The Role of TCOF1 Gene in Health and Disease: Beyond Treacher Collins Syndrome.

The nucleoli are membrane-less nuclear substructures that govern ribosome biogenesis and participate in multiple other cellular processes such as cell cycle progression, stress sensing, and DNA damage response. The proper functioning of these organelles is ensured by specific proteins that maintain nucleolar structure and mediate key nucleolar activities. Among all nucleolar proteins, treacle encoded by TCOF1 gene emerges as one of the most crucial regulators of cellular processes. TCOF1 was initially discovered as a gene involved in the Treacher Collins syndrome, a rare genetic disorder characterized by severe craniofacial deformations. Later studies revealed that treacle regulates ribosome biogenesis, mitosis, proliferation, DNA damage response, and apoptosis. Importantly, several reports indicate that treacle is also involved in cancer development, progression, and response to therapies, and may contribute to other pathologies such as Hirschsprung disease. In this manuscript, we comprehensively review the structure, function, and the regulation of TCOF1/treacle in physiological and pathological processes.

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.

Large duplication in LMBR1 gene in a large Chinese pedigree with triphalangeal thumb polysyndactyly syndrome.

Polydactyly and syndactyly are digital abnormalities in limb-associated birth defects usually caused by genetic disorders. In this study, a five-generation Chinese pedigree was found with triphalangeal thumb polysyndactyly syndrome (TPTPS), showing an autosomal dominant pattern of inheritance. We utilized linkage analysis and whole genome sequencing (WGS) for the genetic diagnosis of this pedigree. Linkage analysis was performed using a genome-wide single nucleotide polymorphism (SNP) chip and three genomic regions were identified in chromosomes 2, 6, and 7 with significant linkage signals. WGS discovered a copy number variation (CNV) mutation caused by a large duplication region at the tail of chromosome 7 located in exons 1-5 of the LMBR1 gene, including the zone of polarizing activity regulatory sequence (ZRS), with a length of approximately 180 kb. A real-time polymerase chain reaction (PCR) assay confirmed the duplication. The findings of our study supported the notion that large duplications including the ZRS caused TPTPS. Our study showed that linkage analysis in combination with WGS could successfully identify the disease locus and causative mutation in TPTPS, which could help elucidate the molecular mechanisms and genotype-phenotype correlations in polydactyly.

Loss-of-function of Endothelin receptor type A results in Oro-Oto-Cardiac syndrome.

Craniofacial morphogenesis is regulated in part by signaling from the Endothelin receptor type A (EDNRA). Pathogenic variants in EDNRA signaling pathway components EDNRA, GNAI3, PCLB4, and EDN1 cause Mandibulofacial Dysostosis with Alopecia (MFDA), Auriculocondylar syndrome (ARCND) 1, 2, and 3, respectively. However, cardiovascular development is normal in MFDA and ARCND individuals, unlike Ednra knockout mice. One explanation may be that partial EDNRA signaling remains in MFDA and ARCND, as mice with reduced, but not absent, EDNRA signaling also lack a cardiovascular phenotype. Here we report an individual with craniofacial and cardiovascular malformations mimicking the Ednra -/- mouse phenotype, including a distinctive micrognathia with microstomia and a hypoplastic aortic arch. Exome sequencing found a novel homozygous missense variant in EDNRA (c.1142A>C; p.Q381P). Bioluminescence resonance energy transfer assays revealed that this amino acid substitution in helix 8 of EDNRA prevents recruitment of G proteins to the receptor, abrogating subsequent receptor activation by its ligand, Endothelin-1. This homozygous variant is thus the first reported loss-of-function EDNRA allele, resulting in a syndrome we have named Oro-Oto-Cardiac Syndrome. Further, our results illustrate that EDNRA signaling is required for both normal human craniofacial and cardiovascular development, and that limited EDNRA signaling is likely retained in ARCND and MFDA individuals. This work illustrates a straightforward approach to identifying the functional consequence of novel genetic variants in signaling molecules associated with malformation syndromes.

Mandibulofacial dysostosis Guion-Almeida type caused by novel EFTUD2 splice site variants in two Asian children.

Mandibulofacial dysostosis type Guion-Almeida (MFDGA) is a rare disease entity that results in congenital craniofacial anomalies that are caused by abnormal development of the first and second pharyngeal arches. MFDGA is characterized by malar and mandibular hypoplasia, microcephaly, developmental delay, dysplastic ears, and a distinctive facial appearance. Extracraniofacial malformations include esophageal atresia, congenital heart disease, and radial ray abnormalities. Heterozygous mutations in the elongation factor Tu GTP-binding domain containing 2 (EFTUD2) gene have been shown to result in MFDGA. To date, there have been a total of 108 individuals reported in the literature, of whom 95 patients have a confirmed EFTUD2 mutation. The majority of individuals reported in the literature have been of White ethnic origin. Here, we report two individuals of Asian ancestry with MFDGA, each harboring a novel, pathogenic splice site variant in EFTUD2.

