTS AND METHODS: Eighty-nine FND cases were evaluated. Eight of them had ALX1-related FND3, 3 had ALX3-related FND1, and 2 had ALX4-related FND2. Phenotype characteristics of ALX-related FNDs were evaluated, and relevant surgical interventions were assessed. RESULTS: The ALX1-related FND3 phenotype is striking due to the involvement of the eyes in addition to the presence of hypertelorism, facial clefts, and nasal deformities. A widened philtrum and prominent philtral columns are remarkable features of the ALX3-related FND1, whereas the ALX4-related FND2 has more severe deformities: severe hypertelorism, brachycephaly, large parietal bone defects, broad nasal dorsum, and alopecia. Facial bipartition, box osteotomies, eyelid coloboma repair, cleft lip and palate repair, nasal reconstruction, and fronto-orbital advancement can be performed in ALX-related FNDs based on the characteristics of each subtype. CONCLUSIONS: This genetic classification system will help surgeon diagnose patients with FND with unique features and draw a roadmap for their treatment with a better surgical perspective.

Prenatal diagnosis of isolated frontonasal dysplasia: A case report.

We report a case of mild frontonasal dysplasia, a complex and rare malformation affecting the central portion of the face, especially the eyes, nose, and forehead, which was diagnosed at 20 weeks of gestation. The diagnosis was made by two- and four-dimensional ultrasound and confirmed at autopsy after pregnancy termination. A review of the literature is presented.

Maternal SLE and brachytelephalangic chondrodysplasia punctata in a patient with unrelated de novo RAF1 and SIX2 variants.

Our improved tools to identify the aetiologies in patients with multiple abnormalities resulted in the finding that some patients have more than a single genetic condition and that some of the diagnoses made in the past are acquired rather than inherited. However, limited knowledge has been accumulated regarding the phenotypic outcome of the interaction between different genetic conditions identified in the same patients. We report a newborn girl with brachytelephalangic chondrodysplasia punctata (BCDP) as well as frontonasal dysplasia, ptosis, bilateral hearing loss, vertebral anomalies, and pulmonary hypoplasia who was found, by whole exome sequencing, to have a de novo pathogenic variant in RAF1 (c.770C>T, [p.Ser257Leu]) and a likely pathogenic variant in SIX2 (c.760G>A [p.A254T]), as well as maternal systemic lupus erythematosus (SLE). This case shows that BCDP is most probably not a diagnostic entity and can be associated with various conditions associated with CDP including maternal SLE.

Pai syndrome: a review.

BACKGROUND: Pai syndrome is a rare idiopathic developmental condition characterized by midline craniofacial abnormalities. It was originally described as the presence of a median cleft lip, cutaneous polyps of the nasal mucosa and face, and midline lipomas of the central nervous system, mostly at the corpus callosum. However, there is great phenotypical variability and these characteristics are rarely all present at once. OBJECTIVE: The aim of this review was to analyze the available evidence regarding Pai syndrome in order to better delineate this rare condition and its features. METHODS: We analyzed the PubMed database using the words "Pai syndrome", "frontonasal dysplasia", "cleft lip", "nasal polyp", "facial polyp", and "corpus callosum lipoma", including reviews, case reports and case series. CONCLUSION: There is no consensus regarding the diagnostic criteria of Pai syndrome up to date. It is usually diagnosed at birth, and its incidence is often underestimated. At present, the etiology of Pai syndrome is unknown. Several hypotheses regarding its genetic background have been made; however, there are not enough data yet to elucidate this point. An improved awareness could help in diagnosing the condition and performing the necessary investigations. These patients should have a multidisciplinary follow-up.

Identification of a novel homozygous ALX4 mutation in two unrelated patients with frontonasal dysplasia type-2.

We report two unrelated boys with frontonasal dysplasias type-2 (FND-2) who shared an identical novel homozygous ALX4 mutation c.291delG (p.Q98Sfs*83). Both patients presented with a large skull defect but one had bilateral parietal meningocele-like cysts that lie along with the bony defect and increased in size with age. Scalp alopecia, hypertelorism, and clefted alae nasi were also detected in both of them. Furthermore, impalpable gonads were noted, being unilateral in one and bilateral in the other. Neuroimaging showed small dysplastic occipital lobes with dysgyria and midline subarachnoid cyst. Additional dysplastic corpus callosum and small cerebellar vermis were observed in one patient. Parietal foramina were noted in the parents of one patient. Our findings highlight the dosage effect of ALX4 and underscore the challenges of prenatal genetic counseling. Further, the indirect role of ALX4 in the development of the occipital lobe and posterior fossa is discussed.

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.

Aristaless-Like Homeobox protein 1 (ALX1) variant associated with craniofacial structure and frontonasal dysplasia in Burmese cats.

Frontonasal dysplasia (FND) can have severe presentations that are medically and socially debilitating. Several genes are implicated in FND conditions, including Aristaless-Like Homeobox 1 (ALX1), which is associated with FND3. Breeds of cats are selected and bred for extremes in craniofacial morphologies. In particular, a lineage of Burmese cats with severe brachycephyla is extremely popular and is termed Contemporary Burmese. Genetic studies demonstrated that the brachycephyla of the Contemporary Burmese is a simple co-dominant trait, however, the homozygous cats have a severe craniofacial defect that is incompatible with life. The craniofacial defect of the Burmese was genetically analyzed over a 20 year period, using various genetic analysis techniques. Family-based linkage analysis localized the trait to cat chromosome B4. Genome-wide association studies and other genetic analyses of SNP data refined a critical region. Sequence analysis identified a 12bp in frame deletion in ALX1, c.496delCTCTCAGGACTG, which is 100% concordant with the craniofacial defect and not found in cats not related to the Contemporary Burmese.