Mandibulofacial dysostosis with microcephaly: A case presenting with seizures.

We report a case of mandibulofacial dysostosis with microcephaly presenting with seizures. The proband, a 6-year-old Korean boy, had microcephaly, malar and mandibular hypoplasia, and deafness. He showed developmental delay and had suffered recurrent seizures beginning at 21months of age. Electroencephalography revealed occasional spike discharges from the right frontal area. Head magnetic resonance imaging revealed dilatation of the lateral ventricles and a small frontal lobe volume. Whole exome sequencing revealed a de novo frame shift mutation, c.2698_2701 del, of EFTUD2. The epileptic focus was consistent with the reduced frontal lobe volume on head magnetic resonance imaging. Seizures are thus a main feature of mandibulofacial dysostosis with microcephaly, which results from an embryonic development defect due to the EFTUD2 mutation.

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.

Rodriguez acrofacial dysostosis is caused by apparently de novo heterozygous mutations in the SF3B4 gene.

Acrofacial dysostosis syndrome of Rodriguez is characterized by severe mandibular underdevelopment, upper limb phocomelia with absent fingers, absent fibulae, cleft palate, microtia, and abnormal pulmonary function. First reported in three siblings it was assumed to be an autosomal recessive condition. However, subsequent publication reported a further five simplex occurrences and a living patient with a heterozygous mutation in the SF3B4 gene. Exome sequencing was performed on four fetuses with this disorder, including one of the originally described affected siblings. We identified two heterozygous frameshift mutations in the SF3B4 gene in three of the four fetuses investigated. The observed mutation was apparently de novo in one fetus for whom parental DNA was available. Thus, Acrofacial dysostosis syndrome of Rodriguez is an autosomal dominant condition and the recurrences identified in the initial report were likely due to gonadal mosaicism. © 2016 Wiley Periodicals, Inc.

The Roles of RNA Polymerase I and III Subunits Polr1c and Polr1d in Craniofacial Development and in Zebrafish Models of Treacher Collins Syndrome.

Ribosome biogenesis is a global process required for growth and proliferation of all cells, yet perturbation of ribosome biogenesis during human development often leads to tissue-specific defects termed ribosomopathies. Transcription of the ribosomal RNAs (rRNAs) by RNA polymerases (Pol) I and III, is considered a rate limiting step of ribosome biogenesis and mutations in the genes coding for RNA Pol I and III subunits, POLR1C and POLR1D cause Treacher Collins syndrome, a rare congenital craniofacial disorder. Our understanding of the functions of individual RNA polymerase subunits, however, remains poor. We discovered that polr1c and polr1d are dynamically expressed during zebrafish embryonic development, particularly in craniofacial tissues. Consistent with this pattern of activity, polr1c and polr1d homozygous mutant zebrafish exhibit cartilage hypoplasia and cranioskeletal anomalies characteristic of humans with Treacher Collins syndrome. Mechanistically, we discovered that polr1c and polr1d loss-of-function results in deficient ribosome biogenesis, Tp53-dependent neuroepithelial cell death and a deficiency of migrating neural crest cells, which are the primary progenitors of the craniofacial skeleton. More importantly, we show that genetic inhibition of tp53 can suppress neuroepithelial cell death and ameliorate the skeletal anomalies in polr1c and polr1d mutants, providing a potential avenue to prevent the pathogenesis of Treacher Collins syndrome. Our work therefore has uncovered tissue-specific roles for polr1c and polr1d in rRNA transcription, ribosome biogenesis, and neural crest and craniofacial development during embryogenesis. Furthermore, we have established polr1c and polr1d mutant zebrafish as models of Treacher Collins syndrome together with a unifying mechanism underlying its pathogenesis and possible prevention.

Elevated plasma dihydroorotate in Miller syndrome: Biochemical, diagnostic and clinical implications, and treatment with uridine.

BACKGROUND: Miller syndrome (post-axial acrofacial dysostosis) arises from gene mutations for the mitochondrial enzyme dihydroorotate dehydrogenase (DHODH). Nonetheless, despite demonstrated loss of enzyme activity dihydroorotate (DHO) has not been shown to accumulate, but paradoxically urine orotate has been reported to be raised, confusing the metabolic diagnosis. METHODS: We analysed plasma and urine from a 4-year-old male Miller syndrome patient. DHODH mutations were determined by PCR and Sanger sequencing. Analysis of DHO and orotic acid (OA) in urine, plasma and blood-spot cards was performed using liquid chromatography-tandem mass spectrometry. In vitro stability of DHO in distilled water and control urine was assessed for up to 60h. The patient received a 3-month trial of oral uridine for behavioural problems. RESULTS: The patient had early liver complications that are atypical of Miller syndrome. DHODH genotyping demonstrated compound-heterozygosity for frameshift and missense mutations. DHO was grossly raised in urine and plasma, and was detectable in dried spots of blood and plasma. OA was raised in urine but undetectable in plasma. DHO did not spontaneously degrade to OA. Uridine therapy did not appear to resolve behavioural problems during treatment, but it lowered plasma DHO. CONCLUSION: This case with grossly raised plasma DHO represents the first biochemical confirmation of functional DHODH deficiency. DHO was also easily detectable in dried plasma and blood spots. We concluded that DHO oxidation to OA must occur enzymatically during renal secretion. This case resolved the biochemical conundrum in previous reports of Miller syndrome patients, and opened the possibility of rapid biochemical screening.

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.

Acromelic frontonasal dysostosis and ZSWIM6 mutation: phenotypic spectrum and mosaicism.

Acromelic frontonasal dysostosis (AFND) is a distinctive and rare frontonasal malformation that presents in combination with brain and limb abnormalities. A single recurrent heterozygous missense substitution in ZSWIM6, encoding a protein of unknown function, was previously shown to underlie this disorder in four unrelated cases. Here we describe four additional individuals from three families, comprising two sporadic subjects (one of whom had no limb malformation) and a mildly affected female with a severely affected son. In the latter family we demonstrate parental mosaicism through deep sequencing of DNA isolated from a variety of tissues, which each contain different levels of mutation. This has important implications for genetic counselling.

Nasal sequelae of Treacher Collins syndrome.

OBJECTIVE: This study aimed to determine external and endonasal deformity, and satisfaction with nasal functioning and appearance, in Treacher Collins syndrome. STUDY DESIGN: A cross-sectional cohort study was conducted. METHODS: Eleven adult patients with Treacher Collins syndrome were compared with 151 controls in terms of satisfaction with nasal functioning and appearance by means of the Nasal Appearance and Function Evaluation Questionnaire. In all patients with Treacher Collins syndrome, external nasal deformities were scored on standardized digital photographs of the nose as rated independently by three experienced physicians. Endonasal deformity was determined by standardized nasal endoscopy. RESULTS: The patients were relatively satisfied with the various esthetic nasal subunits. The most significant functional problems were snoring (P = 0.001) and quality of phonation (P = 0.003). The main external nasal deformities were the dorsal hump (73%), external deviation (≤55%), the bifid or bulbous nasal tip (55%), and columellar septal luxation (55%). In 82% of the patients, a septal deviation was found, often associated with spurs. CONCLUSION: Satisfaction with esthetics of the nose was fair, but these patients suffer from the functional problems of snoring and impaired quality of phonation. A structured nasal ENT physical examination with nasal endoscopy might determine aspects requiring more attention during treatment. Septorhinoplasty can be performed at an adult age if there is a considerable esthetic wish of the patient and/or nasal obstruction combined with septal deviation. Attention should be paid to dorsal hump reduction, correction of the deviated external osseous framework, septoplasty, and correction of the nasal tip shape. LEVEL OF EVIDENCE: 2b.

Acrofacial Dysostosis, Cincinnati Type, a Mandibulofacial Dysostosis Syndrome with Limb Anomalies, Is Caused by POLR1A Dysfunction.

We report three individuals with a cranioskeletal malformation syndrome that we define as acrofacial dysostosis, Cincinnati type. Each individual has a heterozygous mutation in POLR1A, which encodes a core component of RNA polymerase 1. All three individuals exhibit varying degrees of mandibulofacial dysostosis, and two additionally have limb anomalies. Consistent with this observation, we discovered that polr1a mutant zebrafish exhibited cranioskeletal anomalies mimicking the human phenotype. polr1a loss of function led to perturbed ribosome biogenesis and p53-dependent cell death, resulting in a deficiency of neural-crest-derived skeletal precursor cells and consequently craniofacial anomalies. Our findings expand the genotypic and phenotypic heterogeneity of congenital acrofacial disorders caused by disruption of ribosome biogenesis.

Is there an effect of obstructive sleep apnea syndrome on oxidative stress and inflammatory parameters in patients with craniofacial anomalies?