Exome sequencing revealed a novel splice site variant in the ALX1 gene underlying frontonasal dysplasia.

Frontonasal dysplasia (FND) is a heterogeneous group of disorders characterized by hypertelorism, telecanthus, broad nasal root, wide prominent nasal bridge, short and wide nasal ridge, broad columella and smooth philtrum. To date one X-linked and three autosomal recessive forms of FND have been reported in different ethnic groups. We sought to identify the gene responsible for FND in a consanguineous Pakistani family segregating the disorder in autosomal recessive pattern. Genome-wide homozygosity mapping using 250KNsp array revealed five homozygous regions in the selected affected individuals. Exome sequencing found a novel splice acceptor site variant (c.661-1G>C: NM_006982.2) in ALX1. Sanger sequencing confirmed the correct segregation of the pathogenic variant in the whole family. Our study concludes that the splice site variant identified in the ALX1 gene causes mild form of FND.

Clinical delineation of a subtype of frontonasal dysplasia with creased nasal ridge and upper limb anomalies: Report of six unrelated patients.

Frontonasal dysplasias are rare congenital malformations of frontonasal process-derived structures, characterized by median cleft, nasal anomalies, widely spaced eyes, and cranium bifidum occultum. Several entities of syndromic frontonasal dysplasia have been described, among which, to date, only a few have identified molecular bases. We clinically ascertained a cohort of 124 individuals referred for frontonasal dysplasia. We identified six individuals with a similar phenotype, including one discordant monozygous twin. Facial features were remarkable by nasal deformity with creased ridge and depressed or absent tip, widely spaced eyes, almond-shaped palpebral fissures, and downturned corners of the mouth. All had apparently normal psychomotor development. In addition, upper limb anomalies, frontonasal encephalocele, corpus callosum agenesis, choanal atresia, and congenital heart defect were observed. We identified five reports in the literature of patients presenting with the same phenotype. Exome sequencing was performed on DNA extracted from blood of two individuals, no candidate gene was identified. In conclusion, we report six novel simplex individuals presenting with a specific frontonasal dysplasia entity associating recognizable facial features, limb and visceral malformations, and apparently normal development. The identification of discordant monozygotic twins supports the hypothesis of a mosaic disorder. Although previous patients have been reported, this is the first series, allowing delineation of a clinical subtype of frontonasal dysplasia, paving the way toward the identification of its molecular etiology.

Oculoauriculofrontonasal Dysplasia Syndrome With Additional Clinical Features.

Oculo-auriculo-vertebral spectrum and frontonasal dysplasia are two well-known examples of dysmorphology syndromes. Oculoauriculofrontonasal syndrome (OAFNS) is a clinical entity involving the characteristics of both OAVS and FND and is thought to be a result of the abnormal development of structures in the first and the second branchial arches, including the abnormal morphogenesis of maxillary processes. Herein we report a case of OAFNS with cliteral hypertrophy, premaxillary teeth, and inguinal hernia, features not previously reported in the literature.

Tooth Abnormalities and Occlusal Disorders in Individuals With Frontonasal Dysplasia.

OBJECTIVE: Frontonasal dysplasia is a rare developmental defect of the midface, and little is known about the dental involvement in individuals with this condition. This study investigated tooth abnormalities and occlusal disorders in individuals with frontonasal dysplasia. DESIGN: Cross-sectional. SETTING: Hospital for Rehabilitation of Craniofacial Anomalies, University of São Paulo, Bauru, Brazil. INTERVENTIONS: Clinical oral examination, analysis of patient records, and panoramic radiographs. PARTICIPANTS: A total of 20 individuals with frontonasal dysplasia aged 7 to 17 years. MAIN OUTCOME MEASURES: Prevalence of the several tooth abnormalities and occlusal disorders analyzed. RESULTS: A total of 19 individuals presented at least one tooth abnormality, with highly variable findings. In radiographs, 20% of individuals (all presenting oral clefts) presented agenesis of lateral incisors and second premolars. No supernumerary teeth were observed; 65% of individuals exhibited occlusal alterations, especially anterior open bite in the two individuals with median cleft lip. CONCLUSIONS: Variable clinical and radiographic alterations were observed, probably due to the large variety of phenotypic characteristics. No specific dental alteration could be related with frontonasal dysplasia.

A new frontonasal dysplasia syndrome associated with deletion of the SIX2 gene.

The frontonasal dysplasias are a group of craniofacial phenotypes characterized by hypertelorism, nasal clefting, frontal bossing, and abnormal hairline. These conditions are caused by recessive mutations in members of the aristaless gene family, resulting in abnormal cranial neural crest migration and differentiation. We report a family with a dominantly inherited craniofacial phenotype comprised of frontal bossing with high hairline, ptosis, hypertelorism, broad nasal tip, large anterior fontanelle, cranial base anomalies, and sagittal synostosis. Chromosomal microarray identified a heterozygous 108.3 kilobase deletion of chromosome 2p21 segregating with phenotype and limited to the sine oculis homeobox gene SIX2 and surrounding noncoding DNA. Similar to the human SIX2 deletion phenotype, one mouse model of frontonasal dysplasia, brachyrrhine, exhibits dominant inheritance and impaired cranial base chondrogenesis associated with reduced Six2 expression. We report the first human autosomal dominant frontonasal dysplasia syndrome associated with SIX2 deletion and with phenotypic similarities to murine models of Six2 Loss-of-function.