The aim of this study was to test the hypothesis that obstructive sleep apnea syndrome (OSAS) exhibits oxidative stress and inflammation in patients who have a congenital, craniofacial anomaly.This prospective, cross-sectional cohort study included ambulant sleep study data to asses OSAS in patients with syndromic craniosynostosis and Treacher Collins syndrome. Laboratory analyses were performed including malondialdehyde, tumor necrosis factor α (TNF-α), interleukin 6, and high-sensitivity C-reactive protein.Forty-eight patients were included; 11 were adults; 37 were children. The patients' body mass indexes were normal, with a median (SD) of 0.7 (-1.82 to 2.48) in children and 20.5 (15.2-29.4) in adults. Obstructive sleep apnea syndrome was diagnosed in 23 of 48 patients. It was mild (median obstructive apnea-hypopnea index [oAHI], 2.3; oxygenation-desaturation index [ODI], 0.9) in 16 patients and moderate/severe in 7 patients (median oAHI, 10.8; ODI, 5.0). Neither oxidative stress nor inflammation had a correlation with the oAHI and ODI. Only TNF-α was found significantly higher in both the OSAS and non-OSAS groups compared with the reference values (median, 15.1 pg/mL and 12.3 pg/mL versus 4.05 [0.0-8.1 pg/mL], P < 0.001 and P < 0.001, respectively).Based on our findings we conclude that (mainly mild) OSAS, oxidative stress, as well as high-sensitivity C-reactive protein and interleukin 6 levels are not abnormal in the day time in a population of nonobese patients with a craniofacial anomaly. The increased level of TNF-α cannot be explained by OSAS. Future research should focus on mapping chronobiologic changes for further interpretation of the results.

Association between obstructive sleep apnea and health-related quality of life in individuals affected with Treacher Collins syndrome.

Although the relationship between Quality of Life (QoL) and obstructive sleep apnea (OSA) has been reported in several studies, little is known about this relationship among individuals affected with Treacher Collins syndrome (TCS). The aim of this study was to examine the associations between obstructive sleep and QoL in TCS patients. Thirty-six individuals with TCS (8-75 years) were invited to participate in expanded medical examinations, including a sleep study, polysomnography, as well as to respond to questionnaires about health related Health-related quality of life (HRQoL). Twenty-three (64 %) responded to the invitation, but four were later excluded due to additional diagnoses or unconfirmed TCS, and four were below 12 years and excluded due to different scoring rules for sleep and respiratory disturbances in young children and adults. The remaining group comprised 15 adults and adolescents with TCS, 5 male (33 %) and 10 female (66 %). The participants were between 12 and 75 years of age (mean 38.6, SD 18.5). Obstructive sleep was found in 87 % of the patients and several sleep apnea parameters, among these wake time after sleep, subjective snoring and mean saturation, were associated with poorer HRQoL. OSA appears to account for reduced HRQoL in adolescents and adults with TCS.

Craniofacial development: current concepts in the molecular basis of Treacher Collins syndrome.

The human face and skull are an elegant example of the anatomical sophistication that results from the interplay between the molecular cascades and the tissue interactions that are necessary for the proper development of the craniofacial complex. When it fails to develop normally the consequences can have life-long implications for the biological, psychological, and aesthetic wellbeing of an affected person. Among the many syndromes that affect the region, understanding of the biology that underlies Treacher Collins syndrome has advanced in the last decade, particularly concerning the causative TCOF1 gene that encodes TREACLE protein, a serine/alanine-rich nucleolar phosphoprotein with an essential function during ribosome biogenesis in cranial neural crest cells. Abnormal growth and differentiation of these cells affect much of the craniofacial skeleton.

Orofacial functions and oral health associated with Treacher Collins syndrome.

OBJECTIVE: The aim of this study was to describe orofacial features and functions and oral health associated with Treacher Collins syndrome (TCS) in relation to the variable phenotypic expression of the condition. MATERIALS AND METHODS: The Nordic Orofacial Test-Screening (NOT-S), MHC Questionnaire, MHC Observation chart and clinical examinations of nasal and pharyngeal conditions and chewing and swallowing function were used to assess 19 individuals aged 5-74 years (median 34 years). TCS severity scores were calculated by a clinical geneticist. RESULTS: Orofacial features characterizing the study group were altered profile, increased mandibular angle, narrow hypopharynx and facial asymmetry. Basic orofacial functions such as breathing, eating, facial expression and speech were affected in all subjects demonstrating orofacial dysfunction in at least two NOT-S domains (median NOT-S total score 4/12, range 2-7). Significant correlation was found between the TCS severity scores reflecting phenotypic expression and the NOT-S total scores reflecting orofacial function. Self-reported experience of dry oral mucosa was common. Overall, dental health was good with few carious lesions diagnosed, but considerable need for orthodontic treatment was documented. CONCLUSIONS: Altered orofacial features and functions in TCS are common and often persist into late adolescence and adulthood. The functional level was correlated with the phenotypic variability of the condition. The standard of oral health was satisfactory. The findings indicated that individuals with TCS are likely to require lifelong health services related to their oral condition.